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Applied Catalysis A, General (v.365, #2)

Editorial Board (pp. co2).

Contents (pp. iii-viii).

Catalysis by supported Lewis acids: An efficient method for transesterification of phosphotriesters by Daniel P. Sheng; Ismail O. Kady (pp. 149-152).

Lewis acids (ZnCl₂, CoCl₂, NiCl₂, TiCl₄, and CdCl₂) when supported on silica gel can effectively catalyze transesterification of organophosphotriesters. In anhydrous acetonitrile and in the presence of excess alcohol, such reactions follow pseudo-first-order kinetics. Progress and efficacy of these reactions were monitored by UV–vis and³¹P NMR spectroscopy.Lewis acids (ZnCl₂, CoCl₂, NiCl₂, TiCl₄, and CdCl₂) when supported on silica gel can effectively catalyze transesterification of organophosphotriesters. In anhydrous acetonitrile and in the presence of excess alcohol, such reactions follow pseudo-first-order kinetics. Progress and efficacy of these reactions were monitored by UV–vis and³¹P NMR spectroscopy.

Keywords: Phosphotriesters; Transesterification; Heterogeneous catalysis; Lewis acids; Silica gel

Single and binary sulfur removal components from model diesel fuel using granular activated carbon from dates’ stones activated by ZnCl₂ by Hisham S. Bamufleh (pp. 153-158).

Samples of granulated activated carbon (GAC) produced from dates’ stones as adsorbent by chemical activation using ZnCl₂ as an activator were used in desulfurization of a model diesel fuel composed of n-C₁₀H₃₄ and dibenzothiophene (4,6-DMDBT) as sulfur containing compound. The adsorption data were fitted to both Freundlich and Langmuir isotherms to estimate the adsorption parameters.Samples of granulated activated carbon (GAC) produced from dates’ stones as adsorbent by chemical activation using ZnCl₂ as an activator were used in desulfurization of a model diesel fuel composed of n-decane (n-C₁₀H₂₂) and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) as sulfur containing compound. The adsorption data were fitted to both Freundlich and Langmuir isotherms to estimate the adsorption parameters. The optimum operating conditions for GAC preparation based on high adsorption capacity using ZnCl₂ are T_carb=600°C, θ_carb=3.0h and R=0.5. Comparison with dibenzothiophene (DBT) adsorption using the same GAC showed that 4,6-DMDBT has a lower adsorption capacity than DBT due to steric effects caused by the existing two methyl groups. Finally adsorption of binary mixtures of DBT and 4,6-DMDBT on GAC were experimentally obtained, fitted and analyzed using extended Langmuir, extended Freundlich and ideal adsorption solution theory, IAST, models.

Keywords: Diesel fuel; Granular activated carbon; Zinc chloride; Desulfurization; 4,6-Dimethyl dibenzothiophene (4,6-DMDBT); Nitrogen adsorption; Binary adsorption; IAST

Copper–cerium oxide catalysts supported on monoclinic zirconia: Structural features and catalytic behavior in preferential oxidation of carbon monoxide in hydrogen excess by Vera P. Pakharukova; Ella M. Moroz; Vladimir V. Kriventsov; Dmitry A. Zyuzin; Gulnara R. Kosmambetova; Peter E. Strizhak (pp. 159-164).

Copper–cerium oxide catalysts supported on monoclinic zirconia exhibited a good performance in preferential oxidation of CO in hydrogen-rich gases. The influence of catalyst composition on the state, structure and catalytic activity of copper species was investigated. The high activity was related to a high concentration of the finely dispersed copper (II) oxide clusters and the copper ions strongly interacting with CeO₂.Copper–cerium oxide catalysts supported on monoclinic zirconia CuO/CeO₂/ZrO₂ were tested in the preferential oxidation of CO in hydrogen-rich gases and the optimal catalyst composition was determined. The state and the structure of copper species in the catalysts were investigated by X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) analysis. While a small amount of copper incorporated into the surface layers of the CeO₂ lattice, the disordered oxide clusters were the main copper species in the catalysts with copper content ≤5wt.%. The increase in the copper loading (>10wt.%) led to predominant formation of bulk CuO phase coupled with catalyst deactivation.

Keywords: Preferential CO oxidation; CeO; ₂; ZrO; ₂; Copper oxide clusters; Structure–activity relation; XAFS

Esterification via saccharine mediated silica solid catalyst by Farook Adam; Kasim Mohammed Hello; Hasnah Osman (pp. 165-172).

The weakly basic catalyst RHAC-Sac is believed to use the amine group in the catalytic esterification of carboxylic acids. It forms a strong conjugate acid pair through resonance with the SO₂ group. This can capture a proton from ethyl alcohol to form an alcoholic-ethoxide which can act as a nucleophile. The reaction takes place on the catalyst surface continuously with elimination of water.Saccharine (Sac) was immobilized onto rice husk ash (RHA) silica via 3-(chloropropyl)triethoxysilane (CPTES) to form a new catalyst, RHAC-Sac. The saccharine loading on the silica was found to be ca. 82%. The²⁹Si MAS NMR showed the presence of T², T³, Q³ and Q⁴ silicon centers. The¹³C MAS NMR showed that RHAC-Sac had three chemical shifts consistent with the three carbon atoms of the propyl group and a series of chemical shifts consistent with the presence of the aromatic ring. RHAC-Sac had a specific surface area of 250m²g⁻¹ and a narrow average pore size of 3.28nm. RHAC-Sac was used as a catalyst in the esterification reaction between ethyl alcohol and acetic acid. A 66% conversion was achieved at 85°C with 100% selectivity for the ester. The stoichiometric composition of acid:alcohol=1:1 was found to give the highest conversion. The use of Sac as a homogeneous catalyst also gave similar results to that of RHAC-Sac. RHAC-Sac could be reused several times by regenerating at 150°C.

