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Applied Catalysis A, General (v.391, #1-2)

Contents (pp. v-xix).

Editorial Board (pp. co2).

Contents (pp. v-xix).

Editorial Board (pp. co2).

Preface for Helmut Knözinger's special issue by Gerhard Mestl (pp. 1-2).

Reduced iron sites in Fe–BEA and Fe–ZSM-5 zeolites: FTIR study of CO adsorption and¹²C¹⁶O–¹³C¹⁸O co-adsorption by Mihail Mihaylov; Elena Ivanova; Kristina Chakarova; Paunka Novachka; Konstantin Hadjiivanov (pp. 3-10).

We report on the FTIR observation of new tri- and tetra-carbonyl complexes produced with reduced iron sites in zeolites. In order to clarify the structure of the polycarbonyls, adsorption of CO isotopic mixtures was studied. It was demonstrated that the use of¹²C¹⁶O–¹³C¹⁸O mixture provided a better resolution of the carbonyl bands as compared to the conventional¹²C¹⁶O–¹³C¹⁶O mixture.Accessible iron in oxidized Fe–ZSM-5 and Fe–BEA zeolites is mainly in the form of Fe³⁺ species that do not interact with CO. Some exchanged cations are stabilized as Fe²⁺ species and form carbonyls detected in the 2205–2190cm⁻¹ region. Evacuation of the samples at 673K provokes autoreduction of part of Fe³⁺ and creation of more Fe²⁺ sites detectable by CO. Reduction of the samples with CO at 673K leads to a significant increase of the number of Fe²⁺ sites and creation of new reduced iron sites (supposed to be Fe⁺ cations). With CO the latter forms tri- and tetra-carbonyl complexes. In order to clarify the structure of these species, adsorption of CO isotopic mixtures is studied. It is demonstrated that the use of¹²C¹⁶O–¹³C¹⁸O mixture provided a better resolution of the carbonyl bands as compared to the conventional¹²C¹⁶O–¹³C¹⁶O mixture.

Keywords: Adsorption; CO; Fe–ZSM-5; Fe–BEA; FTIR spectroscopy

In situ FTIR characterization of NH₃ adsorption and reaction with O₂ and CO on Pd-based FCC emission control additives by Behnam Bahrami; Vasileios G. Komvokis; Udayshankar G. Singh; Michael S. Ziebarth; Oleg S. Alexeev; Michael D. Amiridis (pp. 11-21).

Display Omitted▶ NH₃ can decompose on Ce n⁺/Na⁺/γ-Al₂O₃ and react with surface oxygen. ▶ Products are trapped on the catalyst surface in the form of nitrates and nitrites. ▶ At 400°C NH₃ further reacts with surface nitrites/nitrates to form N₂. ▶ NH₃ and CO react over Pd n⁺/Ce n⁺/Na⁺/γ-Al₂O₃ to form surface isocyanates.The adsorption of NH₃ and its reaction with O₂ and CO over Ce n⁺/Na⁺/γ-Al₂O₃ and Pd/Ce n⁺/Na⁺/γ-Al₂O₃ was examined by FTIR spectroscopy in a wide range of temperatures. Ammonia undergoes decomposition on the surfaces of these materials at elevated temperatures with a fraction of the NH₃ species being oxidized by lattice oxygen to NO_x, which is trapped on the surface in the form of nitrites. The presence of O₂ in the feed accelerates the formation of surface nitrite and nitrate species. The reaction of these species with ammonia at 400°C is fast, producing N₂. The presence of CO in the gaseous feed leads to the formation of surface isocyanates, presumably through the reaction with partially dehydrogenated surface NH_x species. The PdO component mildly promotes the formation of these isocyanate species. Both the NCO and NO₃⁻/NO₂⁻ species identified on the surfaces of these materials at elevated temperatures are active intermediates, participating in further reactions which ultimately lead to the reduction of NO_x and CO emissions. The contribution of these intermediates to a possible N₂ formation reaction network should be accounted for when FCC regenerators are operating under partial or incomplete burn combustion modes.

Keywords: FTIR spectroscopy; FCC additives; NO; _x; reduction; Palladium; Ammonia; Isocyanates; Nitrites; Nitrates

CO adsorption and oxidation studies on nanofabricated model catalysts using multilayer enhanced IRAS technique by P. Deshlahra; K. Pfeifer; G.H. Bernstein; E.E. Wolf (pp. 22-30).

Multilayer enhanced FTIR study on Pt/SiO₂/Au thin film structures show changes in the spectra of CO adsorbed after different types of sample pretreatment: O₂ followed by H₂ (run 1), H₂ (run 2), O₂–CO–H₂ (run 3), and H₂ (run 4). A pretreatment in CO (run 3) also caused significant morphological changes in the Pt film.Display Omitted▶ Novel FTIR enhancement technique suitable for multilayer model catalysts. ▶ Reduction treatment causes red-shift in spectra of adsorbed CO. ▶ Spectral changes sensitive to Pt particle size and nanowire width. ▶ Baseline changes indicate surface oxygen coverage.CO adsorption and oxidation studies have been performed on model Pt catalysts using multilayer enhanced infrared reflection absorption spectroscopy (MEIRAS) technique demonstrated in our laboratory. The multilayer model catalysts prepared for this study consist of semitransparent thin Pt films or Pt nanowires over SiO₂ or TiO₂ dielectric films of varying thicknesses with reflecting gold films underneath. CO adsorption results show that different types of oxidation and reduction pretreatments on Pt/SiO₂/Au thin film catalysts lead to changes in the CO stretch region of the spectra and in morphology of Pt films. Ignition behavior of CO oxidation reaction was studied on these catalysts and a change in the baseline of the spectra was observed as an indication of change in surface oxygen coverage with change in reaction conditions. CO adsorption studies on Pt/TiO₂/Au nanowires catalysts show a shift in the peak position towards lower wavenumbers with a decrease nanowire width. The results indicate that these spectral changes might be related to the boundary adsorption sites near the edges of Pt particles and nanowires. Further, experiments involving modification of boundary sites at Pt/TiO₂ junctions by applying external voltage to a catalytic nanodiode with Pt nanowires on TiO₂ are in progress.

Keywords: Model catalysts; Nanofabrication; CO oxidation; Chemisorption; FTIR enhancement; Multilayer structure

CO adsorption and oxidation studies on nanofabricated model catalysts using multilayer enhanced IRAS technique by P. Deshlahra; K. Pfeifer; G.H. Bernstein; E.E. Wolf (pp. 22-30).

Keywords: Model catalysts; Nanofabrication; CO oxidation; Chemisorption; FTIR enhancement; Multilayer structure

The interaction of carbon monoxide with clean and surface-modified zinc oxide nanoparticles: A UHV-FTIRS study by Heshmat Noei; Christof Wöll; Martin Muhler; Yuemin Wang (pp. 31-35).

The high-quality vibrational data recorded by UHV-FTIRS allow for detailed conclusions on the interaction of CO with differently modified polycrystalline ZnO surfaces. Importantly, the present study provides direct spectroscopic evidence that the binding energy of CO on ZnO nanoparticles is substantially increased in the presence of pre-adsorbed CO₂.The interaction of CO with differently modified polycrystalline ZnO has been studied by FTIR spectroscopy under ultrahigh vacuum conditions (UHV-FTIRS). After exposing the clean, adsorbate-free ZnO nanoparticles to CO at 110K we observe an intense vibrational band at 2187cm⁻¹ which is assigned to a majority of CO species bound to the Zn²⁺ sites on the mixed-terminated ZnO(101¯0) surface. After the exposure of CO₂-pretreated ZnO nanoparticles to CO at 110K, a new CO band is observed at 2215cm⁻¹, which originates from CO species adsorbed on the “free” Zn sites embedded within the (2×1) tridentate carbonate structure on the ZnO(101¯0) surface. UHV-FTIRS data recorded at different sample temperatures demonstrate that the binding energy of CO on polycrystalline ZnO is substantially increased in the presence of pre-adsorbed CO₂. The presence of hydroxyl species on the ZnO powder particles does not lead to substantial changes of the CO vibrational bands detected at 110K under UHV conditions.

Keywords: Vibrational spectroscopy; Carbon monoxide; Zinc oxide; Infrared spectroscopy; Carbon dioxide; Hydroxyl groups; Heterogeneous catalysis

The interaction of carbon monoxide with clean and surface-modified zinc oxide nanoparticles: A UHV-FTIRS study by Heshmat Noei; Christof Wöll; Martin Muhler; Yuemin Wang (pp. 31-35).

Keywords: Vibrational spectroscopy; Carbon monoxide; Zinc oxide; Infrared spectroscopy; Carbon dioxide; Hydroxyl groups; Heterogeneous catalysis

The generality of surface vanadium oxide phases in mixed oxide catalysts by Israel E. Wachs (pp. 36-42).

The nature of VO_x sites in mixed oxides of supported VO_x, pure oxides and mixed oxides, molecular sieves, zeolites, clays, hydrotalcites, stochiometric bulk oxides and bulk solid solutions were investigated. For supported metal oxides, zeolites and molecular sieves, the VO_x species are exclusively present as surface VO_x phases below monolayer coverage or the maximum dispersion limits. For layered clays and hydrotalcites, the VO_x is present in the hydroxide layers at modest temperatures and react with the clays and hydrotalcites at higher temperatures (>350°C) when their layered structures decompose. Surface VO_x species are always also present for bulk oxides and bulk solid solutions. The rapid diffusion kinetics of VO_x, due to its low Tammann temperature, coupled with the lower surface free-energy of vanadium oxide are responsible for the universal presence of surface VO_x sites on all mixed oxide materials. Furthermore, surface reactivity studies demonstrate that the surface VO_x sites are the catalytic active sites for all mixed oxide catalytic materials.Display Omitted▶ Surface VO_x species are present for supported metal oxides, zeolites, and molecular sieves contain VOx species at or below monolayer coverage. ▶ VO_x is present in the hydroxide layers of clays and hydrotalcites. ▶ Surface VO_x is always present for bulk oxides and bulk solid solutions. ▶ Surface VO_x sites are the catalytic active sites for all V-containing mixed oxide catalytic materials.The nature of VO_x sites in mixed oxides of supported VO_x (on both pure oxide and mixed oxide supports), molecular sieves, zeolites, clays, hydrotalcites, stochiometric bulk oxides and bulk solid solutions were investigated. For supported metal oxides, zeolites and molecular sieves, the VO_x species are exclusively present as surface VO_x phases below monolayer coverage or the maximum dispersion limits. For layered clays and hydrotalcites, the VO_x is present in the hydroxide layers at modest temperatures and react with the clays and hydrotalcites at higher temperatures (>350°C) when their layered structures decompose. Surface VO_x species are always also present for bulk oxides and bulk solid solutions. The rapid diffusion kinetics of VO_x, due to its low Tammann temperature, coupled with the lower surface free-energy of vanadium oxide are responsible for the universal presence of surface VO_x sites on all mixed oxide materials. Furthermore, surface reactivity studies demonstrate that the surface VO_x sites are the catalytic active sites for all V-containing mixed oxide catalytic materials.

Keywords: Catalysts; Oxides; Mixed; Vanadium; Supported; Zeolites; Molecular sieves; Clays; Hydrotalcites; POMs; Bulk and surface

The generality of surface vanadium oxide phases in mixed oxide catalysts by Israel E. Wachs (pp. 36-42).

Keywords: Catalysts; Oxides; Mixed; Vanadium; Supported; Zeolites; Molecular sieves; Clays; Hydrotalcites; POMs; Bulk and surface

Catalytic coatings for structured supports and reactors: VO_x/TiO₂ catalyst coated on stainless steel in the oxidative dehydrogenation of propane by Axel Löfberg; Thierry Giornelli; Sébastien Paul; Elisabeth Bordes-Richard (pp. 43-51).

The catalytic properties of thin films of VO_x/TiO₂ coated on stainless steel plates in the oxidative dehydrogenation of propane to propene were investigated in a specially designed reactor. Structural characteristics and catalytic properties were compared to those of VO_x/TiO₂ powders of the same composition.Display Omitted▶ Improved heat and mass transfers can increase selectivity in oxidative dehydrogenation of propane. ▶ Well characterized VO_x/TiO₂ coatings onto stainless steel plates were prepared. ▶ Structural properties of VO_x/TiO₂ plates were compared to VO_x/TiO₂ powders. ▶ Catalytic properties in plate reactor and in fixed bed reactor were compared. ▶ Poisoning by iron is the main reason why plates were less selective than powders.The catalytic properties of VO_x/TiO₂ when coated as a thin layer on stainless steel plates figuring out the walls of a reactor were studied in the oxidative dehydrogenation of propane to propene. The method to obtain mechanically stable but catalytically active and selective coatings consisted of dip-coating plates in titanium oxide suspension, followed by grafting of oxovanadium precursor specie in various amounts. In that way the textural and structural properties of coated plates were very similar to those of VO_x/TiO₂ powders of the same composition as seen from Raman and XPS experiments. The catalytic properties were investigated in a specially designed plate reactor and compared to those of the same catalyst used as powders in a conventional fixed bed reactor. The lower activity of plates vs. powders for the same composition and amount of active phase was attributed to the negative role played by iron diffusing towards the surface and poisoning the vanadate specie.

Keywords: VO; _x; /TiO; ₂; Oxidative dehydrogenation of propane; Catalytic coatings of stainless steel; Catalytic wall reactor

Synthesis, characterization and catalytic performance of titania supported VPO catalysts for the ammoxidation of 3-picoline by V.N. Kalevaru; N. Madaan; A. Martin (pp. 52-62).

. TiO₂ supported VPO catalysts are found to be highly active and selective for the ammoxidation of 3-picoline to nicotinonitrile. Significantly high conversion of 3-picoline (X=ca. 100%) and high yield of nitrile (Y-NN=83%) could be obtained over 20wt% VPO/TiO₂ catalyst.Display Omitted▶ Ammoxidation of 3-picoline to nicotinonitrile. ▶ Titania supported VPO catalyst are quite active and selective for this reaction. ▶ Varying VPO loading has strong influence on the performance of the catalyst. ▶ Acidity characteristics play key role on the catalyst properties. ▶ Conversion of 3-picoline ∼ 100% and the yield of NN=80% were obtained.Series of vanadium phosphorus oxide (VPO) catalysts supported over titania (anatase) were synthesised with varying contents of VPO (5–50wt%). These solids were characterised by ICP-OES, TG/DTA, BET, XRD, FTIR (Py-ads) and XPS. The catalytic activity was evaluated for ammoxidation of 3-picoline (3-pic) to nicotinonitrile (NN) in a fixed bed catalytic reactor. Thermal analysis provided good hints on the phase transformation of VHP precursor into active VPP phase at around 400°C. BET surface areas and pore volumes are found to depend on VPO loading and varied in the range from 70m²/g to 133m²/g. XRD demonstrates the formation of (VO)₂P₂O₇ (VPP) phase. XPS showed that an average oxidation state of vanadium around 4.0, which is found to be unaltered in the spent samples. FTIR (Py-ads) revealed the presence of both Lewis and Brønsted sites with varying proportions, which again depend upon VPO loading. Correlation of acidic properties (Lewis and Brønsted acid sites) of the catalysts with that of performance of catalysts was explored. VPO loading has a clear influence on the acidic properties and thereby catalytic activity and selectivity. Catalytic results showed that the supported catalysts gave better performance compared to bulk VPO. Yield of NN increased up to 20wt% VPO loading and then decreased with further increase in VPO content. Among all catalysts tested, the 20wt% VPO/TiO₂ exhibited the best performance (X-3-pic=ca. 100% and Y-NN=83%).

