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Applied Catalysis A, General (v.357, #2)

Editorial Board (pp. co2).

Contents (pp. iii-vi).

Structural rearrangement and catalytic properties of the Wells–Dawson (NH₄)₆P₂Mo₁₈O₆₂ heteropolycompound in the 2-butanol reaction by E. Arendt; K.M. McEvoy; E.M. Gaigneaux (pp. 115-124).

Structural changes of the ammonium phospho-molybdic Wells–Dawson salt (NH₄)₆P₂Mo₁₈O₆₂were examined using X-ray diffraction, X-ray photoelectron and infrared spectroscopies and its catalytic properties in the 2-butanol oxygen-assisted reaction were tested as a function of temperature. A significant evolution of the catalytic behavior occurs while the working catalyst is in the course of its reorganisation to a Keggin structure. Precisely, a particular species formed in situ and presenting intermediate characteristics between those of Wells–Dawson and Keggin structures exerts a beneficial effect on the selectivity to methyl-ethyl-ketone. This high selectivity towards the selective oxidation route was however found to be ephemeral and the selectivity decline was correlated to a no proper stabilization of this most active intermediate.Structural changes of the ammonium phospho-molybdic Wells–Dawson salt (NH₄)₆P₂Mo₁₈O₆₂ were examined by several solid state techniques during the oxygen-assisted catalytic reaction of 2-butanol. A significant evolution of the catalytic behavior occurs while the working catalyst is in the course of its reorganisation to a Keggin structure. Precisely, a particular species formed in situ and presenting intermediate characteristics between those of Wells–Dawson and Keggin structures exerts a beneficial effect on the selectivity to methyl-ethyl-ketone. This high selectivity towards the oxidative dehydrogenation was however found to be ephemeral and the selectivity decline was correlated to a no proper stabilization of this most active intermediate.

Keywords: Wells–Dawson heteropolycompound; Keggin heteropolycompound; 2-Butanol oxygen-assisted reaction; Structure–activity relationships

Photodegradation of methylene blue by in situ generated titania supported on a NaA zeolite by Diego Ivan Petkowicz; Rodrigo Brambilla; Cláudio Radtke; Carlos Daniel Silva da Silva; Zênis N. da Rocha; Sibele B.C. Pergher; João H.Z. dos Santos (pp. 125-134).

In situ generated titania was prepared by the impregnation, followed by calcination of TiCl4 on NaA zeolites, prepared using rice husk and chrysotile as silicon sources. Catalyst activity was shown to be comparable to that exhibited by commercial P-25. Experiments carried out in natural sunlight reached 92% decomposition of the methylene blue dye.The degradation of methylene blue dye was evaluated for a series of in situ generated titania resulting from the impregnation of TiCl₄ into a series of NaA zeolites, which were synthesized using alternative silicon sources, namely rice husk and chrysotile, and submitted to different treatments. The resulting catalysts were characterized by X-ray diffraction spectrometry, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, diffuse reflectance and transmittance infrared Fourier transform spectroscopy, energy dispersive X-ray scanning electron microscopy and differential pulse voltammetry. The generated titania are present in the form of anatase phase, without alteration of the zeolite framework. Homogeneous distribution of Ti is reached for up to 10wt.% Ti, where higher contents seem to afford isolated conglomerates. The highest catalyst activity was reached with samples having 10wt.% Ti. Catalyst activity was shown to be comparable to that exhibited by commercial P-25 after 1h of UV light exposition. Experiments carried out in natural sunlight reached 92% decomposition of the methylene blue dye.

Keywords: Photocatalysis; Chrysotile; Rice husk; Zeolite NaA; Dye

Application of an active immobilized iron oxide with catalytic H₂O₂ for the mineralization of phenol in a batch photo-fluidized bed reactor by Chun-Ping Huang; Yao-Hui Huang (pp. 135-141).

