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Applied Catalysis A, General (v.313, #2)
Photocatalytic properties of TiO2 modified with gold nanoparticles in the degradation of oxalic acid in aqueous solution by V. Iliev; D. Tomova; R. Todorovska; D. Oliver; L. Petrov; D. Todorovsky; M. Uzunova-Bujnova (pp. 115-121).
The commercially available TiO2-catalyst (Degussa P25) was supported by spray pyrolysis deposition method on the outer surface of the quartz tubes, incorporated in photocatalytic reactor. The crystal structure and the morphology of the films were studied. The immobilized TiO2 is modified with nanosized gold particles by the photoreduction method to obtain different noble metal loading (0.05–0.4wt.%). The characterization of the synthesized catalysts was carried out by the BET method, X-ray photoelectron spectroscopy (XPS), SEM, TEM and the adsorption of the model pollutant was determined. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized gold particles. The presence of low amounts of gold on the TiO2 surface leads to an increase of its photocatalytic activity. The maximum value of the photocatalytic activity was registered with the ≈0.16wt.% Au on TiO2 sample. At this concentration the activity of the Au-modified TiO2 is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir–Hinshelwood model.
Keywords: Gold; TiO; 2; Spray pyrolysis; Photocatalytic decomposition; Oxalic acid; XPS; TEM
Silica-bound imidazole as a heterogeneous axial ligand for Mn(salophen)Cl: Efficient, recoverable and recyclable catalyst for epoxidation of alkenes and hydroxylation of alkanes with sodium periodate by Valiollah Mirkhani; Majid Moghadam; Shahram Tangestaninejad; Bahram Bahramian (pp. 122-129).
Choloropropylated silica-gel reacts with imidazole to give imidazole modified silica, which can bound to manganese(III) salophen complex via ligand-to-metal coordination bond. Silica-bound imidazole (SiIm), is not only a heterogeneous axial base but also is a support for immobilization of Mn(III) salophen. The catalyst, Mn(salophen)Cl-SiIm, has been characterized by FT-IR, UV–vis spectroscopic techniques, SEM, thermal and elemental analysis. Mn(salophen)Cl-SiIm catalyze alkene epoxidation with sodium periodate as oxidant at room temperature. The effect of reaction parameters such as solvent and oxidant in the epoxidation of cis-cyclooctene were investigated. This catalytic system shows a good activity in the epoxidation of linear alkenes, which is higher than the homogeneous analogs, Mn(salophen). Alkylaromatics and cycloalkanes were oxidized efficiently to their corresponding alcohols and ketones in the presence of this catalyst. The obtained results showed that this catalyst is a robust and stable heterogeneous catalyst and can be recovered quantitatively by simple filtration and reused without loss of its acivity.
Keywords: Silica; Manganese salophen; Periodate; Epoxidation; Hydroxylation
DRIFTS and DRS studies of Phillips ethylene polymerization catalysts by V.N. Panchenko; V.A. Zakharov; E.A. Paukshtis (pp. 130-136).
Formation of the CrO3/SiO2 catalyst prepared by the reaction of CrO3 vapor with silica pre-dehydroxylated at 250–800°C was studied by the DRIFT and DRS methods. It was found that CrO3 reacts with the silica OH-groups at 250°C to produce various chromate species and water. The latter is removed from the catalyst surface by vacuumation at 250°C. It was found the nature of CrO3 interaction with silica and the structure and composition of the surface species depend on silica dehydroxylation temperature. The reactions of CrO3 with the silica dehydroxylated at 250, 400 and 800°C yielded, respectively, monochromates; mono- and dichromates; polychromates. The catalyst activity at ethylene polymerization strongly increases with increasing dehydroxylation temperature, especially in the range of 250–400°C. The results obtained prove di- and polychromates to be the active components of the Phillips type chromium-oxide catalysts from which the active centers are formed at interaction of the active component with co-catalyst (AlEt3) and ethylene. Active centers contain the surface organo-chromium compounds with chromium ions in low oxidation states (lower than Cr(VI)).
Keywords: Phillips catalyst; Chromium-oxide catalyst; Ethylene polymerization; CrO; 3; Silica; DRS; DRIFTS
Nano-structured nickel–molybdenum carbide catalyst for low-temperature water-gas shift reaction by Masatoshi Nagai; Amin Md. Zahidul; Kenji Matsuda (pp. 137-145).
