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Applied Catalysis A, General (v.286, #1)

Inside front cover - Editorial Board (pp. co2).

Newsbrief (pp. n1-n4).

Vanadium aluminium oxynitride catalysts for propane ammoxidation reaction by Mihaela Florea; Ricardo Prada Silvy; Paul Grange (pp. 1-10).

The influence of the V/Al ratio composition on the physico-chemical and catalytic properties of the vanadium aluminium oxynitride system was investigated. The samples were prepared by co-precipitation of vanadium and aluminium solutions containing different metal compositions (0.1–0.9V/Al) at pH 5.5 and characterized by XRD, XPS, Raman and BET surface area. Catalytic activity measurements for the propane ammoxidation reaction were carried out under optimal acrylonitrile selectivity conditions.X-ray diffraction pattern indicated that all the catalysts in both oxide precursor and nitride state show amorphous character. BET surface area was higher for the sample with V/Al ratio of 0.25, before and after nitridation treatment. This sample showed optimal catalytic performances, with 50% acrylonitrile selectivity and 60% propane conversion. The optimal nitridation degree, which induces an optimal reduction degree of vanadium, would explain the maximal catalytic activity observed for the sample prepared using the V/Al ratio composition of 0.25.

Keywords: Vanadium; Ammoxidation; Acrylonitrile

Metal oxide catalysts for DME steam reforming: Ga₂O₃ and Ga₂O₃–Al₂O₃ catalysts with and without copper by Thomas Mathew; Yusuke Yamada; Atsushi Ueda; Hiroshi Shioyama; Tetsuhiko Kobayashi (pp. 11-22).

The steam reforming of dimethyl ether (DME) was performed on Cu/Ga_xAl10−_xO₁₅ and Ga_xAl10−_xO₁₅ catalysts (where ‘ x’ varies from 0 to 10). The presence of Ga₂O₃ in Al₂O₃ significantly affects the catalytic performance with respect to the DME conversion and the H₂ yield. It was found that the activity increases with the Ga₂O₃ concentration for Ga_xAl10−_xO₁₅. The DME steam reforming activity on Cu/Ga_xAl10−_xO₁₅ showed an improvement in the stability and H₂ yield as the Ga₂O₃ concentration increased. A correlation between the XPS results and the DME steam reforming activity for Cu/Ga_xAl10−_xO₁₅ reveals that the heterogeneity of the surface is important for achieving a high H₂ yield. The specific interaction between Ga₂O₃ and Cu plays a decisive role in the distribution of Cu, which makes Cu/Ga_xAl10−_xO₁₅ active and stable for the reaction.

Keywords: Fuel cells; DME steam reforming; Ga; ₂; O; ₃; –Al; ₂; O; ₃; Mixed oxides

Catalytic activities and coking resistance of Ni/perovskites in steam reforming of methane by Kohei Urasaki; Yasushi Sekine; Sho Kawabe; Eiichi Kikuchi; Masahiko Matsukata (pp. 23-29).

Steam reforming of methane for the purpose of hydrogen production was performed using nickel catalysts supported on a variety of perovskites, including LaAlO₃, LaFeO₃, SrTiO₃, BaTiO₃, La_0.4Ba_0.6Co_0.2Fe_0.8O_3−δ, to compare the catalytic activity and resistance to coking of these catalysts to those of the conventional Ni/α-Al₂O₃ catalyst. Ni/LaAlO₃ and Ni/SrTiO₃ showed high catalytic activities among the Ni/perovskites and longer-term stabilities than the conventional catalyst. Temperature programmed oxidation of carbon deposited on used catalysts revealed that inactive carbon species detected on Ni/α-Al₂O₃ were not formed in the case of Ni/LaAlO₃. The results of temperature programmed reduction confirmed that consumption and recovery of the lattice oxygen in perovskites occurred during the reaction, and that the reducibility of perovskites had a great impact on the steam reforming activity. The lattice oxygen in perovskites is considered to play important roles in promoting the oxidation of CH_x fragments adsorbed on metallic nickel.

