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Applied Catalysis A, General (v.302, #2)

Editorial Board (pp. co2).

Ru-doped Ni catalysts effective for the steam reforming of methane without the pre-reduction treatment with H₂ by Jin Hyeok Jeong; Jung Won Lee; Dong Joo Seo; Yutaek Seo; Wang Lai Yoon; Deuk Ki Lee; Dong Hyun Kim (pp. 151-156).

Ru-added Ni catalysts supported on Al₂O₃ or MgAl₂O₄ were prepared and tested for the methane steam reforming to investigate the Ru-induced effects on the catalytic activity, the suppression of carbon deposition and the in situ self-activation of the oxidized catalysts during the reforming. The Ni catalysts promoted with a small amount of Ru (≤1wt%) showed a moderate reforming activity without a pre-reduction treatment using H₂; however, the Ni catalysts unpromoted with Ru were active only after reducing the catalysts with H₂. Among the Ru-added Ni catalysts, the catalyst prepared by sequentially impregnating Ru by 0.5wt% over the calcined sample of 20wt% Ni/Al₂O₃ showed higher reforming activity than the catalyst prepared by the co-impregnation of 0.5% Ru and 20% Ni over Al₂O₃. It was also revealed that the Ru doping greatly suppressed carbon growth on the Ni/Al₂O₃ catalysts. Between the two support materials, MgAl₂O₄-supported catalysts were more active than Al₂O₃-supported catalysts. Most of the Ni on the MgAl₂O₄ support were finely dispersed NiO clusters, while the Ni on the Al₂O₃ support was hard-to-reduce NiAl₂O₄. The presence of Ru in a highly dispersed state appears to facilitate the reduction of such Ni-oxides and to decrease the coking propensity of the catalyst in the steam reforming of CH₄.

Keywords: Steam reforming; Methane; Ru-promotion; Ni-based catalyst; Reduction; MgAl; ₂; O; ₄

Hydrogen production by partial oxidation of methanol over gold catalysts supported on TiO₂-MO_x (M=Fe, Co, Zn) composite oxides by Feg-Wen Chang; Hsin-Yin Yu; L. Selva Roselin; Hsien-Chang Yang; Ti-Cheng Ou (pp. 157-167).

Hydrogen production by partial oxidation of methanol (POM) has been investigated over Au/TiO₂-MO_x (M=Fe, Co and Zn) catalysts in the temperature range of 423–548K. The catalysts were characterized by ICP, BET, XRD, TEM and XPS analyses. The XRD analysis confirms the desired structure and phase purity of Fe₂O₃, Co₃O₄, ZnO and TiO₂ samples and the presence of gold in these materials. TEM observations show that the gold particles are stabilized against sintering during calcination and after catalytic tests, in the presence of MO_x in Au/TiO₂ catalysts. The XPS analysis detects the existence of metallic gold (Au⁰), non-metallic gold (Au δ⁺) and Au₂O₃ species in the uncalcined catalyst samples both before and after reaction, and the existence of metallic gold (Au⁰) and Au₂O₃ species in the calcined catalyst samples. The catalytic activity of Au/TiO₂ for the POM reaction to produce hydrogen is improved by using additional support (MO_x), probably due to a combination of factors, such as increasing the mobility of the lattice oxygen, maintaining the adequate oxidation state of the active gold particles and controlling the sintering of gold particles. Therefore, MO_x can act as a structural promoter and/or as a cocatalyst. The most active catalyst is Au/TiO₂-Fe₂O₃. Although Fe₂O₃ in Au/TiO₂ catalysts increases the catalytic activity, a surfeit of Fe₂O₃ lowers the activity for hydrogen formation. Calcination of the catalyst samples results in a decrease of the catalytic activity. The sample dried at 373K in air exhibits the highest activity for POM reaction. Both methanol conversion and hydrogen selectivity are increased with increase in reaction temperature. The reaction pathway is suggested to consist of consecutive methanol combustion, partial oxidation, steam reforming and decomposition. CO produced by methanol decomposition and/or by reverse water gas shift is subsequently transformed into CO₂ and H₂ by the water gas shift and/or CO oxidation.

Keywords: Gold catalyst; Titania-metal oxide composite support; Partial oxidation of methanol; Hydrogen; Deposition–precipitation

Selective oxidation of CO in excess hydrogen over CuO/Ce_xSn1−_xO₂ catalysts by Yin-Zu Chen; Biing-Jye Liaw; Chen-Wei Huang (pp. 168-176).