The water-gas shift (WGS) reaction over nickel–molybdenum (Ni–Mo) carbide catalysts was investigated at 453K. The oxide precursors and the carburized catalysts were characterized based on the adsorption of N2 and CO, XRD, high-resolution tunnel electron microscopy (HRTEM), temperature-programmed reaction with 20% CH4/H2 or with He, and X-ray photoelectron spectroscopy. The 873K-carburized Ni0.25Mo0.75 catalyst (Ni0.25Mo0.75C-873) exhibited the highest rate of CO conversion among the catalysts carburized at 823, 923, and 973K with various Ni contents. The Ni0.25Mo0.75C-873 catalyst contained β-Mo2C and amorphous Ni–Mo oxycarbide (NiMoC3.6O1.4) which turned to Ni6Mo6C after being heated under flowing He. The TEM image showed that Ni0.25Mo0.75C-873 consisted of Ni particles dispersed on plate-like sheets of β-Mo2C and amorphous Ni–Mo carbides.
Keywords: Ni–Mo; Carbide; Water-gas shift; Low temperature; XRD; XPS; TPC
Solvent free esterification reactions using Lewis acids in solid phase catalysis by Sandro L. Barbosa; Miguel J. Dabdoub; Gabriela R. Hurtado; Stanlei I. Klein; Adriano C.M. Baroni; Christielle Cunha (pp. 146-150).
A clean, efficient and fast method for esterification reactions for sterically (biodiesels) or otherwise inactive (aromatic) precursors was developed, using catalysts supported in a solid phase under “solvent free� conditions, and whose reactions can be promoted by MW irradiation.
Keywords: Esterification; Solid phase catalysis; Microwave; Solvent free
Mesoporous smectites incorporated with alkali metal cations as solid base catalysts by Shin-Ichiro Fujita; Bhalchandra M. Bhanage; Daishi Aoki; Yuri Ochiai; Nobuhiro Iwasa; Masahiko Arai (pp. 151-159).
A series of magnesium containing mesoporous smectites incorporated with alkali hydroxide (NaOH, KOH or LiOH) has been prepared and employed for such base-catalyzed model reactions as transesterification of ethyl acetate with methanol, Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate and one-pot synthesis of dimethyl carbonate (DMC) from propylene oxide, carbon dioxide and methanol. The effects of the quantity and kind of the incorporated alkali atoms on the catalytic properties of the smectites were investigated. Characterization of the smectites has shown that the incorporation of alkali atoms reduces their surface area and total pore volume but enhances the amount and strength of their basic sites. The product yield of the transesterification was increased with the content of alkali atoms incorporated. It has been suggested that the moderately basic sites are responsible for this reaction. The yield of the Knoevenagel reaction depends little on the alkali atom content. Increasing the content of alkali atoms causes the increase in the DMC yield of the one-pot synthesis and the decrease in the yield of methanolysis of propylene oxide, which is the side reaction of the one-pot synthesis. The incorporation of Li was less effective than Na and K for the one-pot reaction. The structures of basic sites over the alkali-incorporated smectites have been discussed.
Keywords: Mesoporous materials; Alkali metal hydroxide; Transesterification; C–C bond formation; Carbon dioxide; Chemical fixation
Distribution of Brønsted acid sites on beta zeolite H-BEA: A periodic density functional theory calculation by Harunori Fujita; Tomonori Kanougi; Takashi Atoguchi (pp. 160-166).
We performed a density functional theory calculation of a beta zeolite (H-BEA) crystal unit cell containing two Al atoms and two protons. Two protons were put in a zeolite framework in order to compensate the excess charge caused by the substitution of Si (4+) atoms by Al (3+) atoms. These protons act as Brønsted acids. Thus, our unit cell model contains two Brønsted acids distributed among possible T sites of zeolite framework. The overall structure was optimized in a periodic boundary condition. In the most stable structure, we found that these two Brønsted acid sites were mutually spatially very close. In addition, we found in this stable structure that two protons were shared by a hydrogen bond between these Brønsted acid sites. This hydrogen bond was revealed to be a cause of the stability of the most stable positioning of the two Brønsted acid sites.
Keywords: H-BEA; Periodic DFT; Brønsted acid site; Hydrogen bond; Acid site distribution
Pore-size distributions from nitrogen adsorption revisited: Models comparison with controlled-pore glasses by O. Šolcová; L. Matějová; P. Schneider (pp. 167-176).