Keywords: Steam reforming of methane; Lattice oxygen; Coking; Hydrogen; Ni/LaAlO; ₃; Ni/LaFeO; ₃; Ni/SrTiO; ₃; Ni/BaTiO; ₃; Ni/La; _0.4; Ba; _0.6; Co; _0.2; Fe; _0.8; O; _3−δ

Gaseous catalytic hydrogenation of nitrobenzene to aniline in a two-stage fluidized bed reactor by Shigang Diao; Weizhong Qian; Guohua Luo; Fei Wei; Yao Wang (pp. 30-35).

Gaseous hydrogenation of nitrobenzene over a Cu/SiO₂ catalyst has been studied in a two-stage and in a single-stage fluidized bed reactor, at 513–553K and atmospheric pressure. The placement of the second perforated plate in the fluidized bed reactor inhibits the backmixing of gases and solids and consequently increases the local molar ratio of hydrogen to nitrobenzene in the second stage. Thus, the conversion of nitrobenzene and the selectivity of aniline production and the stable life of the catalyst are significantly increased in the two-stage fluidized bed reactor, as compared with those in the single-stage one. A comparison of the coke formation and the burning characteristics of cokes in different reactors has also been presented. It suggests the simple catalyst regeneration for the two-stage fluidized bed technology. This work provides an effective method to produce aniline with higher purity.

Keywords: Hydrogenation; Nitrobenzene; Catalyst deactivation; Multi-stage fluidized bed reactor; Copper catalyst

Characterization of Pt-impregnated MCM-41 and MCM-48 and their catalytic performances in selective catalytic reduction for NO_x by Jea-Hun Jang; Sung-Chul Lee; Dong-Jin Kim; Misook Kang; Suk-Jin Choung (pp. 36-43).

This study focuses on the comparison of de-NO_x mechanisms and surface physical properties between Pt-impregnated MCM-41 and Pt-impregnated MCM-48 with different framework dimensions. In the de-NO_x reaction, NO reduction occurred from 250�C with reducing reagent (propylene) combustion in both the catalysts. The conversion reached a maximum (60%) at 300�C, however, in the case of Pt/MCM-41, while it was enhanced and kept at a high temperature of 550�C without any conversion decrease in Pt/MCM-48. This result could be attributed to the differences in structural dimension, surface acidity, adsorption abilities of the reducing agent and NO, and the different Pt-active species on MCM-41 and MCM-48. The adsorption ability for NO, the reducing agent (propylene), and NH₃ definitely increased on Pt/MCM-48 compared with Pt/MCM-41. The XPS and XRD results suggest that the PtO and PtO₂ had a role as active species on Pt/MCM-48, while only the PtO was active on Pt/MCM-41. The results of the physical properties mentioned and of in situ IR spectra suggested that the de-NO_x reaction in Pt/MCM-41 progressed by partial oxidation and reduction for the reducing agent and NO, respectively. This resulted in the production of NCO and C_xH_yO_z^* intermediates. In contrast, the complete oxidation and reduction of these occurred on Pt/MCM-48.

Keywords: MCM-41; MCM-48; PtO; PtO; ₂; NCO; C; _x; H; _y; O; _z; ^*

A novel route to produce 4- t-butyltoluene by t-butylation of toluene with t-butylalcohol over mesoporous Al-MCM-41 molecular sieves by M. Selvaraj; S.H. Jeon; J. Han; P.K. Sinha; T.G. Lee (pp. 44-51).

t-Butylation of toluene with t-butylalcohol ( t-BuOH) as alkylating agent was conducted under liquid phase reaction conditions over Al-MCM-41 with different Si/Al ratios for highly selective synthesis of 4- t-butyltoluene. For the reactions, the influences of various reaction parameters such as reaction temperature, time and t-BuOH to toluene ratio are discussed. With increasing the Si/Al ratios of Al-MCM-41 catalysts from 21 to 104, the conversion of toluene, and the yield and selectivity of 4- t-butyltoluene decreased because the number of Br�nsted acid sites in Al-MCM-41catalysts is found to decrease almost linearly with increasing ratios of Si/Al. The conversion and selectivity is increased in Al-MCM-41(21) with each cycling of reaction. The Si/Al ratio of 21 is found to be more suitable for the t-butylation of toluene to highly selective synthesis of 4- t-butyltoluene. Thus the selectivity of 4- t-butyltoluene is higher in Al-MCM-41(21) than that in other Al-MCM-41 samples.

