Applied Catalysis A, General (v.239, #1-2)
EDITORIAL BOARD (iii).
Effect of calcination temperatures and precipitant on the catalytic performance of Au/ZnO catalysts for CO oxidation at ambient temperature and in humid circumstances by Gui Ying Wang; Wen Xiang Zhang; Hong Lei Lian; Da Zhen Jiang; Tong Hao Wu (1-10).
Various Au/ZnO catalysts have been prepared by a coprecipitation method and have been tested for CO oxidation at ambient temperature and in the presence of water in the feed stream. It was found that Au/ZnO catalysts exhibited excellent CO oxidation activity and stability, and the catalytic performance was greatly dependent on the calcination temperatures and on the kind of precipitants. The most stable catalyst was obtained using Na2CO3 as precipitant and calcining at 240 °C; it can completely oxidize CO to CO2 for more than 1700 h under the following conditions: 0.5% CO, 10% O2, 1.8% H2O, balanced with Ar, GHSV=12,000 h−1. The XRD, BET, TEM and TG–DTA investigations of the catalysts revealed that the particle size of Au and ZnO, the S BET and the type of zinc species were the primary factors influencing the stability of Au/ZnO catalysts. Furthermore, sintering of metallic gold and the accumulation of carbonate-like species during CO oxidation were observed; these processes may be responsible for the deactivation of the Au/ZnO catalysts.
Keywords: Au/ZnO catalysts; CO oxidation; Ambient temperature; Humid circumstances; Calcination temperatures; Precipitant; Stability;
Vapour-phase nitration of benzene over superacid WO3/ZrO2 catalysts by V.V Brei; S.V Prudius; O.V Melezhyk (11-16).
Superacid WO3/ZrO2 catalysts have been found to show a high activity and stability in the reaction of gas-phase nitration of benzene with 70% HNO3. At 170 °C and under atmospheric pressure the yield of nitrobenzene is within 65–80% at 99% selectivity for mononitrobenzene. The space time yield of nitrobenzene increases with increasing flow rate of reagents and amounts to 0.64 g/(gcat h).
Keywords: Nitration of benzene; Solid superacids; Zirconia; WO3/ZrO2, catalyst;
Benzene hydrogenation over amorphous NiB/bentonite catalyst and promoting effect of Nd by Rongbin Zhang; Fengyi Li; Ning Zhang; Qiujie Shi (17-23).
The supported amorphous NiB/bentonite (Bn) catalyst was prepared by impregnation, following the chemical reduction with KBH4 solution. The gas-phase benzene hydrogenation was used as a probe reaction to evaluate the catalytic activity. The amorphous NiB/bentonite catalyst exhibited higher activity than the Ni/bentonite catalyst; the difference is due to the formation of amorphous structure and the electronic interaction between Ni and B. Its activity and sulfur resistance were higher than those of the corresponding amorphous NiB/Al2O3 catalyst, owing to the better dispersion of active Ni and the stronger acidity over bentonite. Nd in suitable concentration could further enhance the hydrogenation activity and sulfur resistance by improving the surface area of active Ni. Such results were discussed based on various characterizations, including X-ray diffraction (XRD), inductively coupled plasma (ICP), temperature programmed desorption of hydrogen (H2-TPD), chemisorption and poisoning of carbon disulfide (CS2).
Keywords: Amorphous alloy; Benzene hydrogenation; Bentonite; Sulfur resistance;
Synthesis, characterization and aqueous-biphase hydrogenation of olefins by the ruthenium complexes Ru(CO)3(TPPMS)2 and RuH2(CO)(TPPMS)3 by P.J Baricelli; G Rodrı́guez; M Rodrı́guez; E Lujano; Francisco López-Linares (25-34).
The new water-soluble ruthenium complexes Ru(CO)3(TPPMS)2 (I) and RuH2(CO)(TPPMS)3 (II), where TPPMS is the m-sulfophenyldiphenylphosphine (C6H5)P(m-C6H4SO3Na) in the sodium salt form, were prepared in highly purity content (90% for I and 95% for II) and characterized by using different spectroscopic techniques. These ruthenium complexes showed high stability and solubility in water, enough for using as a catalyst precursor in the two phase catalytic hydrogenation of 1-hexene, styrene, 1-decene, cyclohexene and allylbenzene under moderate reaction conditions. The similar reaction profile obtained during the hydrogenation of 1-hexene, when each complex are used separately, accompanied with the NMR analysis of the final aqueous phase when Ru(CO)3(TPPMS)2 (I) is used as a catalyst precursor, shows that the Ru(CO)3(TPPMS)2 (I) is transformed selectively to RuH2(CO)(TPPMS)3 (II) during the hydrogenation pathway. The mercury test in independent experiments showed no interference of the Hg with the evolution of the reaction, demonstrating that the catalysis is performed by molecular species and the recycling nature of this complexes is demonstrated during the 1-hexene hydrogenation, where at the end of the catalytic reaction, all metal remains in the aqueous phase indicating no leaching of the ruthenium during the reaction as was proved by atomic absorption experiments.