Keywords: Ammoxidation; 3-Picoline; Nicotinonitrile; VPO catalysts; Acidity characteristics

Synthesis, characterization and catalytic performance of titania supported VPO catalysts for the ammoxidation of 3-picoline by V.N. Kalevaru; N. Madaan; A. Martin (pp. 52-62).

Keywords: Ammoxidation; 3-Picoline; Nicotinonitrile; VPO catalysts; Acidity characteristics

Phase formation and selective oxidation of propane over MoVTeNbO_x catalysts with varying compositions by Frederik N. Naraschewski; Chinthala Praveen Kumar; Andreas Jentys; Johannes A. Lercher (pp. 63-69).

. The selective oxidation of propane to acrylic acid on MoVTeNbO_x catalysts with varying concentrations of vanadium, tellurium and niobium was investigated. Catalysts containing pure M1 phase were obtained over the compositional range of MoV_0.14–0.22Te_0.1–0.2Nb_0.1–0.2O_x. The catalytic activity is directly correlated to the concentration of vanadium in this phase.Display Omitted▶ The selective oxidation of propane to acrylic acid on MoVTeNbO_x catalysts was investigated. ▶ The M1 phase was obtained over the compositional range of MoV_0.14–0.22Te_0.1–0.2Nb_0.1–0.2O_x. ▶ The catalytic activity is directly correlated to the concentration of V, but independent of the Te concentration. ▶ The presence of the M1 phase is not a stringent requirement for the oxidative dehydrogenation of propane to propene. ▶ The M1 phase is required to oxidize the intermediately formed propene with high selectivity to acrylic acid.The selective oxidation of propane to acrylic acid on MoVTeNbO_x catalysts with varying concentrations of vanadium, tellurium and niobium was investigated. Catalysts containing M1 phase were obtained over the compositional range of MoV_0.14–0.22Te_0.1–0.2Nb_0.1–0.2O_x. Vanadium containing sites in the M1 phase are drastically more active for propane activation than in other materials studied. The catalytic activity is directly correlated to its fraction in the overall material and in particular the M1 phase. High concentrations of tellurium induce the formation of the M2 phase decreasing so the overall activity of the catalysts. The intrinsic activity of the M1 phase is, however, independent of the tellurium concentration. Although the presence of the M1 phase is not a stringent requirement for the oxidative dehydrogenation of propane to propene, it is required to oxidize the intermediately formed propene with high selectivity to acrylic acid. The active sites for propane activation and propene oxidation are structurally coupled, because the ratio between the rates of the two reactions was always 1:25. Oxygen defect sites in mixed oxides seem to enhance interaction with acrylic acid and lead to decarboxylation and total oxidation.

Keywords: MoVTeNb; Mixed oxides; Selective oxidation; Propane; Acrylic acid

Selection of mixed conducting oxides for oxidative dehydrogenation of propane with pulse experiments by Salvatore Crapanzano; Igor V. Babich; Leon Lefferts (pp. 70-77).

In this study, propane pulse experiments at 550°C are used as a method to select suitable oxides for operation of catalytic dense membrane reactor (CDMR) for selective oxidation of propane. La₂NiO4+_δ is the most promising material for membrane application, provided that it is operated in the right window of reduction degree while PrBaCo₂O5+_δ showed low selectivity to C₃H₆ and Ba_0.5Sr_0.5Co_0.8Fe_0.2O3−_δ appears to adsorb CO₂ by forming carbonates.Display Omitted▶ Pulse experiments can be used as method to select materials for operation of catalytic dense membrane reactors. ▶ Pulse experiments reveal the intrinsic activity and selectivity of lattice oxygen ions in the mixed oxides. ▶ La₂NiO₄ is the most promising material for membrane application, contrary to PrBaCo₂O₅ and Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃.In this study, propane pulse experiments at 550°C are used as a method to select suitable oxides for further operation of catalytic dense membrane reactor (CDMR) for oxidative dehydrogenation of propane. Ba_0.5Sr_0.5Co_0.8Fe_0.2O3−_δ (BSCF), La₂NiO4+_δ (LN) and PrBaCo₂O5+_δ (PBC) powders were used as model catalysts to explore the catalytic properties of membrane surfaces in terms of activity and selectivity. Furthermore, as propane pulses induce removal of oxygen from the sample, which is therefore depleted in oxygen by reducing the oxide, crucial information on the effect of the oxygen content in the samples ( i.e. the oxidation degree) on reactivity and selectivity is obtained. It will be shown that LN is the most promising material for membrane application, provided that it is operated in the optimal window of reduction degree, to ensure high selectivity towards C₃H₆. Contrary, PBC and BSCF are not suitable for CDMR. In fact, PBC showed low selectivity to C₃H₆ due to significant formation of CO₂, independent of the oxidation degree of the material and BSCF appears to adsorb CO₂ by forming carbonates, which might be detrimental for long term operation. However, pulse experiments revealed the remarkable stability of BSCF catalyst's activity towards CO₂ adsorption. Despite the presence of carbonate, the material preserved the ability to act as an oxygen source for propane and can be completely regenerated via oxidation. Additionally, the onset temperature in TPR appears to correlate well with the reactivity of lattice oxygen ions with propane, for the three materials studied.

Keywords: Oxidative dehydrogenation; Propane; Catalytic membrane reactor; Pulse experiment

Selection of mixed conducting oxides for oxidative dehydrogenation of propane with pulse experiments by Salvatore Crapanzano; Igor V. Babich; Leon Lefferts (pp. 70-77).

Keywords: Oxidative dehydrogenation; Propane; Catalytic membrane reactor; Pulse experiment

Opposite effect of Al on the performances of MoO₃/SiO₂-Al₂O₃ catalysts in the metathesis and in the partial oxidation of propene by Damien P. Debecker; Damien Hauwaert; Mariana Stoyanova; Axel Barkschat; Uwe Rodemerck; Eric M. Gaigneaux (pp. 78-85).

. Model MoO₃/SiO₂-Al₂O₃ catalysts with different support compositions are evaluated in the selective oxidation of propene and in its self-metathesis. Al increases the acidity of the catalysts. In oxidative conditions Al favours over-oxidation towards carbon oxides. In the metathesis reaction the presence of Al increases the catalysts activity and stability. 15% of Al₂O₃ in the support is the optimum.Display Omitted▶ Al content dictates the acidity of the support and of the catalyst. ▶ Acidity dictates catalytic performances. ▶ Al is deleterious for partial oxidation reaction. ▶ Al is beneificial for the metathesis reaction.The selective oxidation and the metathesis of light alkenes are two important catalytic reactions for the petrochemical industry. This paper highlights the contrasting effect of alumina on the catalytic behaviour of silica and silica-alumina supported molybdenum oxide catalysts in these two reactions. Model MoO₃/SiO₂-Al₂O₃ catalysts with ca. 6% MoO₃ weight loading are prepared via wet impregnation of ammonium heptamolybdate on a set of amorphous mesoporous silica-alumina supports with silica weight content comprised between 100% and 75%. The samples are characterized by ICP-AES, N₂-physisorption, XRD, NH₃-chemisorption and XPS and are evaluated in the selective oxidation of propene to acrolein and in its self-metathesis to form butene and ethene. The addition of aluminium oxide into silicon oxide increases the acidity of the support and of the catalyst. It also affects the nature of the deposited species and the dispersion of Mo. Overall, the effect of Al is negative in the case of the partial oxidation of propene because it favours over-oxidation towards carbon oxides. On the contrary, the presence of Al is crucial for the metathesis reaction. It appears that the acidity, created by the presence of alumina in silica, is beneficial for the metathesis reaction at low temperature. An optimum of activity is found for the catalyst supported on the silica-alumina containing 15wt% of Al₂O₃.

Keywords: Heterogeneous metathesis catalyst; Olefin disproportionation; C; ₃; H; ₆; Mesoporous mixed oxide support; Allylic oxidation; Propylene

The effect of support on redox properties and methanol-oxidation activity of vanadia catalysts by Ivan Baldychev; John M. Vohs; Raymond J. Gorte (pp. 86-91).

The effect of support composition on the catalytic properties of isolated mono-vanadates was studied using reaction rates for the methanol-oxidation reaction and oxygen binding energy from coulometric titration measurements.The effect of support composition on the catalytic properties of isolated mono-vanadates was studied using reaction rates for the methanol-oxidation reaction and oxygen binding from coulometric titration measurements on 2.5wt% V₂O₅/ZrO₂, 2.5wt% V₂O₅/TiO₂, and 5wt% V₂O₅/Al₂O₃. Although a review of the redox properties for the bulk oxides V₂O₅, ZrV₂O₇, AlVO₄, Mg₃(VO₄)₂, and CeVO₄ showed that the environment surrounding the V cations can have a dramatic effect on the redox properties, the majority of sites on supported catalysts showed nearly identical properties, with Δ G of oxidation being −375±25kJ/mol at 748K. The steady-state turnover frequencies for methanol oxidation were also similar (within a factor of 3) on each of the supports over the temperature range from 463 to 528K. Finally, methanol-oxidation rates in the absence of oxygen over the oxidized vanadia/titania catalyst at 443K demonstrated that all of the vanadia sites were active for the reaction and exhibited a similar rate to that observed in the presence of oxygen, showing that the reaction follows a Mars-van Krevelen mechanism.

Keywords: Methanol oxidation; Formaldehyde; Vanadia; Support effects; Zirconia; Titania; Alumina; Redox properties

The effect of support on redox properties and methanol-oxidation activity of vanadia catalysts by Ivan Baldychev; John M. Vohs; Raymond J. Gorte (pp. 86-91).

Keywords: Methanol oxidation; Formaldehyde; Vanadia; Support effects; Zirconia; Titania; Alumina; Redox properties

On the nature of active sites in MoVTeO and MoVTeNbO catalysts: The influence of catalyst activation temperature by P. Concepción; S. Hernández; J.M. López Nieto (pp. 92-101).

MoVTeO and MoVTeNbO catalysts, prepared hydrothermally and heat-treated at 500, 550 or 600°C in a N₂ atmosphere, have been characterized and tested in the partial oxidation of propane to acrylic acid. The heat-treatment has different influence on the formation and stability of M1, the surface characteristics and the catalytic behavior of MoVTeO and MoVTeNbO.MoVTeO and MoVTeNbO catalysts have been prepared, characterized (by XRD, Raman, IR, XPS, oxygen isotopic-exchange and IR of adsorbed methanol) and tested in the partial oxidation of propane to acrylic acid. The catalysts have been prepared hydrothermally and heat-treated at 500, 550 or 600°C in a N₂ atmosphere. The heat-treatment has different influence on the formation and stability of M1, the surface characteristics of catalysts and the catalytic behavior of MoVTeO and MoVTeNbO catalysts. The more selective catalyst was the MoVTeNbO sample heat-treated at 600°C, which present relatively high oxygen isotopic-exchange, the lower onset temperature of¹⁸O₂-consumption and a very low number of acid sites. In addition, it is characterized by the presence of only a type of Mo⁶⁺ species and the absence of Te⁶⁺ species (only Te⁴⁺ is observed) on the catalyst surface. The characteristics of active and selective catalysts are also discussed.

Keywords: Mo–V–Te–Nb oxide catalyst; M1; M2; Partial oxidation of propane; Acrylic acid; Catalyst characterization; Hydrothermal synthesis

On the nature of active sites in MoVTeO and MoVTeNbO catalysts: The influence of catalyst activation temperature by P. Concepción; S. Hernández; J.M. López Nieto (pp. 92-101).

Keywords: Mo–V–Te–Nb oxide catalyst; M1; M2; Partial oxidation of propane; Acrylic acid; Catalyst characterization; Hydrothermal synthesis

Impact of redox properties on dehydration of glycerol to acrolein over heteropolyacids assessed by operando-EPR spectroscopy by Silke Erfle; Udo Armbruster; Ursula Bentrup; Andreas Martin; Angelika Brückner (pp. 102-109).

Vanadium ions doped into supported H₃PMo₁₂O₄₀ and traces of O₂ in the feed suppress reduction of Mo⁶⁺ to Mo⁵⁺ by preferential formation of V⁴⁺. This leads to more active and stable catalysts, since it hinders the formation of highly condensed and deactivating coke species.H₃PMo₁₂O₄₀· xH₂O and H₄PVMo₁₁O₄₀· xH₂O with Keggin structure were supported on SiO₂–Al₂O₃ carriers with Si/Al=0.21 and 0.32 as well as on Al–MCM-41 (Si/Al=10), characterized and monitored by operando-EPR in the dehydration of glycerol to acrolein at 553K using feed streams of glycerol/N₂/H₂O/O₂=1/14.1/36.8/0.68 or 1/14.1/36.8/0. Upon deposition on the supports, the Keggin anions are degraded into fragments containing about 3–6 metal ions. Both the presence of vanadium as well as small amounts of O₂ in the feed keeps the Mo species in a highly oxidized state. This diminishes slightly the acrolein selectivity but also the condensation degree of the carbon deposits which might favour catalyst stability.

Keywords: Operando-EPR; Glycerol dehydration; Acrolein; Catalyst deactivation; Carbon deposits

Effect of Fe, Ga, Ti and Nb substitution in ≈SbVO₄ for propane ammoxidation by Andreas Wickman; Arne Andersson (pp. 110-117).

Propane ammoxidation to acrylonitrile is studied over unsubstituted ≈SbVO4 and its substitutions with Fe, Ga, Ti and Nb. The catalytic data indicates that a catalyst selective to acrylonitrile should have structurally isolated ensembles with propane activating V-sites and nitrogen inserting Sb-sites.Substitution in rutile-type ≈SbVO₄ was made with Fe³⁺ and Ga³⁺ replacing V³⁺, and Nb⁵⁺ replacing Sb⁵⁺. Moreover, preparations with Ti were synthesised where Ti⁴⁺ ions substitute for both V⁴⁺ and V³⁺/Sb⁵⁺ pairs. ≈SbVO₄-related phases containing Ti together with Fe and Ga were also prepared. The samples were characterised using X-ray diffraction, DRIFT and Raman spectroscopy. The characterisations show the formation of a cation deficient single rutile-type phase. Use of the samples in propane ammoxidation to produce acrylonitrile reveals, compared with the pure ≈SbVO₄ phase, that Fe, Ga and Ti substitution in ≈SbVO₄ results in lower activity but considerably higher selectivity to acrylonitrile at the same level of propane conversion. Niobium substitution, on the contrary, gives no improved catalytic properties. Correlations are presented between the catalytic and structural properties of the catalysts. It is demonstrated that isolation in the structure of the propane activating V–O^. sites in a surrounding of nitrogen inserting Sb-sites results in improved selectivity for acrylonitrile formation.

