Applied Catalysis A, General (v.253, #1)

Selective oxidation of n-butane over iron-doped vanadyl pyrophosphate prepared from lamellar vanadyl n-hexylphosphate by Yuichi Kamiya; Yuki Kijima; Takuya Ohkura; Atsushi Satsuma; Tadashi Hattori (1-13).
Intercalation of Fe(acac)3 into lamellar vanadyl n-hexylphosphate, VO{(n-C6H13)0.6/H0.4}PO4·(n-C6H13OH)0.5 followed by calcination, has been investigated for preparation of Fe-doped (VO)2P2O7 catalyst; selective oxidation of n-butane to maleic anhydride was performed. Fe(acac)3 was successfully intercalated into the vanadyl n-hexylphosphate by heating in toluene. The obtained precursor was transformed to single phase (VO)2P2O7 by a calcination at 823 K in the presence of a mixture of 5% n-butane and 20% O2 in N2 (balance). The doped Fe ions uniformly spread in the bulk of the catalyst and were substituted for V4+ in the (VO)2P2O7 crystal. The catalytic activity for maleic anhydride formation per unit surface area on the Fe-doped catalyst was higher than that on the Fe-free catalyst prepared by calcination of the vanadyl n-hexylphosphate. Rates of reduction with n-butane and re-oxidation with air in the top few surface layers of the catalysts were estimated from weight decreases and increases detected on a TG/DTA apparatus. The Fe-doped catalysts gave high rates of both the reduction and re-oxidation, especially re-oxidation. XPS studies confirmed that the surface of the Fe-doped catalysts was in a higher oxidation state under the steady state of the reaction. In addition, the Fe-doped catalysts showed a smaller reaction order on partial pressure of O2. Therefore, the doped Fe can enhance the redox ability, especially the re-oxidation, of the catalyst, resulting in the high catalytic performance.
Keywords: Vanadyl n-hexylphosphate; Vanadyl pyrophosphate; Intercalation; Selective oxidation of n-butane; Redox property;

Synthesis of polysulfides using diisobutylene, sulfur, and hydrogen sulfide over solid base catalysts by Eika W Qian; Shigeru Yamada; Jeayoung Lee; Shujiro Otsuki; Miki Ishii; Daisuke Ota; Kazuo Hirabayashi; Atsushi Ishihara; Toshiaki Kabe (15-27).
A series of solid base catalysts were prepared with several alkali and alkaline earth metal species. The catalysts were used in one-stage synthesis processes of polysulfides using diisobutylene (DIB), sulfur, and hydrogen sulfide (H2S). The possibility of using solid base catalyst as an alternative for a liquid amine catalyst and the effects of preparation conditions on the catalytic activity were discussed. Alumina-supported potassium catalysts showed a catalytic activity comparable to that of dicyclohexylamine. The alkali metal catalysts proved to be more effective than alkaline earth metal catalysts. Further, a three-stage mechanism for polysulfide synthesis using the system of diisobutylene, sulfur, and hydrogen sulfide in the presence of solid base catalysts was suggested. Moreover, a novel [ 14 C ]CO2 radioisotope pulse tracer method was developed to determine the amount of CO2 adsorption on solid base catalysts at the temperatures between 100–400 °C and under 0.6–3.1 MPa. The relationship between the uptake amount of CO2 on the alkali metal catalysts and the catalytic activity in syntheses of polysulfides was discussed.
Keywords: Polysulfide synthesis; Alkali metal catalyst; Alkaline earth metal catalyst; Bis-(1,1,3,3-tetramethylbutyl)-polysulfide; Solid base catalyst; Carbon dioxide adsorption;

Synthesis of dipentaerythritol (DPE) by dehydration of pentaerythritol (PE) has been studied using heteropoly compounds and various solid acids. Heteropoly compounds such as H3PW12O40, H4SiW12O40 and their supported catalysts were found to be effective. The addition of water in the reactant suppressed the consecutive reaction of dipentaerythritol with pentaerythritol over H3PW12O40. Under atmospheric pressure at 463 K, silica-supported H3PW12O40 gave 30% yield, while zeolites (H-β, H-mordenite, and H-Y) and SiO2-Al2O3 were inactive. Turnover number reached 31 over 20 wt.% H3PW12O40/SiO2, indicating that this reaction took place catalytically on it.
Keywords: Dipentaerythritol; Erythritol; Dehydration; Heteropolyacid; Silica;