Keywords: Surface modification; Silica surface; Saccharine; Rice husk silica; Esterification

Comparison of the promotion effects on sulfated mesoporous zirconia catalysts achieved by alumina and gallium by Chi-Chau Hwang; Chung-Yuan Mou (pp. 173-179).

The catalytic activities in butane isomerization of Al- and Ga-promoted sulfated mesoporous zirconia catalysts (AS/MP-ZrO₂ and GS/MP-ZrO₂) were compared. The better promotional effect in Ga was attributed to its stronger ability in oxidative dehydrogenation of butane to generate butene, which then forms carbenium for the isomerization reaction.Mesoporous zirconia, hydrothermally synthesized from surfactant templating, was directly impregnated with aluminum sulfate or gallium sulfate to give the solid acids, Al- and Ga-promoted sulfated mesoporous zirconia catalysts (AS/MP-ZrO₂ and GS/MP-ZrO₂). The promotional effects achieved by these two catalysts for the n-butane isomerization were compared to clarify the differences in mechanism in catalytic activities in butane isomerization. The catalysis was found to be strongly promoted by the addition of a proper amount of alumina or gallium. The activities of Ga-promoted catalysts were higher than those of Al-promoted catalysts. Diffuse-reflectance infrared Fourier-transformed (DRIFT) spectra and temperature programmed desorption mass (TPD-MS) analyses were employed to identify and quantify properties of the acid sites on catalyst surfaces. The 3AS/MP-ZrO₂ catalyst shows a slightly higher acidity in strength and amount than that of 3GS/MP-ZrO₂, but much higher than that of the unpromoted 3S/MP-ZrO₂ catalyst. All three catalysts were further compared in their redox properties, with the H₂-temperature programmed reduction (TPR) analysis showing totally different tendencies (redox ability: 3GS>3S>3AS/MP-ZrO₂). A small concentration of olefins accompanied with water formation were observed by in situ DRIFT spectra and quantified by the Baeyer test. The results show that this occurs via oxidative dehydrogenation of butane by the sulfate groups to form butene, which leads to butyl carbenium species for skeleton isomerization. The catalytic promotion effect of alumina on sulfated zirconia is mainly due to a balanced increase of acid sites; on the other hand, gallium promotes sulfated zirconia through enhancing both the surface acidity and its redox properties on the surface.

Keywords: Butane isomerization; Mesoporous; Sulfated zirconia; Alumina; Gallium; Oxidative dehydrogenation

Copper-containing hexagonal mesoporous silicas for styrene epoxidation using tert-butylhydroperoxide by Xinning Lu; Youzhu Yuan (pp. 180-186).

Copper-containing hexagonal mesoporous silicas with appropriate Si/Cu atomic ratios synthesized by one-pot sol–gel method could show excellent performance and stability in the styrene epoxidation using aqueous tert-butylhydroperoxide. A styrene conversion over 95% with epoxide selectivity up to 84% could be obtained over the Cu-HMS material with a Si/Cu atomic ratio of 40.Copper-containing hexagonal mesoporous silicas (Cu-HMS) with different Si/Cu atomic ratios were synthesized by one-pot sol–gel method using dodecylamine surfactant as templating agent. The structure was characterized by X-ray diffraction, N₂ adsorption–desorption, infrared spectroscopy, transmission electron microscopy, ultraviolet and visible diffuse reflectance spectroscopy, electron spin resonance and H₂ temperature-programmed reduction. The results show that the Cu-HMS material is an efficient catalyst for epoxidation of styrene with use of aqueous tert-butylhydroperoxide. The catalytic performance is dependent on Si/Cu atomic ratio and reaction solvent. A styrene conversion of 99% with epoxide selectivity up to 84% can be obtained over the Cu-HMS material with Si/Cu atomic ratio of 40 in the case of using a mixed solvent of acetonitrile and N, N-dimethylformamide. No significant loss in the catalytic performance is observed during catalyst reuse. The enhanced catalytic performance over Cu-HMS material may be attributed to the homogeneous dispersion and uniformity of active Cu²⁺ species.

Keywords: Copper; Cu-HMS; Styrene; Epoxidation

NOx abatement for lean-burn engines under lean–rich atmosphere over mixed NSR-SCR catalysts: Influences of the addition of a SCR catalyst and of the operational conditions by E.C. Corbos; M. Haneda; X. Courtois; P. Marecot; D. Duprez; H. Hamada (pp. 187-193).