Keywords: Aqueous-biphase catalysis; Olefin; Hydrogenation; Ruthenium complexes;
Development of a low temperature light paraffin isomerization catalysts with improved resistance to water and sulphur by combinatorial methods by José M Serra; Antonio Chica; Avelino Corma (35-42).
By means of combinatorial techniques (high-throughput catalyst preparation and testing systems, and a genetic algorithm (GA)), a search of new more tioresistant catalysts for low temperature isomerization of light paraffins has been conducted. After three evolving cycles catalysts have been found that not only are active and selective but also are more resistant to deactivation by water and sulphur than the corresponding conventional ones. The results have been reproduced in a pilot plant and the stability is shown.
Keywords: Sulphated zirconia; Isomerization; Light straight run; Genetic algorithm; High-throughput; Sulphur resistant; Water resistant; Combinatorial chemistry;
Activation of methane to syngas over a Ni/TiO2 catalyst by Q.G. Yan; W.Z. Weng; H.L. Wan; H. Toghiani; R.K. Toghiani; C.U. Pittman (43-58).
Partial oxidation of methane (POM) to syngas and CH4/CO2 reforming have been investigated over a Ni/TiO2 catalyst in a fixed-bed reactor. The Ni/TiO2 catalyst has high initial activity but undergoes significant deactivation during the partial oxidation of methane reaction. Deactivation is due largely to the oxidation of Ni(0) to NiTiO3. After the partial oxidation of methane at 700 °C the catalyst was pale yellow. XRD confirmed that Ni(0) had been converted to NiTiO3 and oxygen pulse reactions found only traces of carbon were present after the POM reaction. The Ni/TiO2 catalyst has a high activity and a long term stability in the CO2 reforming reaction. XRD found Ni(0) was present after the reforming reaction but NiO and NiTiO3 were absent. Activation of methane over Ni/TiO2 was also investigated using pulse reaction techniques in the absence of gas phase oxygen. Methane pulse reactions demonstrated that the mechanism of methane oxidation changes as the oxidation state of nickel changes. CH4 may have been oxidized by oxygen from solid NiO or by active oxygen within the TiO2 support via the non-selective Rideal–Eley mechanism over the oxidized Ni/TiO2 catalyst surface. In contrast, CH4 is efficiently converted to CO and H2 via a direct oxidation mechanism when Ni/TiO2 is reduced. Pulse reaction studies provide evidence that the oxidation state of nickel controls the methane activation mechanism and the product distribution.
Keywords: Methane; Ni/TiO2 catalyst; Syngas; Partial oxidation; CO2 reforming; Oxidation state of nickel; TiO2;
On the use of 1-butene double-bond isomerization as a probe reaction on cesium-loaded zeolite X by Junhui Li; Robert J Davis (59-70).
Oxides of cesium and potassium were synthesized in the supercages of zeolite X by impregnation and decomposition of acetate precursors. The alkali-loaded zeolites were characterized by N2 adsorption, CO2 adsorption microcalorimetry and stepwise TPD of CO2. For a loading of about two alkali metal atoms per zeolite supercage, the majority of CO2 adsorption sites at 373 K were characterized by a −ΔH ads of about 80–100 kJ mol−1. The initial turnover frequency (TOFi) for 1-butene isomerization, based on excess cesium atoms, followed the order CsOx/CsX, CsOx/KX, KOx/KX, which parallels the expected ranking of base strength based on composition. For CsOx/CsX, the TOFi was independent of Cs loading, which suggests that active sites were non-interacting and that heat and mass transfer artifacts were absent in the kinetic data. Studies of catalyst deactivation showed that trace impurities in the feed were the likely cause of activity loss with time on stream. Selective poisoning of active sites with CO2 indicated that only about 5% of the sites counted by CO2 adsorption at 373 K were active for butene isomerization. Evidently, the very low active site density made these catalysts vulnerable to trace impurities in the feed.
Keywords: Base catalysis; Cesium oxide; Isomerization of butene; Deactivation; Adsorption of carbon dioxide; Zeolite X;
Dehydrogenation of ethylbenzene in the presence of CO2 over an alumina-supported iron oxide catalyst by Masahiro Saito; Hiroshi Kimura; Naoki Mimura; Jingang Wu; Kazuhisa Murata (71-77).
