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Applied Catalysis A, General (v.282, #1-2)

EDITORIAL BOARD (pp. iii).

CONTENTS LIST (pp. v-vi).

Do you really have a better catalyst? by John N. Armor (pp. 1-4).

Density functional study of carbon dioxide hydrogenation on molybdenum carbide and metal by Hiroyuki Tominaga; Masatoshi Nagai (pp. 5-13).

The density functional theory with a cluster approach was used to study the relative stabilities and reactivities of the surface species of molybdenum carbide and metal during the hydrogenation of carbon dioxide. The adsorption of CO₂ on a Mo₄C₂ cluster produces an optimized structure with the adsorption energy of −212.2kJ/mol, higher than that on the Mo₄ cluster. The first hydrogenation of CO₂ on the Mo₄C₂ cluster led to ▪ through the cleavage of CO and O of the adsorbed carbon dioxide with hydrogen addition. This step has a lower activation energy than that for the Mo₄ cluster to HO₂CMo₄, which was formed by hydrogen addition to the adsorbed carbon dioxide without CO cleavage. The second hydrogenation of ▪ to ▪ involved a higher activation energy than the cleavage of CO and OH of HO₂CMo₄ with hydrogen to yield ▪. The difference in the adsorption stabilities of CO₂ on the Mo₄C₂ and Mo₄ clusters was also explained by the difference in the electronic structures and the orbital interactions near the highest orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. The experimental result of the CO₂ hydrogenation showed that Mo carbide preferentially catalyzed the reverse gas shift reaction to yield CO and H₂O compared to Mo metal. The density functional theory (DFT) calculation accounts for the higher activity of molybdenum carbide for CO₂ hydrogenation being higher than that of molybdenum metal.

Keywords: DFT; Mo carbide; Mo metal; CO; ₂; Hydrogenation

Hydroisomerization of n-octane over platinum catalysts with or without binder by Antonio de Lucas; Jos� Luis Valverde; Paula S�nchez; Fernando Dorado; Mar�a Jes�s Ramos (pp. 15-24).

The catalytic performance for the hydroisomerization of n-octane (conversion, selectivity and yield) of sets of bifunctional catalysts based on mordenite, beta and ZSM-5 zeolites with or without a binder (bentonite) were compared. As hydrogenating–dehydrogenating function, platinum supported by impregnation (1wt.%) was used. It was found that the activity decreased in the following order: ZSM-5>beta>mordenite-based catalysts. A decrease in the activity of agglomerated samples, because of the neutralization of the acid sites by the binder, was expected. The activity decrease was significantly high for ZSM-5 zeolite but the opposite effect was observed for beta zeolite. The presence of aluminium extraframework (EFAL) species in the beta agglomerated sample should be the responsible of this behaviour because of a synergetic effect between these EFAL species and the structural Brönsted acid sites causing an increase of the acid strength.The octane isomers selectivity for the agglomerated mordenite and beta samples was very similar to that in the non-agglomerated ones. ZSM-5 agglomerated sample yielded higher isomer selectivity than the non-agglomerated one. The higher neutralization of the acid sites by the binder was the responsible to that because leads to a higher concentration of carbenium ions, which provide the octane isomers. Also, the binder provided meso and macropores to the zeolite where the metal was likely located avoiding a possible pore partial blockage, with the consequently lower diffusional constraint of the reactants.

Keywords: Zeolites; Hydroisomerization; Binder; n; -Octane

Simple fabrication of nano-sized NiO₂ powder and its application to oxidation reactions by Hongbing Ji; Tingting Wang; Meiying Zhang; Yuanbin She; Lefu Wang (pp. 25-30).

A novel, facile, and environmentally-friendly process for fabrication of NiO₂ was developed and used as both a stoichiometric oxidant and an effective catalyst for benzyl alcohol oxidation. That simultaneous stoichiometric and catalytic reactions might exist in many reactions is proposed.

Keywords: NiO; ₂; Stoichiometric oxidant; Catalyst; Benzyl alcohol oxidation

The Rh, Co, Ru metal-catalyzed hydroformylation of hex-1-ene using triphenylphosphine, triphenylarsine and triphenylantimony as ligands by Vivek K. Srivastava; Ram S. Shukla; Hari C. Bajaj; Raksh V. Jasra (pp. 31-38).

A comparative study has been made of transition metal-catalyzed hydroformylation of hex-1-ene using rhodium, cobalt and ruthenium complexes of triphenylphosphine, triphenylarsine and triphenylantimony as catalysts. The catalytic activities of the ligands with the studied metals vary in the order: Ph₃P≈Ph₃As>Ph₃Sb under employed reaction conditions.The hydroformylation activity of M/AsPh₃ systems was comparable and even higher under some experimental conditions than that of M/PPh₃ systems. The only significant difference, which makes M/PPh₃ systems better than M/AsPh₃ systems, was the higher normal/iso (n/iso) ratio of heptanal for M/PPh₃ systems.

Keywords: Hex-1-ene; Ligands; Hydroformylation; σ-Donor/π-acceptor ratio; Transition metals

Acidity and catalytic properties for methane conversion of Mo/HZSM-5 catalyst modified by reacting with organometallic complex by Peng Wu; Qiubin Kan; Xuxu Wang; Dongyang Wang; Haijun Xing; Piaoping Yang; Tonghao Wu (pp. 39-44).

The selective modification of the external surface of HZSM-5 by large organometallic complexes was used to reduce the densities of external acid sites and MoO_x species retained at external surfaces during the exchange process. The amounts of acid sites and the catalytic properties for non-oxidative aromatization of methane over modified and unmodified samples were studied by NH₃-TPD, FT-IR of d₃-acetonitrile adsorption, and TGA measurements. It was found that acid sites and active MoO_x species mainly located within the channels of the modified zeolites, and these modified Mo/HZSM-5 catalysts showed higher shape-selectivity to major product benzene and lower formation rates and selectivities for large hydrocarbons that normally cause the deactivation of catalysts.

Keywords: Acidity; Modified; Mo/HZSM-5; Methane aromatization; Organometallic complex

Effect of acidity and metal content on the activity and product selectivity for n-decane hydroisomerization and hydrocracking over nickel–tungsten supported on silica–alumina catalysts by Yacine Rezgui; Miloud Guemini (pp. 45-53).