Ce_xSn1−_xO₂ (1− x=0.1–0.5) mixed oxides were prepared as supports of CuO/Ce_xSn1−_xO₂ catalysts. They were characterized and used in the selective oxidation of CO in excess hydrogen. Incorporating Sn⁴⁺ into CeO₂ not only increased the mobility of lattice oxygen but also promoted the activity of the selective CO oxidation. These promoting effects were attributed to the redox behaviors of Ce⁴⁺/Ce³⁺ and Sn⁴⁺/Sn²⁺ in Ce_xSn1−_xO₂ mixed oxides and to the interfacial interaction between fine clusters of CuO and Ce_xSn1−_xO₂. Of these CuO/Ce_xSn1−_xO₂ catalysts, 7% CuO/Ce_0.9Sn_0.1O₂ catalyst was the most active one; it was and more active than the 7% CuO/CeO₂ catalyst, with a T₁₀₀ temperature (80–85°C) for complete conversion that was about 15°C less than that of 7% CuO/CeO₂ (95–100°C). The selective oxidation of CO was still promoted as the incorporated amount of Sn⁴⁺ exceeded 10%, which is different from the result of incorporating Zr⁴⁺ in Ce_xZr1−_xO₂ (1− x>0.1). Such incorporation of Zr⁴⁺ in Ce_xZr1−_xO₂ weakened the selective oxidation. The 7% CuO/Ce_0.9Sn_0.1O₂ catalyst was almost inactive in H₂ oxidation below 110°C, and it achieved a selectivity of approximately 100%. The activity of the 7% CuO/Ce_0.9Sn_0.1O₂ catalyst was weakened in the feed in the presence of CO₂ and H₂O, but the stability of the catalyst was maintained. The 7% CuO/Ce_0.9Sn_0.1O₂ catalyst exhibited a good activity that was comparable with that of the noble metal catalyst of 5% Pt/Al₂O₃ and a good selectivity of much greater than 5% Pt/Al₂O₃.

Keywords: Selective CO oxidation; CuO catalyst; CeO; ₂; oxide; Ce–Sn–O mixed oxides

Effect of phosphorus addition on unsupported Ni–Mo–W sulfide catalysts prepared by the in situ activation of nickel/tetramethylammonium thiomolybdotungstate by H. Nava; J. Espino; G. Berhault; G. Alonso-Nuñez (pp. 177-184).

The effect of phosphorus addition was studied during the synthesis of unsupported trimetallic Ni–Mo–W catalysts prepared by the in situ activation of nickel-containing tetramethylammonium thiomolybdotungstate during the hydrodesulphurization (HDS) of dibenzothiophene (DBT). The trimetallic Ni–Mo–W precursors were prepared by the reaction of tetramethylammonium thiomolybdotungstates salts, [(CH₃)₄N]₄MoWS₈, with NiCl₂ and H₃PO₄ at P/Mo molar ratio of 0, 0.1, 0.5 and 1.0. These precursors are named Ni/[(CH₃)₄N]₄MoWS₈, P_0.1/Ni/[(CH₃)₄N]₄MoWS₈, P_0.5/Ni/[(CH₃)₄N]₄MoWS₈ and P/Ni/[(CH₃)₄N]₄MoWS₈, to give C₁, C₁P_0.1, C₁P_0.5 and C₁P catalysts, respectively. Catalysts were characterized by nitrogen adsorption studies, TEM, EDX, SEM and XRD.The addition of phosphorus has a detrimental effect on the HDS of dibenzothiophene. Phosphorus led to a strong decrease in BET specific surface area (from 46.9m²/g for the C₁ catalyst to 14.3m²/g for the C₁P catalyst) due to a pore plugging phenomenon. X-ray diffraction showed that the structure of unsupported nickel–molybdenum–tungsten sulfide catalysts corresponds to a low-stacked and poorly crystalline 2H–MoS₂ or 2H–WS₂ structure. Phosphorus induces the formation of less-folded slabs without modifying the dispersion along the basal plane or the stacking degree. However, the main effect of phosphorus is to favor the segregation of nickel sulfide and the loss of the promotional effect. This phenomenon would probably result from the stronger interaction of Mo and/or W with P than with Ni during the in situ preparation of these trimetallic NiMoW catalysts.

Keywords: Trimetallic precursors; In situ activation; Hydrodesulfurization; NiMoW catalysts; Phosphorus

Structure and properties of the alumina-supported vanadia catalysts for ethylbenzene dehydrogenation in the presence of carbon dioxide by Shuwei Chen; Zhangfeng Qin; Xiufeng Xu; Jianguo Wang (pp. 185-192).

Dehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of carbon dioxide was investigated over a series of alumina-supported vanadia catalysts (VO_x/Al₂O₃) with the vanadium loading of 0.40–3.00mmol/gAl₂O₃. The catalysts were characterized by XRD, H₂-TPR, TGA, UV-Raman and UV–vis spectroscopy. The catalytic behaviour as well as the structure of VO_x species on alumina depends strongly on the vanadium loading. Catalytic activity increases firstly with increasing the vanadium loading and the ST yield reaches a maximum value of 69.7% at a vanadium loading of 1.50mmol/gAl₂O₃, and then the activity decreases with a further increase in the vanadium loading. This may be related to the fraction of VO_x exposed on the domain surfaces and the reducibility of the surface VO_x species. The catalysts with different vanadium loadings are also different in the deactivation mechanism. The deactivation of VO_x/Al₂O₃ with vanadium loading below 1.50mmol/gAl₂O₃ is mainly ascribed to coke deposition, while the deep reduction of V⁵⁺ species becomes an important factor in the deactivation of catalyst with higher vanadium loading. EB dehydrogenation over VO_x/Al₂O₃ in the presence of carbon dioxide exhibits higher ST yield than that in the presence of an inert nitrogen atmosphere. Such a result can be attributed to the facts that carbon dioxide as a weak oxidant can eliminate hydrogen produced during EB dehydrogenation, regain the oxidation state (lattice oxygen) of reduced vanadium species and alleviate the catalyst deactivation.

Keywords: Alumina-supported vanadia; Ethylbenzene dehydrogenation; Carbon dioxide; Styrene; Catalyst deactivation; Reaction coupling

Rhenium oxide supported on organized mesoporous alumina — A highly active and versatile catalyst for alkene, diene, and cycloalkene metathesis by Roman Hamtil; Naděžda Žilková; Hynek Balcar; Jiří Čejka (pp. 193-200).

A new versatile heterogeneous catalyst for olefin metathesis based on rhenium (VII) oxide supported on organized mesoporous alumina was developed. This catalyst is suitable for metathesis of linear olefins, α-, ω-dienes as well as ring-opening metathesis polymerization of cycloalkenes and cross-metathesis of cycloolefins with linear olefins. This catalyst was found to operate under mild reaction conditions and its activity was much higher than that of corresponding catalyst based on conventional alumina. Catalyst can be used repeatedly and can be easily reactivated. Influence of the catalyst pore size on activity as well as selectivity in individual methathesis reactions was established.

Keywords: Organized mesoporous alumina; Rhenium oxide; Alkene metathesis; Ring-opening metathesis polymerization

Synthesis and diameter control of multi-walled carbon nanotubes over gold nanoparticle catalysts by Mami Yamada; Masa-aki Kawana; Mikio Miyake (pp. 201-207).

The synthesis of multi-walled carbon nanotubes (MWNTs) was performed by the chemical vapor deposition of carbon source (C₂H₂, C₂H_4, methanol, or benzene) using dodecanethiol-stabilized gold nanoparticles (Au-DTs) with monodispersity in size from 3 to 10nm supported on SiO₂–Al₂O₃ as a catalyst. The influences of reaction temperature, size of Au-DT, and carbon sources on the formed MWNTs were investigated. The diameter of MWNTs could be rationally controlled by changing the size of Au-DT only when C₂H₂ was used as a carbon source.

Keywords: Carbon nanotubes; Gold nanoparticles; Catalyst; Chemical vapor deposition; Diameter control

Characterization of bimetallic Ru-Sn supported catalysts and hydrogenation of 1,4-cyclohexanedicarboxylic acid by Zhu Zhiqing; Lu Zihong; Li Bin; Guo Shizhuo (pp. 208-214).

The supported catalysts were prepared by coimpregnation with aqueous solutions of ruthenium and tin salt and characterized by temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), carbon monoxide (CO) and oxygen (O₂) chemisorption measurements. The surface of the reduced Al₂O₃-based bimetallic catalysts would be composed of metallic ruthenium and Sn(II) species. No evidence for substantial amounts of Sn(0) is found on reduced catalysts by XPS measurement. Based on the available evidence from the various techniques, the authors suggested that the high selectivity of the bimetallic Ru-Sn/Al₂O₃ catalyst for production of 1,4-cyclohexanedimethanol would be due to the action not only of the promoter (Sn) but also of the support (alumina).Catalytic hydrogenation of 1,4-cyclohexanedicarboxylic acid to 1,4-cyclohexanedimethanol over Ru-Sn supported catalysts was studied as functions of catalyst composition as well as various catalyst preparation parameters. Hydrogenation activity was affected by the kind of tin compounds and supports used for the preparation of the Ru-Sn catalyst. Stannous chloride and alumina were found to be the appropriate materials for the hydrogenation ofCO group over the Ru-Sn catalysts. The yield for the 1,4-cyclohexanedimethanol on Ru-Sn/Al₂O₃ catalyst increased with Sn/Ru atomic ratio, reaching a maximum at a value of Sn/Ru=1:1, which suggested a promotion of theCO bond hydrogenation by particular bimetallic Ru-Sn ensembles. The Ru-Sn/Al₂O₃ catalysts without any calcination activated in a hydrogen stream at 550°C were effective for the hydrogenation of 1,4-cyclohexanedicarboxylic acid. Finally, we verified the durability of our catalyst by carrying out a catalyst-recycling test over five cycles.