Keywords: Propane ammoxidation; Acrylonitrile; Sb-V-oxide based catalysts; ≈SbVO; ₄; Substitutions with Fe; Ga; Ti and Nb; XRD; DRIFT; Raman spectroscopy

Effect of Fe, Ga, Ti and Nb substitution in ≈SbVO₄ for propane ammoxidation by Andreas Wickman; Arne Andersson (pp. 110-117).

Keywords: Propane ammoxidation; Acrylonitrile; Sb-V-oxide based catalysts; ≈SbVO; ₄; Substitutions with Fe; Ga; Ti and Nb; XRD; DRIFT; Raman spectroscopy

Evidence for the presence of alternative mechanisms in the oxidation of cyclohexanone to adipic acid with oxygen, catalysed by Keggin polyoxometalates by Fabrizio Cavani; Laura Ferroni; Alessandra Frattini; Carlo Lucarelli; Andrea Mazzini; Katerina Raabova; Stefano Alini; Pasquale Accorinti; Pierpaolo Babini (pp. 118-124).

The oxidation of cyclohexanone with air, conducted with polyoxometalates catalysts and water–acetic acid co-solvents, occurs with either a catalytic-redox or an autoxidation mechanism, in function of the conditions used.This report deals with the results of a study on the oxidation of cyclohexanone to adipic acid with air, catalysed by Keggin-type polyoxometalates of composition H3+_xPMo12−_xV_xO₄₀ ( x=1 and 2), which was carried out in a semi-continuous stirred-tank reactor. It was found that when conducted in the presence of a water-only solvent, the reaction proceeds with a redox mechanism, in which the step of reoxidation of the reduced POM by oxygen is rate limiting. When, however, the reaction was carried out with an acetic acid co-solvent, a radical-chain autoxidation mechanism prevailed, especially when very low amounts of catalyst were used. Autoxidation overlapped with the redox mechanism when the catalyst-to-cyclohexanone ratio was increased. Moreover, the composition of the polyoxometalate, that is, the number of V atoms per Keggin unit, affected the relative importance of the two mechanisms. The selectivity to adipic acid achieved was a function of the reaction mechanism, but also was affected by cyclohexanone conversion, due to the presence of a complex reaction network.

Keywords: Adipic acid; Cyclohexanone oxidation; Keggin polyoxometalates; Reaction mechanism; Redox mechanism; Autoxidation

Effect of water on oxidative scission of 1-butene to acetic acid over V₂O₅-TiO₂ catalyst. Transient isotopic and kinetic study by Wladimir Suprun; Ekaterina M. Sadovskaya; Christoph Rüdinger; Hans-Jürgen Eberle; Michal Lutecki; Helmut Papp (pp. 125-136).

The role of water in the oxidation of 1-butene to AcOH over VOx-TiO₂ was investigated using spectroscopic and transient isotopic exchange methods. In particular, DRIFTS, XPS, TPD and SSITKA methods were used. Subsequently, kinetic model was developed for an unambiguous interpretation of the experimental results.The role of water in the oxidation of 1-butene to AcOH over VOx-TiO₂ was investigated using spectroscopic and transient isotopic exchange methods. It was shown that the influence of water strongly depended on the temperature of reaction. In particular, DRIFTS and NH₃-TPD studies confirmed the temperature influence on the acidity and the amount of adsorbed water. XPS investigations suggested that not only oxygen from vanadia, but also from the lattice of titania was involved in the oxygen transfer during the reaction. Formation of oxidation products proceeded over two types of active vanadium oxide centers, i.e., VOH and VO. Hydrated vanadium species exhibited high selectivity towards AcOH formation. On the other hand, VO centers favored total oxidation. Kinetic model was developed for an unambiguous interpretation of the experimental results. Modelled reaction constants of the formation of AcOH over VOH centers were ca. 3.5 times higher than over VO centers. At the same time, the reaction rate constant of total oxidation in the presence of water was ca. 3.2 times lower than in dry flow. Estimated values suggested that in the presence of water the number of VOH centers was substantially lower than VO sites; however their contribution to the rate of AcOH formation was much higher.

Keywords: Vanadia–titania catalyst; Oxidation of 1-butene; Water; Acetic acid; O exchange

Electronic structure of MoO₂. DFT periodic and cluster model studies by Renata Tokarz-Sobieraj; Robert Gryboś; Małgorzata Witko (pp. 137-143).

Display Omitted▶ (011)MoO₂ density of states from DFT calculations agree well with ARUPS spectra. ▶ Strong bond was found between characteristic Mo–Mo pairs, in bulk and on the surface. ▶ Mo(4) active sites are found on thin layer of MoO₂, with unique chemical properties.Electronic properties of MoO₂ bulk and (011) surface are discussed. It is found that Fermi level is located within the band dominated by d molybdenum orbitals, thereby reflecting the metallic character of the system. Results for (011)MoO₂ surface indicate that the surface retains the metallic character of the bulk. Depending on the thickness of the slab used to model the surface (1-layer or 2-layers) the electronic structure and properties change. In the 2-layer slab, bands close to the Fermi level originate both from regular six-fold coordinated Mo(6) centers as well as from five-fold coordinated Mo(5) centers occurring due to surface formation. In the 1-layer slab, peaks right below the Fermi level are dominated by the surface centers that are six-fold coordinated Mo(6) but also centers which are effectively four-fold coordinated Mo(4). This has a profound effect on the reactivity as was tested by a probe reaction of H₂ adsorption, which did not interact with the surface described by the 2-layer slab, but underwent dissociation on the 1-layer slab.The Mo–Mo pairs with bonds of approximately single character, characteristic for the bulk structure, are also present on the surface, both on 1-layer and 2-layer slabs.The local properties of (011)MoO₂ surface are very similar to other transition metal oxides. Metal–oxygen bonds are of a mixed ionic and covalent nature and the nucleophilicity of oxygen increases with the increase of coordination numbers of the corresponding oxygen atoms.

Keywords: Molybdenum dioxide; Metal–metal interactions; DFT calculations; Hydrogen adsorption

Electronic structure of MoO₂. DFT periodic and cluster model studies by Renata Tokarz-Sobieraj; Robert Gryboś; Małgorzata Witko (pp. 137-143).

Keywords: Molybdenum dioxide; Metal–metal interactions; DFT calculations; Hydrogen adsorption

Hydrogen production by catalytic partial oxidation of iso-octane at varying flow rate and fuel/oxygen ratio: From detailed kinetics to reactor behavior by M. Hartmann; L. Maier; O. Deutschmann (pp. 144-152).

. Hydrogen production by catalytic partial oxidation of iso-octane is experimentally and numerically studied over a rhodium/alumina coated honeycomb monolith at millisecond contact times both at varying fuel-to-oxygen ratios and at varying flow rates. At fuel rich conditions, the formation of by-products potentially serving as coke precursors is observed. The quantity of by-products strongly depends on the flow rate. Both fuel conversion and hydrogen yield increase with increasing flow rate, i.e., decreasing residence time. This extraordinary behavior of autothermally operated short-contact time reactors can be understood by the interaction of mass and heat transport and chemical reactions. Therefore, an elementary-step-like heterogeneous reaction mechanism is implemented into a two-dimensional flow field description of a single monolith channel, coupled with a heat balance of the entire monolithic structure.Display Omitted▶ CPOX of iso-octane on Rh is experimentally and numerically studied at varying flow rates and C/O ratios. ▶ The quantity of by-products strongly depends on the flow rate. ▶ Heat loss has a high impact on conversion and H2 yield and can be understand using detailed modelling.Hydrogen production by catalytic partial oxidation of iso-octane is experimentally and numerically studied over a rhodium/alumina coated honeycomb monolith at millisecond contact times by varying both fuel-to-oxygen ratio and flow rates and at varying flow rates. At fuel rich conditions, the formation of by-products potentially serving as coke precursors is observed. The quantity of by-products strongly depends on the flow rate. Both fuel conversion and hydrogen yield increase with increasing flow rate, i.e., decreasing residence time. This extraordinary behavior of autothermally operated short-contact time reactors can be understood by the interaction of mass and heat transport and chemical reactions. Therefore, an elementary-step-like heterogeneous reaction mechanism is implemented into a two-dimensional flow field description of a single monolith channel, coupled with a heat balance of the entire monolithic structure.

Keywords: Partial oxidation; Reforming; Octane; Gasoline; Rhodium; Hydrogen; Modeling and simulation

Selective hydrogenolysis of glycerol over copper catalysts both in liquid and vapour phase: Correlation between the copper surface area and the catalyst's activity by A. Bienholz; H. Hofmann; P. Claus (pp. 153-157).

Display Omitted▶ The hydrogenolysis of glycerol, a two-step reaction via glycerol dehydration to acetol with subsequent hydrogenation to 1,2-propandiol, was performed both in liquid and vapour phase using a set of different copper catalysts. ▶ In the vapour phase complete conversion of glycerol and a selectivity to 1,2-propanediol of 87% was achieved over a Cu/SiO2 catalyst ( SCu = 3.9 m2/g) under optimised reaction conditions. ▶ A plot of the Turnover Number versus the specific copper surface area reveals a linear relationship between these two values regardless of the aggregate state of glycerol during the reaction.The hydrogenolysis of glycerol was performed both in liquid and in vapour phase by the use of different copper catalysts. The reactions in liquid phase were carried out using copper catalysts which differ in their copper content (36–89wt.%) and, thus, in their composition while for the hydrogenolysis of glycerol in the vapour phase a set of different silica supported copper catalysts (Cu/SiO₂, low copper loading) was prepared either by incipient wetness (IW) or by ion exchange technique (IE).Concerning the reactions in the vapour phase complete conversion of glycerol and a selectivity to 1,2-propanediol of 87% was achieved over a Cu/SiO₂_IE catalyst under optimised reaction conditions (255°C, 15 bar, 300ml/min H₂). In liquid phase hydrogenation, 1,2-propanediol was nearly the sole product (selectivity=98%), and conversions up to 52% were obtained according to a space–time–yield of 5.9g_{1,2-propanediol}/(g_Cuh).N₂O chemisorption was carried out in order to determine the specific copper surface area of the catalysts. For both the reaction in liquid phase and in vapour phase there is a linear relationship between the specific copper surface area and the catalytic activity not only for glycerol hydrogenolysis, but also for glycerol dehydration to acetol and the subsequent hydrogenation of the latter to 1,2-propanediol.

Keywords: Glycerol hydrogenolysis; 1,2-Propanediol; Acetol hydrogenation; Copper catalysts; Copper surface area

The influence of the nanostructure on the effect of CO₂ on the properties of Pd–Ag thin-film for H₂ separation by Salvatore Abate; Gabriele Centi; Siglinda Perathoner; Dangsheng S. Su; Gisela Weinberg (pp. 158-168).

Display Omitted▶ Pd–Ag thin-film H₂ membrane nanostructure depends on co- versus sequential EPD. ▶ Dendritic-like nanostructure obtained by electroless plating deposition. ▶ CO₂ in the feed influences performances depending on membrane nanostructure. ▶ Creation of reversible strains and microholes due to combined effect of CO₂ and H₂.The use of co-deposition instead of sequential deposition during the preparation of Pd–Ag thin films by electroless plating deposition leads to two different nanostructures, e.g. a dendritic nanostructure or a more compact and dense film, allowing to analyze the role of this parameter, at equal membrane composition, on the performances. In pure H₂ the permeability to hydrogen of the second type of thin films is 3–4 times higher, but the presence of CO₂ in the feed changes considerably the performances. The results are tentatively interpreted on the basis of a non-permanent in situ modification of the characteristics of the Pd–Ag thin films, with creation of strains and microholes particularly enhanced for the nanostructure present in the sample prepared by co-deposition. These strains and microholes are suggested to derive from the combined effect of CO₂ (with creation of subsurface O and/or C) and of hydrogen diffusion through the thin film, which induces lattice expansion and stress on the nanograins. When the flux of H₂ stops, there is a relatively rapid restoring of the initial situation. Scanning electron microscopy (SEM) characterization after the tests in the presence of CO₂ indicates the presence of desintering consistently with above indications and the creation of crack like voids.

Keywords: Palladium; Thin films; Pd–Ag membrane; H; ₂; separation; Nanostructure; CO; ₂

Friedel–Crafts alkylations on nanoscopic inorganic fluorides by N. Candu; S. Wuttke; E. Kemnitz; S.M. Coman; V.I. Parvulescu (pp. 169-174).

The catalytic potential of nanoscopic MF_x (M=Mg, Al; x=2, 3) has been investigated using batch Friedel–Crafts alkylation of aromatic compounds, including benzene, ethylbenzene, trimethylhydroquinone (TMHQ), and menadiol (MDL), with isophytol and benzyl alcohol. An optimal combination of the catalyst nature, the substrate and alkylating agent reactivities is essential for the successful application of the reaction.Display Omitted▶ The overall rate of the vitamin E synthesis is dictated by the rate of the chromane ring closure step. ▶ Acid strength has a positive influence both on the reaction rate and the selectivity to vitamin E. ▶ Increasing the density of Brřnsted sites in disfavour of the Lewis sites slowers the rate of the alkylation step. ▶ The presence of Brřnsted acid sites is essential to promote the first alkylation synthesis step, while for the general synthesis the Lewis/Brřnsted acid site ratio is a critical feature.The catalytic potential of nanoscopic MF_x (M=Mg, Al; x=2, 3) has been investigated using batch Friedel–Crafts alkylation of aromatic compounds, including benzene, ethylbenzene, trimethylhydroquinone (TMHQ), and menadiol (MDL), with isophytol and benzyl alcohol. The conversion of isophytol was 100% in the reactions with trimethylhydroquinone (TMHQ), menadiol (MDL) and benzene while the highest selectivity in alkylated compounds was achieved with TMHQ (>99%). The different reaction rates of the alkylation reactions are due to the different nucleophylicities of the substrates, and therefore, due to their ability to delocalize the positive charge in the Wheland intermediate by inductive and resonance effects. The conversions of benzyl alcohol varied between 10 and 84% as a function of the catalyst nature and reaction conditions while the highest selectivity to monobenzyl derived compounds (25%) was achieved with ethylbenzene. The formation of high amounts of dibenzyl ether was also observed, indicating the presence of high amounts of Brønsted acid sites in this type of catalysts.

Keywords: Nanoscopic fluorides; Friedel–Crafts alkylation; Vitamins; Benzylation; Diphenylmethane; Benzyl alcohol

Friedel–Crafts alkylations on nanoscopic inorganic fluorides by N. Candu; S. Wuttke; E. Kemnitz; S.M. Coman; V.I. Parvulescu (pp. 169-174).

Keywords: Nanoscopic fluorides; Friedel–Crafts alkylation; Vitamins; Benzylation; Diphenylmethane; Benzyl alcohol

Strong metal–support interactions on rhodium model catalysts by Ch. Linsmeier; E. Taglauer (pp. 175-186).