Ni–W/silica–alumina based catalysts with different nickel and tungsten concentration (nickel ranging from 12 to 17% and tungsten ranging from 8 to 30%) were prepared by sol–gel method. The BET, temperature-programmed desorption of ammonia (TPDA) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) techniques were used to characterize the prepared solids. Afterwards, the catalysts were screened for activity and selectivity in the hydroconversion of n-decane. Under the experimental conditions, yields of isomers as well as cracking products were a function of both metal content and amount of acid sites. Up to 15% Ni content, nickel increased isomerization selectivity, afterwards, the catalytic selectivity decreased. Moreover, the higher the amount of medium acid sites present on the catalyst, the higher its activity and its deactivation.After running on stream for 100min, the catalysts with 15% of nickel and 10% of tungsten (WT(15,10) catalyst) showed the best results (42.3% of conversion and 55% selectivity) at 250°C.

Keywords: Cracking; Decane; Dewaxing; Hydroconversion; Isomerization; Nickel; Tungsten oxide

Selective liquid phase oxidation of toluene with air by Can-Cheng Guo; Qiang Liu; Xu-Tao Wang; Hai-Yang Hu (pp. 55-59).

Catalysis of simple cobalt tetraphenylporphyrin for selective liquid phase oxidation of toluene with air is first reported. By the catalysis of simple cobalt tetraphenylporphyrin, the selective oxidation of toluene with air in the absence of any solvents or promoters will produce benzaldehyde and benzyl alcohol. Compared with the present synthetic method of benzaldehyde and benzyl alcohol by the chlorination of toluene followed by hydrolysis, which has been used in the world industry, the new method has the advantage of friendly environmental effects. The researchers found that the reaction time, temperature, air pressure, the amount of catalyst and the flow rates of air influenced the toluene conversion and the selectivity of benzaldehyde and benzyl alcohol. By the use of 3.2×10⁻⁵M cobalt tetraphenylporphyrin as catalyst, toluene oxidation with air under the optimum conditions of 160°C and 0.8MPa and 0.04m³/h airflow produced benzaldehyde and benzyl alcohol at 60% selectivity and 8.9% conversion of toluene. The mole turnover numbers of the catalyst was about 25,000. A possible mechanism is also suggested.

Keywords: Porphyrin; Toluene; Catalysis; Oxidation; Benzaldehyde; Air

Liquid phase transformation of α-pinene over Beta zeolites containing aluminium or boron, titanium and vanadium as lattice ions by G. G�nd�z; R. Dimitrova; S. Yilmaz; L. Dimitrov (pp. 61-65).

Beta zeolites with different modules (SiO₂/Al₂O₃) and containing B, Ti or V in lattice positions were synthesised by different methods and tested as catalysts in liquid phase transformation of α-pinene at 100°C in a batch reactor. It was established that the hydrogen forms of Beta samples with a SiO₂/Al₂O₃ module of about 55–66 and containing both micro- and mesopores displayed high catalytic activity in liquid phase isomerization of α-pinene. Samples with boron, titanium or vanadium, as lattice ions possess insignificant catalytic activity.

Keywords: α-Pinene; Beta zeolite; Al-Beta; B-Beta; Ti-Beta; V-Beta; Liquid phase; Camphene

Synthesis, characterisation and catalytic properties of vanadium substituted mesoporous aluminophosphates by Ch. Subrahmanyam; B. Louis; B. Viswanathan; A. Renken; T.K. Varadarajan (pp. 67-71).

Vanadium substituted mesoporous AlPO have been synthesised using structure-directing surfactant under hydrothermal synthesis conditions. The presence of V in the framework of AlPO has been established by ESR, XPS, UV–vis DRS and ICP-AES measurements. This system is capable of promoting the oxidation of toluene to aldehyde and benzoic acid when the oxidising agent is 70% tert-butyl hydroperoxide while with 30% H₂O₂ cresols are formed. The activity of V-AlPO has been compared with those obtained with other similar porous materials like V-MCM 48, V-MCM-41, V-Al-Beta and VS-1.

Keywords: V-AlPO; V-MCM-48; Toluene oxidation; Mesoporous materials; tert; -Butyl hydroperoxide (TBHP)

Kinetics of steam reforming of methane on Ru/Al₂O₃ catalyst promoted with Mn oxides by A. Berman; R.K. Karn; M. Epstein (pp. 73-83).

New types of solar heated reformers have been developed in recent years. In these reactors, called volumetric reformers, concentrated solar radiation illuminates directly the catalyst through a transparent window. These solar reformers can operate at higher temperatures (1000–1100°C) since the surface temperature limit of a regular metal tubular reactor used in the industry is eliminated and a much higher heating rate is feasible. The main restriction, so far, of the solar volumetric reformers to operate at these temperatures is caused by the thermal stability of the current available catalysts. A new catalyst, thermally stable at these temperatures, based on Ru supported on α-alumina and promoted with Mn oxides, has been investigated. The experimental results show that the activity of this catalyst in steam reforming of methane was practically unchanged after operation at 1100°C for 100h. The structure of the catalyst was studied by XRD. The fresh sample contained α-Al₂O₃ and MnO₂. Under the reaction conditions at high temperatures MnO₂ is reduced to form Mn₃O₄ and spinel MnAl₂O₄. SEM micrographs show large islands of Mn oxides over α-Al₂O₃ particles.The kinetics of the steam reforming of methane on Ru/(α-Al₂O₃+MnO_x) catalysts was studied in a flow reactor operated in differential mode at the temperature range of 500–900°C and total pressure of 1–7atm. Conversion of methane was 2–8%. The results show that the reaction order with respect to methane is <1 at 450–500°C and close to 1 at 700–900°C. The reaction order with respect to steam is negative at all temperature range. The kinetic equation was derived from the mechanism of the steam reforming reaction as developed in this paper. This mechanism involves the following main stages:(a)dissociative adsorption of methane on Ru surface;(b)adsorption of steam on the catalyst support in a molecular form;(c)dissociative adsorption of steam on the Ru surface;(d)oxidation of the surface carbon.

Keywords: Ruthenium catalyst; Solar system reforming; Kinetics; High temperature stability

Synthesis and characterization of chromium(III)-doped magnesium fluoride catalysts by J. Krishna Murthy; Udo Gross; Stephan R�diger; Ercan �nveren; Wolfgang Unger; Erhard Kemnitz (pp. 85-91).