Saucy–Marbet ketonizations of two unsaturated alcohols (3,7-dimethyl-oct-6-en-1-yn-3-ol (dehydrolinalool (DLL)) and 2-methyl-3-butyn-2-ol (MB)) with 2-methoxypropene (MP), generally performed in a batch reactor using homogeneous acid catalysts, have been studied in a continuous fixed-bed reactor containing a commercial alkyl sulfonic acid polysiloxane catalyst. The solid acid catalyst showed an initial transient period of several hours till stable operation was reached. Similar products were observed as in corresponding homogeneous catalytic reactions indicating similar reaction pathways. However, the heterogeneous catalytic reactions showed lower selectivity to the desired products than the corresponding homogeneous reactions reported in the literature. This behaviour is traced to the complex transformation the unsaturated ether (2-methoxypropene) undergoes upon interaction with the surface of the solid acid catalyst. Furthermore, both Brønsted and Lewis-acid sites were found to be present on the catalyst surface. These factors are proposed to be the main reasons for the less efficient use of reactants observed in the heterogeneous catalytic reactions. A maximum yield of 54% to the desired product could be achieved in the heterogeneous catalytic ketonization of 3,7-dimethyl-oct-6-en-1-yn-3-ol and 45% for the 2-methyl-3-butyn-2-ol ketonization, respectively. The studies indicate that the continuous ketonization in a fixed-bed reactor is feasible, but for technical application more selective acid catalysts are necessary to compete with the generally used homogeneous catalytic routes.
Keywords: Alkyl sulfonic acid polysiloxane; Saucy–Marbet ketonization; Fixed-bed reactor; Unsaturated alcohol; 2-Methoxypropene; Condensation; Chain elongation;

The density functional theory (B3LYP/6-31G(d,p)) and our-own-N-layered integrated molecular orbital + molecular mechanics (ONIOM) approach utilizing two-layer ONIOM schemes (B3LYP/6-31G(d,p): UFF) have been employed to investigate the structures of alkali-exchanged faujasite (FAU) and ZSM-5 zeolites, and their interactions with ethylene and benzene. Inclusion of the extended zeolite framework has an effect on the structure and energetics of the adsorption complexes and leads to differentiation of different types of zeolites (ZSM-5 and FAU), which cannot be drawn from typical small quantum clusters. The ONIOM binding energies of the Li-ZSM-5 and Li-FAU zeolites that are bound to an ethylene are −16.94 and −14.27 kcal/mol, respectively, and to a benzene are −28.78 and −19.46 kcal/mol, respectively, which agrees favorably with the known adsorption trend of these two zeolites. On the other hand, the quantum cluster models yield virtually the same binding energies for both zeolites/C2H4 complexes (−12.25 kcal/mol versus −12.91 kcal/mol) and even yield an unreasonable trend of adsorption energies for zeolites/C6H6 complexes (−11.91, −15.75 kcal/mol, for Li-ZSM-5 and Li-FAU, respectively). For the larger cation-exchanged Na-ZSM-5/C2H4 and Na-FAU/C2H4 complexes, the calculated interaction energies (−15.67 kcal/mol versus −11.83 kcal/mol) are predicted to be lower than those of smaller Li-zeolites following the conventional electrostatic trend. With the inclusion of basis set correction and the effects of the extended framework included in the ONIOM model, the interaction energy for the Na-FAU/C2H4 complex is predicted to be −8.65 kcal/mol, which can be compared favorably with the experimental data (8.8–9.6 kcal/mol) for ethylene adsorption on a Na-Y zeolite.
Keywords: ZSM-5 zeolite; Faujasite zeolite; DFT-study; Ethylene adsorption; ONIOM;

Combustion of dilute propane over transition metal-doped ZrO2 (cubic) catalysts by Vasant R Choudhary; Subhabrata Banerjee; Suryakant G Pataskar (65-74).
Combustion of dilute propane (0.9 mol% propane in air) over transition metal (viz. Co, Mn, Cr, Fe and Ni) doped ZrO2 (cubic) catalysts (transition metal/Zr mole ratio=0.25) at different temperatures (200–500 °C) and space velocities (25,000–100,000 cm3  g−1  h−1) has been investigated. The doping of transition metal in ZrO2 was confirmed by XRD and temperature-programmed reduction by H2 of the catalyst. The catalysts have been compared for their propane combustion activity (measured in terms of the temperature required for 50% conversion at different space velocities and also the propane combustion rate at 50% conversion at different temperatures) and also for their activation energy and frequency factor in the propane combustion. The propane combustion performance of the catalysts was in the following order: Co-doped ZrO2>Mn-doped ZrO2>Cr-doped ZrO2>Fe-doped ZrO2>Ni-doped ZrO2. Among the Co-, Mn- and Cr-doped ZrO2 catalysts, the activation energy is the lowest and the frequency factor was the highest for the Co-doped ZrO2 catalyst. The propane combustion activity of the Co-doped ZrO2 is found to be optimum for the Co/Zr ratio of about 0.25. The pulse reaction of pure propane in the absence of O2 over the Co-doped ZrO2 indicated the involvement of lattice oxygen from the catalyst in the propane combustion. It has also been shown that because of the doping of cobalt in ZrO2, the lattice oxygen in the catalyst becomes mobile or the mobility of lattice oxygen is enhanced.
Keywords: Combustion of dilute propane; Co-doped ZrO2 catalyst; Mn-doped ZrO2 catalyst; Cr-doped ZrO2 catalyst; Mobility of lattice oxygen;