Keywords: Al-MCM-41; Catalytic activity; Br�nsted acidity; Conversion of toluene; Selectivity of 4-; t; -butyltoluene

Catalytic synthesis of ethyl- tert-butyl ether on Dawson type heteropolyacid by Joanna Poźniczek; Anna Micek-Ilnicka; Anna Lubańska; Adam Bielański (pp. 52-60).

Catalytic formation of ethyl- tert-butyl ether (ETBE) by nucleophilic addition of ethanol to isobutene on Dawson-type heteropolyacid H₆P₂W₁₈O₆₂· nH₂O (HP2W) has been studied in the temperature range of 35–80°C. The yield of ETBE reached a maximum of 43% at 40°C and then decreased with increasing temperature. Such behaviour is typical for reversible exothermic reactions approaching equilibrium and results in the decrease of the yield with temperature. At 40°C the activity of the catalyst depended on the pre-treatment temperature and, hence, on the content of water of crystallisation. Samples pre-heated at 80 and 95°C, containing about eight H₂O molecules per anion, exhibited the highest activity. Under these conditions the ETBE yield is slightly above 40%. The samples calcined at 150 and 200°C, containing about three H₂O per anion, exhibited a yield of about 27%. Parallel sorption experiments of ethanol on octahydrated and trihydrated HP2W have shown that, in the former case, the sorption of ethanol was nearly twice as large as that in the latter case. The differences show that the sorption capacity of the samples depends on the secondary structure of the heteropolyacid. These differences have been assumed also as explanation for the observed levels of catalytic activity. In all experiments carried out at 40°C the selectivity to ETBE was over 90% but it decreased to a few percent at 80°C.

Keywords: ETBE synthesis; Dawson; Heteropolyacid; Catalyst

Alkylation of phenol with cyclohexene over solid acids: Insight in selectivity of O- versus C-alkylation by Ganapati D. Yadav; Parveen Kumar (pp. 61-70).

Alkylation of phenol with cyclohexene with acid catalysts leads to the formation of both O- and C-alkylated products, which are all useful in a variety of industries. The O-alkylated product cyclohexyl phenyl ether is a valuable perfume and can also serve as a precursor to diphenyl ether, a very important bulk chemical. The efficacy of various acid catalysts such as sulphated zirconia, sulphonic acid treated hexagonal mesoporous silica (SO₃-HMS), 20% (w/w) dodecatungstophospheric acid (DTP) supported on K-10 clay, 20% (w/w) cesium salt of DTP (Cs_2.5H_0.5PW₁₂O₄₀) supported on K-10 clay (Cs-DTP/K-10) and 20% (w/w) DTP/HMS was studied to improve the selectivity to cyclohexyl phenyl ether. A mixture of 2-cyclohexylphenol, 4-cyclohexylphenol and cyclohexyl phenyl ether was obtained with different selectivities. However, 20% (w/w) DTP/K-10 clay was the most active and selective catalyst for O-alkylation in the range of 45–70°C at atmospheric pressure. The selectivity to O- versus C-alkylation is strongly dependent on temperature, and at lower temperatures, the selectivity to cyclohexyl phenyl ether increases. The best operating temperature is 60°C. A mathematical model is built to interpret the kinetic data and develop a mechanism.