Keywords: Ru-Sn catalysts; 1,4-Cyclohexanedicarboxylic acid; 1,4-Cyclohexanedimethanol

Decreased CO production in methanol steam reforming over Cu/ZrO₂ catalysts prepared by the microemulsion technique by Inga Ritzkopf; Sascha Vukojević; Claudia Weidenthaler; Jan-Dierk Grunwaldt; Ferdi Schüth (pp. 215-223).

Production of hydrogen by methanol steam reforming has been studied over a series of Cu/ZrO₂ catalysts prepared by the microemulsion technique. Catalytic activity was compared to that of a commercial Cu/ZnO catalyst. The synthesized catalysts have been characterized and investigated with respect to methanol conversion, CO formation, and long term stability. Both TPR and XANES/EXAFS indicate that two different Cu species are present in the as-prepared samples. The materials have BET surface areas of up to 165m²/g. Characterization by XRD and TEM revealed that the Cu/ZrO₂ catalysts consist of tetragonal zirconia particles with a homogenous distribution of copper and zirconium in the material. Methanol steam reforming over these Cu/ZrO₂ materials results in substantially reduced CO formation at high methanol conversions compared to the commercial Cu/ZnO catalyst.

Keywords: Zirconium oxide; Microemulsion; In situ EXAFS; XPS; TPR; Methanol steam reforming; CO formation; Copper

In situ infrared study of the catalytic ignition of methane on Pt/Al₂O₃ by A. Bourane; C. Cao; K.L. Hohn (pp. 224-231).

The ignition process of the partial oxidation of methane over Pt/Al₂O₃ catalysts has been investigated at atmospheric pressure using in situ DRIFT spectroscopy. Contacting methane with the catalyst shows that the dissociative adsorption of methane, evidenced by the appearance of the linearly adsorbed CO species, is delayed to higher temperatures for an oxygen-covered surface compared to an oxygen-free surface. Carbonate species were progressively obtained on the surface before the ignition temperature when interacting CH₄/O₂/He mixtures with the catalyst. They result from the interaction of produced carbon dioxide with the support. The temperature at which the carbonate species appears is lower for lower concentration of oxygen in the mixture. It has been shown that oxygen is mainly covering the surface until the ignition temperature. Competition between the two reactants is therefore assumed. It has been found that the state of platinum has a large effect on the ignition temperature, with the highest ignition temperature found for oxidized sample (platinum particle diameter, D_Pt=1.9–2.2nm), the next highest for freshly reduced sample ( D_Pt=1.7–1.9nm), and the lowest on aged sample ( D_Pt=4–5nm). All of these results linked to microcalorimetry measurements and literature data suggest that the heat of adsorption of oxygen is a key factor for ignition of the surface reaction.

Keywords: Ignition temperature; In situ DRIFT spectroscopy; Heat of adsorption of oxygen; Catalytic partial oxidation; Methane

Effect of basic properties of MgO on the heterogeneous synthesis of flavanone by Zheng Liu; José A. Cortés-Concepción; Michael Mustian; Michael D. Amiridis (pp. 232-236).

The effect of the surface basicity of MgO on the heterogeneous synthesis of flavanone from benzaldehyde and 2′-hydroxyacetophenone was examined through a series of MgO samples modified with different anions. CO₂ temperature programmed desorption (TPD) was used to characterize the basic properties of these samples. The results indicate that basic sites with different strengths exist on the MgO surface. Introduction of different anions completely eliminates the weak basic sites (i.e., those desorbing CO₂ in the 300–420K range) and reduces substantially the number of medium strength sites (i.e., those desorbing CO₂ in the 420–650K range). In contrast, no substantial effect was observed – with the exception of the chloride-treated sample – on the stronger basic sites (i.e., those desorbing CO₂ above 650K). A strong correlation was observed between the number of basic sites of “medium�? strength and the catalytic activity of these samples for the heterogeneous synthesis of flavanone. These sites are most likely involved in the activation of 2′-hydroxyacetophenone for the Claisen–Schmidt condensation with benzaldehyde, which represents the first step in the synthesis of flavanone.

Keywords: Fine chemicals and pharmaceuticals; Flavanone; Benzaldehyde; 2′-Hydroxyacetophenone; MgO; Basicity

Product composition as a function of temperature over NiAl-layered double hydroxide derived catalysts in steam reforming of methanol by Caixia Qi; J.C. Amphlett; Brant A. Peppley (pp. 237-243).

