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Partial oxidn. of toluene on V/Ti oxide catalysts is a reaction of industrial interest. In spite of the detailed study of the nature of surface vanadia species, there is an evident lack of the information concerning their reactivity. The present work demonstrates an application of the transient response techniques in combination with \"in situ\" DRIFT and FT-Raman spectroscopy for the discrimination of the reactivity of different vanadia species. Catalysts consisting of 0.35-3.7 monolayers of vanadia on titania were studied. In anaerobic conditions, conversion of toluene to benzaldehyde (BA) with selectivity close to 100% was found. BA is formed mainly by nucleophilic (O2-) oxygen in isolated monomeric vanadia species, while electrophilic oxygen (O-) present in polymeric and bulk vanadia species is responsible for the formation of carbon oxides. An addn. of potassium was obsd. to increase the yield of BA. [on SciFinder (R)]

Hydrogen prodn. from toluene by steam reforming, partial oxidn. and autothermal reforming was studied by step-response method in a tubular fixed-bed reactor, at temps. between 550 Deg-700 Deg. Nickel in the form of a wire grid is a valuable catalyst, whereas an addn. of palladium acts as a promoter for water formation. [on SciFinder (R)]

This study addresses the development of a compact reactor for oxidative steam-reforming of methanol (OSRM) to produce hydrogen in autothermal mode for fuel cells. The string reactor uses catalytically active brass wires with a diameter of 500 mu m placed in parallel into a tube. The micro-channels in the reactor for gases are formed between the wires presenting hydrodynamics similar to the one in multi-channel micro-reactors. Due to the high thermal conductivity of brass, the heat generated during methanol oxidation at the reactor entrance is transferred to the zone of the endothermic steam-reforming. The catalysts are prepared by Al-alloy formation on the surface of the brass wires followed by the partial leaching of Al. The catalyst presents a porous layer with the morphology of Raney metals and the chemical composition consistent with the Cu/Zn/Al-mixed oxide. The catalyst surface was additionally modified by incorporating chromium leading to Cr/Cu-spinel. This decreases the degree of the reduction of copper oxide and sintering leading to a stable catalyst. The catalyst was tested in OSRM showing high activity and selectivity to carbon dioxide and hydrogen. The string reactor presents nearly isothermal profile since the temperatures gradient within the reactor length is about 3 K. Micro-structured string reactor presents a short start-up and a fast transient behavior showing a rapid temperature change when adjusting the oxygen amount introduced into the reactor. (c) 2006 Elsevier B.V. All rights reserved.

Magnetic resonance microimaging (MRM) was employed to obtain quantitative velocity maps of water flowing in the channels possessing unconventional cross-section shapes formed by a bundle of parallel fibers within a tubular string-type reactor. The maps obtained demonstrate the presence of large amounts of an almost stagnant liquid in the stretched corners of the cross-sections representing distorted triangles or squares. This fact together with the irregularity of the filaments packing in the model string-type reactor was demonstrated to lead to a broad residence time distributions (RTDs) for liquid flow. Next, the pulsed field gradient NMR (PFG NMR) technique was employed to compare transport of water with that of butane gas in the same model string-type reactor. The experimentally measured average propagators (travel distance probability density functions) have demonstrated that Taylor dispersion can lead to much better RTDs for gas as compared to liquid in channels with sub-millimeter equivalent diameters. The PFG NMR data were compared with the RTD obtained using the conventional tracer time-of-flight transient response method. It is concluded that due to the differences in the quantities actually measured by the two techniques, and the significant differences in the measurement length scales (microns to 1–2 cm for NMR/MRM, tens of centimeters for transient response methods), there is no reliable way of directly comparing these results. The information obtained by NMR/MRM and more conventional techniques such as time-of-flight should be considered as complementary. In particular, NMR/MRM can reveal the reasons for the observed overall reactor performance by providing access to the transport processes on short length scales inside the reactor and by revealing structure–transport interrelations