Cr³⁺-doped MgF₂ systems are synthesised by a novel non-aqueous soft chemistry route using different Cr precursors and varying Cr loading. These systems have been characterized by X-ray powder diffraction (XRD), BET surface area, TPD of ammonia, FT-IR pyridine adsorption analysis and X-ray photoelectron spectroscopy, and tested for their catalytic activity in dismutation of CCl₂F₂ and CF₃–CHClF. Catalysts synthesised starting from CrO₃ or (CH₃CO₂)₇Cr₃(OH)₂ showed better catalytic activity than those prepared with CrCl₃. FT-IR pyridine adsorption studies reveal that the catalytic activity is highly correlated with the Lewis acid strength. In TPD of NH₃ catalysts prepared from CrO₃ and (CH₃CO₂)₇Cr₃(OH)₂, precursors showed a similar behaviour, different from that of catalysts prepared from CrCl₃.

Keywords: Lewis acid; Heterogeneous catalysis; Metal fluoride; Doped systems

Solid acid characteristics and isobutane/butene alkylation by Alexandru Platon; William J. Thomson (pp. 93-100).

Catalytic behavior during gas-phase, batch alkylation experiments employing isobutane and 1-butene at 80�C was studied for Beta zeolites with SiO₂/Al₂O₃ (SAR) ratios of 25 (25BEA) and 75 (75BEA), ZSM-5 and sulfated zirconia (SZ). The observed alkylation performance was compared to the low-temperature hydride transfer (HT) activity of the studied catalysts and with their acidity, adsorption capacity and surface area measurements. For all materials studied, a correlation was observed between the measured HT activity and the amount of trimethylpentane (TMP) produced per acid site. The 25BEA catalyst produced the highest amount of trimethylpentane (TMP) and also had the most elevated HT activity. ZSM-5 was found to be inactive for both HT and alkylation, and although SZ had moderate alkylation activity, it also had a higher cracking activity than other materials. Modification by water vapor exposure of 25BEA and SZ did not create any noticeable change in Br�nsted acidity, but a dramatic decrease in TMP production was detected on the modified catalysts and explained by competitive adsorption between water and isobutane. The apparent butene conversion correlated well with the total catalyst surface area rather than with the total amount of acid sites. In all the catalysts studied a much stronger interaction with butene than with isobutane was observed, suggesting that competitive adsorption between the two reactants limits isobutane access to the active sites, resulting in limited hydride transfer.

Keywords: Hydride transfer; Alkylation of isobutane; Butene; Cyclohexene; Solid acid catalyst; Zeolite Beta; Sulfated zirconia; ZSM-5

Nonisothermality in packed bed reactors for steam reforming of methanol by Ayman Karim; Jaime Bravo; Abhaya Datye (pp. 101-109).

We have studied the kinetics of methanol steam reforming on a commercial CuO/ZnO/Al₂O₃ catalyst in a packed bed reactor. The objective of this work was to assess the impact of deviations from isothermality in packed bed reactors on the rates of methanol steam reforming. Preliminary experiments with catalyst dilution showed higher apparent rate constants as the catalyst was diluted, implying heat transfer limitations in the bed. We therefore varied the reactor diameter from 4.1 mm down to 1 mm in order to improve heat transfer. The smaller diameter reactor showed higher apparent catalyst activity. This increased reactivity could be explained using a 2D pseudo-homogeneous reactor model. The heat transfer limitations result in a temperature gradient of up to 40 K in the 4.1 mm reactor. Even the 1 mm reactor suffers from temperature variations of up to 22 K. Since packed bed reactors are most commonly used for the production of H₂ via steam reforming, it is important to recognize the role of these heat transfer limitations. Transport limitations can lead to falsified kinetics and lowered catalyst productivity.

Keywords: Methanol steam reforming; Heat transfer limitations; Packed bed microreactor; CuO/ZnO/Al; ₂; O; ₃; catalyst; Reactor modeling

Metal sintering mechanisms and regeneration of palladium/alumina hydrogenation catalysts by R.-J. Liu; P.A. Crozier; C.M. Smith; D.A. Hucul; J. Blackson; G. Salaita (pp. 111-121).

We have investigated the role of different Pd sintering mechanisms on the regeneration process for alumina supported Pd hydrogenation catalysts. The Pd sintering mechanisms are strongly influenced by the catalyst morphology. In the case of fresh catalyst, Pd particles sit directly on the alumina surface and sintering occurs via a traditional ripening and coalescence mechanisms and was significant only at 600�C or above. For the used catalyst, Pd particles are supported mostly on green oil residue and this dramatically changed the sintering mechanism during the regeneration process. Catalytic gasification of green oil residue around the Pd particles in an oxidizing environment permits movement and coalescence to take place at relatively low temperatures. During the stripping, Pd particles are passively brought into contact as hydrocarbon is gasified and the exothermic nature of the process raises the temperature to about 500�C. At this temperature, chance contact between metal particles results in rapid coalescence and gives rise to particle sintering even at temperatures well below the Tamman temperature. This passive contact process is the dominant mechanism for Pd coarsening during catalyst regeneration.

Keywords: Pd catalyst; Sintering; Environmental transmission electron microscopy; Oxidation environment; Alumina support; Catalyst regeneration; Green oil formation; Hydrogenation of acetylene

On the performance of a highly loaded Co/SiO₂ catalyst in the gas phase hydrogenation of crotonaldehyde by F. Djerboua; D. Benachour; R. Touroude (pp. 123-133).

This paper reports on the performance and its relation with the structure of a highly loaded (41wt.%) Co/SiO₂ catalyst in the gas phase hydrogenation of crotonaldehyde when varying the thermal treatments to which the catalyst precursor has been subjected.The optimum calcination and reduction temperatures were identified where the highest selectivity to crotyl alcohol (around 90%) was obtained with the catalyst calcined at 400�C and reduced at 350�C even at conversions as high as 60%. Higher temperature of calcination was found to lower the crotyl alcohol selectivity. Both, lower and higher reduction temperatures will not favour the crotyl alcohol formation. These results were interpreted and correlated with the surface structure of the catalyst which was shown by temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) analysis. Depending on the thermal conditions imposed, the surface consisted of either Co metal, or coexisting metal and its oxide; structure which favours the high crotyl alcohol selectivity. By TEM analysis, large particles (diameter exceeding 50nm) were identified after reduction at 350�C. A global activation energy of 44kJ/mol was obtained with this catalyst. In the light of the obtained results a discussion on the reaction mechanism involving metal, metal-oxide double sites has been put forward. It was emphasised that, for selective hydrogenation of crotonaldehyde into unsaturated alcohol, Co catalysts compete favourably with platinum based catalysts.