Keywords: Alkylation; Selectivity; Phenol; Cyclohexene; Cyclohexyl phenyl ether; 2-Cyclohexyl phenol; 4-Cyclohexyl phenol; Heteropoly acid; Clay; Dodectatungstophosphoric acid; Sulphated zirconia; Hexagonal mesoporous silica

Hydroisomerization-cracking of n-octane on heteropolyacid H₃PW₁₂O₄₀ supported on ZrO₂, SiO₂ and carbon by Juan C. Yori; Javier M. Grau; Viviana M. Ben�tez; Jorge Sep�lveda (pp. 71-78).

Heavy paraffins ( n-C_8–20) are inexpensive refinery cuts of low octane number that can be upgraded to fuel-grade gasoline (C₄–C₇) by means of simultaneous hydrocracking and hydroisomerization over bifunctional metal/acid catalysts. The addition of Pt to pure tungstophosphoric acid (HPA) and supported on ZrO₂ (HPA/Z), SiO₂ (HPA/Si) and carbon (HPA/C) was studied in n-octane hydroisomerization-cracking reaction (300°C, 0.1MPa, WHSV=1h⁻¹, H₂/ n-C₈=6). Catalysts were characterized by specific surface area; temperature-programmed reduction, XRD measurements, FT-IR spectroscopy and temperature-programmed desorption of probe molecules (pyridine and 2,4,6-trimethyl pyridine).Supported HPA samples showed initial specific activity values expressed by mass unit of HPA higher than pure HPA. The order at 5min on stream was HPA/Z>HPA/C>HPA/Si∼pure HPA. All the samples deactivated by coking. The Pt addition had two effects: (i) increased surface proton content of the samples and thus their activity in n-C₈ hydroconversion (a linear relationship between specific activity values and Brönsted acidity was found), (ii) increased stability of samples allowing the attainments of a fast pseudo-steady state. The increase in activity due to Pt incorporation may be related with the formation of a new surface species of Pt into the HPA network. The fast stabilization of the samples was related to the inhibition of the coke precursors produced by the metallic Pt that remained on the surface of catalysts.Catalysts provides between 5 and 110 additional RON points over those of a model feedstock of n-octane. The RON gain is better correlated to the Brönsted acidity of samples, thus confirming that the production of branched isomers from long alkanes does not require highly acidic sites. Pt-HPA/Z showed the best catalytic performance with a RON gain of 101 points. A linear relation between the production of light gases (C₁–C₃) and the RON gain indicates that octane boosting can only be got at the expense of the isomerizate yield.The RON gain and the production of light gases were compared with the corresponding to a catalysts of Pt deposited on sulfated zirconia (Pt/SZ). The results encouraged the use of Pt-HPA/Z as an alternative to produce a new hydroisomerization-cracking catalysts for the treatment of heavy alkanes in order to produce light isoalkanes.

Keywords: Tungstophosphoric acid; Supported bifunctional catalysts; n; -Octane hydroisomerization-cracking; RON enhancement

Isomerization of n-butane over sulfated zirconia catalyst under supercritical conditions by Takako Funamoto; Takamasa Nakagawa; Kohichi Segawa (pp. 79-84).

Heterogeneous catalytic processes in supercritical fluids offer environmentally benign alternatives to current catalyst technologies. In the case of isomerization of light alkanes over solid acid catalysts at atmospheric pressure, the catalysts deactivate rapidly due to coke formation on the catalyst surface. To solve this problem, we studied the isomerization of n-butane over sulfated zirconia in a n-butane supercritical condition of reactant and products. Under the supercritical condition, no significant deactivation was observed, and the steady state activity was maintained. Furthermore, the active sites of sulfated zirconia were characterized by FT-IR spectroscopy: it was found that Lewis acid sites on sulfated zirconia play an important role in the isomerization of n-butane.

Keywords: Isomerization of; n; -butane; Isomerization of light alkane; Supercritical fluid; Sulfated zirconia

Structural and textural characteristics of Ce-containing mordenite and ZSM-5 solids and FT-IR spectroscopic investigation of the reactivity of NO gas adsorbed on them by T.M. Salama; M.M. Mohamed; I. Othman A; G.A. El-Shobaky (pp. 85-95).