The NOx removal efficiency under lean/rich atmosphere can be greatly improved by the addition of a SCR catalyst (Cu/ZSM-5 or Co/Al₂O₃) to a model Pt–Rh/Ba/Al₂O₃ NSR catalyst. The improved performance is ascribed to NOx reduction on the SCR catalyst with the NH₃ released from the NSR model catalyst, and it was observed regardless of the reductant used (CO or H₂) and of the reduction time (10, 5 or 2.5s).Mixtures of equal amounts of a Pt–Rh/Ba/Al₂O₃ NOx storage reduction (NSR) model catalyst and Ag/Al₂O₃, Co/Al₂O₃ or Cu/ZSM-5 selective catalytic reduction (SCR) model catalyst were evaluated for the NOx removal activity under lean–rich atmosphere. NOx removal activity was increased by adding Co/Al₂O₃ or Cu/ZSM-5 to Pt–Rh/Ba/Al₂O₃ while adding Ag/Al₂O₃ had no significant influence. Experiments performed by using two catalytic beds (upstream Pt–Rh/Ba/Al₂O₃ and downstream Co/Al₂O₃ or Cu/ZSM-5) suggested that both SCR catalysts are able to reduce NOx with the NH₃ produced during the rich step on Pt–Rh/Ba/Al₂O₃. Among the studied catalysts, the Pt–RhBa/Al₂O₃+Cu/ZSM-5 physically mixed one showed the highest activity. This catalyst mixture presented an improved performance, as compared to the NSR catalyst, regardless of the reductant used (CO and/or H₂) or of the reduction time (10, 5 or 2.5s). The highest activity was obtained by using both CO and H₂ as reductant during the rich pulse. The addition of water in the inlet gas led to a decrease of the NOx removal activity of the catalyst mixture. Nevertheless, the NOx removal activity of the mixed Pt–RhBa/Al₂O₃+Cu/ZSM-5 catalyst was still significantly higher than that of Pt–RhBa/Al₂O₃.

Keywords: NOx storage and reduction; Selective catalytic reduction; Ammonia; Pt–Rh; Ba; Ag; Cu; Co; Alumina; Reduction time; NCO

Facile synthesis of cyclic carbonates from CO₂ and epoxides with cobalt(II)/onium salt based catalysts by Ahlam Sibaouih; Paul Ryan; Markku Leskelä; Bernhard Rieger; Timo Repo (pp. 194-198).

Efficient catalytic systems based on the combination of cobalt(II)/onium salts for the coupling reaction of CO₂ and epoxides is reported. The influences of various reaction parameters including CO₂ pressure, reaction temperature and amount of onium salts were further investigated. A reaction mechanism of CoCl₂/TBACl is proposed based on the observed catalytic species via ESI-MS measurement.Efficient catalytic systems based on the combination of cobalt(II)/onium salts for the coupling reaction of CO₂ and epoxides are reported. The catalytic systems work under mild reaction conditions (e.g. 10bar and 120°C) and produce cyclic carbonates with high turnover frequencies (TOF) and selectivity. From a series of onium salts, bis(triphenylphosphoranylidene)ammonium chloride proved to be the most active cocatalyst (TOF=2314), while tetrabutyl ammonium chloride (TOF=2223) and 1,3-bis(2,4,6trimethylphenyl)imidazolium chloride (TOF=2174) provided only slightly reduced activities under similar conditions. The influence of various reaction parameters including CO₂ pressure, reaction temperature and loading of onium salt was determined. In order to obtain an insight into the catalytic process, the reaction was followed by electrospray ionisation-mass spectrometry. Additionally, in situ FT-IR measurements show that the catalyst is stable even with low loading (0.025mol%) and as a result, the reaction proceeds steadily over several hours.

Keywords: CO; ₂; Epoxide; Cyclic carbonate; Onium salt; CoCl; ₂

Catalyst testing in a multiple-parallel, gas–liquid, powder-packed bed microreactor by Daniël van Herk; Pedro Castaño; Michiel Makkee; Jacob A. Moulijn; Michiel T. Kreutzer (pp. 199-206).

The use of a three-phase plug-flow microreactor with powder catalysts to obtain intrinsic kinetics is reported. We compare reaction rates obtained in both our microreactor and a standard hydrogenation autoclave. In this work we stress the impact of hydrodynamic anomalies, most importantly stagnant zones of gas and liquid, which occurred in reactor columns where diluent and catalyst were unevenly distributed.The use of a three-phase plug-flow microreactor with powder catalysts to obtain intrinsic kinetics is reported. Our test reaction is the hydrogenation of biphenyl over a Pt-Pd/Al₂O₃ catalyst. We compare reaction rates obtained in both our microreactor and a standard hydrogenation autoclave. The reactor design consists of six parallel reactor tubes with an inner diameter of 2.2mm and a maximum catalyst-bed length of 200mm.Co-flowing two phases very slowly over the bed needs more care than running only a liquid or a gas. Our main contribution in this work is to stress the impact of hydrodynamic anomalies, most importantly stagnant zones of gas and liquid, which occurred in reactor columns where diluent and catalyst were unevenly distributed. Such packing irregularities caused huge variations in conversion levels from tube to tube. In contrast, using a proper way to load the solids evenly, we could get the same results in each reactor tube. The values of these kinetic constants were identical to the ones we obtained in the autoclave. The well-known effect that too much dilution causes loss of conversion is found to be stronger than that in gas–solid systems. We visualized flow patterns in a 2-dimensional reactor mock-up and found such stagnant zones in segregated beds. Scaling down a continuous packed-bed reactor to reliably measure catalytic kinetics for gas–liquid–solid reactions is possible under specified conditions described herein.