Keywords: Co/SiO; ₂; catalyst; Crotonaldehyde hydrogenation; Crotyl alcohol selectivity; Metal-oxide double site; Structure–selectivity relationship

Carbon accumulation, deactivation and reactivation of Pt catalysts upon exposure to hydrocarbons by Zolt�n Pa�l; Attila Wootsch; Robert Schl�gl; Ute Wild (pp. 135-145).

The formation and catalytic effect of carbonaceous deposits was studied on monofunctional Pt catalysts: Pt black (PtN, i.e., reduced with hydrazine), Pt/SiO₂ (EUROPT-1), Pt on “herringbone�? graphite nanofiber (Pt/GNF-H, GNF being able to store hydrogen) and Pt/CeO₂ (ceria tending to consume spilt over hydrogen). They were exposed to hexane or t,t-hexa-2,4-diene between 483 and 663K, with or without H₂. Hydrocarbon transformations during these deactivating exposures as well as in subsequent standard test reaction with hexane in hydrogen excess were studied. Carbon accumulation on Pt black after analogous deactivating treatments was also examined by electron spectroscopy (XPS and UPS). The abundance of hydrogen on Pt sites controlled the activity and selectivity containing much PtC species. The amount of surface C could reach ∼45% causing almost total activity loss, but even ∼30% C on Pt blacks decreased markedly the catalytic activity, due to massive 3D deposits. “Disordered�? carbon selectively poisoned the formation of saturated C₆ products and fragmentation. The yield of dehydrogenation to hexenes was a good universal indicator of deactivation for each catalyst. Four regions were distinguished: “beneficial�?, “selective�?, “non-selective�? and “severe�? deactivation.

Keywords: Pt; Platinum black; Monofunctional Pt; Deactivation; Hexane; Hydrogen; Aromatization; Isomerization; XPS; UPS

Promoting effect of Al₂O₃ on catalytic activity of NiSO₄/ZrO₂ for ethylene dimerization by Jong Rack Sohn; Eun Suk Cho (pp. 147-154).

The NiSO₄/Al₂O₃–ZrO₂ catalysts containing different nickel sulfate and Al₂O₃ contents were prepared by the impregnation method. Here the support, Al₂O₃–ZrO₂, was prepared by the coprecipitation method using a mixed aqueous solution of zirconium oxychloride and aluminum nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20wt.%, indicating good dispersion of nickel sulfate on the surface of Al₂O₃–ZrO₂. The addition of nickel sulfate (or Al₂O₃) to ZrO₂ shifted the phase transition of ZrO₂ (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Al₂O₃) and ZrO₂. 10-NiSO₄/5-Al₂O₃–ZrO₂ containing 10wt.% NiSO₄ and 5mol% Al₂O₃, and calcined at 700°C exhibited a maximum catalytic activity for ethylene dimerization. NiSO₄/Al₂O₃–ZrO₂ catalysts was very effective for ethylene dimerization even at room temperature, but Al₂O₃–ZrO₂ without NiSO₄ did not exhibit any catalytic activity at all. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Al₂O₃ up to 5mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Al₂O₃ and ZrO₂ and due to consequent formation of AlOZr bond.

Keywords: NiSO; ₄; /Al; ₂; O; ₃; –ZrO; ₂; catalyst; Promoting effect of Al; ₂; O; ₃; Acidic properties; Ethylene dimerization

Vapour-phase selective O-methylation of catechol with methanol over Ti-containing aluminium phosphate catalysts by Xiaomei Zhu; Xuemei Li; Mingjun Jia; Gang Liu; Wenxiang Zhang; Dazhen Jiang (pp. 155-161).

Vapour-phase O-methylation of catechol with methanol has been investigated over Ti-containing aluminium phosphate catalysts (denoted as Al_0.77Ti_xP, where x is between 0 and 1.15) prepared by non-uniform precipitation method. The catalytic activities increase with the increase of Ti/P ratio in the range 0–0.23, while further increase of Ti content leads to the decrease of activities. Meanwhile, the selectivity to guaiacol decreased gradually with the increase of Ti/P ratio. The results of various means of characterization demonstrate that the addition of titanium considerably affects the structure of the catalysts, as well as the strength and amount of the acidic and basic sites. The presence of stronger Lewis acidic and/or basic sites in the higher Ti content catalysts should be responsible for the formation of side products ( C-alkylation products) and coke, thus quickening the deactivation process of the catalysts. On the other hand, the weak acidic–basic characteristics of the lower Ti content catalysts result in the high selectivity to mono- O-methylation product (guaiacol), and the excellent durability of the catalysts.

Keywords: O; -Methylation; Catechol; Methanol; Guaiacol; Aluminium phosphates

Activity of CoMo/γ-Al₂O₃ as a catalyst in hydrodesulfurization: effects of Co/Mo ratio and drying condition by Y.S. Al-Zeghayer; P. Sunderland; W. Al-Masry; F. Al-Mubaddel; A.A. Ibrahim; B.K. Bhartiya; B.Y. Jibril (pp. 163-171).

A series of γ-alumina-supported cobalt–molybdenum hydrodesulfurization catalysts have been prepared with different ratios of cobalt to molybdenum (0.0–1.0) and under different drying temperatures (323, 373 and 423K). The active components ions were loaded on the alumina via an incipient wetness impregnation method. The catalysts were converted to active sulfide form using dimethyldisulfide. Hydrodesulfurization (HDS) of dibenzothiophene (DBT) was tested at 550–683K and 10atm. Samples of the catalysts were characterized using SEM and XPS techniques. Changes in grain sizes and binding energy due to the cobalt–molybdenum interactions have been observed. The catalyst activities based on dibenzothiophene conversion rate constants and product (biphenyl BP and cyclohexylbenzene CHB) distributions, depended strongly on the Co/Mo ratios. CHB/BP ratio as high as 0.2 was obtained for Co/Mo of 0.2–0.4, while for higher Co/Mo ratios, no CHB was observed. The ratio of about 0.4 exhibited the highest rate constant. The drying temperature was found to improve the activities, with the lowest temperature showing the best performance in terms of dibenzothiophene degree of conversion. Such results suggest that cobalt and molybdenum are associated in a fixed proportion and that their distribution on the support surface, which in turn improves catalyst performance, could be modified by the catalyst preparation conditions.

Keywords: CoMo/γ-Al; ₂; O; ₃; catalysts; Cobalt/molybdenum ratios; Hydrodesulfurization; Dibenzothiophene; Dimethyldisulfide; Co/Mo ratio; Drying condition; SEM; XPS

Physicochemical and catalytic properties in methane combustion of La1−_xCa_xMnO3±_y (0≤ x≤1; −0.04≤ y≤0.24) perovskite-type oxide by Narj�s Harrouch Batis; Pierre Delichere; Habib Batis (pp. 173-180).