The in situ interaction of nitric oxide (NO) gas on the cerium framework-substituted ZSM-5 and mordenite zeolites was studied by FT-IR spectroscopy. Samples of ZSM-5 and mordnite-containing cerium (7.5wt.% expressed as CeO₂) have been hydrothermally synthesized from starting gel upon which the introduction of cerium is being made during synthesis of zeolites. The morphological and textural characteristics of cerium-free and cerium-containing zeolites were studied using XRD, FT-IR in the TO range, and N₂ adsorption at −196°C. The results revealed that the insertion of cerium in both zeolites led to a decrease in their degree of crystallinity. Such a decrease was 36% for Ce-ZSM-5 while it was 18% for Ce-mordenite. The results indicated a significant decrease in nitrogen sorption capacity (BET) by 31% from 624 to 431m²/g and also a decrease of the micropore volume by 27.8% from 0.579 to 0.418cm³/g for Ce-ZSM-5. These results were found on the other extreme in case of Ce-mordenite. The presence of Ce did not affect the cell volume of ZSM-5 much, while it increased that of mordenite. Most of Ce^IV ions were embedded in the framework of mordenite, where they exposed as extra-framework CeO₂ and cerium silicate in ZSM-5. The in situ interaction of NO on Ce-zeolites was studied using an FT-IR quartz cell. The adsorption of NO gas led to the formation of a series of nitrosyl species: N₂O (2245cm⁻¹), NO⁺ (2160cm⁻¹), NO (1910cm⁻¹), N₂O₃ (1880, 1580cm⁻¹), (NO)_2s,as (1844, 1734–1720cm⁻¹), NO₂ (1630cm⁻¹) and ionic compounds were stable upon evacuation, i.e. nitrato and nitrito NO_x⁻ ( x=2–3) (1300–1500cm⁻¹). Such nitrosyl complexes were favorably formed on Ce-ZSM-5 than on Ce-mordenite due to facilitated intervention of the cerium couple (Ce^III/Ce^IV) on the former than on the latter.

Keywords: Ce-mordenite; Ce-ZSM-5; FT-IR investigation; NO adsorption

Kinetics of catalytic hydrogenation ofβ-ionone and application of a presaturated one-liquid flow reactor for the production of fine chemicals by S. Peter; L. Datsevich; A. Jess (pp. 96-110).

Fine chemicals are commonly produced in batch or semibatch reactors, which are frequently operated on a rather limited basis with respect to the knowledge of the kinetics. A typical example is the hydrogenation of the flavor-substanceβ-ionone. The previously unknown kinetics were studied under industrially relevant conditions (180–230°C, 5–90 bar, Raney-Ni). The conversion of the triple-unsaturatedβ-ionone up to complete hydrogenation proceeds via a network of three parallel and four consecutive reactions. The kinetic parameters were determined, including the influence of external and particularly internal diffusion. Furthermore, the applicability of the presaturated one-liquid flow (POLF) reactor was studied. In this steady-state system, the liquid is externally presaturated with hydrogen, and then fed into a fixed-bed reactor. This leads to a simple – e.g. with respect to scale-up – two-phase system (liquid and solid catalyst) compared to common three-phase batch reactors (and also to “steady-state alternatives�? like a trickle bed). For the given reaction, a liquid recycle is installed to compensate the low hydrogen-solubility. Results of experiments and modelling show the good applicability of the POLF-reactor with respect to temperature control, required reactor size, and the inherent advantages of a steady-state process.

Keywords: Multiphase reaction; Fixed-bed reactor; Fine chemistry; Hydrogenation; Flavor substance; Presaturated one-liquid flow; POLF-reactor; Ionone

Effect of S-compounds and CO on hydrogenation of aldehydes over reduced and sulfided Ni–Mo/Al₂O₃ catalysts by Xueqin Wang; Ramzi Y. Saleh; Umit S. Ozkan (pp. 111-119).