The catalytic production of hydrogen by steam reforming of methanol has been carried out over a NiAl-layered double hydroxide precursor and its calcined products in the temperature range of 200–400°C and atmospheric pressure. The reaction starts at approximately 300°C. H₂, CO, CO₂ and CH₄ are mainly produced. The reformate composition, however, largely depends on the calcination temperature of the precursor, the reaction temperature and the pretreatment temperature of the catalyst in the reactive stream prior to reaction. A desirable reformate mixture with high selectivity to H₂ and CO₂ was found using the calcined catalysts over the temperature range of 310–340°C.

Keywords: Steam reforming of methanol; H; ₂; production; Ni-based catalysts; Layered double hydroxide

Effect of NO_x and C₃H₆ partial pressures on the activity of Pt-beta-coated cordierite monoliths for deNO_x C₃H₆-SCR by A. Bueno-López; M.J. Illán-Gómez; C. Salinas-Martínez de Lecea (pp. 244-249).

The influence of NO_x and C₃H₆ partial pressures (from 500 to 2000ppm) in NO_x reduction under O₂-rich conditions, catalyzed by a Pt-beta-coated monolith, has been studied. Reactivity measurements in the temperature range from 170 to 240°C were carried out in a horizontal reactor at 5600h⁻¹. NO_x reduction is not affected by C₃H₆ and NO_x concentration from 170 to 190°C, only depending on temperature. Above 190°C, NO_x reduction increases as the NO_x/C₃H₆ ratio decreases. The temperatures for the maximum NO_x reduction and total C₃H₆ conversion are not coupled for all gas compositions. At temperatures lower than 200°C, C₃H₆–NO_x reaction is predominant, and above a certain temperature that depends on the gas composition, the C₃H₆–O₂ reaction is the main C₃H₆-conversion pathway. This behaviour is consistent with NO_x reduction and C₃H₆ conversion activation energies (72±11 and 133±18kJ/mol, respectively). At temperature higher than 200°C, the mass transfer of reactants affects the overall reaction rate. For practical application, the temperature window of the process is between 190 and 220°C, but the actual temperature must be selected depending on the gas composition.

Keywords: Pt catalyst; Beta zeolite; Cordierite monolith; deNO; _x

Copper-2,2′-bipyridines: Catalytic performance and structures in aqueous alkaline solutions by Heikki Korpi; Väinö Sippola; Ilari Filpponen; Jussi Sipilä; Outi Krause; Markku Leskelä; Timo Repo (pp. 250-256).

2,2′-Bipyridine and ten modified 2,2′-bipyridines were complexed in situ with copper(II) sulphate in aqueous alkaline solution. In oxidation studies with these complexes, the substituents of the bipyridine ring were found to have a significant effect on the catalytic activity. Parallel screening revealed that Cu-complexes with the bipyridine ligands substituted in 4,4′- and 5,5′-positions were highly active in the oxidation of veratryl alcohol with molecular oxygen. More detailed studies with 4,4′-disubstituted bipyridines showed that the electron donating methyl and methoxy substituents enhance the oxidation activity of Cu–bipyridine. The most effective Cu-complexes in the oxidation of veratryl alcohol also catalysed the oxidation of 2,2′-biphenol and the oxidative depolymerisation of the carbohydrate model compound dextran. The performance of Cu-2,2′-bipyridines in oxygen delignification of softwood pulp were in accordance with the model compound studies; the catalysts lowered the lignin content of the pulp, but they also tended to damage the cellulose fibres. According to the oxidation results, the complex distribution calculations and the UV–vis studies the structures of the active species were [Cu(2,2′-bipyridine)₂OH]⁺ and [Cu(4,4′-dimethoxy-2,2′-bipyridine)₂OH]⁺.

Keywords: Catalytic oxidation; Copper; 2,2′-Bipyridine; Complex structure; UV–vis spectroscopy

Structural and catalytic aspects of sol–gel derived copper manganese oxides as low-temperature CO oxidation catalyst by M. Krämer; T. Schmidt; K. Stöwe; W.F. Maier (pp. 257-263).

The influence of the preparation method on structural properties and on the catalytic activity of sol–gel derived binary copper manganese oxides for CO oxidation in dry air at room temperature has been investigated. The catalysts were characterised by means of BET and X-ray diffraction. All results were compared with a commercial Hopcalite sample. Subsequent conventional optimisation of the most active sample – prepared by the so-called ethylene–glycol method (EG I) – including compositional and calcination temperature variation revealed Cu₂₀Mn₈₀O_x (EG I) calcined at 400°C as very active catalyst. Sintering processes induced by the crystallisation of the amorphous material above 400°C cause a dramatic decrease of the catalysts’ surface area accompanied by deactivation. XPS data recordings were used to investigate the oxidation states of the metals in this catalyst and in the reference material. In conclusion a combination of high surface area, amorphous state and the presence of Cu²⁺ and Mn³⁺ was found to be essential for the high catalytic activity of the binary copper manganese oxides. The reactivity of the best catalyst was tested under application-relevant conditions, i.e. in moist air and at low-temperature fuel cell conditions.

