Novel Catalytic Dielectric Barrier Discharge Reactor for Gas-Phase Abatement of Isopropanol

Catalytic gas-phase abatement of air containing 250ppm of isopropanol (IPA) was carried out with a novel dielectric barrier discharge (DBD) reactor with the inner catalytic electrode made of sintered metal fibers (SMF). The optimization of the reactor performance was carried out by varying the voltage from 12.5 to 22.5kV and the frequency in the range 200-275Hz. The performance was significantly improved by modifying SMF with Mn and Co oxide. Under the experimental conditions used, the MnO x /SMF showed a higher activity towards total oxidation of IPA as compared to CoO x /SMF and SMF electrodes. The complete destruction of 250ppm of IPA was attained with a specific input energy of ∼235J/L using the MnO x /SMF catalytic electrode, whereas, the total oxidation was achieved at 760J/L. The better performance of the MnO x /SMF compared to other catalytic electrodes suggests the formation of short-lived active species on its surface by the in-situ decomposition of ozon

Catalytic activity of FeZSM-5 zeolites in benzene hydroxylation by N2O: The role of geometry characterized by fractal dimensions

The fractal dimensions of FeZSM-5 zeolites were used to characterize the change in their geometry depending on different post-synthesis treatments. The fractal dimension values were estimated from the Dubinin-Astakhov isotherms of nitrogen adsorption and related to the activity of these zeolites in the benzene hydroxylation to phenol by nitrous oxide. The zeolites had two different iron contents (350 and 5800 ppm) and a Si/Al ratio of 42. The catalysts were activated by steaming (823 K) and/or calcinations in He (1323 K). The FeZSM-5 activated by steaming exhibited fractal dimensions lower than the samples activated by calcinations. The steamed samples also had activities in the benzene hydroxylation per Fe(II) site (TOF values) somewhat higher as compared to the zeolites activated by calcinations. This indicates the importance of the zeolite geometry for the reaction of bulky benzene molecule within a confined space. (c) 2005 Elsevier B.V. All rights reserved

Detoxification of diluted azo-dyes at biocompatible pH with the oxone/Co2+ reagent in dark and light processes

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

Structure sensitivity of selective acetylene hydrogenation over the catalysts with shape-controlled palladium nanoparticles

The structure sensitivity of acetylene hydrogenation on catalysts with controlled shape of palladium nanoparticles was studied. Palladium particles of cubic (Pdcub), cuboctahedral (Pdco) and octahedral (Pdoct) shapes were obtained by a colloidal method. Poly(N-vinyl)pyrrolidone (PVP) was used as the stabilizer of colloidal solutions. In order to eliminate the effect of the polymer on the properties of the catalyst, PVP was removed from the surface of the particles after their transfer to the support by simultaneous treatment with ozone and UV radiation. This allowed complete cleaning of the catalyst surface from the organic stabilizer without any change in the morphology of particles. The effectiveness of this treatment method was confirmed by X-ray photoelectron spectroscopy and scanning electron microscopy. It was found experimentally that the shape of nanoparticles does not influence the catalyst selectivity, but the activity decreases in the order Pdoct > Pdco > Pdcub. Since octahedrons consist of (111) faces, the cubes contain only (100) faces, and the cuboctahedrons are composed of faces of both types, Pd111 is more active than Pd100. Calculations with the use of a statistical method showed that the ∼3-nm Pd octahedrons are nanoparticles with optimum shape and size, giving maximum catalyst activit

Combined XPS and TPD study of oxygen-functionalized carbon nanofibers grown on sintered metal fibers

A novel composite material consisting of carbon nanofibers (CNF) grown on sintered metal fibers (SMF) filters was modified by H2O2 or plasma-generated O3. Coupling TPD and XPS techniques in the same UHV apparatus allowed the direct correlation between the nature of the created O-functional groups and their evolution as CO and CO2 upon heating. The two oxidative treatments yielded different distributions of O-containing groups. The relative contribution of oxidized carbon was very low in the C1s region, so the functional groups were better analyzed in the O1s region. The quantification of the released oxygen by integration of the TPD CO, CO2 and H2O spectra, compared with the intensity loss of the XPS O1s spectra showed a good agreement. In order to fit the data adequately, the set of O1s spectra was decomposed in at least four peaks for the differently activated samples. Finally, it was shown that functional groups formed by H2O2-treatment (mostly non-phenolic OH groups) are thermally more stable than the ones formed by O3-treatment. The latter treatment increases the concentration of carboxylic functionalities, which decomposes at temperatures < 800 K; O3-activated CNF therefore should show a more pronounced acidic behavior

Membrane reactor microstructured by filamentous catalyst

A novel design of microstructured membrane reactor with micro-channels formed between closely packed catalytic filaments is reported. The system comprises filaments of 7 mm in diam. and has a laminar flow with a short radial diffusion time. This leads to low pressure drop and to a narrow residence time distribution (RTD) during reactor operation. The latter device in combination with a membrane permeable to hydrogen is used in non-oxidative propane dehydrogenation. The catalytic filaments of Pt/Sn on alumina were active/selective and sustained periodic regeneration. This innovative micro-reactor system allowed to control the selectivity to propene due to a narrow RTD. At propane conversions exceeding equil., selectivities towards propene up to 97% were attained. [on SciFinder (R)

Hydrogen production by catalytic cracking of methane over nickel gauze under periodic reactor operation

The catalytic cracking of methane over nickel gauze is proposed as an attractive alternative for the prodn. of CO-free hydrogen. The catalyst deactivates due to intensive coke deposition. Therefore, the reactor was operated periodically with the reaction followed by the catalyst regeneration by burning of coke in oxidative atm. The optimal reaction performance was found to consist of reaction periods of 4 min followed by 4 min regeneration periods. [on SciFinder (R)

Novel membrane reactor with filamentous catalytic bed for propane dehydrogenation

A novel membrane reactor with two zones containing structured filamentous catalytic beds was proposed for propane nonoxidative dehydrogenation. Catalytic filaments with a similar to7 similar to mum diameter consist of silica cove-red by porous alumina with 0.5% Pt/1% Sn. These filaments were placed in parallel in a tubular membrane reactor. The hydrodynamic characteristics of the reactor correspond to the properties of a multichannelled microreactor with laminar flow, a low pressure drop, and a narrow residence time distribution. A propane conversion of 0.34 at 823 K was reached, instead of the 0.24 equilibrium value. The catalyst demonstrated a suitable stability under periodic regeneration in oxidative atmosphere

Compact string reactor for authotermal hydrogen production

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

Membrane reactor microstructured by filamentous catalyst

Du voyage à la scène révolutionnaire Lors de son arrivée à Alexandrie, Volney ressent le choc de cette « langue dont les sons barbares et l’accent âcre et guttural effraient » l’oreille, ainsi que l’écrit le jeune homme dans le récit de voyage qu’il publie en 1787. Il n’en décide pas moins d’apprendre l’arabe parlé, huit mois durant, au Liban, et ne commence réellement son voyage qu’une fois cette compétence acquise. Très vite, il découvre la conduite désordonnée et fantaisiste des Occidentau..