The dehydrogenation of ethylbenzene (EB) in the presence of CO2 over an alumina-supported iron oxide catalyst was investigated at temperatures ranging from 798 to 873 K under atmospheric pressure. The yield of styrene increased with an increase in W/F and reached its highest value (74%) at a W/F of around 40 g-cat min/mmol-EB, where the selectivity to styrene was 96%. The highest yield of styrene in the dehydrogenation in the presence of CO2 was higher than the yield of styrene at equilibrium of the simple dehydrogenation in the absence of CO2, probably because CO2 was involved in the dehydrogenation and/or in the reaction with H2 produced in the dehydrogenation. The yield of styrene increased with increasing reaction temperature, but the selectivity to styrene slightly decreased with an increase in reaction temperature from 848 to 873 K. The yield of styrene was the highest at CO2/ethylbenzene ratios ranging from 5 to 10. The selectivity to styrene increased a little with an increase in the CO2/ethylbenzene ratio from 15 to 30. The amount of carbonaceous deposits on the catalyst during the dehydrogenation in the presence of CO2 increased with an increase in the reaction temperature and in the CO2/ethylbenzene ratio. The decrease in the catalyst activity with time on stream was smaller in the dehydrogenation in the presence of CO2 than in the dehydrogenation in the absence of CO2.
Keywords: Dehydrogenation; Ethylbenzene; CO2; Iron oxide catalyst;
Aqueous phosphine–Rh complexes supported on non-porous fumed-silica nanoparticles for higher olefin hydroformylation by Zhihua Li; Qingrong Peng; Youzhu Yuan (79-86).
Non-porous fumed-silica nanoparticles were used as supports for the first time to immobilize water-soluble complex HRh(CO)(P(m-C6H4SO3Na)3 (1) [P(m-C6H4SO3Na)3, i.e. trisodium salt of tri-(m-sulfophenyl)-phosphine, TPPTS] to obtain supported aqueous-phase catalysts (SAPC) (fumed-SiO2-SAPC) for hydroformylation of 1-hexene. The experimental results proved that the structure of support and the support hydration were the determining factors contributing to the hydroformylation performance. The fumed-SiO2-SAPC where the water-soluble rhodium complexes were well dispersed onto the external surface of the silica nanoparticles presented a higher hydroformylation performance over a relatively wider range of support hydration as compared to the SAPC with conventional porous granular-SiO2 support (porous SiO2-SAPC). A positive effect on the reaction performance was observed from the particle size and surface area of the fumed-silica nanoparticles. The hydroformylation performance with fumed-SiO2-SAPC was promoted by an addition of basic alkali metal salts such as Na2CO3, K2CO3, and NaH2PO4, which depressed the oxidation of ligand TPPTS to OTPPTS [OTPPTS, i.e. trisodium salt of tri-(m-sulfophenyl)-phosphine oxide, OP(m-C6H4SO3Na)3] as evidenced by 31 P NMR observation.
Keywords: Non-porous fumed silicas; Supported aqueous-phase Rh catalyst; SAPC; Hydroformylation; 1-Hexene; 31 P NMR;
Surface structure and catalytic behavior of silica-supported copper catalysts prepared by impregnation and sol–gel methods by Zhenlü Wang; Qingsheng Liu; Jianfeng Yu; Tonghao Wu; Guojia Wang (87-94).
Supported copper on silica catalysts prepared by sol–gel and impregnation methods were studied in this paper. The surface structures of these catalysts were characterized by various techniques, including BET, XRD, FTIR, XPS, TPR, and ESR. The results showed that the distribution of copper species was in different ways in the catalysts prepared by the two methods. Cu(II) species highly dispersed in the silica matrix for the sol–gel catalyst, while copper oxide clusters are dominant in the CuO-SiO2 sample prepared by the impregnation method. The catalysts were then used for dehydrogenation of 2-butanol. Obvious differences of catalytic behavior were observed for the catalysts prepared by the two methods. High selectivity (>90%) toward dehydrogenation and high 2-butanol conversion was observed for the impregnated catalyst; however, for the CuO-SiO2 sol–gel catalyst, very low dehydrogenation selectivity and 2-butanol conversion were obtained. The surface structures of catalysts were closely related to the preparation methods, and the catalytic behaviors were affected subsequently. The copper oxide clusters, which may be reduced to Cu0, are responsible for the dehydrogenation reaction. The highly dispersed Cu(II) ions were inactive for catalyze 2-butanol dehydrogenation.
Keywords: Cu-SiO2; Sol–gel; Impregnation; 2-Butanol; Dehydrogenation;
Redox behaviour of La-Cr compounds formed in CrO x /La2O3 mixed oxides and CrO x /La2O3/ZrO2 catalysts by D.L Hoang; A Dittmar; J Radnik; K.-W Brzezinka; K Witke (95-110).