Keywords: Copper manganese oxide; Low-temperature CO oxidation; Catalyst; Sol–gel

Influence of double promotion on HDS catalysts prepared by urea-matrix combustion synthesis by Sergio L. González-Cortés; Tian-Cun Xiao; Tsung-Wu Lin; Malcolm L.H. Green (pp. 264-273).

The stringent environmental regulations in the US, Japan and Europe are requiring significant improvement in the quality of transportation fuels. A new strategy based on urea-matrix combustion method for the synthesis of alumina-supported molybdate-based mixed oxides (i.e., bimetallic and trimetallic oxides) has been applied. This permits to control the alumina–mixed oxide interaction and therefore the HDS catalytic behaviour. The oxidic and sulfurized states of the HDS catalysts were characterized by X-ray diffraction (XRD), laser Raman spectroscopy (LRS), temperature-programmed reduction (TPR) and high resolution transmission electron microscopy (HRTEM). Catalyst performance was evaluated using a tubular fixed-bed reactor and the hydrodesulfurization of thiophene under normal pressure as model reaction.It has been found that Ni-promoted alumina-supported MoO₃ catalyst precursor presented a non well-ordered structure of Ni–Mo phase supported on alumina surface. However, when cobalt was added to Ni–Mo precursor the β-isomorph stability was significantly improved and the formation of alumina-supported β-Co_0.5Ni_0.5MoO₄ was observed. The activation treatments markedly affect the catalyst structure and hence the HDS catalytic performance. The catalyst series pretreated in H₂S–H₂ was 2–3 times more active than those C₄H₄S–H₂-pretreated catalysts and ca. 2–10 times more active than the pre-reduced samples. A significantly greater HDS activity of H₂S–H₂-pretreated Co_0.5Mg_0.5MoS_x/γ-Al₂O₃ catalyst was observed, which is attributed to the fact that both promoters are into the same network interacting directly with the molybdenum. This feature hinders not only the segregation of cobalt sulfide, but also the formation of long MoS₂ slabs.

Keywords: Alumina-supported molybdate-based mixed oxides; HDS reactions; Co–Ni-promoted MoS; ₂; catalysts; Urea-matrix combustion method

The effect of water on the acidity of TiO₂ and sulfated titania by Apoorva P. Kulkarni; Darrin S. Muggli (pp. 274-282).

Temperature-programmed desorptions (TPD) of isopropylamine (IPA), NH₃, and pyridine were compared with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of pyridine to determine the effect of H₂O on the acidities of three titania catalysts. Brønsted acidity increased in the following order: Degussa P-25 TiO₂2 synthesized in our laboratory ( p-TiO₂)4²⁻/TiO₂). Although the traditional interpretation of pyridine infrared spectra showed an apparent increase in Brønsted acidity upon treating SO₄²⁻/TiO₂ with H₂O, IPA TPD spectra showed that H₂O displaced IPA from approximately one-third to one-half of the Brønsted sites. Similarly, H₂O treatment prior to TPD displaced significant amounts of both NH₃ and pyridine. The primary effect of H₂O is displacement of strongly adsorbed basic probe molecules from Brønsted sites, rather than the conversion of Lewis sites to Brønsted sites.

Keywords: Sulfated titania; TPD; Isopropylamine; Brønsted; Lewis; Ammonia; Pyridine; DRIFTS; Acidity

Direct propylene epoxidation over modified Ag/CaCO₃ catalysts by Jiqing Lu; Juan J. Bravo-Suárez; Masatake Haruta; S. Ted Oyama (pp. 283-295).