A water-fluidized type photo-reactor is designed to mineralize phenol and to avoid the resulting iron species being leached from the surface of the iron oxide. The advantages of this photo-reactor are as follows: (1) it is easier to carry larger and heavier solids than air-suspended type photo-reactor; (2) it is easy to control temperature; (3) the water-fluidized type photo-reactor does not lead to foam in the presence of phenol.A batch photo-fluidized bed reactor (photo-FBR) is designed for the mineralization of phenol and the minimization of iron species leached from an active immobilized iron oxide (denoted as SiG2). The hydroxyl radical (OH), which is produced from the reaction of hydrogen peroxide (H₂O₂) and SiG2 under irradiation by a 400-W Hg-vapor lamp, was confirmed by electron paramagnetic resonance signals of 5,5-DIMETHYL-1-pyrroline- N-oxide (DMPO)-OH (aqueous solution). The mineralization of phenol was more efficient in the presence of light. In general, a decrease of solution pH is commonly ascribed to the formation of carboxylic acids (acetic acid, oxalic acid, formic acid etc.) during the degradation of phenol. However, in this study, an interesting phenomenon was observed. The solution pH first decreased and then rose during the reaction in the presence of light. Also, in this case, the variation of solution pH reflected the degree of mineralization in this study. The approximately 98% mineralization of phenol led to fewer iron species being leached from SiG2 in the photo-FBR. A savings of more than 40% of the H₂O₂ dosage required for the phenol mineralization process was confirmed. In a batch photo-FBR, the system loading reflects the ratio of catalyst weight to the reaction volume. About 96%, 86% and 11% of the total organic carbons were removed after 180min, resulting in catalyst weight to reaction volume ratios of 30:1, 20:1 and 13:1, respectively. The activity of SiG2 did not decline after six reactions. The reactions for photo-assisted SiG2 in the presence of hydrogen peroxide and phenol were summarized.

Keywords: Photo-Fenton; Iron oxide; Mineralization; Phenol; Fluidized bed reactor

Characterization and hydrotreating performance of NiMo catalysts supported on nanostructured titanate by Edisson Morgado Jr.; José L. Zotin; Marco A.S. de Abreu; Danielle de Oliveira Rosas; Paula M. Jardim; Bojan A. Marinkovic (pp. 142-149).

Sulfided NiMo-catalysts supported on precursor nanostructured titanate (NiMoS/NSTi) showed similar activity for tetralin hydrogenation as compared to reference catalysts supported on TiO₂-anatase and gamma-alumina. However, the NiMoS/NSTi catalyst showed the highest yields towards ring opening of tetralin, which was related to the higher Brönsted acidity of the nanostructured support as measured by decomposition of adsorbed n-propylamine.A nanostructured protonated titanate, synthesized by alkaline hydrothermal treatment of TiO₂, has been investigated as a precursor support for NiMo hydrotreating catalyst and compared to alumina and titania as reference carriers. Each of the three powders was extrudated and calcined to obtain the properly shaped support, which was analyzed with respect to textural and acidity properties and then metal impregnated by insipient wetness method and sulfided at constant conditions to produce the final catalyst. The corresponding NiMo catalysts in the precursor oxide form were characterized by X-ray diffraction (XRD), thermogravimetry (TGA), transmission electron microscopy (TEM), temperature programmed reduction (TPR) and N₂ adsorption, whereas the active sulfided form was thoroughly examined by TEM and tested as for their tetralin hydrogenation activity. The results indicated that in spite of the higher surface area of the precursor NiMo-catalyst supported on the nanostructured carrier, its layered nature and one-dimensional morphology was lost after sulfidation under H₂S/H₂ atmosphere at 300°C. The dispersion of the sulfided active phase as examined by high resolution TEM was similar to that exhibited by the counterparts supported on alumina and nanocrystalline anatase, which was in agreement with the similar activities for tetralin hydrogenation found for the three tested catalysts. On the other hand, the titanate derived catalyst showed higher yields of ring opening of tetralin than the alumina supported catalyst, which was tentatively explained by the higher Brönsted acidity of the nanostructured support as measured by decomposition of adsorbed n-propylamine.

Keywords: Hydrotreating catalysts; Sulfided NiMo; Nanostructured TiO; ₂; Titanate; Tetralin hydrogenation

Imines derived from (1S,2R)-norephedrine as catalysts in the enantioselective addition of diethylzinc to aldehydes by Magdalena Jaworska; Krzysztof Z. Łączkowski; Mirosław Wełniak; Magdalena Welke; Andrzej Wojtczak (pp. 150-158).