Keywords: Hydrogenation; High-throughput experimentation; Trickle bed; Packing

Effect of dealumination by acid treatment of a HMCM-22 zeolite on the acidity and activity of the pore systems by P. Matias; J.M. Lopes; P. Ayrault; S. Laforge; P. Magnoux; M. Guisnet; F. Ramôa Ribeiro (pp. 207-213).

Acid leaching of a HMCM-22 zeolite (Si/Al=14.5) was carried out at 100°C with a 4M nitric acid solution. The change with time in the acid and catalytic properties of the pore systems shows that the dealumination rate significantly increases with the accessibility of their Al atoms: outer cups>supercages≫sinusoidal channels.Acid leaching of a HMCM-22 zeolite (Si/Al=14.5) was carried out at 100°C for different times (3, 30, 60 and 480min) with a 4M nitric acid solution. The resulting samples were characterised by elemental analysis, X-ray diffraction, pyridine adsorption followed by infrared spectroscopy (FTIR) and nitrogen adsorption and their catalytic properties were established with methylcyclohexane transformation at 350°C. The role played in this reaction by the three micropore systems was established by coupling selective deactivation of supercages by coking and poisoning of the outer cup acid sites with 2,4-dimethylquinoline. The change in the acid and catalytic properties with the time of acid treatment shows that dealumination is dominated by the accessibility of the framework Al atoms. Thus, the outer cup acid sites are highly sensitive to the acid treatment. The acidity and activity of the supercages are also strongly affected whereas those of the narrow sinusoidal channels are hardly affected.

Keywords: Dealumination; Acid leaching; MCM-22 zeolite; Pore systems; Methylcyclohexane transformation

Comparison of simple and economical photocatalyst immobilisation procedures by L.L.P. Lim; R.J. Lynch; S.-I. In (pp. 214-221).

This study compared substrates and coating solutions in order to determine a suitable immobilisation procedure for groundwater remediation application. The hybrid coating on woven fibreglass (HWF below) showed the highest deposition and photocatalytic activity among the combinations studied. The photocatalytic efficiency of the coating methods was in the following order: hybrid (H)>P90 slurry (90)=P25 slurry (25)≫reverse micelles (RM)>sol–gel (S).Sol–gel peptised for 1h (S1), sol–gel peptised for 6h (S6), sol–gel peptised for 12h (ST), hybrid (H), reverse micelles (RM), P25 slurry (25), P90 slurry (90), fibreglass (FB), woven fibreglass (WF), aluminium plate (AP), glass slide (GS).Photocatalysis is extremely useful for the removal of organic contaminants in water. However, the conditions used for preparing and fixing the catalyst to a substrate have a great effect on its performance. The determination of a suitable immobilisation procedure for specific application becomes more complicated with a plethora of methods developed over the years. The aim of this paper is to determine a suitable titanium dioxide immobilisation procedure using an economical and simple method. Various dip coating alternatives are compared: sol–gel, reverse micelles, hybrid and TiO₂ slurries. The coatings were evaluated in terms of deposition and photocatalytic activity, by weight and methylene blue demineralisation, respectively. A hybrid coating on woven fibreglass exhibited the highest amount of deposition and photocatalytic activity. Five coating cycles calcined at 500°C for 1h are sufficient in obtaining a favourable coating performance. SEM images showed that woven fibreglass, coated 5 times and calcined at 500°C for 1h, was well coated. However, some cracking and detachment was observed. The hybrid procedure outlined above will be applied in subsequent studies in our research on removal of groundwater contaminants. This work may be useful to researchers by providing the relative performance of different dip-coating alternatives tested under identical conditions.

Keywords: Dip coating; Catalyst immobilisation; Photocatalysis; TiO; ₂

TAP reactor study of the deep oxidation of propane using cobalt oxide and gold-containing cobalt oxide catalysts by Benjamin Solsona; Tomás García; Graham J. Hutchings; Stuart H. Taylor; Michiel Makkee (pp. 222-230).

Propane oxidation to CO₂ can be described via a Mars–Van Krevelen mechanism, and this was confirmed using isotopically labelled oxygen experiments. TAP reactor study indicates that the enhanced catalytic activity for gold on cobalt oxide is linked to the higher concentration of oxygen vacancies and the faster reoxidation of the catalyst.A transient reactor study of the oxidation of propane to CO₂ on gold-free and gold-doped CoO_x catalysts has been carried out. It has been demonstrated that the presence of gold markedly promotes the catalytic reactivity of cobalt oxide in the total oxidation of propane. Both catalysts oxidised propane directly to CO₂ via a Mars–Van Krevelen mechanism, and this was confirmed using isotopically labelled oxygen experiments. The increased activity of the gold catalyst is related to the faster reoxidation of the cobalt oxide when gold is present in the catalyst, since the reaction step in which the catalyst is reduced, due to propane oxidation, is similar for both catalysts. The faster reoxidation of the gold catalyst can be linked to the higher concentration of oxygen vacancies in the catalysts, determined by O₂ uptake results obtained from transient studies in the presence of oxygen.