Display Omitted▶ SMSI on oxide-supported rhodium catalysts are investigated by ISS and XPS. ▶ 773K reduction leads to encapsulation of Rh/titania model catalysts by oxide layer. ▶ Monolayer surface oxide leads to expected reduction in CO chemisorption. ▶ XPS following ambient pressure H₂ reduction shows no indication for Ti³⁺ at surface.Reactive processes on catalyst surfaces are studied in this work for Rh/metal oxide model systems by means of surface science techniques. Published results in the literature deal with titania, alumina, and silica as support materials and are briefly reviewed. For the present studies Rh/Al₂O₃ and Rh/TiO₂ model catalysts with about one monolayer Rh coverage are specially prepared and analyzed by ion scattering spectroscopy, X-ray photoelectron spectroscopy, and thermal desorption measurements as main techniques. In part these measurements are supported by a variety of other analytical and imaging techniques. For thermal treatment in hydrogen atmosphere at low and elevated pressures a complete Rh encapsulation by titania is observed for temperatures above 773K. The results from ion bombardment depth profiling are corroborated by the concomitant drastic reduction of the CO adsorption capacity of these samples. The model catalysts thus exhibit the typical features of ‘strong metal–support interaction’. The effect was not found for alumina supports, for which thermal treatments mainly resulted in gradual interdiffusion of the various surface species. These results also demonstrate that characteristic catalyst behavior can be successfully studied by applying surface science methods to model catalysts.

Keywords: Model catalyst; Rhodium; Titania; Alumina; Strong metal–support interactions; SMSI; Surface analysis; ISS; XPS; TPD

Strong metal–support interactions on rhodium model catalysts by Ch. Linsmeier; E. Taglauer (pp. 175-186).

Keywords: Model catalyst; Rhodium; Titania; Alumina; Strong metal–support interactions; SMSI; Surface analysis; ISS; XPS; TPD

Nano-structural investigation of Ag/Al₂O₃ catalyst for selective removal of O₂ with excess H₂ in the presence of C₂H₄ by B. Inceesungvorn; J. López-Castro; J.J. Calvino; S. Bernal; F.C. Meunier; C. Hardacre; K. Griffin; J.J. Delgado (pp. 187-193).

. Ag/γ-Al₂O₃ is a very active and highly selective catalyst toward the oxygen removal with excess H₂ in the presence of unsaturated hydrocarbons. In situ diffuse reflectance UV–visible spectroscopy and quasi in situ TEM were used to study the sintering/redispersion of the metal during different thermo-chemical treatments. The effect of the reaction feed on the metal dispersion and the formation of active sites is also discussed.Display Omitted▶ In situ catalyst characterization by diffuse reflectance UV-visble. ▶ Silver catalyst for selective removal of oxygen. ▶ Ethene purification.▶ Quasi in situ TEM characterization of solids.Ag/γ-Al₂O₃ catalysts have been characterized in-depth during different thermo-chemical treatments by in situ diffuse reflectance UV–visible spectroscopy and quasi in situ Transmission Electron Microscopy. The combination of these techniques indicates that sintering and redispersion of silver is clearly observed from the increases and decreases in the absorption band intensity over the range of 250–600nm due to the presence of silver clusters and silver nanoparticles. These results allow us to study the effect of the reaction feed on the metal dispersion at different operation conditions and discuss the formation of active sites during the selective catalytic reduction of O₂ with excess H₂ in the presence of unsaturated hydrocarbons. In this case high catalytic activity and selectivity toward the oxygen removal was achieved for this catalyst.

Keywords: Silver catalyst; In situ; diffuse reflectance UV–visible spectroscopy; Quasi in situ; TEM

Catalytic performance of niobium species in crystalline and amorphous solids—Gas and liquid phase oxidation by M. Ziolek; P. Decyk; I. Sobczak; M. Trejda; J. Florek; H. Golinska. W. Klimas; A. Wojtaszek (pp. 194-204).

Nb-containing molecular sieves and Nb₂O₅ (crystalline and amorphous) were used as catalysts in gas phase oxidation of methanol with oxygen, liquid phase oxidation of glycerol with oxygen and cyclohexene with hydrogen peroxide. H₂O₂ interacts with the amorphous catalysts towards ONb(V)O₂ radicals very active in epoxidation of cyclohexene. It is not the case for Nb in crystalline catalysts, which are active in chemisorption of alcohols.Display Omitted▶ Difference in oxidation activity if Nb located in amorphous or crystalline catalyst. ▶ H₂O₂ as oxidant – formation of active ONb(V)O₂ radicals if amorphous catalyst. ▶ Nb in amorphous oxide – active but not selective in MeOH oxidation. ▶ Nb dispersed in amorphous mesoporous silica active and selective in oxidation. ▶ Nb in supports promotes stabilization of active species loaded (Cu, Au, Sb–V–O_x).This paper is devoted to the role of niobium, located in crystalline and amorphous catalysts, in catalytic oxidation reactions. Bulk niobium(V) oxides (crystalline and amorphous), NbMCM-41, NbSBA-3, NbSBA-15 and NbY materials were used as catalysts in gas phase oxidation of methanol with oxygen, liquid phase oxidation of glycerol with oxygen and liquid phase oxidation of cyclohexene with hydrogen peroxide. When H₂O₂ was applied as an oxidation agent the amorphous materials containing niobium species were the most effective catalysts because Nb in such catalysts strongly interacts with H₂O₂ resulting in the formation of active ONb(V)O₂ radicals. It was not the case for crystalline catalysts containing niobium. The results obtained for Nb-containing materials used as supports for copper, gold and binary Sb–V–O_x oxides indicated that niobium species promotes stabilization of the active species loaded. Moreover, it was shown that gold loaded on crystalline niobia increases the catalytic activity in dehydrogenation of methanol and glycerol, which is the first step of their oxidation with oxygen.

Keywords: Ordered mesoporous niobiosilicas; Nb; ₂; O; ₅; Au; Cu; Sb–V–O; _x; Oxidation of methanol; Glycerol and cyclohexene

Oxidative coupling of methane over Ca- and alkali metal-doped ThO₂ by Tinku Baidya; Niels van Vegten; Yijiao Jiang; Frank Krumeich; Alfons Baiker (pp. 205-214).

The Ca-doped ThO₂ catalyst shows high catalytic activity and selectivity toward C₂₊ products for oxidative coupling of methane due to favorable formation of oxide ion radical in the defect lattice.Th_0.8Ca_0.2O2−_δ and Na/K dispersed Th_0.8Ca_0.2O2−_δ catalysts, synthesized by the citric acid gel method, have been tested concerning their efficiency in the oxidative coupling of methane. The structural properties of the catalysts were characterized by BET, XRD, Raman, TEM, TPD, and EPR techniques. The presence of oxide ion vacancies due to Ca ion incorporation into ThO₂ lattice was evidenced by Raman spectroscopy. EPR revealed the formation of radical oxygen in the Ca-doped ThO₂ sample after oxygen treatment at 500°C. Th_0.8Ca_0.2O2−_δ showed high catalytic activity reaching about 24% methane conversion (rate: 2.3molg⁻¹h⁻¹) at 56% selectivity toward C n₊ products at 600°C, whose performance is comparable to that of the well known Sr doped La₂O₃ catalyst. Other reference catalysts like 1.9%Mn–4%Na₂WO₄/SiO₂ and 5%Li/MgO showed considerably lower activity under these conditions. The high catalytic activity and selectivity of the Ca-doped sample is likely due to formation of stable activeO˙− species in the oxide ion vacancy site in the lattice.

Keywords: Thoria; Ca and alkali metal doping; Oxidative coupling of methane; Oxide ion vacancy; Oxide ion radical

Oxidative coupling of methane over Ca- and alkali metal-doped ThO₂ by Tinku Baidya; Niels van Vegten; Yijiao Jiang; Frank Krumeich; Alfons Baiker (pp. 205-214).

Keywords: Thoria; Ca and alkali metal doping; Oxidative coupling of methane; Oxide ion vacancy; Oxide ion radical

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films by Rhys Lloyd; Thomas W. Hansen; Wolfgang Ranke; Friederike C. Jentoft; Robert Schlögl (pp. 215-224).

The sites on sulfated zirconia were characterised by first creating a model system in the form of a nanocrystalline film and then using ultraviolet photoelectron spectroscopy to follow the adsorption of n-butane. Isobars and isosteric heats of adsorption are deduced from the data, and the site distribution is elucidated.Display Omitted▶ Nanocrystalline thin films of sulfated zirconia synthesized. ▶ Formation of amorphous or tetragonal phase attributed to surface energy effects. ▶ UP spectra of adsorbed n-butane measured. ▶ n-Butane heats of adsorption deduced and adsorption site distribution elucidated. ▶ Adsorbate–adsorbate interactions present at coverages of 5–8% of a monolayer.Nanocrystalline thin films of the alkane skeletal isomerisation catalyst sulfated zirconia were successfully deposited on a silicon substrate in order to allow the application of surface science techniques. Thermal treatment of the films was optimised to chemically mimic the powder preparation process, resulting in films possessing the essential features (including tetragonal phase, nanocrystallinity and sulfur content of ∼3at.%) of active powder catalysts. The n-butane adsorption–desorption equilibrium under isobaric conditions (10⁻⁸–10⁻⁶hPa) over the temperature range 300–100K was monitored by photoelectron spectroscopy. Analysis of the isobars revealed strong and weak n-butane chemisorption sites, releasing heats of between 59–40 and 47–34kJ/mol, corresponding to 5 and 25% of a monolayer coverage, respectively. The total amount of chemisorbed n-butane coincides with the estimated number of surface sulfate groups. An increase in adsorption heat was observed between coverages of ∼5–8% of a monolayer, indicating adsorbate–adsorbate interactions. It follows that adjacent sites are present and isomerisation by a bimolecular surface reaction is feasible. Physisorption on the films generates heats of ∼28kJ/mol, for coverages from 30% up to a complete monolayer. Multilayer adsorption results in the formation of an electrically insulating adsorbate structure. It is proposed that the strong chemisorption sites correspond to an interaction with a minority disulfate species.

Keywords: Sulfated zirconia; Model system; TEM; XPS; UPS; Butane; Heats of adsorption

Nitridation of BaO supported on mesoporous materials: Basicity characterization and catalytic properties by Guangjun Wu; Shaoliang Jiang; Landong Li; Naijia Guan (pp. 225-233).

Nitridation was used to improve the surface basicity of BaO supported on MCM-41 and SBA-15 mesoporous materials. Obviously, the as-prepared mesoporous materials with stronger basicity exhibited better base catalytic results in the conversion of 2-propanol..Display Omitted▶ The surface basicity of BaO-MCM-41 and BaO-SBA-15 is improved by nitridation. ▶ The Ba₂SiO₄ and -NH- base species are formed on the surface after nitridation. ▶ BaO-MCM-41N and BaO-SBA-15N present enhanced basic catalytic properties.Nitridation has drawn much attention as a novel method to prepare solid base materials. In the present work, nitridation was employed to improve the basic property of BaO supported on mesoporous materials. Ba₂SiO₄ and Ba₄Si₆O₁₆ basic species were formed after BaO loading on MCM-41 and SBA-15, respectively while only Ba₂SiO₄ species were observed both on MCM-41 and SBA-15 after nitridation. Basic species, bridging –NH– groups, were introduced into the framework of BaO-MCM-41/SBA-15 by nitridation with the mesoporous structure preserved. The surface basic property of obtained samples was analyzed by IR spectra using CDCl₃ and CO₂ as probe molecules and XPS. The enhancement in the surface basicity was observed after nitridation. Compared with BaO-MCM-41/SBA-15, the N-incorporated materials with stronger basicity exhibited higher activities in Knoevenagel condensation and the conversion of 2-propanol.

Keywords: BaO; Mesoporous materials; Nitridation; Basicity; Base-catalyzed reactions

Nitridation of BaO supported on mesoporous materials: Basicity characterization and catalytic properties by Guangjun Wu; Shaoliang Jiang; Landong Li; Naijia Guan (pp. 225-233).

Keywords: BaO; Mesoporous materials; Nitridation; Basicity; Base-catalyzed reactions

Shape selective methanol to olefins over highly thermostable DDR catalysts by Yasukazu Kumita; Jorge Gascon; Eli Stavitski; Jacob A. Moulijn; Freek Kapteijn (pp. 234-243).

ZSM-58, having a DDR topology, is shown to be a very attractive catalyst for the direct formation of propylene and ethylene via conversion of methanol. Mainly propylene, ethylene and linear butenes (trans-but-2-ene and butadiene) are formed when materials with the DDR topology are used as catalysts during the MTO process. The ratio propylene/ethylene can be tuned by changing the reaction conditions.Display Omitted▶ Propylene and ethylene are the major products when ZSM-58 is used as catalysts for the MTO process. ▶ Propylene/ethylene ratio can be tuned. ▶ Activity is fully recovered after regeneration in air.ZSM-58, having a DDR topology, is shown to be a very attractive catalyst for the direct formation of propylene and ethylene via conversion of methanol. A performance similar to the state of the art SAPO-34 catalysts is achieved, while no olefins longer than C₄ are formed. In addition, ZSM-58 has a much higher thermostability than SAPO catalysts.Mainly propylene, ethylene and linear butenes (trans-but-2-ene and butadiene) are formed when materials with the DDR topology are used as catalysts during the MTO process. The ratio propylene/ethylene can be tuned by changing the reaction conditions or the degree of catalyst coking. An optimum in performance, in terms of stability and selectivity, is found for catalysts containing one acid site (one Al) per accessible cavity. Deactivation of the catalysts takes place due to formation of coke and homogeneous blocking of the catalysts porosity. Activity is fully recovered after regeneration in air.

Keywords: DDR; ZSM-58; MTO; ZSM-5; NH3-TPD

Shape selective methanol to olefins over highly thermostable DDR catalysts by Yasukazu Kumita; Jorge Gascon; Eli Stavitski; Jacob A. Moulijn; Freek Kapteijn (pp. 234-243).

Keywords: DDR; ZSM-58; MTO; ZSM-5; NH3-TPD

Control of metal ion species in zeolites by distribution of aluminium in the framework: From structural analysis to performance under real conditions of SCR-NO x and NO, N₂O decomposition by J. Dědeček; L. Čapek; P. Sazama; Z. Sobalík; B. Wichterlová (pp. 244-253).

