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Applied Catalysis A, General (v.296, #2)

Editorial Board (pp. co2).

Newsbrief (pp. n5-n11).

Stability of supported and promoted-molybdenum carbide catalysts in dry-methane reforming by Anna R.S. Darujati; William J. Thomson (pp. 139-147).

The stability of molybdenum carbide (Mo₂C) in dry-methane reforming (DMR) was studied over Al₂O₃, ZrO₂ and MgO supports and in the presence of Ce, K and Zr promoters at 900°C, 1bar, a GHSV of 3800h⁻¹ and a stoichiometric feed. All catalysts deactivated via moving front oxidation under these conditions. The γ-alumina appeared to be superior compared to other supports due to its high surface area and high thermal stability, and Mo₂C/γ-Al₂O₃ had a much higher activity than a bulk Mo₂C catalyst. Over this support, a high Mo loading was found to be crucial for maintaining the stability of the catalyst due to the higher concentration of more reducible Mo oxides and the higher CH₄ conversion over the carbide. The impregnation order was found to be an important factor for Ce, and the 3wt.% Ce-Mo₂C/Al₂O₃ was found to be the most stable catalyst due to the redox properties of the Ce promoter. On the other hand, the addition of CO in the feed, while preventing oxidation of all catalysts, resulted in slow deactivation due to coking over the Ce-promoted catalyst.

Keywords: Molybdenum carbide; Supports; Promoter; Oxidation; Stability; Dry-methane reforming

Structure–activity relationships for sulfated zirconias — comparison of mesoporous samples based on organic precursors by Cornelia Breitkopf; Arnd Garsuch; Helmut Papp (pp. 148-156).

Sulfated zirconias were obtained by hydrolysis of zirconium propoxide precursors. Digestion of the hydrous oxides in ammonia or sodium hydroxide resulted in materials with different active centres as revealed by the catalytic conversion of n-butane to iso-butane. The activity correlates to the number of highly acidic centres. The pHs of the solutions were systematically varied from 9 to 13. Moreover, the formation of crystalline phases and the pore size distribution were studied in dependence of the variation of the calcination temperature (773 and 873K) and the aging time (3h or 24h). It could be shown that the activity can be directed via preparation of a special morphology. Sulfation of the samples changed the pore size distribution from monomodal to bimodal and caused a shift to lower pore diameters. The samples were characterized by means of N₂-physisorption, X-ray diffraction, temperature programmed desorption of ammonia, DTG.

Keywords: Mesoporous zirconia; Control of morphology; n; -Butane isomerization; Poisoning of centres

Platinum dispersion measurements for Pt/BaO/Al₂O₃, NO_x storage catalysts by Jazaer Dawody; Lisa Eurenius; Hussam Abdulhamid; Magnus Skoglundh; Eva Olsson; Erik Fridell (pp. 157-168).

In this investigation different experimental methods to determine the platinum dispersion of Pt/BaO/Al₂O₃ NO_x storage catalysts are compared. The dispersion of platinum is determined independently using temperature programmed desorption of CO, dissociation of N₂O, static volumetric CO and H₂ chemisorption, dynamic CO chemisorption and transmission electron microscopy. For Pt/BaO/Al₂O₃, reproducible results are obtained when the platinum dispersion is determined from N₂O dissociation, CO and H₂ chemisorption. However, repeated CO-TPD experiments result in decreased amount of desorbed CO, which limits this method to determine platinum dispersion for Pt/BaO/Al₂O₃ samples. For Pt/Al₂O₃, similar values for platinum dispersion are obtained for all methods used in the study.In addition to the platinum dispersion investigations, the surface morphology of Pt/BaO/Al₂O₃ samples and the distribution of different elements are studied using SEM-EDS. The SEM-EDS analyses show that the platinum is evenly distributed over the entire sample surface, while the distribution of barium is more uneven.

Keywords: Characterization; Platinum dispersion; TEM; SEM; EDS; CO chemisorption; CO TPD; H; ₂; chemisorption; N; ₂; O dissociation; Barium

Hydrodeoxygenation of benzophenone on Pd catalysts by Martina Bejblová; Petr Zámostný; Libor Červený; Jiří Čejka (pp. 169-175).