A series of chiral imine ligands was prepared from (1S,2R)-norephedrine and applied for the enantioselective addition of diethylzinc to aldehydes. The absolute configuration of the addition product depends on the imine's nitrogen substituent. The highest ee (97%) was observed for imine with 9-anthryl substituent, when applied for p-methoxybenzaldehyde as substrate. Imine ligands derived 2-hydroxyacetophenone and with 9-anthryl substituent reveal strong absorbance in UV–vis spectra. Intermediates for the imines – diethylzinc – based catalysis and probable mechanisms were proposed.Purpose of the research was to determine the activity of chiral imine ligands prepared from (1S,2R)-norephedrine for the enantioselective addition of diethylzinc to aldehydes. Imine ligands reveal medium enantioselectivity, with the ee exceeding 30%. The highest ee (97%) was obtained for imine with 9-anthryl substituent, when p-methoxybenzaldehyde was used as substrate. The yields of the reaction obtained after 24–72h reached 76–96%. The absolute configuration of the addition product depends on the geometry of presented transition states and π–π stacking interactions between the investigated ligands and the benzaldehyde substrate. Imine ligands derived 2-hydroxyacetophenone and with 9-anthryl substituent reveal strong absorbance in UV–vis spectra. Intermediates for the imines – diethylzinc – based catalysis and probable mechanisms were proposed.

Keywords: Imine; Diethylzinc addition; Norephedrine derivatives; Activity

Gold catalysts supported on ceria doped by rare earth metals for water gas shift reaction: Influence of the preparation method by D. Andreeva; I. Ivanov; L. Ilieva; M.V. Abrashev; R. Zanella; J.W. Sobczak; W. Lisowski; M. Kantcheva; G. Avdeev; K. Petrov (pp. 159-169).

Gold catalysts based on ceria, doped by various RE metals (La, Sm, Gd, Yb, Y) were studied. The influence of the preparation methods on structure, properties and catalytic activity in the WGS reaction was investigated. All samples were characterized using a combination of X-ray diffraction, high resolution transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy and TPR.Gold catalysts based on ceria, doped by various RE metals (La, Sm, Gd, Yb, Y) were studied. The influence of the preparation methods on structure, properties and catalytic activity in the WGS reaction was investigated. The catalysts’ supports were prepared using two different methods: co-precipitation (CP) and mechanochemical activation (MA). The catalysts were tested in a wide temperature interval without and after reactivation. All samples were characterized using a combination of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS) and TPR. It was found that the catalytic activity of MA catalysts is higher than CP ones. The gold catalysts based on ceria doped by Yb and Sm exhibited the highest activity. After reactivation in air the MA samples almost kept the WGS activity same, while the CP catalysts increased it. The catalysts of a single- and double-phase structure are formed as a result of CP and MA preparation, respectively. There are no big differences in the gold particles size (2–3nm) depending on dopants and on the preparation techniques. The RS spectra analysis indicates that most probably the oxygen vacancies are adjacent to Me³⁺ dopant and the ceria structure seems to be better ordered than in the case of alumina as a dopant. There is no distinct correlation between reducibility and WGS activity. The XPS analysis disclose positively charged gold particles in addition to metallic gold within a surface region of fresh samples and only metallic gold on the samples after catalytic processing. There is no simple correlation between the concentration of Ce³⁺ in the samples and their WGS activity.

Keywords: Gold catalysts; WGS; Ceria doped by Yb, Sm, Gd, Y, La; XRD; HRTEM; Raman; XPS; TPR

Catalytic behaviour of carbon supported platinum group metals in the hydrogenation and isomerization of methyl oleate by I.V. Deliy; I.L. Simakova; N. Ravasio; R. Psaro (pp. 170-177).

Kinetic peculiarities of cis methyl oleate hydrogenation over Pd/C, Ru/C, Rh/C, Pt/C and Ir/C were studied. Liquid phase hydrogenation was carried out at temperature 298≤ T≤373K and under hydrogen pressure within 1–10bar using n-octane as a solvent. GLC and FTIR techniques were employed to characterize the reaction products. The effects of the catalyst amount, cis methyl oleate concentration, reaction temperature, and hydrogen pressure on the rates of methyl oleate hydrogenation and cis-trans isomerization were investigated. A simple reaction scheme involving cis methyl oleate hydrogenation and cis-trans isomerization was proposed for kinetic modeling. A good agreement was obtained between the calculated kinetic curves and the experimental data for the isomerization and hydrogenation of methyl oleate. It was shown that the second-row metals (Ru, Rh, Pd) display high activity in isomerization whereas the third-row metals (Ir, Pt) exhibit minor activity.Kinetic peculiarities of cis and trans methyl oleate transformation in the course of cis methyl oleate hydrogenation over Pd/C, Ru/C, Rh/C, Pt/C and Ir/C catalysts were investigated. Among the studied catalysts based on group 8 metals the highest catalytic activity in the cis methyl oleate hydrogenation with minor methyl elaidate formation is revealed over Pt catalyst.