Two kinds of organically modified mesoporous titanosilicate supports, Ti-MCM-48- and Ti-MCM-41-type, with different surface chemical properties and texture were prepared by two-step and one-step synthesis, respectively. The direct vapor-phase epoxidation of propylene with O2 and H2 was performed over Au nanoparticles deposited on the above supports. Both the supports and the Au catalysts were characterized by XRD, UV-Vis, N2 adsorption–desorption isotherms, FT-IR, ICP, TEM, and ADF-EELS. Over Au-deposited on trimethylsilylated Ti-MCM-48 supports, an optimum reaction temperature for the highest yield of propylene oxide (PO) while maintaining selectivity above 80% was 523 K. This temperature was 100 K higher than over the non-silylated Au catalyst. Catalyst deactivation with time-on-stream was appreciably depressed for the silylated ones, which could be explained by the change of surface property from hydrophilic to hydrophobic. Over Au-deposited on Ti-MCM-41-type amorphous supports, but not on pure Ti-MCM-41, excellent catalyst stability with time-on-stream was observed from the very early stage of reaction at 473 K. In terms of PO formation rate per unit weight of Au, Au/Ti-MCM-41-type amorphous support with a very low Au loading of 0.015 wt.% and Ti/Si molar ratio of 1/100 was found to be more active by one order of magnitude than Au/Ti-MCM-48 with a high Au loading of 0.57 wt.% and Ti/Si molar ratio of 2/100; the former also presented higher H2 efficiency. Organic modification did not change this feature. FT-IR spectra showed strong adsorption of water even on the Au catalyst composed of trimethyl silylated Ti-MCM-48 and the partial regeneration of hydroxylated surfaces during reaction at 523 K. This may partly explain why the silylated catalysts still deactivate in the reaction mixture.
Keywords: Propylene epoxidation; Gold catalyst; Mesoporous titanosilicates; Trimethylsilylation; Amorphous Ti-MCM-41;

Oxidative desulfurization of fuel oil by Danhong Wang; Eika Weihua Qian; Hiroshi Amano; Kazuhiro Okata; Atsushi Ishihara; Toshiaki Kabe (91-99).
The oxidation of sulfur compounds in kerosene was conducted with tert-butyl hydroperoxide (t-BuOOH) in the presence of various catalysts. The oxidation activities of dibenzothiophene (DBT) in kerosene for a series of Mo catalysts supported on Al2O3 with various Mo contents were estimated. The results show that the oxidation activity of DBT increased with increasing Mo content up to about 16 wt.% and decreased when Mo content was beyond this value. The oxidation of benzothiophene (BT), dibenzothiophene (DBT), 4-methyl dibenzothiophene (4-MDBT), and 4,6-dimethyl dibenzothiophene (4,6-DMDBT) dissolved in decalin was also carried out on 16 wt.% Mo/Al2O3 catalyst with t-BuOOH to investigate the oxidation reactivities of these sulfur compounds. The results indicated that the oxidation reactivities of these sulfur compounds decreased in the order of DBT>4-MDBT>4,6-DMDBT⪢BT. Analyses of the oxidative reactions of the sulfur compounds suggested that the oxidative reaction of each sulfur compound can be treated as a first-order reaction. The oxidation mechanism is then discussed.
Keywords: Oxidative desulfurization; t-BuOOH; DBTs; Mo/Al2O3 catalyst;

Molybdenum carbides and carbonaceous carbons on Mo/Al-FSM16 for methane conversion by Masatoshi Nagai; Toshihiro Nishibayashi; Shinzo Omi (101-112).
The catalytic activity of 12.0 wt.% Mo/Al-FSM16 (Si/Al=30) was related to the Mo carbides and carbonaceous carbons during CH4 conversion at 973 K. The material had been carburized during the temperature-programmed reaction with 20% CH4/H2 at 973 K, with and without purging in He. The temperature-programmed surface reaction and X-ray diffraction analysis showed that the carburized catalysts consisted of Mo carbides (α-Mo2C1−x , β-Mo2C, and η-Mo3C2) and carbonaceous carbons (pyrolytic and graphitic carbons). The purging treatments of the carburized catalysts at 973 K for 1 or 2 h lowered the activity, due to a decrease in the carbonaceous carbon releases of C2H2, C2H4, CO2, and H2O and due to the Mo carbides changing to other forms. The CH4 conversion was responsible for η-Mo3C2 conjugation to pyrolytic carbons, which played the role of the intermediate species. The IR study revealed that CH2 and CH3 species were formed as the intermediates of the pyrolytic species for CH4 formation. The pulse experiments of C2H4, C2H6, C3H8, and C4H8 showed that hydrogen was readily formed through the adsorbed C2H4 and C3H8 species as intermediates and that benzene was formed through the adsorbed C4H8 species.
Keywords: Carbonaceous carbon; CH4 conversion; He-purging; Mo/Al-FSM16; Mo carbide;