Catalytic hydrogenation and hydrogenolysis of benzophenone in a liquid phase at the reaction temperature of 130°C and pressure 6MPa on supported palladium catalysts were investigated. A number of different supports including active carbon, alumina, Beta and ZSM-5 zeolites with different Si/Al ratios and MCM-41 was tested. The effects of solvent, support and its acidity on the course of benzophenone transformations were studied. Catalysts using acid zeolite or active carbon as supports were found very effective in hydrodeoxygenation reaction. Based on the kinetic model applied, possibilities of conversion of benzophenone to diphenylmethane were discussed. The model confirmed that both the possible mechanisms (the hydrogenation–hydrogenolytic and the direct hydrogenolysis of the CO bond of benzophenone) took place in a significant manner.

Keywords: Hydrogenation; Hydrogenolysis; Deoxygenation; Benzophenone

Oxidative dehydrogenation of ethane in a fluidized bed membrane reactor by Desislava Ahchieva; Mirko Peglow; Stefan Heinrich; Lothar M�rl; Tania Wolff; Frank Klose (pp. 176-185).

The performance of a pilot scale fluidized bed membrane reactor (FLBMR) was studied experimentally in comparison to the conventional operation as a fluidized bed reactor (FLBR) for the catalytic oxidative dehydrogenation of ethane using a γ-alumina supported vanadium oxide catalyst. For both reactor configurations, the influence of process parameters such as temperature and contact time was investigated. Further, the experimental data obtained were compared to previous experiments with a fixed-bed reactor (FBR) and a packed-bed membrane reactor (PBMR) operated with a similar catalyst.For identical overall feed rates, the distributed oxidant feeding in the FLBMR improves the selectivity to ethylene significantly. The beneficial effect of oxidant dosing over the membrane is most pronounced at high temperatures and long contact times. Under limiting oxidant supply the FLBMR and the PBMR show a similar performance, but under moderate oxygen excess the FLBMR outperforms the PBMR significantly. The maximum ethylene yield observed in the FLBMR was 37% compared to 35% for the PBMR. Beside a high productivity, for the FLBMR a broader favorable operation range with respect to the oxygen–hydrocarbon ratio was observed, what indicates a lower sensitivity against oscillations and disturbances in the reactant feed, corresponding to a higher safety of operation. Because of an excellent heat transfer characteristics, the fluidized bed membrane reactor concept is very promising for maximizing the yield of the desired intermediates also in large-scale plants, especially for strongly exothermic reactions.

Keywords: Fluidized bed reactor; Membrane reactor; Oxidative dehydrogenation; Ethane

Catalytic dehydrogenation and cracking of industrial dipentene over M/SBA-15 (M=Al, Zn) catalysts by Junming Du; Hualong Xu; Jiang Shen; Jingjing Huang; Wei Shen; Dongyuan Zhao (pp. 186-193).

Al- and Zn-containing mesoporous molecular sieves (SBA-15) were prepared by an impregnation method and were used as catalysts for the catalytic dehydrogenation and cracking of industrial dipentene, an important natural feedstock. The catalysts were characterized by X-Ray fluorescence spectroscopy (XRF), X-Ray diffraction (XRD), N₂ adsorption/desorption, transmission electron microscopy (TEM), magic angle spinning nuclear magnetic resonance (²⁷Al MAS NMR) and Fourier transform infrared spectroscopy (FT-IR) techniques. The characterization results suggest that the active components were introduced without changing the mesostructure of SBA-15. FT-IR revealed that Al/SBA-15 shows weak Br�nsted acidity and strong Lewis acidity, while Zn/SBA-15 only possesses moderate Lewis acidity. Dehydrogenation and cracking products, such as toluene, were found in the dipentene conversion over Al/SBA-15, while for Zn/SBA-15, p-cymene was the major dehydrogenation product. Along with the strong Br�nsted acidity and high cracking activity of HZSM-5, our results suggest that the reaction pathway is determined by the acidic sites. Stability tests showed the deactivation is also related to the acidity. The highest yield of p-cymene reaches to 86.7% on Zn/SBA-15 at 723K.

Keywords: Dipentene; p-; Cymene; Toluene; M/SBA-15 (M; =; Al, Zn); Catalytic cracking; Dehydrogenation

Photo reduction of CO₂ to methanol using optical-fiber photoreactor by Jeffrey C.S. Wu; Hung-Ming Lin; Chao-Ling Lai (pp. 194-200).