Keywords: Pd/C; Pt/C; Ru/C; Rh/C and Ir/C catalysts; Methyl oleate hydrogenation; Cis-trans; isomerization; Kinetics

The partial oxidation of propane on mixed metal oxides—A short overview by Hans-Günther Lintz; Steffen Peter Müller (pp. 178-183).

The partial oxidation of propane on Mo-V-Te-Nb mixed oxides has been intensively studied. Considerable knowledge concerning the preparation of the catalyst and its phase composition was gained and led to an improvement of the performance in the one-step approach to acrylic acid. The results indicate the existence of a limit of the maximum yield which can be obtained so far.Recently much attention has been paid to the partial oxidation of propane to acrylic acid on multi-component mixed oxide catalysts in view of the development of a one-step industrial process. Much progress has been made in the understanding of the different parameters of the reacting systems but sufficient performance of the catalysts has still not been attained. The actual situation is described in a short overview and the remaining problems are pointed out.

Keywords: Propane; Acrylic acid; Mo-V-Te-Nb mixed oxides; Selectivity; Reaction network

Efficient synthesis of quinoxaline derivatives over ZrO₂/M_xO_y (M=Al, Ga, In and La) mixed metal oxides supported on MCM-41 mesoporous molecular sieves by S. Ajaikumar; A. Pandurangan (pp. 184-192).

Various weight percentages of ZrO₂/M_xO_y (where M=Al, Ga, In and La) mixed metal oxides were supported on Si-MCM-41 by a wet impregnation method. The characteristic structural features of the materials were probed by XRD, BET surface area, ammonia TPD, SEM and TEM techniques. Medicinally important quinoxaline derivatives were efficiently synthesized by the liquid phase condensation reaction of various 1,2-diamines with 1,2-diketones using the prepared catalysts.Mesoporous Si-MCM-41 was synthesized by a hydrothermal crystallisation method. Various weight percentages of ZrO₂/M_xO_y (where M=Al, Ga, In and La) mixed metal oxides were loaded by wet impregnation using methanol solutions. The characteristic structural features of the materials were determined by various physico-chemical techniques, such as XRD, BET surface area measurement, ammonia TPD, SEM and TEM. The regular meso structure of Si-MCM-41 with a uniform pore size is very well preserved after optimum loading of binary metal oxides. XRD patterns revealed the hexagonal nature of the support; it retained its structure with maximum loading of 17wt.% ZrO₂ and 4wt.% M_xO_y mixed oxides. BET measurements show the abrupt decrease in surface area, pore size and pore volume at higher loading of metal oxides. TEM studies of the material shows regular arrangement of hexagonal pores present in the host Si-MCM-41 and the fine dispersion of metal oxides over the support. NH₃-TPD experiments indicated the variations in the acid strength as the metal oxides were loaded. The acid strength of the catalysts follows the order: 17% ZrO₂/4% Ga₂O₃/MCM-41≈17% ZrO₂/4% Al₂O₃/MCM-41>17% ZrO₂/4% La₂O₃/MCM-41>17% ZrO₂/4% In₂O₃/MCM-41>17% ZrO₂/MCM-41. Medicinally important quinoxaline derivatives were efficiently synthesized by the liquid phase condensation reaction of various 1,2-diamines with 1,2-diketones using the prepared catalysts. Various reaction parameters were optimized to improve product yield.

Keywords: ZrO; ₂; /Ga; ₂; O; ₃; /MCM-41; Condensation; 1,2-Diamines; 1,2-Diketones; Quinaxaline derivatives

Selective catalytic reduction of nitrogen oxide by ammonia on Mn(Fe)-substituted Sr(La) aluminates by Marina V. Bukhtiyarova; Aleksandra S. Ivanova; Lyudmila M. Plyasova; Galina S. Litvak; Vladimir A. Rogov; Vasilii V. Kaichev; Elena M. Slavinskaya; Pavel A. Kuznetsov; Irina A. Polukhina (pp. 193-205).