Effects of sulfur compounds and CO molecule on the catalytic performance of the reduced and sulfided NiMo/Al₂O₃ catalysts in hydrogenation of linear aldehydes (hexanal and propanal) are studied. Although the steady-state reaction experiments showed a decrease in activity and selectivity of reduced catalysts when a model sulfur compound was introduced into the feed, the reaction performance of the reduced catalyst still remained superior to that of the sulfided catalysts. The studies with XPS, TPD, and volumetric chemisorption measurement techniques shown that, there is partial sulfidation of the reduced catalysts when exposed to sulfur under reaction conditions, however, it does not convert the catalyst to a molybdenum sulfide phase. Instead oxygen–sulfur exchange on the surface leaves behind oxisulfide species, with catalytic activity closely resembling that of the reduced catalysts. The presence of CO in the feed mixture leads to a decrease in hydrogenation activity and selectivity for both reduced and sulfided catalysts, due to the competitive adsorption between aldehyde and CO, although the effect of CO is completely reversible.

Keywords: Aldehyde hydrogenation; Reduced Ni-Mo catalysts; Sulfided Ni-Mo catalysts; Effect of sulfur compound; Effect of CO

Development of CO-resistive catalysts for the one-step amination of dodecyl alcohol to N, N-dimethyldodecylamine, and effect of carbon monoxide on activity of Cu/Ni-based catalysts by Hiroshi Kimura; Kouzo Ishikawa; Kenji Nishino; Seiji Nomura (pp. 120-127).

Dodecyl aldehyde is the intermediate in the one-step amination of dodecyl alcohol and dimethylamine (HNMe₂) to the corresponding tertiary amine, N, N-dimethyldodecylamine (RNMe₂). Carbon monoxide (CO) generated by the decarbonylation of dodecyl aldehyde, significantly poisons the Cu/Ni-based colloidal catalysts stabilized by barium stearate (Cu/Ni/Ba). Therefore, the prevention of CO generation or removal of CO from the reaction system was required to maintain the catalytic activity. A copper-based CO absorber was effective for removing CO, but the methanation of CO was not effective because of a significant decrease in activity of the Cu/Ni/Ba colloidal catalyst and a significant transalkylation of HNMe₂. The incorporation of a small amount of triphenylphosphite (P(OPh)₃) with the Cu/Ni/Ba colloidal catalyst (Cu:Ni:Ba:P(OPh)₃ mole ratio=5:1:1:0.16) caused a significant reduction in CO poisoning. Water was also a catalyst poison for the Cu/Ni/Ba colloidal catalyst, and cupric hydroxide significantly decreased the catalytic activity.

Keywords: Amination; Cu/Ni/Ba; Carbon monoxide; Catalyst poison; CO-resistive catalyst

Alumina-promoted mesoporous sulfated zirconia: A catalyst for n-butane isomerization by Jung-Hui Wang; Chung-Yuan Mou (pp. 128-136).

Mesoporous sulfated zirconia (MP-ZrO₂) were synthesized hydrothermally using Zr(O- nPr)₄ as zirconium precursor, ammonium sulfate as sulfur source and CTABr as template. Then the as-synthesized mesoporous materials were directly impregnated with aluminum sulfate to give the acidic Al-promoted mesoporous sulfated zirconia. (AS/MP-ZrO₂). The AS/MP-ZrO₂ catalyst was characterized by nitrogen physisorption (BET) for texture properties, by X-ray diffraction (XRD) for confirming the phase and by TEM for particle sizes. The catalytic conversion of n-butane isomerization was measured in a flow reactor. With the addition of a proper amount of aluminum as a promoter, the catalytic behavior for n-butane isomerization at low temperature in flow system was strongly promoted. The increase of activity was determined primarily by the amount of alumina addition and by the temperature of calcination. The highest catalytic performance is for the catalyst prepared at an optimum 3mol.% Al loading and calcination at 650�C. The nature of the acidic sites was determined by X-ray photoelectron spectroscopy (XPS) measurements of N 1s of the adsorbed pyridine. Three kinds of acid sites were identified on the catalyst: a Lewis site, a weak Br�nsted site and a strong Br�nsted site. The catalytic activities are correlated with the amount of weak Br�nsted acid sites. The remarkable activity and stability of the Al-promoted catalysts are due to a balanced distribution of acid sites strength with an enhanced amount of weak Br�nsted acid sites.