For the comparative study focused on comparison of models for evaluation of pore-size distributions (PSD) from nitrogen physical adsorption isotherms (at 77K) a series of controlled-pore glasses (CPG10) with wide range of nominal pore sizes was used.The absence of micropores in CPG10 samples was proved by comparing adsorption isotherms at low relative pressures, x. This permitted construction of the dependence of adsorbed film thickness, t, on x [ t( x)] commonly used in evaluation of textural properties of porous samples.Fifteen models for cylindrical pore geometry based on the Barret, Joyner and Halenda (BJH) and Broekhoff and deBoer (BdB) approaches with different t( x) dependencies and two evaluation algorithms were compared. Additionally a model which is based on modified non-local density functional theory with density-dependent weights and Tarazona prescription (NLDFT) was applied. It appears that the BdB model, which uses the t( x) dependence obtained for CPG10, produces PSD's from adsorption and desorption isotherm branches located at the same pore radius.
Keywords: Pore size distribution; Physical adsorption; Standard nitrogen isotherm; Texture properties; Corning porous glass
Sunflower oil hydrogenation on Pd/Al2O3 catalysts in single-phase conditions using supercritical propane by C. Piqueras; S. Bottini; D. Damiani (pp. 177-188).
Several Pd catalysts were prepared on α and γ alumina using palladium acetylacetonate and palladium nitrate as a precursor. The characterization of these catalysts by H2 chemisorption, XRD and TEM microscopy confirm the presence of different dispersed metallic particles from 1.9 to 12.1nm. These catalysts were tested in the sunflower oil hydrogenation under supercritical conditions using propane as solvent and 5% mol of hydrogen concentration. The well-known Weisz–Prater criterion was used to determine the extent of mass transport phenomena. While hydrogen mass transport was found free from limitations, oil transport had limitations in some experiments. The reaction is moderately structure sensitive since the turnover number decreases 3 times as the exposed metal percentage (metal dispersion) increases from 9 to 60%. An influence on the selectivities to trans isomers, monounsaturated and saturated fatty acids was found when the metallic particle size was decreased. These results are explained by the high adsorption strength of the high-unsaturated fatty acids onto the small particles and the promotion of a “shunt� reaction from linoleic to saturated compounds.
Keywords: Hydrogenation; Sunflower oil; Propane; Supercritical fluid
n-Octane aromatization over Pt/KL of varying morphology and channel lengths by Supak Trakarnroek; Siriporn Jongpatiwut; Thirasak Rirksomboon; Somchai Osuwan; Daniel E. Resasco (pp. 189-199).
Various Pt/KL catalysts were prepared over a series of zeolites with different crystallite size and shape. To control the crystallite size and shape and consequently the channel lengths, different zeolite synthesis parameters were varied. X-ray diffraction (XRD) analysis of the synthesized KL zeolites indicated a high degree of crystallinity in all samples. The crystallite morphologies and the length/diameter (L/D) ratios in each sample were characterized by scanning electron microscopy (SEM). The Pt/KL catalysts were prepared by loading 1wt% of Pt on these supports, using the vapor phase impregnation (VPI) method. They were characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO, volumetric hydrogen chemisorption, and transmission electron microscopy (TEM).It was found that KL zeolites with cylindrical shape are effective catalyst supports for n-octane aromatization, but the effectiveness strongly depends on the channel length of the zeolite crystallite as well as the dispersion and location of the Pt clusters. The different Pt/KL catalysts in the series were compared in the aromatization of n-octane at 500°C and atmospheric pressure. It was found that the catalysts with shorter channel length exhibited improved activity, selectivity, and catalyst life.Some of these differences can be ascribed to a different distribution of Pt clusters and different metal dispersions. That is, while the cylindrical-shape KL zeolites with short channels (i.e., cylindrical crystallites with low L/D ratio) favored a high dispersion of Pt inside the zeolite, those with longer channels (i.e., high L/D ratio) resulted in a large fraction of Pt cluster outside the zeolite. By contrast, KL zeolites synthesized with nanosize crystallites and having a high external-to-internal surface area ratio yield much lower Pt dispersions and exhibited a large fraction of Pt clusters located outside the pores, which can explain the differences in activity and selectivity. On the other hand, differences in aromatic product distribution observed for the different morphologies are related to a varying extent of secondary reactions. That is, for a given conversion level, the catalysts with shorter channels had a much lower extent of secondary hydrogenolysis. Consequently, more C8-aromatics are preserved in the product and less benzene and toluene are produced compared to the catalysts with longer channels.
Keywords: n; -Octane aromatization; Pt/KL zeolite; Vapor phase impregnation; DRIFTS; TPO
Catalytic oxidation of thiophenes and thioethers with hydrogen peroxide in the presence of W-containing layered double hydroxides by Vasile Hulea; Alina-Livia Maciuca; François Fajula; Emil Dumitriu (pp. 200-207).