Butylated hydroxy anisoles, are very valuable and dominant food anti-oxidants and they are produced by highly polluting Friedel–Crafts alkylation of 4-methoxyphenol using homogeneous acids or from hydroquinone in a two-step reaction using alkylation followed by etherification using dimethyl sulphate under alkaline conditions. The current paper reports the activities of Filtrol-24, K-10 montmorillonite clay, dodecatungstophosphoric acid (DTP) supported on K-10 clay, sulphated zirconia and cation exchange resin Deloxane ASP in the alkylation of 4-methoxyphenol with MTBE.The order of catalytic activity of the solid acid catalysts studies is: Filtrol-24>DTP/K-10>Deloxane ASP resin>K-10 Montmorillonite clay>S-ZrO 2 Only two products 2-tert-butyl-4-methoxyphenol and 2,5-di-tert-butyl-4-methoxyphenol were formed with maximum selectivity to the monoalkylated product, both of which are used as anti-oxidants either as a mixture or alone. The effects of various parameters were studied to arrive at the reaction kinetics. The reaction is intrinsically kinetically controlled with an activation energy of 12.81 kcal/mol.
Keywords: Alkylation; MTBE; 4-Methoxyphenol; 4-Hydroxyanisole; Butylated hydroxyanisoles; Solid acids; Filtrol; Sulfated zirconia; Ion exchange resins; Heteropoly acid;

Catalysts for hydroprocessing of Maya heavy crude by S.K Maity; J Ancheyta; L Soberanis; F Alonso (125-134).
In this work the effect of active metals, promoters, phosphorous and lithium on hydroprocessing reactions of Maya heavy crude was studied. Four reactions (hydrodemetallization (HDM), hydrodesulfurization (HDS), hydrodenitrogenation (HDN), and asphaltene conversion (HDAsp)) were carried out on seven different catalysts. The support of these catalysts was prepared by urea hydrolysis method. Temperature programmed reduction (TPR) results showed that more reducible species were present on cobalt promoted catalyst compared with unpromoted one. We observed that active metal was more dispersed on P containing catalyst. The conversions, determined as Time Weighted Mean Conversion (TWMC), were very high for a PCoMo catalyst, however, it exhibited a rapid fall of activation. A linear correlation was found between the loss of specific surface area (SSA) and coke formation. The catalysts deactivation was mainly due to coke formation over catalyst surface. Cobalt promoted catalysts showed higher initial HDM conversion compared with Ni one. Mo active metal was better for HDM reaction. Even though lithium-doped catalyst showed slightly higher activities it had no effect on catalyst life.
Keywords: Maya heavy crude; TPR; HDM; HDS; HDN; HDAsp; Deactivation;

Pt catalysts supported on mixed CeO2-Al2O3 carriers with different CeO2 loading (0.5–10.3 wt.%) were prepared by wetness impregnation method. The catalysts were characterized by S BET, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and thermogravimetric analysis (TG). It was shown that pretreatment temperature and the concentration of CeO2 in the support influences significantly on the morphology of Pt. XRD showed the formation of nanocrystallites of Pt on the surface of alumina and low-loaded CeO2 (≤6 wt.%) samples at higher temperature of calcination (1073 K). Amorphous Pt was observed in all reduced samples. XPS spectra showed the presence of interaction between Pt and Ce, which leads to easy surface reduction of both, ceria and platinum, as revealed by TPR patterns. The effect of CeO2 loading on the catalytic behavior of supported Pt catalysts in the reaction of CO2 reforming of CH4 was determined. Addition of cerium oxide results in improvement of catalytic performance for the reforming of methane with CO2. Pt catalyst with 1 wt.% of CeO2 exhibited the highest specific activity and stability, due to the increase in the metal–support interface area, caused by the higher Pt dispersion.
Keywords: Pt catalysts; CeO2-Al2O3 carriers; CO2 reforming of methane;

Nickel on TiO2-modified Al2O3 sol–gel oxides by José Escobar; José Antonio De Los Reyes; Tomás Viveros (151-163).
Nickel catalysts supported on Al2O3-TiO2 sol–gel mixed oxides were prepared by equilibrium wet impregnation (EWI) and the resulting oxidic precursors were characterized by AAS, N2 physisorption, XRD and UV-Vis DRS. By varying the support composition different nickel speciation on the calcined precursors was evidenced. The main role of TiO2 appeared to be two-fold: (a) inhibition of the formation of hardly reducible spinel-like species and (b) increased dispersion of the metallic phase (as determined by H2 chemisorption). For equimolar Al2O3-TiO2 supports a H2 chemisorption suppresion effect in the case of ∼10 wt.% Ni catalyst suggested an strong metal support interaction state (SMSI). By increasing the metal loading (∼20 wt.%) this phenomenon was no longer observed and a beneficial influence of the support composition on the properties of the metallic phase was registered.
Keywords: Al2O3-TiO2 mixed oxides; Wet impregnation; Nickel catalysts; SMSI state;