A novel composite material based on carbon nanofibers (CNF) grown on sintered metal fibers (SMFInconel) filter was investigated for its favorable properties as catalytic support. The CNF were formed directly over the SMFInconel by thermal (650 degrees C) chemical vapor deposition of ethane-hydrogen mixture. The CNF/SMFInconel composite consists of metal fibers entangled by CNF network of microns thickness and strongly anchored to the metal surface. The properties of the CNF/SMFInconel were controlled by the synthesis conditions. The CNF coating reduced the filter porosity and decreased the material permeability, but the pressure drop during the gas passage through the reactor remained low for CNF fraction < 10 %. Palladium was deposited on CNF previously activated by boiling in hydrogen peroxide. The activity and selectivity of Pd degrees/CNF/SMFInconel catalysts were tested in the selective hydrogenation of acetylene and compared with Pd supported on activated carbon fibers (Pd degrees/ACF). The TOF was one order of magnitude higher for Pd degrees/CNF/SMFInconel as compared to Pd degrees/ACF. This effect was attributed to a strong metal-support interaction of Pd degrees-nanoparticles with the graphitized CNF. The reaction was found to be structure sensitive leading to a decrease of TOF for the Pd degrees-particles < 3 nm.

Accelerated bleaching and photobleaching of diluted solutions of Methyl Orange and other dyes occur only when Co2+-ions are present in solution mediating oxone (2KHSO(5)center dot KHSO4 center dot K2SO4) decomposition. The bleaching of Methyl Orange, Orange II and Methylene Blue dyes in dilute solutions (0.01 mM) proceeds within a few minutes and occurs at biocompatible pH leading to a decrease in the toxicity of the initial solution under simulated daylight radiation. A reduction in the toxicity of 35% was observed at biocompatible pH-values when a solution Orange II (0.01 mM) was irradiated in the presence of oxone (0.06 mM)/Co2+ (0.004 mM). Only traces of Co2+ were necessary to accelerate the decomposition of the dyes in the presence of oxone in the dark and even more under daylight irradiation. The photobleaching proceeds with a photonic efficiency of similar to 0.24. The solution parameters were optimized for the photobleaching of azo-dyes by the oxone/Co2+ reagent. H2O2 generation was observed to be possible only as long as Orange II was present in the solution. The decomposition kinetics of H2O2 was followed under solar radiation. The dye decomposition was also investigated as a function of the applied light intensity. No saturation effects were observed when simulated solar light with 90% AM1 was applied. The photobleaching reaction proceeded with acceptable kinetics with light intensities 5-10 times lower than AM1. This makes the photocatalytic treatment suitable under diffuse daylight. (c) 2006 Elsevier B.V. All rights reserved.

Gas phase methylation of catechol by methanol over modified gamma-alumina catalysts is studied experimentally. The catalyst composition and the reaction conditions are optimized to attain the highest selectivity towards 3-methylcatechol (C-methylation) or guaiacol (O-methylation and to diminish the catalyst deactivation. The modified gamma-alumina {Li+ 3 % Mg2+ 5 %/gamma-Al2O3} was found to be the best with respect to the 3-methylcatechol formation. At 350 degrees C and at a conversion level of 28% the selectivity of 92% towards 3-methylcatehcol was reached. The deactivation was observed to be lower if compared to pure gamma-alumina. Selectivity towards guaiacol formation increased with surface acidity and reached 89% over phosphated gamma-alumina at 270 degrees C. The catalyst structure was determined with a high confidence factor via "full-profile X-ray analysis". The experimental data relating to activity/selectivity as well as catalyst stability to coke formation were explained from the model found for the catalyst structure.

Gold nanoparticles were supported on activated carbon fibers (ACF) using the aq. soln. of [Au(en)2]Cl3 via ion-exchange with surface hydroxyl groups followed by redn. in H2. The obtained catalysts were tested in CO oxidn. at room temp. Surface phenolic groups fix Au3+-ions leading to the formation of small Au particles (.apprx.5 nm) after the redn. with high activity in the reaction. AAS, TPD, HRTEM/EDAX and XPS were used for characterization of the catalysts and supports.

NOVELTY - A 2-butene-1,4-diol is prepared by hydrogenating 2-butyne-1,4-diol in the presence of a structured catalyst and in the absence of a solvent. USE - For preparing 2-butene-2,4-diol that is an important industrial intermediate in the preparation of vitamin B6, pharmaceuticals, and insecticides. ADVANTAGE - The 2-butene-1,4-diol can be prepared in high yield and selectivity by catalytic hydrogenation of 2-butyne-1,4-diol over a structured catalyst in the absence of a solvent. Since hydrogen is sparingly soluble in solvents, e.g. water, the absence of such solvents increases the economy of the hydrogenation process in that it results in higher turnover per time unit. The process avoids separation and recycling of a solvent for environmental protection.