The redox behaviour of chromium oxide in CrO x /La2O3, CrO x /La2O3/ZrO2 and CrO x /ZrO2 mixed oxide systems has been investigated by temperature-programmed reduction (TPR), photoelectron spectroscopy (XPS) and Raman spectroscopy (RS). The formation of La-Cr compounds such as La2CrO6, LaCrO4 was shown to occur by calcination of CrO x /La2O3 and CrO x /La2O3/ZrO2 at 600 °C. With a Cr content of ca. 4 wt.%, it was revealed that, having been reduced to Cr3+-containing compounds, La2CrO6 and/or LaCrO4 in both systems may be restored by reoxidation at 600 °C. In the case of CrO x /La2O3/ZrO2 catalysts, it is suggested that these compounds were real surface species anchored as an overlayer on zirconia. Such a structure may stabilise, on the one hand, the tetragonal modification of zirconia and, on the other hand, highly dispersed state of Cr species in calcined as well as in reduced catalysts.
Keywords: Chromia containing catalysts; Redox reversibility; La-Cr compounds; Temperature-programmed reduction; XPS; Raman spectroscopy;
Fischer–Tropsch synthesis: induction and steady-state activity of high-alpha potassium promoted iron catalysts by Mingsheng Luo; Robert J O’Brien; Shiqi Bao; Burtron H Davis (111-120).
Iron Fischer–Tropsch synthesis (FTS) catalysts with different potassium loadings showed different induction periods during which the conversion increased from a low initial level to a peak value before declining to attain a lower stable activity at the same reaction conditions. A lower K loading produced a slightly higher peak conversion and a shorter induction period. Although, the induction period and the peak conversion were slightly dependent on the K loading for the iron catalyst, the stabilized conversions and the stabilization periods were independent of potassium content. The C2C4 olefin to paraffin ratio of the gaseous products and the CO2 selectivity did not change significantly as the potassium content increased from 5 to 10%. An increase in reaction temperature produced a new induction period and a higher conversion than was obtained before the reaction temperature was increased. The H2/CO ratio also had an important influence on FTS conversions. Increasing the H2/CO ratio in the feed gas lowered the H2 utilization. A higher H2/CO ratio feedstock gas produced lower FTS catalyst activity compared to a low H2/CO ratio gas.
Keywords: Catalyst; Iron; Fischer–Tropsch synthesis; Promoter; K; Induction period; Catalyst activation;
Interaction of CO, NO and NO/CO over Pd/γ-Al2O3 and Pd-WO x /γ-Al2O3 catalysts by Ana M. Sica; Carlos E. Gigola (121-139).
The interaction of NO, CO and NO/CO mixtures over low loaded Pd/γ-Al2O3 and Pd-WO x /γ-Al2O3 catalysts was investigated by a combination of FTIR, TPR, chemisorption and catalytic studies. NO and CO interaction with the alumina support gives rise to adsorbed nitrates and carbonates in addition to species associated with the palladium surface. The characterization work demonstrated the presence of a Pd–W interaction that facilitates the formation of reduced W species, makes the Pd more resistant to oxidation and decreases the intensity and shifts the location of the CO and NO adsorption bands to higher frequencies, indicating a weaker bond of these molecules with the Pd surface. These results suggest that an important redistribution of charge takes place in the valence d-band of palladium when the metal particles are in contact with reduced W species. Strong isocyanates bands are formed from NO/CO mixtures on both Pd/γ-Al2O3 and Pd-WO x /γ-Al2O3 catalysts but a different temperature dependence of the band intensity due to the influence of W is observed; maximum isocyanate formation that occurs at 548 K on Pd/γ-Al2O3 is shifted to 623 K on Pd-WO x /γ-Al2O3. Catalytic tests revealed that the presence of reduced W promotes the NO dissociation reaction on Pd acting as an “oxygen scavenger”. However, at comparable levels of conversion, the Pd-W catalyst enhances the formation of N2O and has a detrimental effect on the NO+CO reaction. From the FTIR results and the catalytic test the formation and reactivity of surface isocyanate species and gas phase N2O were found to be closely related.
Keywords: Palladium catalyst; Palladium-tungsten catalyst; NO decomposition; NO+CO reaction; In situ FTIR; Surface isocyanates;
Kinetics study of esterification of acetic acid with isobutanol in the presence of amberlite catalyst by Mehmet Rıza Altıokka; Alime Çıtak (141-148).
Kinetic data on the esterification of acetic acid with isobutanol have been obtained from both the uncatalyzed and heterogeneously catalyzed reactions using a stirred batch reactor in dioxane. The equilibrium constant, which is independent of temperature ranging from 318 to 368 K, was found to be 4. The uncatalyzed reaction was proved to be second-order reversible. In the presence of the catalyst, on the other hand, the reaction has been found to occur between an adsorbed alcohol molecule and a molecule of acid in the bulk fluid (Eley–Rideal model). It has also been observed that the initial reaction rate decreases with alcohol and water concentrations and it linearly increases with that of acid. The temperature dependency of the constants appearing in the rate expression were also determined.
