A variety of carbon-modified titania powders were prepared by impregnation method using a commercial available titania powder, Hombikat UV100, as matrix material while a range of alcohols from propanol to hexanol were used as precursors of carbon sources. Rising the carbon number of alcoholic precursor molecule, the modified titania showed increasing visible activities of NOx photodegradation. The catalyst modified with cyclohexanol exhibited the best activities of 62%, 62%, 59%, and 54% for the total NOx removal under UV, blue, green, and red light irradiation, respectively. The high activity with long wavelength irradiation suggested a good capability of photocatalysis in full visible light spectrum. Analysis of UV-visible spectrum indicated that carbon modification promoted visible light absorption and red shift in band gap. XPS spectroscopic analysis identified the existence of carbonate species (C=O), which increased with the increasing carbon number of precursor molecule. Photoluminescence spectra demonstrated that the carbonate species suppressed the recombination rate of electron-hole pair. As a result, a mechanism of visible-light-active photocatalyst was proposed according to the formation of carbonate species on carbon-modified TiO2.

Photocatalytic titanium dioxide was synthesized by an acid-catalyzed sol-gel process with titanium n-butoxide as the precursor. Several factors including adsorption, wavelength, aniline concentration, and pH were examined to measure their impact on the photocatalytic activity of synthetic TiO2, using aniline as the target compound under visible light irradiation by light-emitting diodes. Under blue-light illumination, the as-synthesized TiO2 exhibited photocatalytic activity of whereas commercial TiO2 (Degussa P-25) displayed no photoreaction under the same conditions. This photoactivity was more pronounced under blue, green, yellow, and red light, and that corresponded very well with the adsorption spectrum of as-synthesized TiO2. As the initial aniline concentration increased from 0.047 to 0.80 mM, the degradation efficiency of aniline decreased from 72% to 18% after irradiation for 4 h with 1 g/L TiO2. The reaction followed the Langmuir-Hinshelwood kinetic model with the adsorption equilibrium and rate constant having values of 15.89 1/mM and 9.96 x 10(-4)/(mM min), respectively. For the photocatalysis of aniline by this visible-light-activated TiO2, the optimum pH was 7 in the range 4-10. (C) 2011 Elsevier B.V. All rights reserved.

The visible light active catalysts, PtOx-doped TiO2 (PtOx–TiO2) and PtOx-loaded TiO2 (PtOx/TiO2), were successfully synthesized by the acid-catalyzed sol–gel process and the impregnation method. Pt(NH3)4(NO3)2 or H2Pt(OH)6 was employed as the PtOx precursor. By comparing the results of De-NOx, the modified photocatalysts exhibited a higher visible-light-responsive activity, and a lower NO2 selectivity than the unmodified ones. The FE-SEM images suggested that the particle size was unchanged after modification. The XRD patterns showed that the crystal structure still remained as anatase phase. Nitrogen adsorption revealed no significant change in surface areas for all samples. The UV–vis spectra indicated that PtOx promoted the absorption of visible light. Furthermore, the XPS spectra evidenced that the mixed valence states of PtO–PtO2 coexisted on the surface of TiO2. The adding of PtOx on TiO2 not only promoted the visible-light-responsive activity of converting NO to NO2 but also increased the consecutive reaction rate of NO2 to NO3−.

This study investigates photocatalytic degradation of nitrogen oxides overtitania-based photocatalysts illuminated by ultraviolet and visible light. The TiO2 photocatalyst was synthesized in a sol-gel process using titanium butoxide as the precursor. After calcination between 150 and 300 degrees C, the synthesized TiO2 responded strongly to visible light photocatalytically degrading NO(x), probably because of the existence of carbonaceous species that act as sensitizers. The optimum calcination temperature was found to be around 200 degrees C. Additionally, platinum ion-doped TiO2 was prepared by impregnation using Pt(NH3)4(NO3)2 as a dopant, which improved the photocatalytic activity that degraded NO(x) in the visible light region. The Pt ion was doped in oxide form at the surface of TiO2 and was expected to be responsible for sensitization. At an optimum calcination temperature of around 200 degrees C, the Pt ion-doped TiO2 exhibited higher activity in the further oxidation of NO2 to NO3- clearly reducing NO2 selectivity. The TiO2 catalysts chemically prepared by either the sol-gel process or impregnation exhibited stronger activity than conventional TiO2 when illuminated under a fluorescent lamp. Rinsing with water was responsible for the restored reactivity of prepared TiO2 catalysts for NO(x) degradation.

This paper presents a mathematical model based on the reaction rate expressions to describe the displacement of methane conversion in the steam reforming. The effect of several parameters including weight hourly space velocity (WHSV), load-to-surface ratio, reaction pressure, hydrogen partial pressure in permeate side and reaction temperature were investigated. Simulation and experimental results showed that a conversion higher than 80% could be achieved in a palladium membrane reactor at reaction temperature of 500°C relative to 850°C in a conventional fixed bed reactor (FBR). Besides, the yield of CO (<2%) in membrane reactor was much lower than that (>50%) in the FBR, which indicated the significant depression of CO production in use of membrane reactor.