Formation of vanadia species during the calcination of ball milled mixt. of V2O5 with TiO2 was studied by Raman spectroscopy in situ and at ambient conditions. Calcination in air leads to fast (1-3 h) spreading of vanadia over TiO2 followed by a slower process giving a monolayer vanadia. The calcinated catalyst showed higher activity during toluene oxidn. than the uncalcinated one, but the selectivity towards C7-oxygenated products (benzaldehyde and HOBz) remains unchanged. The activity of the catalysts is ascribed to the formation of vanadia species in the monolayer. The details of the parallel-consecutive reaction scheme of toluene oxidn. are presented from steady-state and transient kinetics studies. Different O species seem to participate in the deep and partial oxidn. of toluene. Coke formation was obsd. during the reaction presenting an av. compn. C2nH1.1n. The amt. of coke on the catalyst was not dependent on the calcination step and the V content in the catalyst. Coke formation is responsible for the deactivation of the catalyst. [on SciFinder (R)]

The title bed is developed with in situ cryst. growth of zeolite ZSM-5 on different supports; metallic grids and glass fibers. The materials are characterized by diverse physicochem. methods. The chem. pretreatment of the support is a crucial parameter for regular crystal deposition. Partial oxidn. of benzene to phenol with N2O serves as a model reaction for studying the efficacy of this type of coating. [on SciFinder (R)]

The reaction of catechol methylation by methanol in gas-phase over modified g-alumina was studied with the aim to correlate catalytic activity and selectivity to acid/base properties of the catalysts. Catalytic activity and selectivity towards guaiacol formation (O-alkylation) was found to increase with surface acidity. A 20-fold change in the O/C-methylation ratio was achieved by varying the catalyst acid/base properties, keeping const. the other reaction parameters.

The repetitive discoloration kinetics of the azo-dye Methyl Orange (taken as a model organic compound) was followed under solar simulated radiation (90 mW/cm2) to assess the performance of the TiO2/Tedlar® composite photocatalyst. The influence of solution parameters on the photo-discoloration process: pH, dye concentration, applied light intensity and concentration of H2O2 were systematically investigated. During the photocatalysis a modification occurs in the TiO2/Tedlar® composite due to the TiO2 interaction with the Tedlar® film. Physical insight is given for the stabilization mechanism of the TiO2 particles in the Tedlar matrix based on the data obtained by X-ray photoelectron spectroscopy (XPS). The F 1s peak of the Tedlar film indicates that the TiO2 is loaded on the Tedlar fluoro-groups. The loading of TiO2 on the 75 μm thick Tedlar® film was 0.9% (w/w) as determined by atomic absorption spectrophotometry (AAS). Attenuated total reflection infrared spectroscopy (ATRIR) shows no formation of additional bands within the photodiscoloration reaction. This shows that an efficient catalysis taking place on the TiO2/Tedlar® surface. The rugosity (mean square roughness, rms) of the TiO2/Tedlar® film was determined by atomic force microscopy (AFM) to be 19.7 nm. This value remained constant during long-term operation. Transmission electron microscopy (TEM) reports the thickness and coverage of TiO2 Degussa P-25 on the Tedlar® surface before and after photocatalysis.

Hydrogen production by non-thermal plasma (NTP) assisted direct decomposition of hydrogen sulfide was carried out in a novel dielectric barrier discharge (DBD) reactor with the inner electrode made of sintered metal fibers (SMF) also functioning as catalyst. The discharge gap between the electrodes and the gas residence time in the discharge was optimized to achieve hydrogen production in an economically feasible manner. Typical results indicate that hydrogen production can be achieved at 160 kJ/mol H-2 (2 kWh/m(3) or 1,6 eV/molecule), which is less than the energy demand during the steam methane reforming (4.3 kWh/m(3) or 3.6 eV/ H-2), the conventional method of hydrogen production.

One-step hydroxylation of benzene to phenol by N2O has been performed over structured catalytic beds made of ZSM-5 coatings on stainless steel grids. The catalysts demonstrated high activity with a selectivity toward phenol formation of 98%. A detailed kinetic study was carried out with a variation in reactant concentrations, benzene/N2O ratio, and residence time. The results obtained suggest a surface reaction between benzene and nitrous oxide adsorbed on two different active sites.