The objective of this work is to understand the role of physicochemical properties of pure and calcium substituted lanthanum manganite perovskite with a particular attention to the importance of the degree of non-stoichiometry.The La1−_xCa_xMnO3±_y (0≤ x≤1; −0.04≤ y≤0.24) oxides were prepared by thermal decomposition of a liquid precursor of lanthanum and calcium nitrates and manganese acetate followed by calcination for 24h at 973K. XRD analysis showed that all samples were single-phase perovskite-type oxides with distorted structure depending on the substitution level. Presently, we have investigated the catalytic activities in methane combustion of this group of oxides. Bulk and surface physicochemical characteristics were determined and reported in this study. XPS analysis revealed the significant changes in the La3d, 4d; Ca2p; O1s and Mn2p characteristics as well as the excess of concentration with respect to the bulk resulting from the incorporation of Ca in La sublattice.Substitution with calcium affected significantly the surface specific area which ranged in 6–17m²/g with a maximum value for an optimal composition x=0.6. The light-off temperature for 50% methane conversion was found to be the lowest for La_0.4Ca_0.6MnO_3.03 composition. Samples with oxygen overstoichiometry showed better catalytic performances (specific and areal activities) than those with oxygen substoichiometry. An optimal fraction, x=0.6 of Ca enhanced significantly these performances.

Keywords: Perovskite; Stoichiometry; Catalysis; Methane combustion

Impregnation of dimeric Cr^III(salen) on silica and its application in epoxide asymmetric ring opening reactions by Bart M.L. Dioos; Pierre A. Jacobs (pp. 181-188).

The heterogeneous asymmetric ring opening (ARO) of epoxides with trimethylsilylazide (TMSN₃) catalysed by a dimeric Cr(salen) catalyst impregnated on a silica material combines high enantioselectivities for epoxide and ring opened product with good conversions and suffers only from low leaching in both batch and continuous flow experiments.

Keywords: Asymmetric ring opening; Epoxides; Impregnation; Dimeric Cr(salen) complex

Synergy effects between bismuth molybdate catalyst phases (Bi/Mo from 0.57 to 2) for the selective oxidation of propylene to arcrolein by Minh Thang Le; Willy J.M. Van Well; Per Stoltze; Isabel Van Driessche; Serge Hoste (pp. 189-194).

In this work, the synergy effect between different phases of bismuth molybdate catalysts was investigated systematically. The catalysts were prepared by spray drying and had a Bi/Mo atomic between 0.57 and 2. It is found that the synergy effect is only observed in mixtures containing γ-phase. A mixture with Bi/Mo ratio=1.3 consisting of γ- and α-phase, exhibits the highest activity. Less homogeneous ‘artificial mixtures’ exhibit reduced synergy effects when compared to homogeneous ‘in situ mixtures’.

Keywords: Bismuth molybdates; Synergy effect; Spray drying; Selective oxidation; Propylene; Catalytic activity

Pre-reforming of natural gas on a Ni catalyst by Thomas Sperle; De Chen; Rune L�deng; Anders Holmen (pp. 195-204).

Pre-reforming of natural gas has been studied on a nickel catalyst at 480–550°C and 20bar using a TEOM (Tapered Element Oscillating Microbalance) reactor. The focus has been on carbon formation and the main objective was to study the influence of C₂–C₃ hydrocarbons in the methane feed on carbon deposition on the catalyst. Coking thresholds for different mixtures of hydrocarbons were determined by varying the steam to carbon (S/C) ratio at various temperatures. The steady-state coking rate decreases with increasing S/C ratio, and increases with increasing carbon number of the hydrocarbon. Unsaturated hydrocarbons show a strong effect on coking rates and on carbon thresholds. For mixtures of methane and propane/propene, the steady-state coking rate as well as the coking threshold decreased with a decrease in the mole fraction of propane/propene and with an increase in the hydrogen mole fraction. The coking rate revealed a complicated temperature dependency, and a minimum in the coking rate and in the coking threshold was detected at 500°C. A relationship between the critical steam to carbon ratio and the thermodynamic carbon activity is also developed based on a suggested reaction mechanism, which can properly predict the role of hydrocarbon, hydrogen and water in carbon formation.

Keywords: Carbon deposition; Steam reforming; TEOM; Carbon threshold; Nickel catalyst; Natural gas; Pre-reforming conditions

Pillared clays as catalysts for hydrocracking of heavy liquid fuels by M.E. Gyftopoulou; M. Millan; A.V. Bridgwater; D. Dugwell; R. Kandiyoti; J.A. Hriljac (pp. 205-214).

Two sets of pillared clays (PILCs), chromia and tin-oxide-pillared montmorillonites and laponites, were successfully prepared at Aston University using both conventional and microwave-assisted methods and characterised by X-ray diffraction and thermogravimetric analysis. Microwave irradiation enabled the preparation of the PILCs in a fraction of time of the conventional methods. X-ray powder diffraction was not a suitable method for characterizing laponite or pillared laponites due to the lack of first order reflections attributed to the small size of individual particles and the random rather than uniform face-to-face orientation of the clay platelets. Laponite appeared to be more thermally stable than montmorillonite. For pillared montmorillonites, dehydroxylation shifted to a lower temperature compared to the starting materials, whereas for tin-oxide-pillared laponites such a shift did not occur. On the other hand for chromia laponite dehydroxylation took place over a much wider temperature range compared to all other materials. The prepared PILCs were employed as catalysts in the hydrocracking of coal-derived liquids in a conventional microbomb reactor at Imperial College exhibiting high-quality performance and remaining active after 4h utilization regardless of high coke deposition. They actually showed an increase in the total conversion when reused.

Keywords: Pillared clay catalysts; Chromia pillars; Tin oxide pillars; Montmorillonite; Laponite; Microwave irradiation; X-ray diffraction; Thermogravimetric analysis; Hydrocracking; Coal liquids

Asymmetric hydroformylation of vinyl arenes catalyzed by furanoside diphosphinites-Rh(I) complexes by Eugeni Guimet; Jos� Parada; Montserrat Di�guez; Aurora Ruiz; Carmen Claver (pp. 215-220).