TiO2–SiO2 supported hydrotreating catalysts: physico-chemical characterization and activities by M.S. Rana; S.K. Maity; J. Ancheyta; G.Murali Dhar; T.S.R. Prasada Rao (165-176).
Hydrotreating of model molecules over high specific surface area (SSA) Co(Ni)Mo/TiO2–SiO2 mixed oxide supported catalysts has been investigated in a micro-catalytic reactor at 400 °C and atmospheric pressure. Activity studies are carried out for thiophene hydrodesulfurization (HDS) and 1-cyclohexene hydrogenation (HYD). The effect of support composition, molybdenum content (2–14 wt.% Mo) and promoters contents (1–5 wt.% Co or Ni) is examined. Supported catalysts are characterized by BET specific surface area, X-ray diffraction (XRD), pore volume, zero point charge (ZPC) and low temperature oxygen chemisorptions (LTOC). Sulfided catalysts showed wide range of activity variation with support composition which relishes that molybdenum sulfided active phases strongly depend on the nature and composition of support. LTOC and catalytic activity results showed similar trend with the effect of molybdenum variation indicating that the number of anion vacancies varies with variation of MoS2 phases. The highest activities were observed at 8 wt.% Mo loading and after that activity decreases with decreasing the anionic vacancies. The characterization results of XRD, ZPC and LTOC are well agreed about the Mo monolayer formation. Incorporation of TiO2 with SiO2 alters the nature of weak interaction of active phases with SiO2 support, and overcome it through poor dispersion on the support surface. Therefore, TiO2 counterpart plays a role to provide high intrinsic activity and generate favorable morphology of MoS2 phases and metal support interaction.
Keywords: CoMo; HDS; HYD; TiO2–SiO2; XRD and O2 chemisorptions;

Liquid phase oxidation of limonene catalyzed by palladium supported on hydrotalcites by Juan Bussi; Alejandro López; Francisco Peña; Pablo Timbal; Daniel Paz; Daniel Lorenzo; Eduardo Dellacasa (177-189).
Palladium supported on copper–magnesium–aluminium hydrotalcites (HTs) were prepared by using coprecipitation and impregnation techniques. The different palladium/hydrotalcites solid catalysts were tested in the liquid phase oxidation of pure limonene using molecular oxygen as the sole oxidant agent. Both palladium and copper were found to influence the conversion versus reaction time profile of limonene oxidation. A chain reaction mechanism is proposed to explain the experimental results. Palladium participates in the formation of allylic radicals through activation of carbon–hydrogen bonds of limonene and in the formation of adducts by cleavage of the carbon–carbon double bonds. Copper catalyzes mainly the decomposition of hydroperoxides leading to radical intermediates. Different oxygen containing derivates from limonene were formed (1,2- and 8,9-epoxylimonene, cis and trans carveol and carvone) according to the chain reaction mechanism. Higher reaction rates and final conversion of limonene over 70% were obtained with a suitable content of copper in the hydrotalcite.
Keywords: Hydrotalcite; Palladium catalysts; Liquid phase oxidation; Limonene; Oxygen containing derivates;

Synergy effects between β and γ phases of bismuth molybdates in the selective catalytic oxidation of 1-butene by Ana Paula Vieira Soares; Lubjmir Dimitrov Dimitrov; Margarida Corte-Real André de Oliveira; Leonel Hilaire; Manuel Farinha Portela; Robert Karl Grasselli (191-200).
β+γ mixed Bi–Mo–O phases with a large range of composition were prepared by coprecipitation for investigating the existence of synergetic effects between β and γ phases for the oxidative dehydrogenation of 1-butene.Results from surface characterization show that the surface of the catalysts always has a composition similar to the β phase but the γ phase grows around β phase. Mixed phases present higher activity and less CO2 selectivity than pure β and γ phases. This result leads to propose that the whole catalyst (bulk and surface) participates in the catalytic process.The synergetic effect between these two phases can be ascribed to the high oxygen mobility in the lattice of the γ phase that allow the migration of oxygen species from the γ to the β phase.
Keywords: Bismuth molybdates; γ-phase; β-phase; γ+β mixed phases; Alkenes isomerization; Dehydrogenation; Synergy effect; TEM; XPS; Raman;