Keywords: Esterification kinetics; Heterogeneous catalysis; Amberlite IR-120; Isobutyl acetate;
Selective oxidation of carbon monoxide in excess hydrogen over Pt-, Ru- and Pd-supported catalysts by P.V Snytnikov; V.A Sobyanin; V.D Belyaev; P.G Tsyrulnikov; N.B Shitova; D.A Shlyapin (149-156).
Selective oxidation of CO in excess hydrogen has been studied over Pt-, Ru- and Pd-supported on Sibunit (porous carbonaceous material) catalysts. The Ru and Pt catalysts were found to be the most active and selective among the studied catalysts. They provided single-step removal of CO from hydrogen-rich stream both in the absence and presence of CO2 and H2O to a PEMFC tolerant level.
Keywords: Hydrogen-rich stream; Carbon monoxide removal; Selective or preferential oxidation;
Oxygen bleaching of kraft pulp catalysed by Mn(III)-substituted polyoxometalates by A. Gaspar; D.V. Evtuguin; C. Pascoal Neto (157-168).
The catalytic response of Mn(III)-substituted polyoxometalates (MSP) of series [XW11MnIII(H2O)O39] n− (X=B, Si, P) on the oxygen bleaching of eucalypt kraft pulp was investigated. All MSP tested showed catalytic activity in the delignification, which depended on MSP redox potentials and rates of their re-oxidation with dioxygen. The best delignification results were obtained with SiW11MnIII, possessing relatively high redox potential (E°=+0.65 V) and being partially re-oxidised by dioxygen during the pulp bleaching. Under the conditions of SiW11MnIII catalysed bleaching (100 °C, 2 h, pH 4) the selectivity of delignification was higher than that in the conventional oxygen–alkaline bleaching. The delignification mechanism was elucidated by kinetic studies and by oxidation experiments with SiW11MnIII using monomeric lignin model compounds (homovanillyl and homoveratryl alcohols). The delignification rate showed a pseudo first order with respect to lignin and a non-integer, lower than one, order for SiW11MnIII and O2. The effective activation energy of the delignification was about 76 kJ/mol. It was suggested that two consecutive one-electron oxidations of lignin substructures by SiW11MnIII is the delignification rate limiting reaction step. The oxidation of phenolic lignin structures was much faster (more than 10 times) than non-phenolic units, i.e. the oxidative delignification is determined by reactivity of phenolic units. The delignification time profile in the reaction system SiW11MnIII/O2 showed a fast initial delignification period corresponding to 35–40% lignin removal followed by a slow delignification period. These features were explained by different reactivity of phenolic and non-phenolic lignin units as well as by the competitive coupling reactions of one-electron oxidised lignin substructures.
Keywords: Manganese-substituted polyoxometalate; Oxidative catalysis; Oxygen delignification; Lignin; Lignin model compound;
Catalytic activity of oxide-supported Pd catalysts on a honeycomb for low-temperature methane oxidation by Ryuji Kikuchi; Shingo Maeda; Kazunari Sasaki; Stefan Wennerström; Yasushi Ozawa; Koichi Eguchi (169-179).
Low-temperature methane oxidation over oxide-supported Pd catalysts coated on a metal or ceramic honeycomb was investigated for gas turbine applications. Al2O3 and SnO2 were used as washcoat material, and a Fe–Cr–Al alloy and cordierite were adopted as metal and ceramic honeycombs, respectively. Pd catalysts on the honeycomb were prepared by varying washcoat loading and washcoat calcination temperature. It was found that the catalytic activities of Pd/SnO2 on metal and ceramic honeycombs improved with increasing washcoat loading and precalcination temperature of the washcoat material. Especially, significant enhancement of the catalytic activity appeared for Pd/SnO2/ceramic honeycomb as the washcoat loading increased from 150 to 200 g/l. The catalytic activity of the honeycomb catalysts was examined under high pressure and space velocity. The temperature at which the increase in CH4 conversion became noticeable was shifted to higher temperature compared to the experiments at lower space velocity and ambient pressure. CH4 conversion over the honeycomb catalysts fluctuated as the catalyst bed inlet temperature was raised. Pd/SnO2/ceramic honeycomb exhibited the highest stable activity for low-temperature methane oxidation.
Keywords: Low-temperature oxidation; Pd/Al2O3; Pd/SnO2; Metal honeycomb; Ceramic honeycomb; Methane combustion;
The drastic effect of platinum on carbon-supported ruthenium-tin catalysts used for hydrogenation reactions of carboxylic acids by Yoshinori Hara; Kouetsu Endou (181-195).