In this work a series of supported Ag catalysts was studied for propylene epoxidation with molecular oxygen as the oxidant. It was found that α-Al₂O₃ and CaCO₃ were suitable supports for propylene epoxidation and that on the latter Ag particles between 400 and 700nm gave the highest selectivity to propylene oxide (PO). Ball-milling treatment of the CaCO₃ catalyst and promotion with NaCl resulted in improved catalytic performance. The highest PO selectivity (45%) was obtained on a ball-milled catalyst with a silver loading of 56wt.% supported on CaCO₃ and promoted with 1wt.% NaCl (Ag(56)–NaCl(1)/CaCO₃). The catalysts were tested with reactant flow rates of C₃H₆:O₂:He=5:10:15cm³min⁻¹, a gas hourly space velocity (GHSV) of 1800h⁻¹, a reaction pressure of 0.3MPa, and a reaction temperature of 533K (260°C). Addition of 500ppm of ethyl chloride (EtCl) to the reactant gases enhanced the stability of the Ag(56)–NaCl(1)/CaCO₃ catalyst. X-ray diffraction (XRD) of the Ag(56)–NaCl(1)/CaCO₃ catalyst detected the existence of AgCl in the catalyst and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy confirmed the presence of surface Ag⁺ species. Scanning electron microscopy showed a roughening of the Ag particles by the ball-milling treatment as well as by the addition of NaCl. The effect of NaCl on the enhancement of the catalytic performance was probably due to both physical and electronic changes in the properties of the catalyst. The NaCl not only helped increase the dispersion of the silver on the CaCO₃ support, but also probably increased the quantity of electrophilic oxygen species favorable for epoxidation. In situ UV–vis spectra suggested that the rapid reduction of Ag⁺ species on the surface of the Ag(56)–NaCl(1)/CaCO₃ catalyst could be the cause of a decline in PO selectivity observed during reaction.

Keywords: Propylene; Epoxidation; Silver; Propylene oxide; NaCl; UV–vis spectroscopy

Surface and catalytic investigations of CuO–Cr₂O₃/Al₂O₃ system by G.A. El-Shobaky; S.M. El-Khouly; A.M. Ghozza; G.M. Mohamed (pp. 296-304).

A series of CuO–Cr₂O₃/Al₂O₃ solids were prepared by the incipient wetness impregnation using Al(OH)₃ solid and chromium and copper nitrates. The amounts of copper and chromium oxides were varied between 12.2 and 13.5wt.% CuO and 3.1 and 8.8wt.% Cr₂O₃. The prepared solids were calcined at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were investigated using XRD and XPS analyses. The surface and catalytic properties of various solids were studied using nitrogen adsorption at −196°C and CO-oxidation by O₂ at 50–250°C. The results showed that the investigated adsorbents are mesoporous solids and measure specific surface areas within the range 73–356m²/g depending on the amount of dopant added and precalcination temperature. Cr₂O₃-treatment of the system investigated brought about a significant decrease in its BET-surface area which was found to decrease by increasing the precalcination temperature of the various solids. However, this treatment resulted in a progressive increase in the activation energy of sintering of different solids subjected to heat treatment at 400–800°C. The concentration of copper and chromium species on top surface layers of the samples precalcined at 400 and 600°C are greater than those present in the bulk of the solids. The doping process effected an increase in the surface concentration of copper species. The increase in precalcination temperature of pure and doped solids from 400 to 600°C effected an inward diffusion of copper and chromium species towards their interior leading to a decrease in surface concentration of these species. Doping CuO/Al₂O₃ system with Cr₂O₃ decreased the crystallinity of CuO phase and enhanced its interaction with Al₂O₃ at 800°C yielding CuAl₂O₄. XPS measurements showed also the possibility of formation of CuCrO₂ on the top surface layers of the heavily doped sample precalcined at 600°C. The catalytic activity and durability of CuO/Al₂O₃ system increased by treatment with Cr₂O₃. Doping of this system did not modify the mechanism of the catalytic reaction but increased the concentrating of catalytically active sites without changing their energetic nature.

Keywords: Cr; ₂; O; ₃; -doping of CuO/Al; ₂; O; ₃; Surface concentration of active sites; CO-oxidation by O; ₂

Characterization of titanium–tin composite oxide films and their visible-light photocatalytic properties by Masahiko Maeda; Kenichi Hirota (pp. 305-308).

Bilayer structures of Ti film on SnO_x film prepared by magnetron sputtering were annealed in ambient oxygen. Depth profiles of compositional elements after oxidation of the Ti/SnO_x structures analyzed by XPS reveal that TiO_x/SnO_x composite films and TiO₂/SnO_x bilayer films were formed when the Ti/SnO_x bilayer structures were fabricated at RT and 300°C, respectively. In the TiO_x/SnO_x composite films, the SnO_x forms impurity levels in the TiO_x bandgap at the same time as it prevents TiO₂ crystallization. These impurity levels are considered to play a role of visible-light absorption. Visible-light response photocatalytic activities are observed only in the TiO_x/SnO_x composite films.

Keywords: Titanium oxide; Tin oxide; Photocatalyst; Magnetron sputtering

Metal-support and preparation influence on the structural and electronic properties of gold catalysts by Maria Pia Casaletto; Alessandro Longo; Anna Maria Venezia; Antonino Martorana; Antonio Prestianni (pp. 309-316).