Hexaaluminates prepared by co-precipitation and calcined at 700–1400°C were characterized by absorption methods, thermal analysis (TA and DTG), X-ray diffraction (XRD) and temperature-programmed reduction (TPR). Among hexaaluminates, the most active ( X_NO≈78%) and selective sample in the selective catalytic reduction (SCR) of NO to N₂ was Sr_0.69La_0.33Mn_2.23Al₁₀O_19.5. This sample was characterized by the highest amount of accessible oxygen and ratio Mn³⁺/Mn²⁺, in which the amount of Mn³⁺ is 65%, determining the red-ox transformation.Aluminates SrMn₂Al₁₀O₁₉, Sr_0.8La_0.2Mn₂Al₁₀O₁₉, LaMn₂Al₉O₁₈, LaMnAl₁₀O₁₈ and SrFeMnAl₁₀O₁₉ prepared by co-precipitation and calcined at 700–1400°C have been characterized by absorption methods, thermal analysis (TG–DTA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). It has been shown that calcination at 1100°C results in the formation of multiphase systems containing mainly hexaaluminate. The specific surface area of the samples calcined at 1100°C has been ranged from 20 to 25m²/g, except for the Sr_0.67Mn_2.28Al₁₀O_19.1 hexaaluminate, whose specific surface area was twice as large. TPR-H₂ of the samples calcined at 700°C proceeded in several steps. The first step was related to the reduction of Mn(Fe)₂O₃ to Mn(Fe)₃O₄ at 345–382°C. The second step was related to the reduction of Mn₃O₄ to MnO. The replacement of the part of Sr (Sr_0.67Mn_2.28Al₁₀O_19.1) by La and of the part of Mn by Fe leaded to the decrease in T_TPR. The amount of H₂ consumed during the reduction of the samples calcined at 700 and 1100°C increases in the series: Sr_0.67Mn_2.28Al₁₀O_19.1 (1100°C)0.89Fe_0.93Mn_1.03Al₁₀O_18.8 (1100°C)0.89Fe_0.93Mn_1.03Al₁₀O_18.8 (700°C)0.67Mn_2.28Al₁₀O_19.1 (700°C)0.69La_0.33Mn_2.23Al₁₀O_19.5 (700°C). Surface concentrations of elements in the samples Sr_0.69La_0.33Mn_2.23Al₁₀O_19.5 and Sr_0.89Fe_0.93Mn_1.03Al₁₀O_18.8 differ from the volume chemical contents. The main components on the surface are in oxidized state: Al³⁺, La³⁺ and Fe³⁺, Mn³⁺ and Mn²⁺. Amount of Mn³⁺ ions is 65 and 49%, respectively. Sr is predominantly localized on the surface as SrCO₃. Among hexaaluminates, the most active ( X_NO≈78%) and selective sample in the selective catalytic reduction (SCR) of NO to N₂ was Sr_0.69La_0.33Mn_2.23Al₁₀O_19.5, This sample was characterized by the highest amount of accessible oxygen and ratio Mn³⁺/Mn²⁺, in which the amount of Mn³⁺ is 65%, determining the red-ox transformation.

Keywords: Hexaaluminate; XRD; TPR; XPS; Reduction NO

Nanoparticulate precursor route to fine particles of TaON and ZrO₂–TaON solid solution and their photocatalytic activity for hydrogen evolution under visible light by Kazuhiko Maeda; Hiroaki Terashima; Kentaro Kase; Kazunari Domen (pp. 206-212).

Using nanoparticulate oxide precursors, fine particles of TaON and a solid solution of ZrO₂ and TaON are prepared. Formation of a solid solution between ZrO₂ and TaON is shown to be an effective approach to enhance photocatalytic activity of TaON for H₂ evolution under visible light ( λ>420nm).Preparation of fine TaON particles is attempted to improve the photocatalytic activity for H₂ evolution from aqueous methanol solution under visible light ( λ>420nm). TaON is synthesized by nitriding Ta₂O₅ powder at 1123K for 15h under a flow of NH₃. When nanoparticulate Ta₂O₅ with a primary particle size of 30–50nm is used as the precursor, fine particles of TaON (FP-TaON) with 50–80nm in size is obtained, but the primary particles aggregate to form larger secondary particles. Nitridation of Zr–Ta mixed oxide (Zr/Ta=0.1) nanoparticles results in the production of a solid solution of monoclinic-ZrO₂ and TaON exhibiting 30–50nm primary particle size with less aggregation and higher activity, as compared to FP-TaON. Suppression of surface defects (reduced tantalum species) produced during nitridation from Ta₂O₅ to TaON is shown to be essential for achieving efficient H₂ evolution using TaON-based photocatalysts.