The incorporation of platinum on bimetallic ruthenium-tin catalysts supported on active carbon has profound effects on the catalytic behavior. The reaction rate was accelerated nearly three times compared with that of the bimetallic system for the hydrogenation of 1,4-cyclohexanedicarboxylic acid (CHDA). Moreover, it turned out that Pt can completely prevent Sn, one component of the catalyst, from dissolving into the reaction mixture, whereas a considerable amount of dissolved Sn was detected in a binary Ru-Sn catalyst during hydrogenation. We verified the durability of our catalyst by carrying out a catalyst recycling test over seven cycles.The characterization of the catalyst has been evaluated by the temperature programmed reduction, X-ray photoelectron spectroscopy and X-ray diffraction as well as electron microscopy. A significant difference in the catalytic properties of the resulting Ru-Pt-Sn catalyst from a binary one exists in the valence state of the tin species, which is present mostly as Sn(0). It is postulated that the high performance of this novel catalyst in terms of activity and durability are related to this point.
Keywords: Liquid-phase hydrogenation; Carboxylic acid hydrogenation; Ruthenium-platinum-tin supported on carbon; Valence state of tin;
Photocatalytic decomposition of 4-nitrophenol over titanium silicalite (TS-1) catalysts by Gun Dae Lee; Soon Ki Jung; Yeon Ju Jeong; Jin Hwan Park; Kwon Taek Lim; Byung Hyun Ahn; Seong Soo Hong (197-208).
Titanium silicalite zeolites (TS-1) having Si/Ti ratios of 3.3, 13.7, and 26.3 were synthesized and used as photocatalysts for decomposition of 4-nitrophenol (4-NP) in aqueous solution. In the dark, the adsorption of 4-NP on TS-1 changed greatly depending on the Si/Ti ratio in TS-1 and the pH of the solution. The amount of 4-NP adsorbed on TS-1 increased with increasing Si/Ti ratio and decreasing pH of solution. The photocatalytic activities of TS-1 zeolites for the decomposition of 4-NP were found to be greatly affected by H2O2. In the absence of H2O2, the TS-1 having lower Si/Ti ratio, and consequently containing a larger amount of extra framework titanium, exhibited higher photocatalytic activity. In contrast, in the presence of H2O2, the TS-1 with higher Si/Ti ratio, in which the titanium content is lower while the fraction of framework titanium is higher, showed a higher increase in photocatalytic activity. Especially in acid conditions, the addition of H2O2 to the reaction solution results in a remarkable enhancement of the photocatalytic activity of TS-1; the apparent rate constant increased with increasing Si/Ti ratio. Such results suggest that, upon UV illumination, •OH radicals can be formed easily from the titanium-hydroperoxide species that are formed by the interaction of framework titanium in TS-1 with H2O2. The enhancement of photocatalytic activity of TS-1 for the decomposition of 4-NP by the addition of H2O2 can be attributed to both the efficient formation of •OH radicals and the close proximity of •OH radicals to the reactant molecules.
Keywords: Titanium silicalite; Photocatalyst; Decomposition of 4-nitrophenol; Hydrogen peroxide; •OH radicals;
Effect of nonframework cations and crystallinity on the basicity of NaX zeolites by U.D Joshi; P.N Joshi; S.S Tamhankar; V.V Joshi; C.V Rode; V.P Shiralkar (209-220).
The basic character of NaX-type zeolites was systematically altered by incorporating nonframework K+, Rb+ and Cs+ cations with ([M]/([M]+[Na]) ca. ∼0.55). Correlation between activity and basicity was established. The role of Lewis basicity was found to be more important than the changes in specific area or micropore volume of different cation-exchanged samples in deciding the catalyst activity in the Knoevenagel condensation reaction. The catalyst activity was found to decrease with lowering the degree of crystallinity in the case of NaX zeolites.
Keywords: NaX zeolite; Nonframework cations; Lewis basicity; Cation kinetic diameter; Knoevenagel condensation; Ball milling; Crystallinity; Basicity;
LEIS-surface analysis of commercial sulfided oxide catalysts by S Helfensteyn; H Tollet; J Degrève; C Creemers (221-228).
Two commercial sulfided oxide catalysts for the hydrotreatment of hydrocarbons were investigated: NiO-MoO3 and CoO-MoO3 on alumina. Fresh and cokes-contaminated pellets were first explored by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The samples were then studied with low energy ion scattering (LEIS). The spectra show a clear distinction between fresh, partly contaminated and heavily contaminated pellets. For both catalysts the comparison of the peak signals suggests that C is preferentially deposited on the Mo- and Al-atoms. This confirms the role that is attributed to Mo in Ni-Mo(Al2O3) catalysts by other authors who found that the introduction of small amounts of Mo into Ni(Al2O3) catalysts greatly improves their resistance to coking. Next the contaminated pellets were regenerated by heat-treatment at 450 °C in a furnace. The LEIS-spectra give evidence that this treatment has no influence on the fresh catalysts, but completely restores the contaminated pellets to their original state. The results clearly demonstrate that, by its monolayer surface sensitivity, LEIS can give clear-cut information even on very rough surfaces of commercial sulfided oxide catalysts.