Production of hydrogen from methanol over binary Cu/ZnO catalysts by Johan Agrell; Magali Boutonnet; Ignacio Melián-Cabrera; José L.G Fierro (201-211).
Mixed copper–zinc oxide catalysts (Cu/ZnO) were prepared by two different techniques, i.e. from hydroxycarbonate precursors formed in aqueous solution and from oxalate precursors formed in water-in-oil microemulsion. Their physicochemical properties were characterised by nitrogen adsorption–desorption, N2O chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxidation (TPO). The BET surface areas ranged from 34 to 87 m2/g, depending on the method of preparation. Cu surface areas between 6.6 and 22 m2/g were measured. It was a general observation that catalysts prepared by microemulsion technique had lower Cu dispersions than expected (3.4–5.7%), due to a proposed partial embedding of Cu in ZnO. The catalyst prepared by carbonate co-precipitation exhibited a significantly higher Cu dispersion (10.3%). In addition, this catalyst displayed better resistance to successive TPR/TPO than the microemulsion catalysts, which exhibited significant Cu crystallite growth. However, the microemulsion route provided well-mixed materials with a narrow particle size distribution and the possibility to obtain high BET surface areas (up to 87 m2/g) by controlling the water/surfactant ratio in the microemulsion. XPS measurements revealed the existence of Cu+ species on the surface of both types of catalysts after exposure to a O2/CH3OH mixture. The surface composition of the hydroxycarbonate-derived sample was unaffected by reduction in hydrogen and exposure to O2/CH3OH, while Zn-enrichment on the surface was observed in the microemulsion catalysts after reduction, indicating sintering of the Cu particles. These observations were consistent with the TPR/TPO measurements.
Keywords: Cu/ZnO catalyst; Hydroxycarbonate precursor; Oxalate precursor; Microemulsion; Characterisation; N2O chemisorption; XPS; TPR/TPO;

Production of hydrogen from methanol over binary Cu/ZnO catalysts by Johan Agrell; Magali Boutonnet; José L.G Fierro (213-223).
The activity for conversion of methanol into hydrogen was investigated over binary Cu/ZnO catalysts derived from precursors prepared by two different techniques, viz. oxalates formed in microemulsion and hydroxycarbonates formed in aqueous solution. Some distinct differences in the reaction pathways were observed. During partial oxidation of methanol under a sub-stoichiometric oxygen/methanol ratio, the microemulsion materials exhibited considerably higher combustion activity in the low-temperature region than a catalyst prepared in aqueous solution. Over the former, oxygen was quickly converted by methanol combustion, after which steam reforming was initiated, producing hydrogen at the expense of water and gradually decreasing the net heat of reaction. Hence, a reaction sequence for the partial oxidation reaction over microemulsion catalysts is proposed, consisting of consecutive methanol combustion and steam reforming, followed by decomposition when all oxygen has been consumed. Over the hydroxycarbonate catalyst, the reaction ignited at a higher temperature, directly producing hydrogen by partial oxidation of methanol. When the two types of catalysts were evaluated in the steam reforming reaction, all catalysts displayed the typical S-shaped dependence of methanol conversion on temperature. However, there was a downward shift in the temperature at which methanol reached complete conversion, favouring the hydroxycarbonate material. Hydrogen was produced selectively over all catalysts, but carbon monoxide formation was more pronounced over the microemulsion materials. The differences in catalytic behaviour are discussed in terms of catalyst morphology and the valence state of Cu in the working catalyst.
Keywords: Cu/ZnO catalyst; Microemulsion; Hydrogen production; Methanol steam reforming; Methanol oxidation (partial); Reaction pathway/network; Cu oxidation state;

Effect of molybdenum additives on the performance of supported nickel catalysts for methane dry reforming by Tiancun Xiao; Thomas Suhartanto; Andrew P.E. York; Jeremy Sloan; Malcolm L.H. Green (225-235).
A series of molybdenum modified alumina supported nickel catalysts have been prepared and tested for methane dry reforming to synthesis gas. The molybdenum additive reduces carbon deposition in the catalyst, and lowers the catalyst activity and selectivity. Increase of the amount of molybdenum additive causes a more rapid decrease in catalyst activity. Using a feedstock of CO2/CH4 ratio=1, the molybdenum-doped nickel catalyst has a greater stability than when CO2/CH4=1.1. Carburisation pretreatment of the molybdenum modified nickel catalyst using 20 vol.% CH4/H2 leads to a small improvement in catalyst stability. The formation of NiMoO4 is believed to be responsible for the decrease of catalyst activity.
Keywords: Supported nickel catalysts; Molybdenum additives; Dry reforming;

Synthesis, characterization, and catalytic activity of SO4/Zr1−x Sn x O2 by R. Sakthivel; H.A. Prescott; J. Deutsch; H. Lieske; E. Kemnitz (237-247).
The Sn-doped zirconia catalysts, SO4/Zr1−x Sn x O2 (x=0, 0.05, 0.10, 0.175, 0.25, 0.35), SO4/ZrO2, and SO4/SnO2, were prepared by hydroxide precipitation. The freeze-dried hydroxides were sulfated with (NH4)2SO4 and calcined at 500 °C for 3 h in O2. The X-ray powder diffraction (XRD) study show that the crystallinity of SO4/Zr1−x Sn x O2 decreases with the incorporation of Sn. The BET surface areas of SO4/Zr1−x Sn x O2 (x=0.05–0.35) range from 90 to 124 m2/g. SO4/ZrO2 has a surface area of 87 m2/g. The surface areas of SO4/SnO2 with 2.16 and 2.88 wt.% S are 152 and 101 m2/g, respectively. The FTIR photoacoustic spectrum of SO4/ZrO2 shows Brønsted acid site bands, whereas SO4/Zr1−x Sn x O2 and SO4/SnO2 have both Brønsted and Lewis acid site bands. Temperature-programmed desorption of ammonia (NH3-TPD) results show that acid site distribution are similar for SO4/Zr1−x Sn x O2 (x=0.05–0.35), but differ from those of SO4/ZrO2 and SO4/SnO2. Activities of these catalysts were examined for the benzoylation of anisole with benzoyl chloride and benzoic anhydride. The surface acidities and catalytic activities of SO4/Zr1−x Sn x O2 were compared with those of SO4/ZrO2 and SO4/SnO2.
Keywords: Sulfated tin-doped zirconia; Freeze drying; Lewis acidity;