Layered double hydroxides (LDH) with Mg2+ and Al3+ cations in the brucite-like layer and W-containing anions in the interlayer have been prepared by direct ion exchange of a MgAl-NO3 LDH precursor with tungstate anions. The W-containing catalysts have been characterised by elemental chemical analysis, powder X-ray diffraction, Raman and UV-DR spectroscopies, thermogravimetric analysis and nitrogen adsorption. The results indicate the presence of both WO42− and W7O246− anions in the interlayer gallery. The catalytic oxidation of organic sulfides and thiophene derivatives using hydrogen peroxide as oxidizing agent, in the presence of W-containing layered double hydroxide as catalyst, was investigated using various organic solvents miscible with water. It was found that W-containing LDHs are active catalysts promoting the fast oxidation of sulfur containing organic compounds with 30% H2O2 under very mild reaction conditions, but the catalytic activity depends on the nature of the W-containing anions. Other factors, like as the structure of the sulfur-containing organic compounds, the reaction temperature and solvent also influence the catalytic conversion.
Keywords: Layered double hydroxide; Tungsten; Oxidation; Hydrogen peroxide; Dibenzothiophene; Thioethers
Heats of adsorption of the linear and bridged CO species on a Ni/Al2O3 catalyst by using the AEIR method by Salim Derrouiche; Daniel Bianchi (pp. 208-217).
The heats of adsorption of the adsorbed CO species on Ni supported catalysts are rarely studied by using classical analytical methods (i.e. microcalorimetry and temperature programmed desorption (TPD)) due to experimental difficulties linked to different parallel surface reactions to the adsorption/desorption processes. In the present study, the heats of adsorption of the linear and bridged CO species (denoted L and B CO, respectively) on a reduced 20% Ni/Al2O3 catalyst are studied by using the adsorption equilibrium infra red method developed previously. After a stabilization procedure of the catalyst, the evolutions of the IR bands of the L and B CO species: 2053 and 1927cm−1, respectively, at Ta=500K and Pa=1kPa, with the adsorption temperature Ta are studied at a constant adsorption pressure Pa. These data provide the evolutions of the coverages θL= f( Ta) and θB= f( Ta) of the two adsorbed CO species with the increase in Ta in isobar conditions. These curves allow us to determine the heats of adsorptionELθL andELθB of the L and B CO species for several values of the coverage θL and θB according to an adsorption model, i.e. EL1=100, EL0=153, EB1=106 and EB0=147kJ/mol at coverages 1 and 0, respectively. These values are consistent with literature data on Ni single crystals. In particular, it is shown that the mathematical formalism of the AEIR method can be applied to literature data on Ni(111) providing ECO θ values similar to those of the present study showing the limited impact of the Ni particle size on the CO adsorption properties. The presence of hydrogen (2% CO/10% H2/He) during the measurement decreases slightly the coverages of the two CO species at high temperatures due to either a decrease in the heats of adsorption (i.e. EL1=97, EL0=131, EB1=89 and EB0=138kJ/mol) or the perturbation of the adsorption equilibrium by hydrogenation of the adsorbed CO species.
Keywords: Carbon monoxide; Chemisorption; Nickel; Alumina; FTIR; Heat of adsorption; Adsorption model
Photocatalytic activities of M2Sb2O7 (M=Ca, Sr) for degrading methyl orange by Xinping Lin; Fuqiang Huang; Wendeng Wang; Yaoming Wang; Yujuan Xia; Jianlin Shi (pp. 218-223).
M2Sb2O7 (M=Ca, Sr) photocatalysts were synthesized by a solid state reaction method. The results concerning methyl orange (MO) photodecomposition generally show that the catalytic efficiency of Sr2Sb2O7 is much higher than that of Ca2Sb2O7 under UV light irradiation. The more open structure in Sr2Sb2O7 is suggested to be responsible for its higher photocatalytic activity. In the investigation on pH-dependent photocatalysis over Sr2Sb2O7 catalyst, the pseudo-first reaction rate k was found to be increased by about six times as the pH value decreases from 6.88 to 3.91. We believe that the decolorization of MO in neutral or alkaline conditions is primarily through a photocatalytic process, while the MO photosensitization and photolysis mechanisms play more important roles in acidic conditions.
Keywords: Photocatalysis; Ca; 2; Sb; 2; O; 7; Sr; 2; Sb; 2; O; 7; MO