Keywords: Ammonolysis; Hydrogen production; Oxynitride; Photocatalyst; Solid solution; Visible light; Water splitting

Influence of ceria and nickel addition to alumina-supported Rh catalyst for propane steam reforming at low temperatures by Yan Li; Xiaoxing Wang; Chao Xie; Chunshan Song (pp. 213-222).

Kinetic studies reveal that loading ceria and Ni onto alumina-supported Rh dramatically increases the propane reforming rates; adding CeO₂ promotes steam and propane adsorption and activation, while adding Ni mainly enhances C₃H₈ adsorption and activation.The influence of ceria and nickel addition to alumina-supported Rh catalyst for steam reforming of propane at low temperatures has been studied by preparing and examining 2wt%Rh/Al₂O₃, 2wt%Rh/20wt%CeO₂–Al₂O₃, and 2wt%Rh–5wt%Ni/20wt%CeO₂–Al₂O₃. TPR characterization showed that adding ceria makes rhodium oxide easier to reduce and the presence of rhodium also makes ceria easier to reduce through Rh–Ce interaction, whereas the addition of Ni makes Rh₂O₃ and ceria more difficult to reduce, likely due to Rh–Ni and Ce–Ni interactions. Adding ceria and nickel significantly improved the catalytic activity of Rh catalyst for propane conversion at 475°C. Kinetic study at different temperatures (450–650°C) indicated that the addition of ceria and Ni can greatly increase the propane reforming rates by lowering the activation energies from 67.6–68.8kJ/mol for 2Rh/Al to 50.1–50.4kJ/mol for 2Rh/20CeAl and to 42.1–42.5kJ/mol for 2Rh5Ni/20CeAl. The feed steam/carbon molar ratios corresponding to maximum reaction rates at 475°C increased from 2.0 for 2Rh/Al to 3.0 for 2Rh/20CeAl and 4.5 for 2Rh5Ni/20CeAl catalyst. A kinetic equation based on Langmuir–Hinshelwood model best fitting the experimental data was applied for the propane steam reforming over the Rh-based catalysts. Kinetic results at different partial pressures of propane and steam revealed that the addition of ceria could enhance the steam and propane adsorption, while the addition of Ni could significantly promote the propane adsorption, probably through working with Rh as propane adsorption sites.

Keywords: Catalyst; Rh; Alumina; Ceria; Ni; Steam reforming; Propane; Kinetics; Langmuir–Hinshelwood model

Spectroscopic study and catalytic evaluation of mesostructured Al-MCM-41 and Pt/H₃PW₁₂O₄₀/Al-MCM-41 catalysts by J.A. Wang; L.F. Chen; L.E. Noreña; J. Navarrete (pp. 223-235).

Grafting 12-tungstophosphoric acid on Al-MCM-41 could greatly enhance both the number and strength of Brönsted acidity. In the n-heptane hydroisomerization at an atmospheric pressure condition, high molar ratio of multibranched to monbranched isoheptanes was obtained over the heteropolyacid promoted Pt/H₃PW₁₂O₄₀/Al-MCM-41 catalysts. The unique selectivity of multibranched isoheptanes was related to ordered mesopore structure and strong surface acidity.Mesostructured Al-MCM-41 materials (referred as CSA n, where n=Si/Al molar ratio=50, 30 and 10, respectively) and 12-tungstophosphoric acid promoted Pt/Al-MCM-41 catalysts were investigated by a variety of spectroscopic techniques. Aluminum ions were distributed within the resultant solid having 4, 5 or 6-coordination, in different proportion, which correlate with the formation of Brönsted acidity. Grafting the H₃PW₁₂O₄₀ heteropolyacid (referred as HPW) on the Al-MCM-41 solids not only noticeably enhanced, by 2–3 times, the number of Brönsted acid sites, but also greatly improved the acidity strength, with respect to that of the bare host. The primary structure of the Keggin units of the supported heteropolyacid was largely preserved after calcination at 350°C; however, small parts of the Keggin units were strongly distorted or deformed due to the strong interaction between the heteropolyanions and the hydroxyl groups of the support. Catalytic evaluation confirmed that 1wt.%Pt/25wt.%HPW/Al-MCM-41 (denoted as Pt/HPW/CSA n) catalysts were very active for n-heptane isomerization in the presence of hydrogen under an atmospheric pressure condition. High yield of multibranched isoheptanes was produced, which was dependent on the pore diameter and the Brönsted acidity of the catalysts. The molar ratio of multibranched to monobranched isoheptanes is much higher than that reported in the literature under similar reaction conditions using zeolite-containing catalysts, showing the potential of producing high octane number fuel through the approach of n-heptane hydroisomerization by using our novel mesostructured catalysts.