CuO/ZnO/SiO2 catalysts for cyclization of propyleneglycol with ethylenediamine to 2-methylpyrazine by Ilnam Park; Jeongho Lee; Youngyoo Rhee; Yohan Han; Hyungrok Kim (249-255).
The cyclization of ethylenediamine with propyleneglycol to 2-methylpyrazine was carried out over CuO/SiO2, ZnO/SiO2 and CuO/ZnO/SiO2 catalysts at 360 °C. CuO/ZnO/SiO2 catalyst, which possesses a proper combination of cyclization (dehydration) and dehydrogenation activity, shows almost quantitative reactant conversions and excellent 2-methylpyrazine selectivity of 87% for 350 h.The improvement in 2-methylpyrazine selectivity and stability of CuO/ZnO/SiO2 catalyst may be attributed to the cooperative combinational effect of CuO/SiO2 catalyst and ZnO/SiO2 catalyst in which the thermally stable Zn2SiO4 phase is developed by the synergic action of CuO component to result in the preservation of Cu(0) species and the dual function activities for the catalytic reaction are properly adjusted.
Keywords: 2-Methylpyrazine; Ethylenediamine; Propyleneglycol; Dehydrogenation; Cyclization;

Synthesis and characterization of ZSM-5 coatings onto cordierite honeycomb supports by M.A Ulla; R Mallada; J Coronas; L Gutierrez; E Miró; J Santamarı́a (257-269).
Zeolite ZSM-5 layers (up to ca. 30% by weight) have been synthesized on cordierite substrates, following either a direct hydrothermal synthesis procedure or a secondary growth method, in this case after seeding of the support. The Si/Al ratio in the synthesis gel ranged from 14 to 100, but layers with a high Al content (i.e. a low Si/Al ratio) could not be prepared directly on the cordierite support. However, MFI layers with a low Si/Al ratio were readily grown after depositing an intermediate Si-rich layer. The results also show that the Si/Al ratio of the synthesis gel has a direct effect on the morphology, crystallinity and orientation of the MFI layer formed.
Keywords: Zeolite coatings; Monolith substrates; Si/Al ratio;

Acidic and catalytic properties of Mo/MCM-22 in methane aromatization: an FTIR study by Z Sobalı́k; Z Tvarůžková; B Wichterlová; V Fı́la; Š Špatenka (271-282).
Acidity investigation of fresh and used Mo/MCM-22 catalyst for methane aromatization is described. For determination of Brønsted acidity, connected with bridged OH groups, and the Lewis acidity, related to Al, quantitative analysis was carried out using FTIR technique and employing d3-acetonitrile as the probe molecule. Acidity changes for both the parent zeolite and the Mo-containing zeolite were analyzed in individual periods of the catalyst development in the methane stream, i.e. during the activation period (up to 70 min), at the optimum performance (between 70 and 150 min), during catalyst deactivation (up to 10 h) and after its regeneration in oxygen. Both bridged hydroxyls (concentration 0.21 mmol/g) and Lewis acidic sites (two types; total concentration 0.14 mmol/g) were present in the parent H/MCM-22 zeolite. Molybdenum incorporation induced a decrease in the concentration of bridged OH groups to about one half of the original value following calcination at 450 °C, while the content of Lewis sites decreased by 20%. The Mo/MCM-22 catalyst at the maximum catalytic performance for benzene production was shown to contain less than 0.01 mmol/g of bridged OH groups. For the parent H/MCM-22 zeolite, treated under the same condition, the Brønsted acidity drops to 50% of its original value and further decreases with time on stream. The Lewis acidity of the parent and Mo-containing zeolites initially decreased by about 15–20% in methane atmosphere, but was nearly constant during the experimental run between 1.5 and 10 h. Regeneration in oxygen produced only a very limited restoration of the OH groups in both the parent and Mo-containing samples, while the formation of new internal SiOH groups indicated deeper destruction of the zeolite lattice. The catalytic activity was partly restored, but not to its original value.These findings support earlier concepts of the role of OH as a trap for molybdenum species during MoO x spreading in the opening steps of the catalyst preparation, while they are contradictory to the assumed role of high concentration of the Brønsted acid sites in zeolite for the aromatization reaction itself.
Keywords: Methane aromatization; FTIR technique; d3-Acetonitrile; MCM-22;