Isolated Al and Al pairs in the framework decisively control the structure, properties and activity of the counter Co, Cu and Fe species in Co-BEA, Cu-MFI and Fe-FER catalysts. This enables to tailor the catalyst structures for reactions of technology importance: C₃H₈-SCR-NO x and decomposition of NO and N₂O under real conditions of wet NO x streams.Display Omitted▶ Distribution of aluminium atoms in the framework controls structure and activity of metallo-zeolites. ▶ Divalent bare cations balanced by Al pairs and metal-oxo species balanced by isolated Al atoms exhibit dramatically different redox behavior. ▶ Co-oxo species in BEA balanced by isolated Al atoms are active in C₃H₈-SCR-NOx under excess of water vapor. ▶ Two Fe ions in FER, each balanced by an Al pair and located at opposite cationic sites are active in N₂O decomposition. ▶ Cu ions charge-balanced by isolated Al atoms and readily reduced are centers for NO decomposition.The structure, properties and activity of the counter Co, Cu and Fe ion species depending on the distribution of aluminium atoms in the framework between Al pairs of Al–O–(Si–O)₂–Al sequences in one ring and isolated Al atoms (Al–O–(Si–O) n_>2–Al sequences) in two rings are analyzed. The effect of the Al distribution on the activity of metal ion species is investigated for reactions of technology importance, i.e. SCR-NO x by propane, and decomposition of NO and N₂O under real conditions of NO x streams. Zeolite samples of BEA, MFI and FER structures, of similar composition for each topology, but with basically different distribution of Al atoms in the framework, were either selected from commercial samples or prepared by the developed synthesis. The concentration of Al pairs and isolated Al atoms in the framework was determined by the combination of²⁹Si MAS NMR and quantitative analysis of the Vis spectra of dehydrated Co-zeolites with Co(II) ions exchanged to a maximum degree. The structure and reactivity of the metal sites was described by UV–Vis, FTIR of skeletal vibrations and adsorbed NO, TPR-H₂ and reactions of C₃H₈-SCR-NO x/H₂O, and NO and N₂O decomposition. It is concluded that the local negative framework charge, originated from Al pairs and isolated Al atoms, constitutes a decisive parameter controlling the structure and reactivity of the counter metal ion species. The bare Co(II), Cu(II) and Fe(II) ions are balanced by Al pairs, while Co-oxo and Cu-oxo or Cu(I) species are adjacent to isolated Al atoms. The Cu(I) ions in vicinity of isolated Al atoms in Cu-MFI zeolites are the most active sites in NO decomposition. Co-oxo species attached to isolated Al atoms in Co-BEA zeolites, in contrast to bare Co(II) ions, exhibit high activity in C₃H₈-SCR-NO x/H₂O in the presence of water vapor. N₂O decomposition to elements over Fe-FER requires two Fe ions at a defined distance of β cationic sites, with each Fe(II) cation charge-balanced by an Al pair.

Keywords: Zeolites; Co-BEA; Cu-MFI; Fe-FER; Framework Al; Al distribution in zeolites; SCR-NO; NO decomposition; N; ₂; O decomposition

Novel extruded fixed-bed MTO catalysts with high olefin selectivity and high resistance against coke deactivation by Jens Freiding; Bettina Kraushaar-Czarnetzki (pp. 254-260).

This report describes the catalytic performances of AlPO₄/ZSM-5 extrudates in comparison to conventional alumina- and silica-bound extrudates in the fixed-bed MTO (methanol to olefins) conversion. The novel AlPO₄/ZSM-5 extrudates are produced with an aluminium phosphate binder which undergoes a phase transition into an AlPO₄-tridymite phase upon calcination of the greenbodies. The finished AlPO₄/ZSM-5 extrudates are macroporous and mechanically very stable. In contrast to alumina, this novel matrix does not exhibit catalytic self-activity, and it does not release aluminium which is incorporated in the zeolite lattice. At temperatures above 400°C, AlPO₄/ZSM-5 extrudates show superior activity, propylene selectivity and stability. The coke deactivation of AlPO₄/ZSM-5 extrudates can further be reduced dramatically, if a pre-reactor is installed upstream, where an equilibrium mixture of dimethyl ether (DME), methanol and water ( X_MeOH=87.7% at 275°C) is produced. In contrast, the insertion of the DME pre-reactor has no significant effect on the coke resistance when extrudates with alumina- or silica-matrices are used.This report describes the catalytic performances of AlPO₄/ZSM-5 extrudates in comparison to alumina- and silica-bound extrudates in the fixed-bed methanol to olefins conversion. The AlPO₄-matrix is macroporous, non-reactive and does not release aluminium into the zeolite lattice. Above 400°C, AlPO₄/ZSM-5 extrudates show superior activity, selectivity and stability. Coke deactivation of AlPO₄/ZSM-5 can further be reduced with a pre-reactor upstream, where dimethyl ether is produced.

Keywords: MTO (methanol to olefins); ZSM-5; Coke deactivation; Extrusion; Aluminium phosphate

Novel extruded fixed-bed MTO catalysts with high olefin selectivity and high resistance against coke deactivation by Jens Freiding; Bettina Kraushaar-Czarnetzki (pp. 254-260).

Keywords: MTO (methanol to olefins); ZSM-5; Coke deactivation; Extrusion; Aluminium phosphate

MOFs meet monoliths: Hierarchical structuring metal organic framework catalysts by Enrique V. Ramos-Fernandez; Mariana Garcia-Domingos; Jana Juan-Alcañiz; Jorge Gascon; Freek Kapteijn (pp. 261-267).

The optimized synthesis and catalytic performance of a monolith supported Metal-Organic Framework, MIL-101(Cr), is presented. The MIL-101(Cr) was immobilized on monoliths using seeding techniques followed by a secondary growth. A monolithic stirrer reactor has been used as playground for exploring reactivation procedures of MIL-101 in the selective oxidation of tetralin.Structuring heterogeneous catalysts from the micro- to the macro-level is essential for efficient catalyst utilization. The optimized synthesis and the catalytic performance of a Metal-Organic Framework, MIL-101(Cr), immobilized on a monolithic structure is presented. Secondary seeded growth is the optimal procedure to obtain uniform coatings of ∼9wt.% inside the monolith channels. A monolithic stirrer reactor has been used as playground for exploring reactivation procedures of MIL-101 for the selective oxidation of tetralin in the liquid phase. The presented results confirm the long-term stability of the catalyst, and the absence of any transport limitations in this reaction. The easy recovery of the catalyst allows performing as many reuses as necessary, something impossible to realize when working in the often-practised slurry operation mode. The reported results demonstrate that MIL-101(Cr) undergoes reversible deactivation attributed to the strong adsorption of products on the Cr sites. Applying the proper regeneration procedure (washing in chlorobenzene and air treatment @ 523K) the initial performance is fully recovered.

Keywords: Selective Oxidation; MOF immobilization; MIL-101(Cr); Tetralin; Monoliths

CO oxidation with Au/TiO₂ aggregates encapsulated in the mesopores of MCM-48: Model studies on activation, deactivation and metal–support interaction by Maurits W.E. van den Berg; Andrea De Toni; Mahuya Bandyopadhyay; Hermann Gies; Wolfgang Grünert (pp. 268-280).

Au/TiO₂ aggregates in MCM-48 exhibit similar CO oxidation activities as conventional Au/TiO₂. In situ EXAFS studies did not indicate an ordered relation at the Au/TiO₂ interface and suggested major activity contributions from sub-nanometer particles. Formed by activation in CO/air feed, these were rapidly poisoned, which could be reverted by thermal inert gas treatment. Complete reduction of Au ions did not cause breakdown of activity, which suggests minor relevance of Au ions.Display Omitted▶ Au/TiO₂ nanoaggregates in MCM-48 with competitive CO oxidation activity. ▶ Au particles sizes per EXAFS below metal-nonmetal transition, no order at Au-TiO₂ interface. ▶ CO oxidation activity observed after complete precursor reduction casts doubt on role of Au ions in CO oxidation. ▶ Drastic activation by thermal inert gas treatment followed by strong self-poisoning suggests steady-state activity coming from a minority of available sites.The activation of Au/TiO₂ clusters encapsulated in MCM-48 and related poisoning phenomena were studied. With these catalysts, which contain extremely disperse Au particles (average size below 1nm still after exposure to 473K according to EXAFS), light-off temperatures of 250–280K were obtained upon activation by precursor reduction in a net oxidizing CO/O₂ feed, which is well comparable with state of the art Au/TiO₂ catalysts. This activation was, however, found to be superimposed by parallel poisoning. In an operando XAFS study with catalyst batches containing Au(III) precursor species of different reducibility for unknown reasons, it was observed that the final activity was strongly influenced by the precursor reduction. Apparently, high activities were achieved by Au particles formed at low temperatures making contact with the clean support surface. Delayed Au(III) reduction produced particles of similar size but much lower activity, probably due to predominant contact with poisoned support species. The catalysts were most active right after an initial incomplete reduction of the Au(III) precursor and deactivated at higher temperature despite further Au(0) formation. However, as complete reduction of Au ions did not cause breakdown of CO oxidation activity, Au ions do not seem to be a part of the active site. The poisoning could be effectively removed by an inert gas treatment at temperatures up to 673K, which resulted in light-off temperatures down to 225K. Turnover frequencies derived for this state agree with data published recently for sub-nanometer bilayered Au particles, which supports the importance of sub-nanometer particles for CO oxidation over Au catalysts. From the absence of significant contributions from support oxygen in the Au L_III EXAFS spectra and of Au-derived signals in Ti K EXAFS spectra of reduced catalysts, it was concluded that there was no ordered relation between metal clusters and support surface, which appears therefore to be irrelevant for CO oxidation.

Keywords: Gold; Titania; MCM-48; CO oxidation; Host–guest systems; In situ XAFS

Palladium–silver bimetallic catalysts with improved activity and selectivity for ethylene epoxidation by J.C. Dellamorte; J. Lauterbach; M.A. Barteau (pp. 281-288).

Display Omitted▶ DFT calculations predict higher ethylene epoxidation selectivity for Pd–Ag catalysts. ▶ Pd–Ag catalysts with 100ppm Pd show higher measured activity and selectivity. ▶ Performance of Pd–Ag catalysts is similar to Cu–Ag catalysts.Palladium addition to silver catalysts for ethylene epoxidation increases both catalyst activity and selectivity to ethylene oxide. These results confirm the predictions from density functional theory calculations that Pd–Ag bimetallics should improve selectivity relative to unpromoted silver. The performance of Pd–Ag catalysts is similar to that of Cu–Ag catalysts investigated previously, although the maximum selectivity obtained for the optimum Pd–Ag catalyst in the present study exceeds that achieved with Cu–Ag catalysts. Although there is evidence for greater complexity in the structure of these catalysts than has been incorporated in DFT models, these results provide an important additional example of catalyst identification and design from first principles.

Keywords: Ethylene oxide; Olefin epoxidation; Palladium; Silver; Bimetallic catalysts; Catalyst design; High-throughput reactor

Palladium–silver bimetallic catalysts with improved activity and selectivity for ethylene epoxidation by J.C. Dellamorte; J. Lauterbach; M.A. Barteau (pp. 281-288).

Keywords: Ethylene oxide; Olefin epoxidation; Palladium; Silver; Bimetallic catalysts; Catalyst design; High-throughput reactor

Investigations on a Pt/TiO₂ catalyst coating for oxidation of SO₂ in a microstructured reactor for operation with forced decreasing temperature profile by P. Pfeifer; T. Zscherpe; K. Haas-Santo; R. Dittmeyer (pp. 289-296).

The process of sulphur trioxide production could be conducted as a one-step process in microreactors with forced decreasing temperature profile. For demonstration of the process, we prepared catalysts with 9wt.% Pt on TiO₂ on microstructured titanium foils by means of a sol–gel method followed by wet impregnation. The catalyst was investigated by various methods to study the Pt distribution. Furthermore, we investigated the start-up behaviour and lifetime of the catalyst.Display Omitted▶ Detailed study on Pt/TiO₂ catalyst layer properties for sulphur dioxide oxidation in microreactors. ▶ Comparison of Pt/TiO₂ catalysts and vanadium catalysts for SO₂ oxidation in microreactors. ▶ Investigation of start-up routines for platinum catalysts for SO₂ oxidation. ▶ Investigation of deactivation of Pt/TiO₂ catalysts in SO₃ generation.The process of sulphur trioxide production could be conducted as a one-step process in microreactors with forced decreasing temperature profile due to their unique heat and mass transfer capabilities. The choice of a very active catalyst in such reactors is one of the key issues to avoid excessive microfabrication and consequently reactor costs. Comparing vanadium to platinum, we found that platinum is the preferred catalyst based on calculations of the ratio of catalyst to reactor volume combined with the specific activity of the catalysts. To demonstrate the feasibility of the one-step process experimentally, we prepared catalysts with 9wt.% Pt on TiO₂ on microstructured titanium foils by means of a sol–gel method followed by wet impregnation. The catalyst was investigated by SEM, EDX, adsorption measurements and microprobe analysis to study the Pt distribution. We found almost equal distribution of platinum in the TiO₂ layer, both with respect to the axial position in the channels as well as regarding the concentration profile of Pt in depth of the support layer. Pores might at least partially be blocked with Pt. Furthermore, we investigated the influence of the start-up behaviour on the lifetime of the catalyst, finding that starting up with the SO₂–O₂ mixture gives the most stable operation. Humidity, which cannot be avoided in the laboratory set-up and the graphite-sealed microreactor, is assumed to be the main reason for deactivation during shut-downs.

Keywords: Forced temperature profile; Microreactor; One-pass synthesis; SO; ₂; oxidation

Bis(pyridyl)siloxane–Pd(II) complex catalyzed oxidation of alcohol to aldehyde: Effect of ligand tethering on catalytic activity and deactivation behavior by Michael N. Missaghi; John. M. Galloway; Harold H. Kung (pp. 297-304).

Ligands containing two pyridyl groups tethered to a flexible methylsiloxane spacer are effective ligands in the Pd(OAc)₂-catalyzed aerobic oxidation of benzyl alcohol to benzaldehyde. The stabilization effect was the strongest for spacers just long enough to favor bidentate coordination of Pd to form a monomeric ring complex.Display Omitted▶ Bis(pyridyl)siloxane ligands are effective in stabilizing Pd(II) complexes. ▶ Ability to stabilize Pd(II) complexes depends strongly on length of ligand. ▶ Bis(pyridyl)siloxane ligands that form monomeric rings preferentially are more effective than others.A series of oligomeric methylsiloxane compounds functionalized with pyridyl groups was synthesized and used as ligands in the aerobic Pd(OAc)₂-catalyzed oxidation of benzyl alcohol to benzaldehyde at 353K. The effect of tethering two pyridine ligands at the terminal positions of linear siloxanes of varying length was systematically investigated, as was the effect of the attachment point of the pyridine ring ( meta or para). It was found that meta-substituted pyridylsiloxanes were generally more effective in protecting the catalyst against Pd agglomeration. For this purpose, the optimal meta-pyridylsiloxane ligands had 4–6 silicon atoms or 10 silicon atoms for para-pyridylsiloxane ligands. The metal–ligand binding properties were used to interpret the catalytic behavior, and the ability of the catalyst stability correlated with ability of the bis-pyridyl ligand to form a mononuclear cyclic complex with Pd.

Keywords: Partial oxidation; Pd(II) catalysis; Ligand tethering; Pyridylsiloxane

Hydrodeoxygenation of guaiacol as model compound for pyrolysis oil on transition metal phosphide hydroprocessing catalysts by H.Y. Zhao; D. Li; P. Bui; S.T. Oyama (pp. 305-310).