Keywords: Low energy ion scattering; Scanning electron microscopy; X-ray spectroscopy; Catalysis; Cobalt oxides; Molybdenum oxides; Nickel oxides; Carbon;
An investigation of the activity and stability of Pd and Pd-Zr modified Y-zeolite catalysts for the removal of PAH, CO, CH4 and NO x emissions by F Klingstedt; A Kalantar Neyestanaki; L.-E Lindfors; T Salmi; T Heikkilä; E Laine (229-240).
Pd-Y- and Pd-Zr-Y-zeolite catalysts were prepared by the ion-exchange of parent NH3-Y-zeolite, thermally pre-treated Y-zeolite and hydrothermally pre-treated Y-zeolite. The activity of the catalysts was studied in conversion of gas mixtures simulating the flue gases from the combustion of biofuels and natural gas driven vehicles (NGVs) at temperature ranges of 120–800 °C. The effect of sulphur-poisoning was examined by the addition of 5 ppm SO2 into the feed gas mixtures. High activity in the removal of the model pollutants was obtained over the fresh catalysts. De-activation was observed as a result of catalyst ageing in the reactants’ flow (800 °C, 6 h) or steam treatment (850 °C, 12 vol.% H2O, 16 h). The de-activation was attributed to the de-alumination as well as to the migration of Pd2+ cations. The catalysts were characterised by XRD, SEM–EDXA, N2-physisorption, O2/SO2/NH3/naphthalene-TPD, XRF and DCP.
Keywords: Pd-Y-zeolite; Catalytic combustion of biofuels; De-activation (de-alumination); Trapping;
XPS characterization of zirconium-promoted CoMo hydrodesulfurization catalysts by S Damyanova; L Petrov; P Grange (241-252).
CoMo hydrodesulfurization catalysts (HDS) supported on mixed ZrO2-Al2O3 and ZrO2-SiO2 oxides have been prepared via a two-step impregnation using the incipient wetness method. The S BET method, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used for characterization of the samples. Increasing the ZrO2 content decreases the surface areas and the pore volumes of supported CoMo catalysts. The effect of Zr content on the dispersion of Mo and Co species is more pronounced in the case of CoMo/ZrO2-SiO2 samples; a higher dispersion corresponds to a higher ZrO2 content. The sulfidation of molybdenum forms MoS2. A higher degree of sulfidation of molybdenum is observed for CoMo catalysts supported on ZrO2-Al2O3. A comparison between surface properties and catalytic activity behaviors of CoMo catalysts in HDS of thiophene is presented.
Keywords: Cobalt; Molybdenum; Zirconium; Hydrodesulfurization catalysts; Sulfidation; XPS;
Phosphorus promotion of Ni (Co)-containing Mo-free catalysts in thiophene hydrodesulfurization by Tamás I Korányi (253-267).
Several unsupported nickel (cobalt)–phosphorus (sulfur) model compounds were prepared, identified and characterized by X-ray diffraction (XRD), electron microscope (EM)/energy dispersive X-ray analysis (EDAX), temperature programmed sulfidation (TPS), BET, thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). They were characterized again following pretreatments (in He, H2 or H2/H2S) at different pressures, then by thiophene hydrodesulfurization (HDS) catalytic activity test at atmospheric pressure. The presence of sulfur (presulfidation by H2S) was not required to convert the model compounds into active catalysts, a beneficial influence of H2S on the activity was only to facilitate the reduction process into the most active Ni2P or less active Co2P phases. Ni(P)/SiO2 catalysts were also prepared, characterized and tested in thiophene HDS. For sulfided P-free Ni/SiO2 catalysts the HDS activity correlated with the Ni3S2 surface area determined by dynamic oxygen chemisorption (DOC). The addition of phosphorus causes a strong increase in HDS activity of silica supported catalysts, which are much higher than could be expected by their nickel sulfide surface area, therefore, the formation of Ni2P (identified by XRD) again explains their high activity. The HDS activity of phosphorus promoted nickel (or cobalt) containing molybdenum-free catalysts is related to the amount and dispersion of Ni2P or Co2P present in the material.
Keywords: Phosphorus promotion; Promotion; Nickel (cobalt) phosphide; Nickel (cobalt) phosphosulfide; Silica supported nickel; Thiophene hydrodesulfurization; Hydrodesulfurization; HDS;
The roles of active sites of nickel sulfate supported on γ-Al2O3 for ethylene dimerization by Jong Rack Sohn; Won Cheon Park (269-278).
A series of catalysts, NiSO4/γ-Al2O3, for ethylene dimerization were prepared by the impregnation method using an aqueous solution of nickel sulfate. Nickel sulfate supported on γ-Al2O3 was found to be very active even at room temperature, giving a maximum in both activity and acidity when catalyst containing 20% NiSO4 was calcined and evacuated at 600 °C. The high catalytic activity of NiSO4/γ-Al2O3 was related to the increase of acidity and acid strength due to the addition of NiSO4. The asymmetric stretching frequency of the SO bonds for NiSO4/γ-Al2O3 samples was related to the acidic properties and catalytic activity. That is, the higher the frequency, the larger both the acidity and catalytic activity. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni+, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO4/γ-Al2O3 and Ni 2p XPS.