Keywords: Cobalt oxide; Gold; Catalytic oxidation; Propane; Transient; Temporal analysis of products (TAP)

Hydroformylation of endocyclic double bonds in para-menthenic terpenes under mild conditions by José G. da Silva; Camila G. Vieira; Eduardo N. dos Santos; Elena V. Gusevskaya (pp. 231-236).

The use of a bulky phosphite ligand, i.e., P(O- o-^tBuPh)₃, allows to perform the rhodium catalyzed hydroformylation of sterically crowded endocyclic double bonds in terpinolene, γ-terpinene, and α-terpinene under relatively mind conditions. Two or three main fragrance para-menthenic aldehydes account for 80–90% of the mass balance for each substrate.Rhodium-catalyzed hydroformylation of a series of para-menthenic terpenes, i.e., terpinolene (1), γ-terpinene (2), and α-terpinene (3), has been studied. The hydroformylation of conjugated diene3 can be performed at a reasonable rate using triphenylphosphine as an auxiliary ligand (P/Rh=20), whereas non-conjugated dienes1 and2 have showed an extremely low reactivity in the Rh/PPh₃ system. The use of a bulky phosphite ligand, i.e., P(O- o-^tBuPh)₃, significantly increased the rate of the hydroformylation of sterically crowded endocyclic double bonds in all three substrates. Dienes1–3 have been efficiently hydroformylated to a mixture of fragrance para-menthenic aldehydes with excellent combined yields (ca. 90%) under relatively mild conditions (80°C, 80atm). Two or three main aldehydes account for 80–90% of the mass balance for each substrate. Differently from the Rh/PPh₃ system, the hydroformylation of conjugated diene3 in the presence of P(O- o-^tBuPh)₃ is not complicated by partial catalyst deactivation, probably, because the ligand prevents the formation of unreactive η³-allyl rhodium complexes. The aldehydes obtained have a pleasant scent and can be useful as components of synthetic fragrances.

Keywords: para-; Menthenic terpenes; Hydroformylation; Rhodium catalyst; Bulky phosphite

Application of continuous kinetic lumping modeling to moderate hydrocracking of heavy oil by Ignacio Elizalde; Miguel A. Rodríguez; Jorge Ancheyta (pp. 237-242).

The continuous lumping approach was used for modeling of hydrocracking of heavy crude oil at moderate reaction conditions. The model parameters were estimated from experimental results obtained in an isothermal fixed bed reactor at different temperatures (380–420°C) and space velocity (1.5, 0.5 and 0.33h⁻¹) at constant pressure and hydrogen-to-oil ratio of 9.8MPa and 5000ft³/bbl respectively. Four model parameters showed linear trend with temperature whereas only one parameter remained almost constant. The optimized values of model parameters were employed to predict results obtained at different reaction conditions from which they were derived. Comparisons between experimental data and predictions using the continuous lumping kinetic model showed good agreement with average absolute error lower than 5%.Continuous lumping approach was used for modeling heavy crude oil hydrocracking. Model parameters were estimated from experimental results obtained at different temperatures and space velocities at constant pressure and hydrogen-to-oil ratio. Four model parameters showed linear trend with temperature whereas one parameter remained almost constant. Optimized values of model parameters were employed to predict results obtained at different reaction conditions from which they were derived. Comparisons between experimental data and predictions using the continuous lumping kinetic model showed good agreement.

Keywords: Continuous kinetic lumping modeling; Hydrocracking; Heavy oil

Synthesis of higher alcohols from syngas over alkali promoted MoS₂ catalysts supported on multi-walled carbon nanotubes by Venkateswara Rao Surisetty; A. Tavasoli; A.K. Dalai (pp. 243-251).

An extensive study of higher alcohol synthesis from synthesis gas using potassium (K) promoted molybdenum sulfide supported on multi-wall carbon nanotubes (MWCNT) catalysts is reported. The optimum conditions for producing the higher alcohols from synthesis gas using gas hourly space velocity (GHSV) of 3.6m³ (STP)/h/kg of catalyst were determined as 320°C and 9.65MPa (1400psig).An extensive study of higher alcohol synthesis from synthesis gas using potassium (K) promoted molybdenum sulfide supported on multi-wall carbon nanotubes (MWCNT) catalysts is reported. Up to 20wt.% of Mo and 9wt.% of K are added to the MWCNT by incipient wetness impregnation method. The catalysts are extensively characterized by different methods and the activity and selectivity of the catalysts are assessed in a fixed-bed micro-reactor. Increasing the amount of K from 3 to 9wt.% increased K–Mo–O interactions, decreased the Mo particle sizes from 20.6 to 12.2nm and increased the percentage dispersion from 20.2% to 30.9%. Most of the metal particles (∼80%) were homogeneously distributed inside the tubes and the rest on the outer surface of the MWCNT. Temperature programmed reduction (TPR) tests showed that increasing the amount of Mo increased the first and second TPR peak temperatures from 516 and 765 to 530 and 835°C, respectively. However, addition of K decreased the peak temperatures from 534 and 825 to 519 and 787°C, respectively. DRIFT spectroscopy of absorbed CO was used to study the nature of active species in the sulfided form of catalysts. Addition of K increased the formation of alcohols and suppressed the formation of hydrocarbons. Catalyst 15wt.% Mo and 9wt.% K supported on MWCNT showed the highest yield (0.11g of total alcohol/g catalyst/h) and selectivity (25.6%) towards alcohols. The optimum conditions for producing the higher alcohols from synthesis gas (mole ratio of H₂ and CO is equal to 2) using gas hourly space velocity (GHSV) of 3.6m³ (STP)/h/kg of catalyst are determined to be 320°C and 9.65MPa (1400psig).