Diphosphinite ligands2 and3, easily prepared from inexpensived(+)-xylose in few steps, were tested in the Rh-catalyzed asymmetric hydroformylation of several vinyl arenes. High regio-selectivities in branched aldehyde (up to 99%) and moderate enantio-selectivity (up to 63%) were found (20–40°C, 30–60bar of syn gas). For the first time, the structure in solution of the species formed under hydroformylation conditions with diphosphinite ligands was determined.

Keywords: Furanoside ligands; Diphosphinite ligands; Asymmetric hydroformylation

Low temperature methanol synthesis from carbon monoxide and hydrogen over ceria supported copper catalyst by Wen-Jie Shen; Yuichi Ichihashi; Yasuyuki Matsumura (pp. 221-226).

High catalytic activity in the methanol synthesis from carbon monoxide and hydrogen can be produced with ceria supported copper catalysts prepared by a coprecipitation method at a reaction temperature below 200°C. In comparison with commercial copper–zinc catalysts, the equivalent activity is obtained at a lower reaction temperature by 60°C, while it is still unstable. Although the reaction atmosphere is reductive, metallic copper particles formed in the pretreatment with hydrogen are oxidized and the catalyst is highly activated. The size of the copper oxide species produced is significantly small, showing dispersion of copper on cerium oxide during the reaction. Hence, the interaction between copper and cerium oxide is probably indispensable for the appearance of the high catalytic activity.

Keywords: Methanol synthesis; Copper; Cerium oxide; TPR; XRD; EXAFS; Formation of copper oxides

Catalyst for ultra-low sulfur and aromatic diesel by Roberto Galiasso Tailleur; Juan Ravigli; Samuel Quenza; Norma Valencia (pp. 227-235).

A WNiPd/TiO₂�Al₂O₃ new catalyst with improved desulfurization and hydrogenating capabilities was tested to produce ultra-low sulfur and aromatics diesel oil. The removal of the sterically hindered sulfur and nitrogen containing polyaromatic molecules is studied. It was observed that the new catalyst surface structure promotes the hydrogenating and ring opening of poly-alkyl-poly-aromatics that are less limiting step than that with conventional catalyst. The catalyst characterization indicated the possible formation of metallic acid sites that contribute to the ring opening reactions. The catalyst study using the extracted aromatics and the raffinated product indicated a large improvement in hydrogenation and a reduction in hydrodealkylation functions for converting these sterically hindered aromatics. The reduction in aromatics families improves diesel engine emissions.

Keywords: Deep hydrogenation and ring opening reactions; WNiPd/TiO; ₂; �Al; ₂; O; ₃; catalyst; Diesel engine emissions

The influence of Pd–Ag catalyst restructuring on the activation energy for ethylene hydrogenation in ethylene–acetylene mixtures by Hugo Zea; Kelvin Lester; Abhaya K. Datye; Ed Rightor; Robert Gulotty; Wendy Waterman; Michael Smith (pp. 237-245).

Hydrogenation of acetylene–ethylene mixtures was studied on Pd/SiO₂ and Pd–Ag/SiO₂ under conditions that correspond to “front-end�? hydrogenation of acetylene. The presence of excess H₂ under “front-end�? hydrogenation conditions can lead to thermal runaway due to the exothermic reaction of ethylene and H₂. In previous work, we found that activation energy was sensitive to catalyst pretreatment: high temperature treatment in H₂ leading to lower apparent activation energy, while pretreatment under oxidizing conditions leading to higher activation energies for ethylene hydrogenation. Since ethylene hydrogenation is a known structure-insensitive reaction, it was puzzling that the apparent activation energy should be so sensitive to catalyst pretreatment. As we show in this work, the presence of co-adsorbed CO (which is present during “front-end�? hydrogenation), and changes in the surface structure of Pd–Ag surfaces together modify the apparent activation energy for ethylene hydrogenation. In situ infrared spectroscopy of adsorbed carbon monoxide reveals how the presence of Ag modifies the proportion of bridged and linearly bound CO on Pd/SiO₂. High temperature reduction further modifies the ratio of bridged to linear CO on Pd–Ag surfaces. Since CO in bridged form is bound more strongly than linearly bound CO, this shift in adsorption geometry modifies the apparent activation energy for ethylene hydrogenation. This work describes how restructuring of bimetallic Pd–Ag surfaces and the presence of a co-adsorbed CO, work together to alter the reaction behavior of an industrially significant selective hydrogenation reaction.

Keywords: Ethylene hydrogenation; Activation energy; Pd–Ag bimetallic catalysts; In situ IR of adbsorbed CO; Catalyst restructuring of Pd–Ag

Preparation and properties of filled monolayer of MoO₃ deposited on Al₂O₃ supports by solvent-assisted spreading by L. Kaluža; Z. Vít; M. Zdražil (pp. 247-253).

Catalysts MoO₃/Al₂O₃ were prepared by solvent-assisted spreading method, which is the reaction of Al₂O₃ support with the slurry of MoO₃ in water. Fifteen Al₂O₃ supports with surface area S_BET in the range of 11–279m²g⁻¹ were used. The method belongs to equilibrium adsorption impregnation methods and provides the catalysts with filled monolayer of molybdena species; the formation of bulk MoO₃ and Al₂(MoO₄)₃ is avoided. The saturated adsorption loading, corresponding to filled monolayer loading, linearly increased with S_BET and the mean density of filled monolayer calculated from the slope was 3.4Monm⁻². The deposited-filled monolayer was X-ray amorphous. Two reduction peaks were observed by temperature-programmed reduction. Their position was independent of Al₂O₃ surface area indicating the same quality of filled monolayer in all catalysts. The samples were sulfided and their activity in hydrodesulfurization (HDS) of thiophene (TH) at the pressure of 1MPa and temperature 280–400°C was tested. Activation energy of all samples was similar and their activity increased linearly with saturated adsorption loading; that again proves the same quality of filled monolayer independently of S_BET of Al₂O₃. It was found with four Al₂O₃ that the catalysts prepared by solvent-assisted spreading were equally or more active (by up to 37%, depending on Al₂O₃) as compared with the corresponding catalysts prepared by conventional impregnation using (NH₄)₆Mo₇O₂₄ solution.

Keywords: MoO; ₃; /Al; ₂; O; ₃; Solvent-assisted spreading; Hydrodesulfurization; Molybdena monolayer

SiO₂-supported dodecatungstophosphoric acid and Nafion-H prepared by ball-milling for catalytic application by Bulcs� R�c; Gabriele Mulas; Anik� Csongr�di; Katalin L�ki; �rp�d Moln�r (pp. 255-265).