Greenhouse gases such as CO₂ are the primary cause of global warming. One of the best routes to remedy CO₂ is to transform it to hydrocarbons using photo reduction. CO₂ was photocatalytically reduced to produce methanol using a Hg lamp with wavelength 365nm in a steady-state optical-fiber photoreactor. The optical-fiber photoreactor, comprised of nearly 120 Cu/TiO₂-coated fibers, was designed and assembled to transmit and spread light uniformly inside the reactor. TiO₂ film was coated on optical fiber using a dip-coating method. Cu-loaded titania solutions were prepared by a thermal hydrolysis method. The thickness of Cu/TiO₂ film was 53nm. The coating film consisted of very fine spherical particles with diameters of near 14nm. The XRD spectra indicated the anatase phase for all TiO₂ and Cu/TiO₂ films. The wavelength of absorption edge on Cu/TiO₂ was near 367nm, equivalent to a bandgap of 3.3eV. The most active Cu species on TiO₂ surface were Cu₂O clusters, and they played an important role for the formation of methanol. The methanol yield increased with UV irradiative intensity. Maximum methanol rate was 0.45μmole/gcath using 1.2wt.%-Cu/TiO₂ catalyst at 1.29bar of CO₂, 0.026bar of H₂O, and 5000s mean residence time under 16W/cm² UV irradiation. Higher than 1.2wt.% Cu loading gave a lower rate of methanol yield because of the masking effect of Cu₂O clusters on the TiO₂ surface. The Langmuir–Hinshelwood model was established by correlating experimental data to describe the kinetic behavior. An optimum pressure ratio of H₂O/CO₂ was found in the photo reduction of CO₂ for maximum methanol yield.

Keywords: Photocatalysis; Renewable energy; Optical-fiber photoreactor; CO; ₂; reduction; TiO; ₂

Hydroformylation of long-chain alkenes with new supported aqueous phase catalysts by Carsten Disser; Christian Muennich; Gerhard Luft (pp. 201-208).

In this paper the development and investigation of a new type of immobilized catalyst for the hydroformylation of long-chain alkenes is presented. The catalyst system consisted of the well known metal complex carbonylhydrido-tris-( m-sulfo-triphenylphosphine)-rhodium which was immobilized on activated carbon treated at high temperature. As starting materials 1-hexene, 1-decene, 1-tetradecene, 2-hexene and 2,3-dimethyl-2-butene were used. For all linear α-olefins the same n/ iso ratio in the product of 2:1 was determined. The reaction rate decreased with increasing chain length and sterical hindrance of the alkene double bond. All hydroformylation experiments were performed in a stirred semi-batch reactor. Catalyst leaching turned out to be a function of solvent polarity. Using n-heptane as solvent the immobilized catalyst remained stable on the carrier. The activity of the immobilized catalyst decreased compared to the homogeneous catalyst system. Water content was identified to be one of the most significant parameters of the reaction rate.The simulation of experimental data was modelled by a semi-empirical rate law. Within the simulation the reaction scheme consisting of hydroformylation, isomerization and aldol reaction was simultaneously calculated. It was possible to determine the reaction orders of all components, rate constants and the activation energies of all reactions.

Keywords: Hydroformylation; SAPC; Modelling; Kinetics; Alkene; Rhodium catalyst

Selective heterogeneous catalytic hydrogenation of nitriles to primary amines in liquid phase by László Hegedűs; Tibor Máthé (pp. 209-215).

A method for selective liquid-phase heterogeneous catalytic hydrogenation of nitriles to primary amines has been developed. Benzonitrile (BN) was hydrogenated to benzylamine (BA) under mild reaction conditions (30°C, 6bar), over supported palladium catalysts, in a mixture of two immiscible solvents (e.g. water/dichloromethane) and in the presence of sodium dihydrogen phosphate (NaH₂PO₄). Complete conversion, very high selectivity (95% to BA) and isolated yield (85–90%) could be achieved by using this process. Very pure product (>99% BA-content) was prepared without applying any special purification procedures.

Keywords: Palladium; Benzonitrile; Benzylamine; Selective hydrogenation; Primary amine

Pt-Re-Sn/Al₂O₃ trimetallic catalysts for naphtha reforming processes without presulfiding step by V.A. Mazzieri; J.M. Grau; C.R. Vera; J.C. Yori; J.M. Parera; C.L. Pieck (pp. 216-221).