Nanostructured gold catalysts supported on CeO₂ and SiO₂ were prepared by the deposition–precipitation (DP) and the solvated metal atom dispersion (SMAD) techniques. The structural and electronic properties of the catalysts were investigated by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). Gold was found as small metal nanoparticles (cluster size ∼2nm) in the SMAD-prepared samples and in ionic state in the DP catalysts. The catalytic activity of the samples was tested in the reaction of low temperature CO oxidation. Gold nanosized particles in a pure metallic state exhibited a worse catalytic performance, both on ceria and silica. The presence of non-metallic Au species seems to be the main requisite for the achievement of the highest CO conversion at the lowest temperature. The higher activity of the Au/CeO₂ (DP) sample with respect to the Au/SiO₂ (DP) catalyst can be ascribed to a better stabilization of the Au⁺¹ ions, probably as AuO^- species, by the cerium oxide.

Keywords: CO oxidation; XPS; XANES; Oxidation state of gold; Particle size effect; Au/CeO; ₂; Au/SiO; ₂

Aldol condensation of citral and acetone over mesoporous catalysts obtained by thermal and chemical activation of magnesium–aluminum hydrotalcite-like precursors by Piotr Kuśtrowski; Dominika Sułkowska; Lucjan Chmielarz; Roman Dziembaj (pp. 317-324).

Hydrotalcite-like materials containing a various amount of magnesium and aluminum cations in the brucite like sheets, and carbonate/nitrate anions in the interlayer space were synthesized by the coprecipitation method. The as-prepared samples were characterized with respect to structure (XRD), chemical composition (elemental analysis and XRF) and thermal stability (evolved gas analysis by mass spectrometry). The thermal treatment of the hydrotalcite-like compounds at an elevated temperature (450–600°C) resulted in a structural transformation of the layer structure into mixed Mg–Al oxides. The textural and acid–base properties of such materials were examined by low-temperature sorption of N₂ and temperature-programmed desorption of NH₃ and CO₂, respectively. An influence of chemical composition and pre-treatment conditions on the catalytic activity and selectivity of the hydrotalcite-derived oxides in the self-condensation of acetone and the cross-condensation of citral and acetone was discussed. The pseudoionone yield was significantly enhanced by rehydration of the hydrotalcite-derived catalysts. The rehydrated samples showed a higher catalytic activity than Ba(OH)₂, which was tested as a standard catalyst of aldol condensation process.

Keywords: Aldol condensation; Aceton; Citral; Hydrotalcite-derived catalysts

Ni-Cu/samaria-doped ceria catalysts for steam reforming of methane in the presence of carbon dioxide by Ta-Jen Huang; Shih-Yao Jhao (pp. 325-332).

A series of samaria-doped ceria (SDC) supported Ni-Cu catalysts have been employed to carry out steam reforming of methane at 673–823K without or in the presence of carbon dioxide. Results show that hydrogen can be produced from H₂O dissociation over SDC and SDC supported Ni and Cu catalysts. The activity of H₂O dissociation over Cu is higher than that over Ni. Carbon dioxide (CO₂) has the ability to oxidize various Ni-Cu/SDC catalysts. The order of CO₂ dissociation reactivity over various Ni-Cu/SDC catalysts is the same as that of steam reforming of methane with or without the presence of carbon dioxide. Ni–Cu interaction enhances the activity of steam reforming of methane. Cu enhances the water–gas shift activity in the presence of CO₂ and this enhancement effect may be quantitatively related to the amount of the Cu–Ni species. The methane conversion rate of steam reforming increases as the CO₂ content in the feed increases. With increasing CO₂ content, H₂O conversion rate decreases but hydrogen (H₂) production rate increases in CO₂-steam reforming; in addition, the net CO₂ production rate decreases but the carbon production rate increases quite extensively. The presence of CO₂ thus requires special attention to the problem of carbon deposition during internal reforming of methane.

Keywords: Carbon dioxide; Steam reforming; Methane; Nickel; Copper; Samaria-doped ceria

An example of misinterpretation of IR spectra of adsorbed species due to gas phase H₂O: Comment on “The surface acidity and characterization of Fe-montmorillonite probed by in situ FT-IR spectroscopy of adsorbed pyridine�? [Appl. Catal. A 294 (2005) 156–160] by Arnaud Travert; Alexandre Vimont; Jean-Claude Lavalley (pp. 333-334).

Infrared; Pyridine; Acidity; Metal oxides

No Title by Mehmet Akçay (pp. 335-335).

Surface acid sites; Fe-montmorillonite; Pyridine adsorption; In situ FT-IR spectroscopy; Temperature-programmed desorption

Erratum to “Selective heterogeneous catalytic hydrogenation of nitriles to primary amines in liquid phase. Part I. Hydrogenation of benzonitrile over palladium�? [Appl. Catal. A: Gen. 296 (2006) 209–215] by László Hegedűs; Tibor Máthé (pp. 336-336).

Calendar of Forthcoming Events (pp. 337-338).

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Applied Catalysis A, General (v.302, #2)