Keywords: Abbreviations; MWCNT; multi-wall carbon nanotubes; TPR; temperature programmed reduction; GHSV; gas hourly space velocity; ICP-MS; inductively coupled plasma-mass spectroscopy; TGA; thermo gravimetric analysis; XRD; X-ray diffraction; TEM; transmission electron microscopy; TPD; temperature programmed desorption; HAS; higher alcohol synthesis; STY; space time yieldHigher alcohol synthesis; Alkali promoted MoS; ₂; catalyst; Multi-wall carbon nanotubes; Water–gas shift reaction

Na-dawsonite derived aluminates for DMC production by transesterification of ethylene carbonate by Georgiana Stoica; Sònia Abelló; Javier Pérez-Ramírez (pp. 252-260).

Tailoring the thermal activation of Na-dawsonite is essential for the optimization of the transesterification of ethylene carbonate with methanol in the synthesis of DMC. The reaction proceeds very fast and efficiently over basic sodium aluminate obtained at temperatures above 873K with a DMC yield up to 65%. Dawsonite-derived aluminates are prospected for multiple green catalytic processes.The transesterification of ethylene carbonate with methanol to dimethyl carbonate, an alternative phosgene-free route to DMC, was investigated over aluminas derived from calcination at different temperatures of Na- and NH₄-dawsonites. The influence of the monovalent cation (NH₄⁺, Na⁺) on the thermal decomposition of the starting dawsonites and derived crystallinity, morphology and porosity of the resulting aluminates was studied. The physico-chemical properties of the dawsonite precursors and the derived oxides were characterized by ICP, in situ XRD, TGA-MS, TEM, N₂ adsorption, FTIR, and²⁷Al MAS-NMR. Phase transitions during thermal decomposition are dependent on the monovalent cation in the original dawsonite, i.e. the NH₄-counterpart is transformed into finely dispersed and highly amorphous aluminas with well-developed porosity in the range 473–1073K, while Na-dawsonite exhibits an intermediate amorphous sodium-containing alumina phase at 523–773K, which crystallizes into sodium aluminate at 773–1073K. Tests were carried out in a parallel reactor system at 298–343K, methanol-to-ethylene carbonate ratios of 2–12, and 0.1–10wt.% catalyst amount. Tailoring the catalyst activation conditions is essential to optimize the transesterification performance, and consequently the production of DMC, a valuable environment-friendly chemical for many potential applications. Any of the oxides derived from NH₄-dawsonite were in active in the reaction. The basicity of the Na-containing oxides, attained by calcination of Na-dawsonite at 973K, is required to obtain an active catalyst, which rendered a maximum DMC yield ca. 65%. Recycling experiments demonstrated that activated dawsonites can be successfully reused.

Keywords: Activated dawsonite; Dimethyl carbonate; Transesterification; Solid base; Sodium aluminate

Facile preparation of SBA-15-supported niobic acid (Nb₂O₅· nH₂O) catalyst and its catalytic activity by Sadanobu Sumiya; Yasunori Oumi; Masahiro Sadakane; Tsuneji Sano (pp. 261-267).

Hydrated niobium oxide (niobic acid) supported on mesopores of SBA-15 was prepared by a simple method that consisted only of HCl treatment of colloidal niobium oxide nanoparticles stabilized with ammonium cations. Nb/SBA-15 catalyst obtained showed excellent catalytic performance for hydrolysis of sucrose.Hydrated niobium oxide (niobic acid) was effectively supported on mesoporous silica SBA-15 by HCl treatment of colloidal niobium oxide solution. The obtained Nb/SBA-15 exhibited high thermal stability, with no crystallization of niobium oxide. The number of generated Brönsted and Lewis acid sites increased with the Nb₂O₅ content. The catalytic activity of Nb/SBA-15 was evaluated to catalyze the hydrolysis of sucrose; Nb/SBA-15 exhibited higher sucrose conversion and TON than both bulk niobic acid and Nb/SBA-15-Oxa prepared according to a previously reported method. Moreover, we found that the choice of acid to be used in the preparation process influences catalytic activity. Nb/SBA-15 prepared by H₃PO₄ treatment yielded the highest sucrose conversion.

Keywords: Niobic acid; Colloidal niobium oxide; SBA-15; Hydrolysis; Sucrose

Preferential oxidation of carbon monoxide in excess hydrogen over platinum catalysts supported on different-pore-sized mesoporous silica by Shengjun Huang; Kenji Hara; Yasuhiro Okubo; Masaaki Yanagi; Hironobu Nambu; Atsushi Fukuoka (pp. 268-273).