Keywords: Al-MCM-41, H; ₃; PW; ₁₂; O; ₄₀; n-Heptane; Mesoporous catalyst; Hydroisomerization; Acidity

Methane decomposition over Ni–MgO–Al₂O₃ catalysts by Wojciech Gac; Andrzej Denis; Tadeusz Borowiecki; Leszek Kępiński (pp. 236-243).

Studies of methane decomposition were performed over nickel alumina catalysts modified with magnesia. The catalysts were obtained by the co-precipitation method. The properties of catalysts were investigated by the temperature programmed reduction (TPR) and hydrogen desorption (TPD) methods. Methane decomposition was studied by the thermogravimetric and transient temperature programmed reaction methods. The nature of carbon deposits formed under different reaction conditions was investigated by the temperature programmed oxidation method (TPO) and high resolution transmission electron microscopy (HRTEM). An introduction of magnesium to the preparation mixture of catalysts led to the formation of smaller nickel crystallites with stronger adsorption sites. It was found out that the activity of catalysts and the properties of carbon deposits were related to the catalysts composition and the reaction temperature. Carbon filaments with fishbone-like packed graphitic layers were formed at 500°C, while the multi-walled nanotubes were observed after reaction performed at 700°C. The increase of magnesium content led to the increase of the rate of methane decomposition at the initial stages of the reaction. Deactivation of the catalysts was related to the insufficient removal of carbon species from the surface of nickel crystallites and the formation of stable, graphitic carbon deposits covering the surface of metal.Methane decomposition was studied over nickel–magnesia–alumina catalyst. An increase of the reaction temperature caused transformation of the carbon filaments with fishbone-like graphitic layers to the multi-walled nanotubes with nickel crystallites located on the tip. The deactivation of the catalysts was related to the insufficient removal of the stable carbon deposits from the surface of nickel crystallites.

Keywords: Hydrogen; Carbon nanomaterials; Nickel catalyst; Deactivation; HRTEM

Role of metals loaded on a TiO₂ surface in the oxidation of xylene in air using an electron beam irradiation/catalytic process by Teruyuki Hakoda; Kanae Matsumoto; Akira Mizuno; Koichi Hirota (pp. 244-249).

Catalytic oxidation of xylene in air was performed under electron beam (EB) irradiation using pure TiO₂ as well as TiO₂ loaded with Ag, Pt, Au, or Mn to clarify the role of loaded metal in the enhancement of oxidation of xylene and its irradiation byproducts to CO₂ in EB-induced non-thermal plasmas. EB irradiation experiments were performed with the catalyst bed placed in both irradiated and non-irradiated spaces. The highest conversion percentage of decomposed xylene to CO₂ was obtained by irradiation/catalytic oxidation using an Ag/TiO₂ bed placed in a non-irradiated space. The greater enhancement of CO₂ production on an Ag/TiO₂ pellet surface compared to that on other metal-loaded TiO₂ pellet surfaces was due to the synergetic effect of strong adsorption of the byproducts on the Ag loaded on TiO₂ and production of active oxygen from decomposition of O₃ in the presence of Ag.This work aimed at clarifying the role of metal loaded on TiO₂ in enhancing the oxidation of organics in electron-beam-induced non-thermal plasmas. The CO₂ production abilities of TiO₂ loaded with various metals were evaluated. Ag/TiO₂ had the greatest CO₂ production ability because of the synergy between adsorption of organics and production of active oxygen from O₃ decomposition.

Keywords: Non-thermal plasma; TiO; ₂; Metal-loaded TiO; ₂; Electron beam; Xylene

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Applied Catalysis A, General (v.357, #2)