Transition metal phosphides were active for the hydrodeoxygenation of guaiacol producing benzene and phenol as the major products. The turnover frequency based on active sites titrated by the chemisorption of CO followed the order: Ni₂P>Co₂P>Fe₂P, WP, MoP. A commercial catalyst 5% Pd/Al₂O₃ produced only catechol, while a commercial CoMoS/Al₂O₃ showed little activity for HDO and deactivated quickly.The gas phase hydrodeoxygenation (HDO) of guaiacol, as a model compound for pyrolysis oil, was tested on a series of novel hydroprocessing catalysts – transition metal phosphides which included Ni₂P/SiO₂, Fe₂P/SiO₂, MoP/SiO₂, Co₂P/SiO₂ and WP/SiO₂. The turnover frequency based on active sites titrated by the chemisorption of CO followed the order: Ni₂P>Co₂P>Fe₂P, WP, MoP. The major products from hydrodeoxygenation of guaiacol for the most active phosphides were benzene and phenol, with a small amount of methoxybenzene formed. Kinetic studies revealed the formation of reaction intermediates such as catechol and cresol at short contact times. A commercial catalyst 5% Pd/Al₂O₃ was more active than the metal phosphides at lower contact time but produced only catechol. A commercial CoMoS/Al₂O₃ deactivated quickly and showed little activity for the HDO of guaiacol at these conditions. Thus, transition metal phosphides are promising materials for catalytic HDO of biofuels.

Keywords: Hydrodeoxygenation; Guaiacol; Biooil; Transition metal phosphides; Ni; ₂; P; CoMoS

Hydrodeoxygenation of guaiacol as model compound for pyrolysis oil on transition metal phosphide hydroprocessing catalysts by H.Y. Zhao; D. Li; P. Bui; S.T. Oyama (pp. 305-310).

Keywords: Hydrodeoxygenation; Guaiacol; Biooil; Transition metal phosphides; Ni; ₂; P; CoMoS

Modification of the catalytic properties of a Pd membrane catalyst for direct hydroxylation of benzene to phenol in a double-membrane reactor by sputtering of different catalyst systems by R. Dittmeyer; L. Bortolotto (pp. 311-318).

The surface of hydrogen-permeable PdCu membranes acting as a catalyst for direct hydroxylation of benzene to phenol in the gas phase in a novel catalytic double-membrane reactor was modified by sputtering on it different catalytic layers. Selectivity reached up to 67% with a Pd₉₀Au₁₀ layer. The PdGa layer showed promising catalytic performance in hydrogen co-feed mode but suffered from a low hydrogen permeance in membrane mode.Display Omitted▶ Distributed supply of O₂ via second membrane gave improved phenol selectivity compared to co-feed mode. ▶ PdAu and PdGa showed improved activity and selectivity for benzene hydroxylation in the gas phase with in situ-H₂O₂ compared to Pd and PdCu. ▶ Poor utilization of H₂ and low reactivity of benzene render the system unattractive.The surface of hydrogen-permeable PdCu membranes acting as a catalyst for direct hydroxylation of benzene to phenol in the gas phase in a novel catalytic double-membrane reactor was modified by sputtering on it different catalytic layers with the aim to increase the formation rate and selectivity to phenol. Three different systems are described: a 1μm thick compact layer of Pd₉₀Au₁₀ (10wt.% Au), a 5μm thick compact layer of PdGa (50at.% Ga) and a thin film of Pd₉₀Au₁₀ deposited on a discontinuous V₂O₅ layer. The different systems were characterized by SEM, EDX, and mainly in terms of their catalytic properties for benzene hydroxylation. The formation rate and the selectivity to phenol could be increased substantially through the catalytic modification. With a maximum phenol selectivity of 67% at 150°C and a maximum phenol formation rate of 1.67×10⁻⁴molh⁻¹m⁻² at 200°C, PdAu reached the best performance in double-membrane operation mode. PdGa showed even more promising results compared to PdAu in kinetic experiments in co-feed operation mode, but suffers from the very low hydrogen permeability of PdGa which stands against its use as a continuous layer in the catalytic membrane reactor.

Keywords: Membrane reactor; Catalyst layer; Palladium; Gallium; Gold; PdGa; PdAu; Benzene; Phenol; Direct hydroxylation

Continuous selective hydrogenation of citral in a trickle-bed reactor using ionic liquid modified catalysts by Nicolai Wörz; Jürgen Arras; Peter Claus (pp. 319-324).

. The influence of the ionic liquid [BMIM][N(CN)₂] on the palladium catalyzed hydrogenation of citral in a trickle-bed reactor has been investigated. Applying the SCILL concept (solid catalyst with ionic liquid layer) it was possible to attain citronellal selectivities close to 100%.Display Omitted▶ Citral hydrogenation has been investigated over supported catalysts with an ionic liquid layer (SCILL) of [BMIM][N(CN)₂] in continuous mode using a trickle-bed reactor (TBR). ▶ The SCILL catalyst exhibits long-term stability. ▶ Selectivities to citronellal close to 100% at high conversion were obtained.The influence of the ionic liquid [BMIM][N(CN)₂] on the palladium catalyzed hydrogenation of citral in a trickle-bed reactor has been investigated. Applying the SCILL concept (solid catalyst with ionic liquid layer), it was possible to attain citronellal selectivities close to 100% at the cost of catalyst activity. However, the yield of this intermediate was approximately four times higher compared to the neat palladium catalyst. The latter and its SCILL counterpart both seem to have long-term stability, which is relevant for any future industrial application. This is the first time that SCILL systems have been compared directly to their IL-free equivalents in continuous mode.

Keywords: Trickle-bed reactor; Liquid phase hydrogenation; Citral; Ionic liquid; SCILL catalyst

Continuous selective hydrogenation of citral in a trickle-bed reactor using ionic liquid modified catalysts by Nicolai Wörz; Jürgen Arras; Peter Claus (pp. 319-324).

Keywords: Trickle-bed reactor; Liquid phase hydrogenation; Citral; Ionic liquid; SCILL catalyst

What drives the selectivity for CO methanation in the methanation of CO₂-rich reformate gases on supported Ru catalysts? by Stephan Eckle; Hans-Georg Anfang; R. Jürgen Behm (pp. 325-333).

The removal of CO from H₂-rich gas mixtures via selective methanation is an attractive way for producing CO-free fuel cell feeds from CO₂ containing reformate. Comparing two supported Ru catalysts, we demonstrate by combined kinetic and in situ IR measurements that the high CO selectivity of a Ru/zeolite catalysis is not driven by a blocking CO adlayer, but by its inherent inactivity towards CO2 dissociation and methanation.Display Omitted▶ Methanation is an attractive way to produce CO-free fuel cell feeds from CO₂ containing reformates. ▶ On Ru/Al₂O₃ the selectivity for CO reforming is determined by CO_ad induced site blocking. ▶ Ru/zeolite shows 100% selectivity even at low CO partial pressures and CO_ad coverages. ▶ Here CO selectivity is due to an inherent low activity for CO₂ dissociation.Aiming at a mechanistic understanding of their selectivity for CO methanation and the underlying physical reasons, we have investigated the selective methanation of CO over two supported Ru catalysts, a Ru/zeolite catalyst and a Ru/Al₂O₃ catalyst, in CO₂-rich reformate gases by combined kinetic and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements. Based on the correlation between CO_ad band intensity/CO_ad coverage and the selectivity for CO methanation over a wide range of CO contents, down to 100ppm, two different mechanisms are identified for the two catalysts. On Ru/Al₂O₃, the selectivity results from blocking of active surface sites by adsorbed CO, while for the Ru/zeolite catalyst we relate this to an inherently low activity of the very small Ru nanoparticles for CO₂ dissociation and subsequent methanation. The underlying reasons and consequences for practical applications are discussed.

Keywords: Selective methanation; CO methanation; Mechanism; CO adsorption; Ru catalyst

What drives the selectivity for CO methanation in the methanation of CO₂-rich reformate gases on supported Ru catalysts? by Stephan Eckle; Hans-Georg Anfang; R. Jürgen Behm (pp. 325-333).

Keywords: Selective methanation; CO methanation; Mechanism; CO adsorption; Ru catalyst

Chemically modified cyclodextrins as supramolecular tools to generate carbon-supported ruthenium nanoparticles: An application towards gas phase hydrogenation by F. Wyrwalski; B. Léger; C. Lancelot; A. Roucoux; E. Monflier; A. Ponchel (pp. 334-341).

Zerovalent ruthenium nanoparticles can be efficiently stabilized by randomly methylated cyclodextrins (CDs) from chemical reduction of ruthenium salt in water followed by their adsorption onto a carbon support. The optimization of the Ru-CD catalytic systems has been carried out by evaluating the gas phase hydrogenation of xylenes under mild reaction conditions, tested separately and in a two-component mixture..Display Omitted▶ Preparation of ruthenium nanoparticles on activated carbon under mild conditions. ▶ Use of non toxic oligosaccharides as pre-stabilizers. ▶ Enhancement of catalytic performances in xylene hydrogenation at 85°C. ▶ Best performances with RaMe-β-CD in a single and two-component mixture. ▶ No pre-reduction at high-temperature.A series of carbon-supported ruthenium catalysts was synthesized from zerovalent ruthenium nanoparticles stabilized by randomly methylated cyclodextrins (α-, β- and γ-CD) followed by their adsorption onto the carbon support. The catalysts were characterized by N₂ physisorption and thermal analyses. The deposited ruthenium nanoparticles were characterized by transmission electron microscopy, which has highlighted predominantly spherical shapes with a mean diameter of 2.4nm. Catalytic activity was investigated in the gas phase hydrogenation of o-, m- and p-xylene at 85°C, both separately and in a two-component mixture ( o- and p-xylene). The catalyst prepared by a 1:3 concentration ratio of RuCl₃ to randomly methylated β-cyclodextrin exhibited the highest hydrogenation activity and stereoselectivity toward the formation of trans-dimethylcyclohexane. The β-cyclodextrin appeared as multifunctional molecular receptors enabling the stabilization and dispersion of the metallic nanoparticles onto the support and the promotion of the catalytic reaction through host–guest interactions.

Keywords: Cyclodextrins; Metallic nanoparticles; Activated carbon; Hydrogenation; Gas phase reactions

Preparation and characterization of Co–Rh bimetallic model catalysts: From thin films to dispersed clusters by Zhou-jun Wang; Fan Yang; Stephanus Axnanda; Chang-jun Liu; D. Wayne Goodman (pp. 342-349).

Two series of bimetallic model catalysts, Co–Rh thin films and Co–Rh/SiO₂ dispersed clusters, were prepared and characterized with various techniques under ultrahigh vacuum conditions. As shown, the surface composition acquired from the line scan EDX analysis for Co–Rh/SiO₂/C/Mo-grid model catalyst is in excellent with those from LEIS experiments for Co–Rh/Mo(100) and Co–Rh/SiO₂/Mo(100) systems, demonstrating the efficacy of various preparation and characterization methodologies for Co–Rh bimetallic model catalysts.Display Omitted▶ Co-Rh model catalysts as thin films on Mo(100) and as dispersed clusters on SiO₂. ▶ Surface composition and electronic structure of Co-Rh thin films. ▶ Surface composition and morphology of the Co-Rh dispersed clusters. ▶ Co substantially enriched on the surface of Co-Rh compared to the total fraction value. ▶ Efficacy of preparation and characterization methodologies for model catalysts.Co–Rh bimetallic model catalysts were prepared as thin films on a Mo(100) substrate and as dispersed clusters on a SiO₂ support under ultrahigh vacuum conditions. The surface composition and electronic structure of the Co–Rh thin films on the Mo(100) substrate were characterized with low energy ion scattering spectroscopy (LEIS) and X-ray photoelectron spectroscopy (XPS). Co–Rh thin films form a stable alloy between 700 and 1000K with substantial surface enrichment of Co. Annealing a 1:1 Co–Rh thin film at 700K for 30min yields an alloy with 79% (atomic concentration) of Co in the outmost surface layer. The surface composition and morphology of the Co–Rh dispersed clusters on the SiO₂ support were determined by LEIS, XPS and transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDX). The Co and Rh atoms mixed to form bimetallic clusters between 700 and 800K with Co segregated to the cluster surface. EDX spectra provided direct proof for the formation of a Co–Rh alloy. TEM images showed that the Co–Rh clusters were highly dispersed on the SiO₂ support and the average particle size of the bimetallic clusters increased monotonically with the total Co fraction.

Keywords: Bimetallic model catalyst; Cobalt; Rhodium; Silica; Phase diagram

Microkinetic analysis of CH₄ CPO tests with CO₂-diluted feed streams by Alessandro Donazzi; Matteo Maestri; Alessandra Beretta; Gianpiero Groppi; Enrico Tronconi; Pio Forzatti (pp. 350-359).

The effect of CO₂ dilution was investigated in autothermal CH₄ catalytic partial oxidation tests at short contact time over Rh-based catalysts. A novel C1 microkinetic scheme and a detailed reactor model were used for the analysis. CO₂ plays an important kinetic role by activating the reverse-WGS reaction, which strongly affects the outlet H₂/CO ratio. Despite the influence on the surface coverages of CO* and H*, the role of CO₂ on the kinetics of methane reforming is negligible, since the coverage of Rh free sites is practically independent from the nature of the diluting gas (CO₂ or N₂).Display Omitted▶ CO₂ recycle in CH₄ CPO activates the RWGS reaction and modifies the H₂/CO ratio. ▶ The role of CO₂ feed enrichment on the kinetics of methane reforming is negligible. ▶ The coverage of Rh free sites is nearly independent of the nature of the diluting gas (CO₂ or N₂).Autothermal CH₄ catalytic partial oxidation (CPO) tests were performed in an adiabatic lab-scale reformer over 2wt% Rh/α-Al₂O₃ catalysts supported on 600cpsi cordierite honeycombs. The effect of adding either CO₂ or N₂ to CH₄/air mixtures was investigated at constant O₂/CH₄ ratio (0.56) and total flow rate (10Nl/min). At increasing dilution the conversion of CH₄ and the gas temperatures decreased. Also, at equal CH₄ concentration, the addition of CO₂ decreased the temperatures and the conversion of CH₄ more importantly than N₂. Thus, in line with previous studies from this and other laboratories, no evidence of a direct dry reforming route was found; the observed thermal behavior appeared largely controlled by the heat capacity of the feed streams. However an important chemical effect of CO₂ addition, not previously appreciated in the literature, was shown by the evolution of the outlet H₂/CO ratio; at increasing N₂ dilution, the H₂/CO ratio slightly increased from about 2 to 2.5, but at increasing CO₂ dilution, the H₂/CO ratio decreased from about 1.7 to 0.7. These trends are in line with the thermodynamics of the reverse water gas shift (RWGS) reaction; such a reaction was thus extremely fast in all the experiments with CO₂, even at the highest values of dilution, while CH₄ conversion did not reach the equilibrium.A C₁ microkinetic model was used to analyze the results. A close match between calculated and measured temperatures, conversions and syngas composition was obtained under all conditions. Notably, the present microkinetic scheme, which incorporates steps for CO₂ adsorption and reactivity, was able to account for the observed net consumption of CO₂ and for the lowering of the H₂/CO ratio in the experiments with CO₂ co-feed. Surface coverages were analyzed for the various investigated conditions and the effects on the kinetics of methane steam reforming were evaluated in detail; the factors which control the onset of a more kinetically controlled regime at high degrees of dilution were highlighted.