Preferential oxidation of carbon monoxide has been studied over low loading of Pt catalysts supported on FSM-type mesoporous silica materials with different pore diameters. Despite the same Pt loading (1wt%) and similar specific surface areas (∼1000m²g⁻¹), the catalysts exhibit different catalytic activities in the reaction. These results are informative for preparing lower Pt loading catalysts and for gaining more understanding of the catalytic role of mesoporous silica.Preferential oxidation (PROX) of carbon monoxide in excess hydrogen has been studied on low Pt loading (0.5–1wt%) catalysts supported on a series of FSM-type mesoporous silica materials. A support effect has been observed, in which the catalytic activities are closely related with the pore diameter of the support, despite their similar specific surface areas. Pt nanoparticles supported on mesoporous silica with 4.0nm pore diameter possess the highest CO conversion over a wide range of reaction temperature, i.e. ca. 100% CO conversion in 298–423K. As a comparison, the Pt particles in small pore supports (1.8nm) exhibit poor performance under the same reaction conditions, which is barely comparable to the Pt catalysts on amorphous silica. The discrepancy in the mesoporous silica is proposed to be related with the different activities of surface silanols in various supports.

Keywords: Mesoporous silica; Pore size; PROX; Pt catalysts

Preparation and characterization of a low particle size Pt/C catalyst electrode for the simultaneous electrochemical promotion of CO and C₃H₆ oxidation by A. de Lucas-Consuegra; A. Princivalle; A. Caravaca; F. Dorado; A. Marouf; C. Guizard; J.L. Valverde; P. Vernoux (pp. 274-280).

A novel technique has been explored for the preparation of a Pt catalyst-working electrode film of low particle size which can be electrochemically promoted at low temperatures. We have used a dispersed Pt/C catalyst powder as the precursor of the catalyst film. The removal of C at low temperatures allows preserving a low Pt particle size.A novel technique was explored for the preparation of a Pt-C catalyst-working electrode film of low particle size (15nm), which can be electrochemically promoted at low temperatures. A Pt/C commercial catalyst powder was used as a precursor of the catalyst film on the solid electrolyte cell. The removal at low temperatures of the initial C matrix on the sprayed catalyst ink, allows to have a Pt/C catalyst-working electrode layer with a suitable morphology, thermal stability and electronic conductivity as supported by several characterization techniques (TGA, XRD, SEM, C analysis and electrical resistance measurements). The Pt-C catalyst film was successfully electrochemically promoted (by potassium ions) for the simultaneous CO and C₃H₆ oxidation reactions under a gas atmosphere which simulates an exhaust stream coming from a gasoline engine. The obtained higher catalytic activity, in comparison with previous studies and the occurrence of an oscillatory phenomenon, which can be electrochemically modified, are interesting results for this new Pt-C based electrochemical catalyst.

Keywords: Electrochemical promotion; NEMCA effect; Electrochemical catalyst; VOCs removal; Pt/C catalyst film

Cyclohexane and toluene oxidation catalyzed by 1,10-phenantroline Cu(II) complexes by Chaline Detoni; Nakédia M.F. Carvalho; Donato A.G. Aranda; B. Louis; O.A.C. Antunes (pp. 281-286).

Mononuclear 1,10-phenantroline Cu(II) complexes: [Cu(phen)₃]Cl₂·7H₂O (1), [Cu(phen)₂Cl]Cl·5H₂O (2), [Cu(phen)Cl₂] (3) were used to oxidize cyclohexane, using hydrogen peroxide as oxidant. All complexes were able to produce cyclohexanol and cyclohexanone with low to moderate yields. Adipic acid was also formed in the reaction. The highest conversion was obtained with the system [Cu(phen)₂Cl]Cl at 70°C, with 67% of total yield. It was also possible to relate the catalytic activity in cyclohexane oxidation, as well as toluene oxidation, with the redox properties of the complexes: the most easily reducible, being also the most active.In this work, we present the cyclohexane oxidation catalyzed by the mononuclear 1,10-phenantroline Cu(II) complexes: [Cu(phen)₃]Cl₂·7H₂O (1), [Cu(phen)₂Cl]Cl·5H₂O (2), [Cu(phen)Cl₂] (3), using hydrogen peroxide as oxidant, in acetonitrile:water (3.5:1) solution. The reactions were carried out at temperatures ranging from 25°C to 70°C. All complexes were able to oxidize cyclohexane into cyclohexanol and cyclohexanone with low to moderate yields. Adipic acid was also formed in the reaction. The highest conversion was obtained with the system [Cu(phen)₂Cl]Cl/H₂O₂/70°C, with 67% total yield. Furthermore, these complexes were also able to oxidize toluene at room temperature.

Keywords: Selective cyclohexane oxidation; Mononuclear Cu(II) complexes; 1,10-Phenantroline; Peroxides; Cyclic voltammetry

Facile condensation of indole with benzaldehyde over Keggin-type heteropoly compounds: An initial effort toward catalyst design by Ezzat Rafiee; Zohre Zolfagharifar; Mohammad Joshaghani; Sara Eavani (pp. 287-291).