The n-heptane reforming and the cyclopentane hydrogenolysis reactions over noble metal monometallic catalysts (0.3% Pt), bimetallic catalysts (0.3% Pt, x% Re, x=0.1, 0.3, 0.9 and 2.0, sulfided) and trimetallic catalysts (0.3% Pt, 0.3% Re, y% Sn, y=0.1, 0.3, 0.6 and 0.9, unsulfided) were studied. The metal function was supported over a chlorided γ-alumina that provided the acid function. The reforming of n-heptane was performed at 450°C, molar ratio H₂/ n-C₇=4 and WHSV=7.3 while the hydrogenolysis of cyclopentane was performed at 350°C, H₂/CP=20 and WHSV=2.4.The sulfided 0.3Pt-0.3Re catalyst (with 0.06% S) was found to be the best performing bimetallic one. It had a great stability, typical of this kind of catalysts, and also produced a reformate with a high iso-heptanes/toluene ratio. This is advantageous for fulfilling the current environmental regulations that limit the amount of aromatic hydrocarbons in reformulated gasolines. The best trimetallic catalyst was 0.3Pt-0.3Re-0.6Sn which had a similar activity and selectivity as sulfided 0.3Pt-0.3Re, though it displayed a higher stability and a lower hydrogenolysis activity, without the need of presulfidation. Tin affected the metal and acid functions of the catalyst simultaneously and inhibited them to such different degrees that a very convenient metal/acid activity ratio was obtained, resulting in an improvement of the activity, selectivity and stability of the catalysts.It can be concluded that it is possible to prepare trimetallic naphtha reforming catalysts of the Pt-Re-Sn kind with a better performance than conventional sulfided Pt-Re catalysts and with the additional advantage that they do not need complicated sulfiding pretreatments. This simplifies the commercial operation of the reformer unit and enables the application of this catalyst to continuously operated processes.

Keywords: Reforming; Trimetallic catalysts; i; -Heptane/toluene ratio

Preparation and optimization of mixed iron cobalt oxide catalysts for conversion of synthesis gas to light olefins by Ali Akbar Mirzaei; Razeieh Habibpour; Eslam Kashi (pp. 222-231).

Iron cobalt oxides were prepared using co-precipitation procedure and studied for the conversion of synthesis gas to light olefins. In particular, the effect of a range of preparation variables such as the precipitate ageing time and [Fe]/[Co] molar ratio of the precipitation solution were investigated in detail. The preparation procedure and also the optimum preparation conditions were identified with respect to the catalyst activity for the hydrogenation of carbon monoxide. The results are interpreted in terms of the structure of the active catalyst and it has been generally concluded that the catalyst containing 40% Fe/60% Co – on molar basis – and aged for 2h, is the most active catalyst for the conversion of synthesis gas to ethylene and propylene. The effect of different promoters and supports along with loadings of optimum support and promoter on the activity and selectivity of this catalyst are studied. It was found that the catalyst containing 40% Fe/60% Co/15wt.% SiO₂/1.5wt.% K is an optimum modified catalyst and gave the best activity and selectivity. The activity and selectivity of all prepared catalysts have been studied in a fixed bed micro reactor in a range of reactor temperatures using synthesis gas with different H₂/CO molar feed ratios. The lifetime of optimum catalyst for 72h has been tested under the optimum reaction conditions and the catalyst was found to be highly stable. Characterization of both precursors and calcined catalysts by X-ray diffraction and scanning electron microscopy showed that the precipitate ageing time and also the [Fe]/[Co] ratio of the precipitation solution influenced the catalyst precursor structure and morphology.

Keywords: Catalyst preparation; Co-precipitation; Effect of ageing; Iron-cobalt oxide; Fischer–Tropsch synthesis; Light olefins

Molybdenum carbide catalyst formation from precursors deposited on active carbons: XRD studies by J. Pielaszek; B. Mierzwa; G. Medjahdi; J.F. Mar�ch�; S. Puricelli; A. Celzard; G. Furdin (pp. 232-237).

Molybdenum carbide is a promising catalyst in many reactions. Its formation was investigated by XRD for two different active carbons: commercial one (NC100) and made out of expanded graphite. They were impregnated by MoCl₅ from vapor phase and carbonized in a stream of hydrogen. XRD studies were performed both in ex situ and in situ conditions. Formation of different crystallographic carbide phases (stable, hexagonal Mo₂C and/or unstable cubic molybdenum carbide) was observed depending on the conditions of carbidization. The reported earlier catalytic behavior at low temperatures were rationalized in terms of formation of these phases and oxy- or oxyhydrocarbides.

Keywords: Molybdenum carbide; Activated carbons; Catalyst characterization; X-ray diffraction

Evaluation of strategies for the immobilization of bidentate ruthenium–phosphine complexes used for the reductive amination of carbon dioxide by Markus Rohr; Michael G�nther; Fabian Jutz; Jan-Dierk Grunwaldt; Hermann Emerich; Wouter van Beek; Alfons Baiker (pp. 238-250).