Acetylene hydrogenation on sol-derived Pd/SiO2 by A. Sárkány; A. Beck; A. Horváth; Zs. Révay; L. Guczi (283-292).
Pd/SiO2 (1.08 wt.%) catalyst has been synthesised via sol-derived route using poly(diallyldimethylammonium chloride) (PDDA) polycation as ionic stabiliser. The immobilised sol (monomer/Pd2+=1.25) fixed at pH = 8.5 onto Aerosil 200 contains Pd particles of 3.1 nm number-mean diameter. The catalyst prepared was subjected to various treatments and the obtained samples were characterised by transmission electron microscopy (TEM), CO and O2 chemisorption, and temperature programmed oxidation (TPO) and temperature programmed desorption (TPD). The immobilised sol showed good thermal stability but oxidation of PDDA to get “polymer free” sample causes sintering of Pd particles. Initial activities and product selectivities for hydrogenation of acetylene in propene were recorded. The immobilised sample even in “as prepared state” possesses hydrogenation activity. Treatments at different temperatures in H2 or Ar enhance the catalytic activity suggesting an increase in space around the metal particle. The PDDA modified sample exhibits better competition selectivity than the “polymer free” sample pointing to surface structure variations caused by geometric/steric effects.
Keywords: Pd sol; PDDA polycation; Acetylene hydrogenation; Competition;

The effect of binders on structure and chemical properties of Fe-K/γ-Al2O3 catalysts for CO2 hydrogenation by Sung-Chul Lee; Jae-Hun Jang; Byung-Yong Lee; Min-Cheol Kang; Misook Kang; Suk-Jin Choung (293-304).
The study is focused on investigating catalytic behavior with and without binder in CO2 hydrogenation. It was found that Fe-K/γ-Al2O3 with alumina binder (FA-A catalyst) had excellent capability of CO2 hydrogenation, whereas Fe-K/γ-Al2O3 with silica binder (FS-A catalyst) showed dramatically decreased capability compared with those of other catalysts. The product selectivity for catalysts with and without binder was compared at the same reaction conditions. The selectivity and activity of Fe-K/γ-Al2O3 with polyvinylalcohol (PVA) binder (FP catalyst) tended to be similar to those of Fe-K/γ-Al2O3 without binder (FN catalyst). FS-A catalyst exhibited higher methane (16 mol%) and C2–C4 selectivity (43.5 mol%) than FN catalyst. For FA-A catalyst, the main products were higher hydrocarbons such as C5+ hydrocarbon. This phenomenon can be explained if the structure and porosity of catalysts with alumina binder have differences in spite of the similarities of main chemical composition. This would mean that the higher hydrocarbon selectivity of FA-A is increased as the amounts of strong acid sites increase.
Keywords: CO2 hydrogenation; Fe-K/γ-Al2O3; Alumina binder; Silica binder; Organic binder;

The aromatization of methane in the presence of H2, CO and CO2 over a 2 wt.% Mo/HZSM-5 catalyst was studied. The results were compared with those for the aromatization reaction in pure methane and with added O2. The addition of O2 up to 5.3% or CO2 up to 12.8% reduces deactivation so that, at the reaction temperature of 770 °C, an aromatic yield of ca. 4% can be maintained for 6 h; in the absence of the gaseous additive, however, the catalyst would have been completely deactivated for aromatic formation within 4 h. XPS analysis revealed that, in the presence of O2 or CO2, the molybdenum oxide supported on the HZSM-5 located at the reactor inlet was not converted to molybdenum carbide, whereas in the zone away from the reactor inlet, Mo2C was found. Investigation by temperature-programmed surface reaction showed that the production of aromatic compounds was always preceded by the reaction of molybdenum oxide with methane to form Mo2C and CO. The beneficial effect of adding CO2 and O2 in low concentration was mainly attributed to the formation of CO and H2 by oxidation and the reforming of methane in the zone closed to the reactor inlet. H2 enhances the stability of the catalyst by suppressing the excessive dehydrogenation of the reaction intermediates into inactive entities. When the concentration of CO2 and O2 was too high, the entire catalyst bed remained oxidized and the methane aromatization reaction could not occur.
Keywords: Methane aromatization; Mo/HZSM-5; Catalyst deactivation; CO2; O2;

Keywords: Dissolution; Anderson-type heteropolyanion; Polyoxometalate; (NH4)3[Al(OH)6Mo6O18]; Hexamolybdoaluminate; HDS;

A new interpretation for the NMR signal observed at +16 ppm in the 27 Al MAS-NMR spectra of Mo and NiMo/Al-MCM-41 catalysts was done. This signal was assigned to an Anderson-type heteropolymolybdate [Al(OH)6Mo6O18]3−, which can be formed during impregnation step of the catalyst preparation, as well as a result of hydration of Al2(MoO4)3 in calcined Mo and NiMo/Al-MCM-41 catalysts.
Keywords: 27 Al MAS-NMR; Anderson-type heteropolyanion; Al-MCM-41; Mo and NiMo catalysts;

PATENTS ALERT (327-331).

CALENDER (333).

CONTENTS CONTINUED (335-336).