Catalytic performances of different Keggin-type heteropoly compounds were investigated in the reaction of indole with benzaldehyde in solventless system. The activity of these catalysts depends on the number of introduced vanadium atoms in H3+_nPMo12−_nV_nO₄₀, cesium content in Cs_xH3−_xPW₁₂O₄₀ and nature of the metal cation in metal substituted polyoxometalates and used support.A series of catalysts derived from Keggin-type heteropoly compounds (HPCs) were prepared and used as catalysts for the reaction of indole with benzaldehyde to afford bis(3-indolyl)phenylmethane. The results showed that the difference in catalytic activity of HPCs in this reaction depends on the number of introduced vanadium atoms in H3+_nPMo12−_nV_nO₄₀, kind of support, cesium content in Cs_xH3−_xPW₁₂O₄₀ and nature of the metal cation in [( n-C₄H₉)₄N](7− n₎PMo₂W₉(M n⁺·H₂O)O₃₉. The product yield was strongly dependent on the acidic characteristics which, in turn, depend on chemical composition of catalysts. In the presence of H3+_nPMo12−_nV_nO₄₀ and Cs_xH3−_xPW₁₂O₄₀, the catalytic activity and acidity decreased with increasing V atom or cesium content. Among supported H3+_nPMo12−_nV_nO_40, H₅PMo₁₀V₂O₄₀/γ-Al₂O₃ is a weaker catalyst than bulk one. [( n-C₄H₉)₄N](7− n₎PMo₂W₉(M n⁺·H₂O)O₃₉ catalysts exhibit a high electron-acceptor character and interesting structural and coordination properties. Catalytic activity of these compounds is related to the difference in their ability to coordinate substrates.

Keywords: Keggin heteropoly compounds; Vanadomolybdophosphoric acids; Cesium Keggin salts; Metal substituted POMs; Acidity

Thermocatalytic decomposition of natural gas over plasma-generated carbon aerosols for sustainable production of hydrogen and carbon by Nazim Muradov; Franklyn Smith; Gary Bockerman; Kirk Scammon (pp. 292-300).

Thermocatalytic decomposition of natural gas over a new type of carbon-based catalyst: non-thermal plasma-generated carbon aerosols is reported. The plasma-generated carbon aerosols exhibited highest catalytic activity for methane decomposition among known carbon catalysts with a comparable surface area.Thermocatalytic decomposition (TD) of natural gas (NG) is a promising CO₂-free approach to hydrogen production, however, the practical realization of the sustainable TD process faces significant technical challenges due to rapid deactivation of existing catalysts by carbon deposits. In this work, the authors report on TD of NG and methane over a new type of carbon-based catalyst: plasma-generated carbon aerosols. The carbon aerosols were produced by non-thermal plasma-assisted decomposition of NG at near-ambient conditions. The plasma-generated carbons exhibit highest catalytic activity for methane (or NG) decomposition among known carbon-based catalysts with a comparable surface area. The nanostructure of the plasma-generated carbons was characterized and found to be consistent with highly disordered (amorphous) carbon. It is demonstrated that the combination of the carbon aerosol generator with the TD reactor provides a means for sustainable production of hydrogen and carbon from NG with a relatively high energy efficiency.

Keywords: Hydrogen; Carbon; Natural gas; Thermocatalytic decomposition; Catalyst; Plasma

Spatially resolving concentration and temperature gradients during the oxidation of propylene on Pt/Al₂O₃ by Osama Shakir; Aleksey Yezerets; Neal W. Currier; William S. Epling (pp. 301-308).

IR-thermography and SpaciMS were used to evaluate temperature and gas species concentration values over a Pt/Al₂O₃ monolith-supported catalyst during propylene oxidation before and after thermal degradation. The distribution of temperature across the monolith and the gradients in gas-species concentrations in a channel during reaction was clearly resolved using the combination of the two minimally invasive techniques, providing a clearer understanding of reaction evolution along the monolith.IR-thermography and spatially resolved capillary-inlet mass spectrometry (SpaciMS) were used simultaneously to monitor dynamic concentration and temperature wave propagation over a Pt/Al₂O₃ monolith-supported catalyst during propylene oxidation. The IR thermography data and gas species data clearly demonstrated where reaction was occurring in the monolith, and changes in the reaction profile as a function of time and temperature. Under the conditions tested, and as expected, back-to-front oxidation light-off was observed. Changes in the temperature and concentration profiles before and after thermal degradation were compared and show that after thermal degradation the ignition front moved toward the inlet significantly more slowly relative to the non-thermally degraded sample. The two minimally invasive techniques proved complimentary in application. A complete data set was obtained with one experiment using IR thermography, while obtaining the spatial profile of the gas species measurements required multiple experiments. The IR thermography data, however, were confounded by conductive and convective heat transfer, but were decoupled from the reaction heat after confirming a relationship between the reaction position and temperature profiles using the SpaciMS gas species data. The combination of the two techniques results in a clear picture of the reactant and product gas species and temperature distribution along the catalyst length.

Keywords: Propylene oxidation; Spatially resolved reactions; Platinum; Alumina; Diesel oxidation catalyst

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Applied Catalysis A, General (v.365, #2)

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Applied Catalysis A, General (v.365, #2)