Dodecatungstophosphoric acid (HPW) and Nafion-H were supported on SiO₂ using the ball-milling technique. Samples were characterized by physical (BET surface, SEM, DSC, XRD, DRIFT and Raman spectroscopies) and chemical (acid–base titration) methods. Catalytic properties were studied in a range of chemical transformations, which can be induced by electrophilic catalysts including Friedel–Crafts reactions (alkylation of toluene with benzyl alcohol, acylation of anisole with acetic anhydride) and the dimerization of α-methylstyrene. Milling conditions (stainless steel or polystyrene apparatus, milling time), loading of the active components, and the type of support were found to have profound effects on the physical characteristics and catalytic performance of the samples. Ball-milled HPW-SiO₂ samples prepared under appropriately selected conditions exhibit catalytic properties similar to catalysts made by impregnation. HPW in ball-milled samples, in turn, proved to be more resistant to extraction with polar solvents (hot methanol) and these catalysts display higher stability in recycling studies. Supported Nafion-H samples prepared by ball-milling show high activities in test reactions. The best catalyst exceeds SAC-13 in the selective synthesis of 1,1,3-trimethyl-3-phenylindane in the dimerization of 2-phenylpropene. Catalysts with high catalytic performance require the use of optimal milling time, because particle coalescence and the resulting decrease in BET surface area hinder the accessibility of the active sites.

Keywords: Dodecatungstophosphoric acid; Nafion-H; Ball-milling; Friedel–Crafts alkylation; Friedel–Crafts acylation; Dimerization of 2-phenylpropene; Catalyst recycling

Selective catalytic reduction of NO_x with ammonia on gallium-exchanged ferrierites by M. Me�?árová; N.A. Miller; N.C. Clark; K.C. Ott; T. Pietraß (pp. 267-272).

Selective catalytic reduction of NO_x on Ga³⁺ exchanged ferrierite zeolites (FER) using ammonia as reductant shows high rates of NO_x conversion, although neither the catalytic reaction mechanism nor the role of the gallium is understood. We investigate the features of the structure of the catalyst and the mechanism of the catalytic reduction of NO_x to N₂ using nuclear magnetic resonance (NMR) spectroscopy, complemented by temperature programmed desorption (TPD) and catalytic conversion measurements. The NMR studies are enabled by the diamagnetic nature of the gallium-exchanged zeolites in contrast to many of the transition metal exchanged zeolites which are often paramagnetic. Two different ferrierite samples were chosen for comparison, one containing significant quantities of K⁺ and Na⁺, the other being largely alkali-free. The gallium-exchanged zeolites and their parent materials were characterized using²⁹Si,²⁷Al,⁷¹Ga, and¹²⁹Xe NMR. Reactions run under batch-mode conditions using ammonia as the reducing agent clearly show the formation of nitrogen in the¹⁵N NMR spectra. Our results show that the acidity of the zeolite is more important for catalytic reduction than the presence of gallium when NO_x is supplied to the catalyst as a 1:1 mixture of NO and NO₂.

Keywords: Selective catalytic reduction; NO; _x; removal; Lean burn catalysis; Gallium; Ferrierite; NMR; TPD

Effect of the synthesis conditions on the redox and catalytic properties in oxidation reactions of LaCo1−_xFe_xO₃ by S�bastien Royer; Fran�ois B�rub�; Serge Kaliaguine (pp. 273-284).

The aim of this work was to study the effect of the synthesis conditions of LaCoO₃ on the redox properties and the catalytic activity for the CH₄ and CO oxidation reactions. Five LaCoO₃ samples were prepared by different methods: solid state (SS), coprecipitation (COP), citrate complexation (CIT) and reactive grinding of the single oxides (RG) and of an amorphous precursor (COPRG). TPD-O₂ experiments showed three kinds of oxygen. First, two surface oxygen species (designated as α-oxygens) were distinguished. The amounts of oxygen desorbing in the two α-oxygen desorption peaks were found to be mainly dependant on the specific surface area of the samples and stay lower than one monolayer (0.7–0.8). The last desorption peak, which is generally attributed to the desorption of some lattice oxygens (β-oxygens), was found to be more dependant on the morphology of the sample. H₂ reduction experiments (TPR-H₂) showed the usual two-step reduction. The reduction temperatures were found to be directly related to the calcination temperatures. H₂ uptakes and XRD analysis suggest a reduction of slightly more than one e⁻ in the first step and the formation of some Co⁰ before the beginning of the second reduction step. Kinetic analysis for the CH₄ oxidation reaction showed that the specific reaction rate is significantly affected by the synthesis procedure. Grinding an amorphous precursor results in a perovskite which combines a high specific surface area (made possible by the use of grinding) and a high activity. The RG sample presents a lower activity than COPRG, due to a higher iron contamination. Nevertheless, the differences observed in the oxidation reaction rate could not be correlated to the redox properties, measured by TPD-O₂ and TPR-H₂, of the catalysts. Then, these methods are not adequate to evaluate the reactivity of the solids. When tested in the CO oxidation reaction, the samples present different comportments than in the CH₄ oxidation reaction. These differences are discussed on the basis of the oxidation mechanisms involved in the two reactions.

Keywords: Perovskite; Redox properties; Catalytic activity in methane oxidation; Synthesis route effect

Preparation of anatase TiO₂ supported on alumina by different metal organic chemical vapor deposition methods by Xingwang Zhang; Minghua Zhou; Lecheng Lei (pp. 285-293).

Two kinds of metal organic chemical vapor deposition (MOCVD) approaches have been employed for the preparation of the photocatalyst of titanium dioxide supported on alumina. One was simultaneous deposition and calcinations, i.e. a one-step process; the other was preliminary gas impregnation of the support followed by a decomposition step, i.e. a two-step process. The results of characterization indicated that the structure of the support was destroyed by a two-step process because of pore blocking. It was found that the one-step process resulted in a superior photocatalyst; this was attributed to higher external surface concentration and more perfect crystalline structure of TiO₂. TiO₂/Al₂O₃ catalysts showed good repeatability.

Keywords: TiO; ₂; /Al; ₂; O; ₃; Preparation; MOCVD; Photodegradation

Effects of vanadium oxidation number on desulfurization performance of FCC catalyst by Jun Long; Yuxia Zhu; Yujian Liu; Zhijian Da; Han Zhou (pp. 295-301).