Keywords: Catalytic partial oxidation; Methane; Rh; CO; ₂; Microkinetic model; Reverse-WGS

Microkinetic analysis of CH₄ CPO tests with CO₂-diluted feed streams by Alessandro Donazzi; Matteo Maestri; Alessandra Beretta; Gianpiero Groppi; Enrico Tronconi; Pio Forzatti (pp. 350-359).

Keywords: Catalytic partial oxidation; Methane; Rh; CO; ₂; Microkinetic model; Reverse-WGS

Production of hydrogen from dimethyl ether on supported Au catalysts by A. Gazsi; I. Ugrai; F. Solymosi (pp. 360-366).

Product distribution in the reforming of DME on 1% K+1% Au/CeO₂+Al₂O₃ (co-impregnated) catalyst at different temperatures (A). The selectivity and yield of H₂ formation in time on stream at 773K (B).The adsorption and reactions of dimethyl ether (DME) were investigated on Au nanoparticles supported by various oxides and carbon Norit. Infrared spectroscopic and temperature programmed desorption studies revealed that DME adsorbs readily on most oxidic supports. A limited dissociation of DME to methoxy species was established on Au particles by IR spectroscopy. As regards the formation of hydrogen, Au/CeO₂ is the most effective catalyst. On Au/Al₂O₃ catalyst the main process was the formation of methanol with a very small amount of hydrogen. Deposition of Au on CeO₂–Al₂O₃ mixed oxide resulted in a very active catalyst for H₂ production. The yield for H₂ in the reforming of DME approached the value of 73% at 723–773K. This feature was explained by the hydrolysis of DME to methanol on alumina, and the fast decomposition of methanol at the Au/CeO₂ interface. Adding potassium promoter to Au/CeO₂–Al₂O₃ catalyst further enhanced the production of hydrogen as indicated by the increase of the yield to ∼87%. No deactivation of the catalyst was experienced at 773K for the measured time, ∼10h.

Keywords: IR spectra of adsorbed dimethyl ether; Decomposition of dimethyl ether; Reforming of dimethyl ether; Hydrogen production; Au catalyst; CeO; ₂; support

Production of hydrogen from dimethyl ether on supported Au catalysts by A. Gazsi; I. Ugrai; F. Solymosi (pp. 360-366).

Keywords: IR spectra of adsorbed dimethyl ether; Decomposition of dimethyl ether; Reforming of dimethyl ether; Hydrogen production; Au catalyst; CeO; ₂; support

XPS characterization of Au/TiO₂ catalysts: Binding energy assessment and irradiation effects by Norbert Kruse; Sergey Chenakin (pp. 367-376).

A comparative XPS study of the surface composition and electronic structure of Au/TiO₂ catalysts and TiO₂ (anatase) was carried out and time-dependent X-ray irradiation damage of the samples was examined. In Au/TiO₂, charge transfer processes triggered by X-ray irradiation were found to develop which caused the variation of core-level binding energies.X-ray photoelectron spectroscopy (XPS) was employed to study the surface composition and electronic structure of Au/TiO₂ catalysts in comparison with TiO₂ (anatase) and to reveal time-dependent X-ray irradiation damage of the samples. The occurrence of Au nano-sized particles on a TiO₂ support was found to result in a slight shift of Ti 2p core-level spectrum and in changes of the valence band and X-ray induced Auger spectra, compared to TiO₂-only. It was shown that for different means of energy referencing the charge-corrected Au 4f_7/2 binding energy in Au/TiO₂ catalysts was 0.15–0.45eV lower than that in pure bulk Au. Exposure to X-rays of Au/TiO₂ catalysts and pure TiO₂ caused a reduction of Ti 4+ oxidation state and desorption of oxygen from the surface. As a result, the surface chemical composition and electronic structure of the samples changed with time. The X-ray irradiation affected charge transfer processes in Au/TiO₂ so that the pattern of X-ray induced damage in the Au-based catalyst turned out to be quite different from that in TiO₂, with some characteristics displaying the very opposite features. Decreasing of the Au 4f_7/2 binding energy and concurrent increasing of the fraction of Ti³⁺ species observed in the beginning of X-ray irradiation of Au/TiO₂ may be taken as direct evidence for charge transfer from oxygen vacancies created by irradiation to Au particles.

Keywords: Au/TiO; ₂; catalyst; TiO; ₂; XPS; X-ray induced damage; Valence band

XPS characterization of Au/TiO₂ catalysts: Binding energy assessment and irradiation effects by Norbert Kruse; Sergey Chenakin (pp. 367-376).

Keywords: Au/TiO; ₂; catalyst; TiO; ₂; XPS; X-ray induced damage; Valence band

Structural properties of an unsupported model Pt–Sn catalyst and its catalytic properties in cyclohexene transformation by Z. Paál; A. Wootsch; D. Teschner; K. Lázár; I.E. Sajó; N. Győrffy; G. Weinberg; A. Knop-Gericke; R. Schlögl (pp. 377-385).

Unsupported PtSn powder was prepared by direct reduction of a solution containing both H₂PtCl₆ and SnCl₄ using hydrazine as the reducing agent. The dark gray powder was characterized with scanning electron microscopy (SEM), EDX analysis, Mössbauer spectroscopy, X-ray diffraction, XPS depth profiling after different treatments: presintering, O₂ and H₂ treatments. SEM showed a conglomerate of small spherical particles (0.2–1.5μm). They contained Pt, various PtSn alloy phases and tin-oxide(s). EDX showed 70–75% Pt and 25–30% Sn on various grains. The mixture of Pt₃Sn and SnO₂ represented the final stabilized state obtained upon repeated heating in air and, finally, H₂. This mixed Pt–Sn was catalytically inactive in “structure-sensitive” reactions, such as methylcyclopentane ring opening or cyclohexane dehydrogenation, but was active in “structure-insensitive” hydrogenation and also in the dehydrogenation of cyclohexene. The relative importance of the latter two reactions depended strongly on the previous treatments of the catalyst—i.e., on its composition, the final stage (Pt₃Sn and SnO₂) being most active, with cyclohexane as the main product.

Keywords: PtSn; Bimetallic catalyst; X-ray diffraction; Mössbauer spectroscopy; XPS; Electron microscopy; Hydrogenation and dehydrogenation of cyclohexene

Dendrimer-based synthesis of Pt catalysts for hydrocarbon conversion by Manuel A. Albiter; Ricardo Morales; Francisco Zaera (pp. 386-393).

Well-defined platinum-based catalysts were prepared using dendrimers as templates. Different treatments were explored for the elimination of the dendrimer material after dispersion onto a silica support and for the activation of the resulting catalysts. Hydrogen pretreatments were found to be best, leading to fairly active catalysts with high selectivity for cis-to-trans conversions in olefins.Well-defined platinum-based catalysts were prepared using fourth-generation hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers as templates. Nanoparticles with an average of 40 Pt atoms and an average diameter of 1.5nm were produced this way, and dispersed on a homemade sol–gel silica support. Different treatments were tested for the activation of the resulting catalyst, including heating in vacuum or in oxygen or hydrogen atmospheres. A combination of electron microscopy, infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and catalytic kinetic measurements were used to investigate the effect of those treatments on the decomposition and elimination of the material associated with the dendrimer and on the activity and selectivity of the resulting catalysts. Neither heating in vacuum nor burning with oxygen was deemed acceptable, because much graphitic material is deposited with the former treatment and metal oxidation is induced by the latter. Hydrogen pretreatments, on the other hand, lead to fairly active catalysts with high selectivity for the conversion of trans olefins to their cis counterparts.

Keywords: Dendrimer-encapsulated nanoparticles; Platinum catalysts; Olefin conversion; Cis–trans isomerization; Selectivity

Dendrimer-based synthesis of Pt catalysts for hydrocarbon conversion by Manuel A. Albiter; Ricardo Morales; Francisco Zaera (pp. 386-393).

Keywords: Dendrimer-encapsulated nanoparticles; Platinum catalysts; Olefin conversion; Cis–trans isomerization; Selectivity

The decarbonylation of acetaldehyde on Pd crystals and on supported catalysts by Michael Bowker; Lucinda Cookson; Jenita Bhantoo; Albert Carley; Edward Hayden; Lee Gilbert; Chris Morgan; Jon Counsell; Polina Yaseneva (pp. 394-399).

The activity of Pd single crystals and a Pd/SiO₂ catalyst have been compared for the decarbonylation/dehydrogenation of acetaldehyde. In fact Pd is a dehydrogenator, not a decarbonylator, but when the both types of Pd become carbided, then they become selective for the decarbonylation reaction, as shown in the figure. This is a GENERAL property of Pd catalysts and is a very important factor in industrial catalysis.The reaction of acetaldehyde with pure Pd (in single crystal form, Pd(110) and Pd(111)) and with nanoparticles of Pd supported on silica have been investigated. The main reactions involved are decarbonylation (to produce CO and methane) and dehydrogenation (to produce CO, H₂ and carbon), and both of these reactions are seen on the unsupported and supported forms of Pd. In general the behaviour is similar, but there is a marked contrast in the temperature dependence of the reaction on single crystals and on the catalysts. On the crystals there is a sharp transition between decarbonylation and dehydrogenation, occurring at 420K, whereas the catalysts show little activity for dehydrogenation, even up to 600K. The reason for this relates to the capacity of the samples to absorb the carbon product of dehydrogenation into the bulk of the sample. The single crystal samples have a very low surface:bulk ratio and C formed at the surface is quickly lost to the bulk above 420K, leaving an apparently clean and reactive Pd surface. The catalysts on the other hand, due to their high surface:bulk ratio, quickly become carbidised and are thereby passivated towards dehydrogenation, favouring high selectivity to decarbonylation. This proves that Pd catalysts are dehydrogenation catalysts and are only more selective to other routes when passivated by bulk carbon (or other additives such as Au).

Keywords: Acetaldehyde decarbonylation; Palladium catalysts; Single crystal Pd; Surface carbon; Acetaldehyde dehydrogenation; Pulsed flow reactor; Molecular beam reactor

Reactivity studies of Au–Pd supported nanoparticles for catalytic applications by Jose Antonio Lopez-Sanchez; Nikolaos Dimitratos; Neil Glanville; Lokesh Kesavan; Ceri Hammond; Jennifer K. Edwards; Albert F. Carley; Christopher J. Kiely; Graham J. Hutchings (pp. 400-406).

The catalytic reactivity of Au–Pd supported nanoparticles synthesised by deposition–precipitation and colloidal methods have been compared. We have focused our attention on the calcination temperature and the improvement of the deposition–precipitation method by using urea and sodium borohydride for the preparation of Au–Pd supported nanoparticles that are very active for both the direct synthesis of H₂O₂ and CO oxidation.The utilisation of gold–palladium nanoparticles either in the form of colloids or supported nanoparticles has received enormous attention in recent years. These materials are very effective for the transformation of organic compounds to highly useful chemical products. The catalytic materials are usually prepared using deposition–precipitation and impregnation techniques, but recently significant attention has been focused on the use of colloidal methods. Here we compare and contrast the preparation and catalytic reactivity of Au–Pd supported nanoparticles synthesised by deposition–precipitation and colloidal methods. The catalyst materials have been evaluated for three different reactions, namely, the oxidation of benzyl alcohol, the direct synthesis of hydrogen peroxide and the oxidation of carbon monoxide. In addition, we have focused our attention on the pre-treatment temperature and the improvement of the deposition–precipitation method by using urea and sodium borohydride for the preparation of highly active Au–Pd supported nanoparticles.

Keywords: Gold and palladium supported catalysts; Hydrogen peroxide synthesis; Benzyl alcohol oxidation; CO oxidation; Sol-immobilisation

Promotional effect of metal encapsulation on reactivity of iron oxide supported Pt catalysts by M. Lewandowski; Y.N. Sun; Z.-H. Qin; S. Shaikhutdinov; H.-J. Freund (pp. 407-410).

High-temperature annealing of Pt particles supported on Fe₃O₄(111) films is shown to result in particles encapsulation by an ultra-thin FeO film which greatly enhances low temperature CO oxidation.We studied reactivity of well-defined Pt model catalysts, supported on crystalline iron oxide Fe₃O₄(111) films, in low temperature CO oxidation. It is shown that pre-annealing in vacuum at ∼850K suppresses CO adsorption but increases CO₂ production rate. This finding is rationalised in terms of strong metal–support interaction between Pt and iron oxide resulting in particles encapsulation by a thin FeO(111) film that catalyses CO oxidation similarly to the extended FeO(111)/Pt(111) surfaces previously studied . The results show that the stability and the atomic structure of the encapsulated layer under reaction conditions play a critical role in oxidation reactions over Pt catalysts supported on reducible oxides.

Keywords: Platinum; Iron oxides; Strong metal–support interaction; CO oxidation

Promotional effect of metal encapsulation on reactivity of iron oxide supported Pt catalysts by M. Lewandowski; Y.N. Sun; Z.-H. Qin; S. Shaikhutdinov; H.-J. Freund (pp. 407-410).

Keywords: Platinum; Iron oxides; Strong metal–support interaction; CO oxidation

Decomposition of nitrous oxide by rhodium catalysts: Effect of rhodium particle size and metal oxide support by Hans Beyer; Jens Emmerich; Konstantinos Chatziapostolou; Klaus Köhler (pp. 411-416).

The catalytic decomposition of N₂O by small rhodium particles ( d_m=1.0–2.4nm) supported on various metal oxides was studied in the absence and presence of oxygen in the feed gas and chloride on the catalyst surface. The superior catalytic performance of Rh/MgO and Rh/SiO₂ compared to Rh/CeO₂, Rh/Al₂O₃ and Rh/TiO₂ is attributed to relatively large rhodium particles ( d_m=2.1–2.4nm). The degree of inhibition caused by oxygen and chloride is found to vary with the acid–base properties of the support materials.The catalytic decomposition of N₂O by small rhodium particles (0.5–4.0nm in diameter) supported on magnesia, silica, ceria, alumina and titania was studied in the absence and presence of oxygen. The impact of the use of rhodium chloride for catalyst preparation was also investigated.Rh/MgO and Rh/SiO₂ are highly active catalysts for the decomposition of N₂O at low reaction temperatures (200–300°C), even in the presence of oxygen. The superior catalytic performance of Rh/MgO and Rh/SiO₂ compared to Rh/CeO₂, Rh/Al₂O₃ and Rh/TiO₂ is attributed to relatively large rhodium particles ( d_m=2.1–2.4nm) present in the more active catalysts compared to very small ones ( d_m=1.0–1.4nm) present in the other catalysts.The degree of inhibition caused by excess oxygen in the feed gas and the impact of chloride ions on the catalytic activity are found to vary with the acid–base properties of the support materials and their influence on the redox properties of the active metal. Both inhibitory effects seem to be interconnected and rise in the same order as the basicity of the support materials.