Keywords: Ethylene dimerization; Nickel sulfate on γ-Al2O3; Acidic properties; Active sites; Asymmetric SO stretching frequency;
Cyclopropanation on a highly active heterogeneous catalyst: CuO/TiO2-Al2O3 by Xiang Liu; Yan Liu; Xiaohong Li; Song Xiang; Yiliang Zhang; Pinliang Ying; Zhaobin Wei; Can Li (279-286).
Some heterogeneous catalysts, cupric oxide supported on different supports, were prepared and employed to catalyze the cyclopropanation of styrene and 2,5-dimethyl-2,4-hexadiene with ethyl diazoacetate (EDA). The catalytic performance for cyclopropanation strongly depends on the nature of the support. A novel catalyst, CuO/TiO2-Al2O3, in which Al2O3 is modified with a monolayer TiO2, is found to be most active and selective for the cyclopropanation reaction. The yields of 93 and 94% cyclopropanes are obtained for styrene and 2,5-dimethyl-2,4-hexadiene at 40 °C as the substrates, respectively. The activity and selectivity in cyclopropanes are optimized with a monolayer dispersion of cupric oxide on the corresponding supports.
Keywords: Styrene; 2,5-Dimethyl-2,4-hexadiene; Cyclopropanation; Heterogeneous catalysts; CuO/TiO2-Al2O3;
Vapor-phase oxidation of 3-picoline to nicotinic acid over Cr1−x Al x VO4 catalysts by Tetsuya Shishido; Zhaoxia Song; Eriko Kadowaki; Ye Wang; Katsuomi Takehira (287-296).
Some metal vanadates were precipitated as the pure phases by adjusting the pH of aqueous solutions of the raw materials. The precipitates were calcined at 550 °C and tested for the vapor phase oxidation of 3-picoline to nicotinic acid. Chromium vanadate showed the highest activity among the vanadates tested; its structure belongs to monoclinic CrVO4-I. An addition of aluminum into CrVO4-I resulted in the formation of the solid solution of Cr1−x Al x VO4 still keeping CrVO4-I structure with high surface area in the range of x≤0.5. Upon further addition of aluminum, CrVO4-I structure changed to AlVO4 structure. The activity increased with increasing the Al content while keeping CrVO4-I structure; the highest activity was obtained at x=0.5. In the CrVO4-I structure, all the V species are isolated as VO4 tetrahedra and show the oxidation activity via its redox properties. NH3-TPD results showed that acidity increased by the replacement of Cr with Al in CrVO4-I. The addition of a large amount of water in the reaction mixture enhanced the yield of nicotinic acid. The highest activity was obtained over the Cr0.5Al0.5VO4 and the total yield of nicotinic acid and pyridine-3-carbaldehyde reached to 69% (selectivity, 86%) at 350 °C. Thus, 3-picoline can be effectively oxidized with O2 in the gas-phase to nicotinic acid on the Cr0.5Al0.5VO4 catalyst having Brønsted acid sites in addition to redox properties.
Keywords: Heterogeneous oxidation; 3-Picoline; Nicotinic acid; Cr0.5Al0.5VO4 catalyst;
Effect of support acid–basic properties on activity and selectivity of Pt catalysts in reaction of methylcyclopentane ring opening by L.B Galperin; J.C Bricker; J.R Holmgren (297-304).
Methylcyclopentane (MCP) ring opening (RO) was studied over platinum containing catalysts prepared on acid and basic (neutral) supports. The acid supports included mordenite, Y, MFI, beta, omega zeolite and gamma alumina modified with chlorine. The basic (neutral) supports included l-zeolite, hydrotalcite, theta and gamma aluminas, SiO2 modified with potassium. It was demonstrated that the selectivity of MCP RO depends on the acid–base properties of the catalysts. In the presence of acid catalysts, selectivity to RO is low and the main reaction is MCP isomerization to cyclohexane (CH) followed by dehydrogenation and formation of aromatics (ARs). On the basic catalysts, the selectivity to RO is very high (up to 98%) as the acid catalyzed isomerization and cracking reactions are almost completely suppressed. The addition of potassium neutralizes the acid active sites of the bifunctional acid catalysts and converts them to monometalic basic catalysts, which are favorable for nonselective MCP RO with C6 paraffins distribution close to statistical distribution.
Keywords: Methylcyclopentane; Ring opening; Acid–basic catalysts;
PATENTS ALERT (305-309).
AUTHOR INDEX (313-314).
SUBJECT INDEX (315-320).
CONTENTS CONTINUED (321-322).