Effects of vanadium on the desulfurization performance of FCC catalysts were investigated with vanadium having different oxidation numbers (abbr. Oxnum). Molecular modeling studies showed that vanadium with low Oxnum could affect the chemical conversion of sulfur compounds. However, the vanadium deposited on equilibrium catalyst was in high Oxnum because of the oxidation in regenerator, so an activation method to reduce vanadium Oxnum named selective activation was introduced. It was proved with electron paramagnetic resonance (EPR) and temperature-programmed reduction (TPR) that vanadium Oxnum decreased when the catalyst was activated. The molecular modeling studies are well consistent with the lab evaluation results. The desulfurization performances of activated equilibrium catalysts were better than that of the unactivated catalysts. Similar results were observed with the lab vanadium-contaminated catalyst. The desulfurization performance of the catalyst was optimized when vanadium Oxnum was close to 2 (VO).

Keywords: FCC catalyst; Desulfurization; Gasoline sulfur; Metal deposit; Oxidation number; Vanadium; Selective activation

Bimetallic Bi–Pt, Ru–Pt and Ru–Pd and trimetallic catalysts for the selective oxidation of glyoxal into glyoxalic acid in aqueous phase by Aurore Deffernez; Sophie Hermans; Michel Devillers (pp. 303-313).

Various bi- and trimetallic associations have been tested as catalysts for the selective oxidation of glyoxal into glyoxalic acid in aqueous phase. All catalysts were supported on carbon and consisted of a noble metal (Pd or Pt) in association with a second (or third) metal acting as promoter (Ru or Bi). Out of all the possible combinations, some families of catalysts were selected as interesting candidates and a detailed kinetic study was undertaken, in order to determine the rate constant associated with the formation of glyoxalic acid. In particular, the BiPt/C catalysts gave very high activity, but low selectivity (due to over-oxidation to oxalic acid), the PdRu/C catalysts gave the highest yields in glyoxalic acid, but with long reaction times and a marked sensitivity to the preparation procedure, while the trimetallic catalysts gave high yields in relatively short periods of time.

Keywords: Oxidation (selective); Liquid phase; Glyoxal; Glyoxalic acid; Palladium; Platinum; Ruthenium; Bismuth; Carbon

Effect of Ru loading and of Ru precursor in Ru/C catalysts for ammonia synthesis by I. Rossetti; L. Forni www.dcfe.unimi.it (pp. 315-320).

One of the key points in the study of Ru/C catalysts for ammonia synthesis is the structure sensitivity of the reaction, which usually determines the proper metal loading, so governing the cost of the final catalyst. In the present work, the effect of Ru loading on catalytic activity and thermal stability (i.e. catalyst resistance against support methanation and metal sintering) was investigated. The optimal Ru loading was found to be around 3.5wt.%, a value considerably lower with respect to that commonly found in literature. Furthermore, top activity was obtained with 10–15% Ru dispersion, higher dispersion values leading to less performing catalysts. Finally, the effect of some different water-soluble Ru precursors on catalyst behaviour was also investigated.

Keywords: Ru loading; Ammonia synthesis; Ru/C catalyst

Photocatalytic oxidation of n-butanol under fluorescent visible light lamp over commercial TiO₂ (Hombicat UV100 and Degussa P25) by J. Kirchnerova; M.-L. Herrera Cohen; C. Guy; D. Klvana (pp. 321-332).

Photocatalytic oxidation (PCO) of volatile organic compounds (VOC) over TiO₂, exploiting visible light of common fluorescent lamps represents an attractive means of indoor air purification. This work compares activity and its variation with calcination of two commercial TiO₂, Hombicat UV100 and Degussa P25, in a complete PCO of n-butanol serving as a convenient representative VOC. The PCO of n-butanol was carried out in a flow through reactor under a relatively long residence time using mostly fluorescent visible (white) light (FWL)-lamp for illumination. Fluorescent black light (UV) (FBL)-lamp was used only for comparison. Under FBL-lamp, 580ppm n-butanol is completely mineralized over both catalysts. Under FWL-lamp the reaction is considerably slower and Degussa P25 appears more active than Hombicat UV100. For 580ppm, steady state conversions of less than 95% are attained, but at 145ppm, a complete mineralization is achieved even over Hombicat UV100. Butanal, propanal and ethanal were identified as the main gaseous intermediate products. In addition, a parallel formation of crotonaldehyde, product of aldolization, was detected. The appearance and concentration of crotonaldehyde depended on PCO conditions, particularly on the characteristics of TiO₂. Thermal treatment of TiO₂ at ≥623K has a negative effect on the activity in PCO of both catalysts. Apparently, the calcination causes modification of the surface available active sites that is in part reflected by diminution of specific surface area. The effect of reactor residence time, of inlet concentration and of the relative light intensity on the efficiency of the process was also evaluated.

Keywords: Photocatalytic oxidation; Commercial titania photocatalysts; Effect of thermal treatment on the titania photocatalyst; n; -Butanol photocatalytic oxidation; Hombicat UV100; Degussa P25; Step-wise photooxidation; Photocatalytically induced aldolization

Storage and formation of pure hydrogen mediated by the redox of modified iron oxides by Sakae Takenaka; Kiyoshi Nomura; Noriko Hanaizumi; Kiyoshi Otsuka (pp. 333-341).

Methods for the storage and formation of pure hydrogen were demonstrated based on the reduction of magnetite with hydrogen (Fe₃O₄+4H₂→3Fe+4H₂O), followed by oxidation of iron metal with water vapor (3Fe+4H₂O→Fe₃O₄+4H₂). Iron oxides containing Cr cations produced hydrogen repeatedly through the redox reactions, whereas pure iron oxide was deactivated quickly for the redox due to sintering. Addition of Cu, Ni or Rh to iron oxides containing Cr cations enhanced the formation rate of hydrogen through the oxidation with water vapor at 573K. These iron oxides can store and form hydrogen repeatedly through the redox. In addition, formation of hydrogen from synthesis gas or methane was demonstrated based on the reduction of iron oxides with synthesis gas or methane, followed by oxidation of iron metal with water vapor. The iron oxides containing both Cr and Ni species can produce hydrogen repeatedly through the redox reactions.

Keywords: Hydrogen; Magnetite; Iron metal; Redox reaction

Corrigendum to “Propane dehydrogenation over a Cr₂O₃/Al₂O₃ catalyst: transient kinetic modeling of propene and coke formation�? [Appl. Catal. A: Gen. 248 (2003) 105–116] by J. Gasc�n; C. T�llez; J. Herguido; M. Men�ndez (pp. 343-343).

CALENDER (pp. 345-345).

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Applied Catalysis A, General (v.282, #1-2)