Keywords: Sulfated zirconia; Mesoporous; Butane; Isomerization; Aluminum; Promoter

Zeolite-catalyzed ecofriendly synthesis of vibrindole A and bis(indolyl)methanes by M. Karthik; C.J. Magesh; P.T. Perumal; M. Palanichamy; Banumathi Arabindoo; V. Murugesan (pp. 137-141).

Electrophilic substitution of indoles with carbonyl compounds was carried out over HY, Hβ and H-ZSM-5 zeolites as effective heterogeneous catalysts. These zeolites afford good to excellent yield of bis(indolyl)methanes at room temperature. Vibrindole A, a novel beneficial compound, has been successfully synthesised for the first time in the presence of zeolite in good yield. The yield of bis(indolyl)methanes increases in the order H-ZSM-5

Keywords: Zeolites; Bis(indolyl)methanes; Vibrindole A; Indole; Aldehydes; Ketones

CO₂-reforming of methane over Ni/SiO₂ catalyst prepared by homogeneous precipitation in sol–gel-derived silica gel by Ryoji Takahashi; Satoshi Sato; Toshiaki Sodesawa; Satoshi Tomiyama (pp. 142-147).

Ni/SiO₂ catalysts with Ni content up to 50wt.% were prepared by depositing nickel hydroxides in a sol–gel-derived wet silica gel, where nickel hydroxides were produced by the increase in pH due to the decomposition of urea. The Ni dispersion in the resulting catalysts is relatively high, and increases monotonically with increasing Ni content up to 40wt.%. The Ni/SiO₂ catalysts have large volume and large-sized mesopores at ≤20wt.% Ni-loading, and have high thermal stability. In the CO₂-reforming of methane, the catalytic activity proportionally increases with increasing Ni content at reaction temperatures between 500 and 900°C. High and steady catalytic activity is achieved when we use the Ni/SiO₂ catalysts with Ni content of 20wt.% under the reaction conditions of high space-time velocity and high temperature.

Keywords: Ni/SiO; ₂; catalyst; CO; ₂; -reforming of methane; Catalyst preparation; Thermal decomposition of urea; Sol–gel method

Effect of boron addition on a MoO₃/Al₂O₃ catalyst by U. Usman; Mayu Takaki; Takeshi Kubota; Yasuaki Okamoto (pp. 148-154).

MoO₃/Al₂O₃ catalysts modified by boron were characterized in oxide and sulfide forms by means of FTIR, XPS, NO adsorption, LRS, and TPD of NH₃. XPS and FTIR showed that boron is highly dispersed as a monolayer over the alumina surface, consuming basic OH groups of alumina. As the density of the OH groups of alumina decreased by the addition of boron, the interactions between Mo oxides and the alumina surface became weak. This allowed larger Mo oxide clusters and finally crystalline MoO₃ to form. Thus, the dispersion of Mo oxides on the surface of alumina decreased, as proved by Raman spectra and the I(Mo3d)/ I(Al2p) XPS intensity ratio. In line with the observations, the dispersion of MoS₂ particles in the sulfided catalyst was decreased by the addition of boron, as evidenced by NO adsorption. A comparison of the XPS and NO adsorption results suggests that there is a parallel correlation between the dispersions of Mo oxides and MoS₂ particles on the alumina surface, especially when Mo oxides are highly dispersed on the surface of alumina. The ammonia TPD profiles suggested that the number of weak and mild acid sites of alumina was increased by the addition of a high loading of boron.

Keywords: MoO; ₃; /Al; ₂; O; ₃; catalysts; Effect of boron addition; Surface hydroxyl groups; XPS; LRS; MoS; ₂; dispersion; MoO; ₃; –alumina interaction

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Applied Catalysis A, General (v.286, #1)