Different routes for the immobilization of highly active bidentate ruthenium–phosphine complexes (RuCl₂(dppe)₂ and RuCl₂(dppp)₂) on silica have been explored and the resulting heterogeneous catalysts were evaluated concerning activity and stability when applied to the formylation of functionalized amines, such as 3-methoxypropylamine, in supercritical carbon dioxide. Two fundamentally different immobilization strategies were applied: covalent linkage and coordinative anchoring of the active complex. The latter immobilization method resulted in strong leaching of the complex under reaction conditions. Structural and textural properties of the heterogeneous catalysts were characterized using various methods, including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). Particular attention was given to a thorough characterization of the catalysts when subjected to reuse. XAS in fluorescence and transmission mode provided deeper insight into the observed deactivation phenomena. Despite the low concentration of Ru in solution (ca. 50ppm) the structural changes could be resolved with both detection modes.

Keywords: Carbon dioxide fixation; Immobilization; Ruthenium phosphine complex; Formylation of amines; Reductive amination of carbon dioxide; 3-Methoxypropylamine; Supercritical carbon dioxide; Fluorescence and transmission EXAFS

Alkylation of naphthalene with isopropanol over a novel catalyst UDCaT-4: Insight into selectivity to 2,6-diisopropylnaphthalene and its kinetics by Ganapati D. Yadav; Sanket S. Salgaonkar (pp. 251-256).

Numerous routes to 2,6-naphthalenedicarboxylic acid, a feedstock for high performance polyester polyethylene naphthalate, exist starting with the alkylation of an aromatic ring. However, the route beginning with naphthalenic compounds has an economic advantage because of reduction in the number of reaction steps to build the naphthalene ring. This has spurred a lot of interest in the shape selective dialkylation of naphthalene. Mono alkylation of naphthalene is simple, but its further shape selective dialkylation to 2,6-dialkylnaphthalene (2-DAN), is challenging. A variety of solid acid catalysts especially zeolites have been reported in studies to investigate the effect of acidity, pore geometry and shape selectivity in this reaction. However, the activity of most catalysts is susceptible to coke formation within a few hours of time on stream. It is in this perspective that we report the novelties of UDCaT-4, a synergistic combination of persulfated alumina and zirconia with hexagonal mesoporous silica, which exhibits tremendous stability, activity and selectivity in the vapour-phase isopropylation of naphthalene with isopropanol to 2,6-diisopropylnaphthalene (DIPN). It leads to better yields and selectivity in comparison with other catalysts reported in literature. A systematic investigation of the effects of various operating parameters was accomplished. Furthermore, a mathematical model was developed to describe the reaction pathway and the model validated with experimental results.

Keywords: Alkylation; Naphthalene; Monoisopropylnaphthalene; Isopropanol; Heterogeneous catalysis; 2,6-Diisopropylnaphthalene; UDCaT-4; Persulfated alumina; Zirconia; Hexagonal mesoporous silica; Selectivity

Kinetic study of NH₃ decomposition over Ni nanoparticles: The role of La promoter, structure sensitivity and compensation effect by Jian Zhang; Hengyong Xu; Wenzhao Li (pp. 257-267).

Some nickel nanoparticles supported on alumina were synthesized and tested for ammonia decomposition. Steady-state reaction kinetic results reveal that the turnover frequency (TOF) increases firstly with decreasing particle size, passes through a maximum in the range of mean size of Ni⁰ 1.8–2.9nm and then decreases. A structure sensitivity of NH₃ decomposition over Ni catalysts is strongly suggested. An excellent fit of experimental data by the Temkin–Pyzhev equation was obtained. A compensation effect between the pre-exponential factor ( k₀) and activation energy ( E_a) was observed and quantified. Moreover, La could partially lower the particle size of Ni⁰ and reduce the stability of reaction intermediates, which could be the main reason for its positive influence on the specific activity of Ni. H₂ temperature-programmed desorption (TPD) and NH₃ temperature-programmed surface reaction (TPSR) were used as supplements to study the influence of Ni⁰ particle size and addition of La on the catalytic behavior.

Keywords: Reaction kinetics; Ammonia decomposition; Nano-sized nickel catalysts; Lanthanum promotion; Structure-sensitivity; Compensation effect

Calendar of Forthcoming Events (pp. 268-268).

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Applied Catalysis A, General (v.296, #2)