Keywords: N; ₂; O; Decomposition; Rhodium catalyst; Particle size; Metal oxide support

Decomposition of nitrous oxide by rhodium catalysts: Effect of rhodium particle size and metal oxide support by Hans Beyer; Jens Emmerich; Konstantinos Chatziapostolou; Klaus Köhler (pp. 411-416).

Keywords: N; ₂; O; Decomposition; Rhodium catalyst; Particle size; Metal oxide support

High-throughput and combinatorial development of multicomponent catalysts for ethanol steam reforming by Gábor P. Szijjártó; András Tompos; József L. Margitfavi (pp. 417-426).

Noble metal-free MgAl₂O₄ supported multicomponent catalysts for steam reforming of ethanol have been designed by means of combinatorial tools and high-throughput approaches. At 500°C a four-component catalyst containing Ni, Co, Ce and Mo has resulted in 4.4mol hydrogen per mole of ethanol. Its advantage is the strong suppression of the formation of carbonaceous deposition.Noble metal-free MgAl₂O₄ supported multicomponent catalysts for steam reforming of ethanol have been designed by means of combinatorial tools and high-throughput approaches. Additionally, the catalysts have been investigated using high-throughput temperature programmed technique. MgAl₂O₄ supported Ni-based catalysts have been found to be the most effective in hydrogen production. It has been revealed that practically no noble metal is required in order to achieve high hydrogen yield. At 500°C a four-component catalyst containing Ni, Co, Ce and Mo has resulted in 4.4mol hydrogen per mole of ethanol. In this system Ni is considered as the active metal, while Co, Ce and Mo are promoters. The results revealed strong synergism between Ni and Co leading to high activity in hydrogen production. In the temperature range between 320 and 370°C pronounced coke formation via the Boudouard reaction was observed over the two-component Ni–Co catalyst. The addition of Ce to NiCo/MgAl₂O₄ system proved to be advantageous, resulting in further improvement in hydrogen yield and suppression of coke formation. The presence of Mo as the fourth component hindered all reactions of CO in the temperature range between 320 and 370°C. Thus, the contribution of reactions, such as WGRS, CO methanation and coke formation were reduced as well. The four-component catalyst has been proved to be highly effective in hydrogen production at higher temperatures. Its advantage is the strong suppression of the formation of carbonaceous deposition. The analysis of results shows also that some of the catalysts compositions can be promising for ethanol pre-reforming producing both hydrogen and methane from ethanol for Molten Carbonate Fuel Cells.

Keywords: Ethanol reforming; Hydrogen production; Multicomponent catalysts; Holographic research strategy; Combinatorial catalysis; High-throughput experimentation

High-throughput and combinatorial development of multicomponent catalysts for ethanol steam reforming by Gábor P. Szijjártó; András Tompos; József L. Margitfavi (pp. 417-426).

Keywords: Ethanol reforming; Hydrogen production; Multicomponent catalysts; Holographic research strategy; Combinatorial catalysis; High-throughput experimentation

Hydrolysis of vegetable oils and fats to fatty acids over solid acid catalysts by J.K. Satyarthi; D. Srinivas; P. Ratnasamy (pp. 427-435).

Solid Fe-Zn double-metal cyanide (DMC) complex exhibits high catalytic activity for hydrolysis of vegetable oils and animal fat. Complete conversion of oil with fatty acids selectivity >73wt% was obtained at temperatures as low as 463K and autogenous pressure. Superior activity of DMC compared to known solid acid catalysts is attributed to its surface hydrophobicity.Solid Fe-Zn double-metal cyanide (DMC) complexes exhibit high catalytic activity for hydrolysis of edible and non-edible vegetable oils and animal fat. In a batch reaction, complete conversion of vegetable oil triglycerides to fatty acids with selectivity greater than 73wt% was obtained at temperatures as low as 463K, autogenous pressure and with 5wt% of catalyst. Catalytic activity of DMC was superior to Amberlyst™70, SAPO-11, H-β, HY, MoO_x/Al₂O₃ and sulfated zirconia. Rates of hydrolysis were greatly enhanced when solvents (tetrahydrofuran or N, N-dimethylformamide), phase transfer agents (tetrapropyl ammonium bromide) and products (a mixture of mono-/diglycerides and fatty acids) or fatty acid was added to the feed. Surface hydrophobicity which enables high wettability and activation of glycerides on active, acidic sites of reusable DMC is attributed to be the major cause for its superior catalytic activity.

Keywords: Hydrolysis of vegetable oils and fats; Fat splitting; Fatty acids; Double-metal cyanide complex; Solid acid catalyst

Hydrolysis of vegetable oils and fats to fatty acids over solid acid catalysts by J.K. Satyarthi; D. Srinivas; P. Ratnasamy (pp. 427-435).

Keywords: Hydrolysis of vegetable oils and fats; Fat splitting; Fatty acids; Double-metal cyanide complex; Solid acid catalyst

Accelerated cellulose depolymerization catalyzed by paired metal chlorides in ionic liquid solvent by Yu Su; Heather M. Brown; Guosheng Li; Xiao-dong Zhou; James E. Amonette; John L. Fulton; Donald M. Camaioni; Z. Conrad Zhang (pp. 436-442).

The rate of cellulose hydrolysis is critically dependent on the ratio of CuCl₂/PdCl₂ in [EMIM]Cl solvent while the total catalyst loading (mol% CuCl₂+mol% PdCl₂) is unchanged. The results of a combination of physical characterization methods for the catalytic system indicate that Cu(II) was reduced during the course of the reaction to Cu(I) only in the presence of a second metal chloride and a carbohydrate source such as cellulose in the ionic liquid system.Display Omitted▶ Paired metal chlorides in an ionic liquid effectively catalyzes low temperature cellulose conversion. ▶ Cellulose is depolymerized to monosaccharide under mild conditions in a single step. ▶ Copper (II) ion is reduced to Cu(I) in the presence of carbohydrates and PdCl₂ in alkylmethylimidazolium chloride ionic liquid. ▶ Ionic liquid solvent can be reused in multiple cycles for cellulose conversion.Efficient hydrolytic depolymerization of crystalline cellulose to sugars is a critical step and has been a major barrier for improved economics in the utilization of cellulosic biomass. A novel catalytic system involving CuCl₂ (primary metal chloride) paired with a second metal chloride, such as CrCl₂, PdCl₂, CrCl₃ or FeCl₃ in 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) ionic liquid solvent has been found to substantially accelerate the rate of cellulose depolymerization under mild conditions. These paired metal chlorides are particularly active for the hydrolytic cleavage of 1,4-glucosidic bonds when compared to the rates of acid-catalyzed hydrolysis at similar temperatures (80–120°C). In contrast, single metal chlorides with the same total molar loading showed much lower activity under similar conditions. Experimental results illustrate the dramatic effect of the second metal chloride in the paired catalytic system. An array of characterization techniques, including electron paramagnetic resonance (EPR) spectroscopy, differential scanning calorimetry (DSC), X-ray absorption fine structure (XAFS) spectroscopy, and X-ray absorption near edge structure (XANES) spectroscopy, in combination with theoretical calculations at the DFT level, was used to reveal a preliminary understanding of possible mechanisms involved in the paired CuCl₂/PdCl₂ catalytic system. We discovered that Cu(II) was reduced during the course of the reaction to Cu(I) only in the presence of a second metal chloride and a carbohydrate source such as cellulose in the ionic liquid system. Our results suggest that Cu(II) generates protons by hydrolysis of water to catalyze the depolymerization step, and serves to regenerate Pd(II) reduced to Pd(0) by side reactions. Pd(II) likely facilitates the depolymerization step by coordinating the catalytic protons, and also promotes the formation of hydroxymethylfurfural (HMF). Our results also suggest that the C2-proton of the imidazolium ring is not activated by the paired metal-chloride catalysts.

Keywords: Ionic liquid; 1-Alkyl-3-methylimidazolium chloride; 1-Ethyl-3-methyl-imidazolium chloride; Cellulose; Biomass; Depolymerization; Catalysis; Bioenergy; Hydrolysis; Glucose; Cellobiose; Maltose; Cellulose conversion; Catalyst; Paired metal chlorides; CuCl; ₂; PdCl; ₂

Innovative porous SiC-based materials: From nanoscopic understandings to tunable carriers serving catalytic needs by Patrick Nguyen; Charlotte Pham (pp. 443-454).

New porous self-bonded beta silicon carbide (SiC) materials have been prepared using metallic silicon powder and carbon black. Pore size distribution has been tailored by varying the raw materials and by adding pore formers. The surface chemistry can be tuned by adding promoters in the process.Display Omitted▶ Synthesis of highly porous shaped self bonded beta SiC and use as catalyst support. ▶ Tailored pore size distribution and specific surface area. ▶ High activity in selective H₂S oxidation. ▶ High selectivity toward Fischer–Tropsch synthesis. ▶ ZrO₂, TiO₂ promoting.Progress in developing a new class of catalyst carrier materials based on porous self-bonded silicon carbide (SiC) is reviewed. Since the demonstration of scalable economically viable β-SiC production process, innovative β-SiC-based materials with tunable physical and chemical properties were successfully synthesized. Silicon carbide has superior mechanical and thermal properties which, coupled to chemical inertness, avoids several of the problems inherent in the use of commercial oxide and carbon based supports and catalysts. High surface area SiC (35m²/g) can now be easily synthesized, with unmatched mechanical properties, tailored pore size distribution (meso- and macroporous network and total pore volume up to 1cm³/g) and at reasonable cost. It can be shaped directly into extrudates, (μ-) spheres, monoliths, open cell foams, 3D forms depending to the downstream applications. Furthermore, it can also be chemically modified for specific catalytic applications through the addition of promoters (oxides like Al₂O₃, TiO₂, ZrO₂, carbides and metals) rendering the fabrication simple and cost effective. In many respects, it combines the best properties of oxide and carbon based supports without suffering many of their disadvantages. New structured TiO₂/SiC composites have been prepared and are expected to be the next photocatalytic media. The ability of the SiC material to be used as catalyst support will be illustrated in the present work by two exothermic reactions, namely the selective oxidation of trace amount of H₂S and the Fischer–Tropsch synthesis. For this later, a direct comparison was also made with a traditional support, i.e. alumina.

Keywords: Catalyst carrier; Tailored porosity; Mechanical strength; Tailored surface chemistry; Porous self-bonded beta (β) silicon carbide (SiC); Al; ₂; O; ₃; TiO; ₂; ZrO; ₂; Thermal conductive; Photocatalyst; Structured material; H; ₂; S oxidation; Fischer–Tropsch synthesis

Innovative porous SiC-based materials: From nanoscopic understandings to tunable carriers serving catalytic needs by Patrick Nguyen; Charlotte Pham (pp. 443-454).

Self-decontaminating layer-by-layer functionalized textiles based on WO₃-modified titanate nanotubes. Application to the solar photocatalytic removal of chemical warfare agents by Mathieu Grandcolas; Laura Sinault; François Mosset; Alain Louvet; Nicolas Keller; Valérie Keller (pp. 455-467).

Self-decontaminating layer-by-layer functionalized photocatalytic textiles exposing a thin layer of a dense network of entangled and high aspect ratio WO₃-modified titanate nanotubes were successfully used under solar light illumination for the photocatalytic degradation of dimethylmethylphosphonate as neurotoxic organophosphorous agent simulant and of the blister organosulfide yperite live chemical weapon agent.Self-decontaminating photocatalytic textiles functionalized by the layer-by-layer approach with high aspect ratio WO₃-modified titanate nanotubes have been developed and successfully used under solar light illumination for the photocatalytic degradation of organophosphorous and organosulfide chemical weapon agents. This multilayer building method, unlike both dipping and spray techniques, has been efficiently applied to textile substrates using polyethyleneimine as counter polyelectrolyte for homogeneously functionalizing textiles by a thin layer of a dense network of entangled WO₃-modified titanate nanotubes, and preparing self-decontaminating photocatalytic textiles highly efficient toward the removal under solar light of the yperite blister live agent and of dimethylmethylphosphonate as neurotoxic agent simulant. Solar light responsive high surface WO₃-modified titanate nanotubes were synthesized by hydro-thermally treating TiO₂ powder, with tungstate salt impregnation prior to the final calcination step.

Keywords: Photocatalysis; Titanate nanotubes; WO; ₃; Solar light; Self-decontaminating textiles; Layer-by-layer deposition; Dimethylmethylphosphonate; Yperite

Closing the operando gap: The application of high energy photons for studying catalytic solids at work by Matthew G. O’Brien; Andrew M. Beale; Simon D.M. Jacques; Marco Di Michiel; Bert M. Weckhuysen (pp. 468-476).

. Here we describe how novel high energy X-ray multiple technique setups help bridge the operando gap when measuring catalysts. The advantages of operating at high energies with respect to sample realism, data quality and beam effects are discussed and examples of single point and spatiotemporal line scan measurements on oxide catalysts are presented.Display Omitted▶ A new setup for monitoring catalysts under operando conditions was developed. ▶ The high energy synchrotron X-rays allow for more operando measurement. ▶ Increased X-ray energy reduces sample damage. ▶ High quality single point measurements of MoO₃ reveals most labile bulk oxygen. ▶ Line scans of Fe₂(MoO₃)₄ reveals spatiotemporal phase and density variation.Understanding the working principles of heterogeneous catalysts represents one of the great challenges in the field of materials science today. Ex situ bulk and surface science techniques provide information on such systems; however it is difficult to know whether any observed change in the physicochemical state of the catalyst would occur under the real working conditions. To counter this operando gap, the last decade has witnessed research efforts pushing towards more operando-like experimental setups to investigate ‘catalysis in action’. The advances in this field have been considerable so that it is now feasible to observe catalytic materials using a variety of techniques (sometimes combined into a single experiment) under conditions approaching those used for commercial operation. There still remain, however, some key differences between the conditions under which the experiments and the measurements are performed and with those required to fully understand a catalyst material in an industrial setting. In this paper we aim to show how multiple high energy techniques can be employed to further close the operando gap and meet the relevant criteria of replicating industrially relevant conditions and gleaning useful high quality data, whilst minimizing sample effects. For this purpose, a new high energy source experimental setup is described. We present results from high energy X-ray experiments on a simple model parent oxide, molybdenum oxide (MoO₃) used for the selective oxidation of methanol as well as a new characterization study on the more complex iron molybdate (Fe₂(MoO₄)₃) catalyst. The advantages and limitations of high energy X-ray experiments will be discussed.

Keywords: In situ spectroscopy; X-rays; Multi-technique; Bulk oxide; Catalysis; MoO; ₃; Iron molybdate

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Applied Catalysis A, General (v.391, #1-2)