As hydrogen energy is receiving greater attention in the dawn of this hew century, the complexity of hydrogen supply becomes an urgent concern for resolution. Hydrogen supply involves production, shipping and storage; cost estimates are presented to show the necessity of utilizing onsite hydrogen generation in the future hydrogen energy system. The methanol steam reforming reaction with a copper catalyst in the presence of a palladium membrane as a means of serving as an onsite hydrogen supply system was studied. In the course of this study our kinetic study indicated an unexpected rate enhancement of the forward reaction. This is attributed to hydrogen spillover from the catalyst allowing the direct transport of the newly produced atomic hydrogen to the membrane surface. This phenomenon is further supported by the chemisorption-permeance of hydrogen through a palladium membrane in the presence of a copper catalyst. The hydrogen permeance through the membrane is increased by the presence of a copper/zinc catalyst on the membrane surface. This indicates that hydrogen spillover or reverse spillover is playing the role of a kinetic bridge connecting the catalyst site and membrane surface. This shortcut bridge enables the newly produced hydrogen atom to diffuse to the membrane surface for permeation out of the system and the active catalyst site to turn over faster for a new run of chemisorption-reaction.

This paper presents a technology for producing high purity hydrogen by using supported palladium (Pd) membrane. The membrane is prepared by electroless plating and is stable among 300–400°C. The membrane shows high permselectivity in range of 200–1400 for H2/N2 and hydrogen permeance of 3–7 m3/m2-h-atm0.5. A mathematical model describing separation behaviour of membrane tube is used to predict the permeation parameters. Accordingly, the hydrogen flux and recovery yield can be calculated as the hydrogen is recovered from the recycle gas of catalytic reformer in refinery operation. A self-heating hydrogen separator containing ten membrane tubes was field-tested for the separation and purification of hydrogen. The supported Pd membranes show very good stability under the real environment of the gas mixture out of catalytic reformer. The total time on stream for the operation was more than 1000 h. The permeated hydrogen flux mainly depends on the pressure and flow rate of feedstock. The higher the pressure and feeding rate, the higher the hydrogen flux. However, the recovery yield of hydrogen decreased with increasing feeding rate. For instance, at the load-to-surface ratio of 4 m3/h-m2, a recovery yield of near 90% could be obtained. As the ratio increased to 8 m3/h-m2, the recovery yield decreased to about 70%. The purity of hydrogen can be raised from around 82 to 99.6% or above, which is apparently higher than those separated by polymeric membranes.

High purity hydrogen has been mainly used as a fuel for low temperature fuel cells such as polymer or alkaline electrolyte fuel cells. Hydrogen is industrially produced by steam reformation of hydrocarbons such as methane, naphtha oil, methanol, etc. Additional purification is invariably required for crude hydrogen and often is a costly step in the whole process. This paper presents an advanced process, in which no additional purification facility is needed, to generate high purity hydrogen (similar to 99.9%) directly from the supported palladium membrane tube incorporated in a steam reforming reactor. The hydrogen produced and purified from the palladium membrane reactor is free of CO and CO2 so that it is suitable for polymer or alkaline electrolyte fuel cells. A unique design of a double-jacketed reactor was set up as a pure hydrogen generator with features of clean emission and energy self-balance. Experiments were conducted to illustrate the process for the direct and continuous generation of high purity hydrogen from methanol. The production flux of pure hydrogen obtained was higher than 5 m(3)/h-m(2) and the recovery yield of hydrogen from methanol was found to be over 70%. This process has opened up a new possibility of on-board hydrogen generation for electric vehicle fuel cells in use of liquid fuel such as gasoline or methanol, which can be refueled fast and are compatible with the infrastructure of the current fuel system. (C) 1999 International Association for Hydgrogen Energy. Published by Elsevier Science Ltd. All rights reserved.

Vapor-phase naphthalene hydrogenation over various supported Pt catalysts was studied in a continuous fixed-bed microreactor. Experimental results indicated that the catalytic activity of the catalyst strongly depended on the nature of the support and the pre-reduction temperature. Reaction order was independent of the support as the reaction was pseudo-first-order with respect to naphthalene in the temperature range studied. By comparing the apparent rate constant over various supported Pt catalysts, Pt supported on TiO2-ZrO2 (1 : 1) reduced at a low temperature showed the highest activity. For higher pre-reduction temperatures, Pt/TiO2-ZrO2 (1 : 1) exhibited the least suppression of H-2 uptake, due to a stabilization effect exerted by ZrO2, which prevents the migration of TiOx moieties and the blockage of the Pt surface. However, the apparent depression of the hydrogenation activity of high-temperature reduced Pt/TiO2-ZrO2 (1 : 1) was significantly greater than the suppression of its hydrogen uptake. Furthermore, the decreasing value of the hydrogenation activity relative to the hydrogen uptake demonstrates electron perturbations between the support and the Pt metal. (C) 2000 Elsevier Science B.V. All rights reserved.

In this paper, we presented an integrated production and purification process of hydrogen by the use of a defect-free palladium membrane. Hydrogen could be purified from a variety of mixtures providing the purity of 3–7N depending on the feeding stream. The permeation parameters are accurately predicted by a separation model as established. The membrane is prepared by electroless plating and is stable among 300–400°C. Using an active catalyst, the rate of steam reforming of methanol was found to be significantly faster than that without a membrane module. In the steam reforming of methane, the reaction temperature was lowered to 500°C to achieve a conversion of 45%, which is 15% higher than the thermodynamic equilibrium conversion.

Oxidative dehydrogenation of cyclohexanol to cyclohexanone over a commercial CuOZnO catalyst was studied in a fixed-bed microreactor. Experimental results showed that the catalyst maintained constant activity at low oxygen: cyclohexanol mol ratios and its stability was dependent on the raction temperature. Both the activity and stability of the catalyst could be improved by using nitrous oxide instead of oxygen as the oxidant or by modifying the catalyst with palladium oxide or heteropoly acid (K3PMo12O40·3H2O). An analysis of the deposit on the spent catalyst showed the existence of oligomers of cyclohexanone. The accumulation of these higher molecular weight products on the catalyst is believed to be the major cause of the catalyst deactivation.