Plasma pretreatment of cobalt Fischer–Tropsch catalysts through glow discharge decomposes cobalt nitrate at much lower temperatures than conventional calcination,and smaller superparamagnetic Co metal particles (<7 nm) are formed (see schematic representation). The Fischer–Tropsch reaction rates with these catalysts are higher than or comparable to those of their counterparts prepared by conventional calcination at 473 K.

The structure of cobalt species at different stages of the genesis of monometallic and Pt-promoted cobalt alumina-supported Fischer–Tropsch catalysts was studied using X-ray diffraction, UV–visible spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, and DSC–TGA thermal analysis. The catalysts were prepared by incipient wetness impregnation using solutions of cobalt nitrate and dihydrogen hexachloroplatinate. Both variation of catalyst calcination temperature between 473 and 773 K and promotion with 0.1 wt% of Pt had no significant affect on the size of supported Co3O4 crystallites. The size of cobalt oxide particles in the calcined catalysts seems to be influenced primarily by the pore diameter of the support. Cobalt reducibility was relatively low in monometallic cobalt alumina-supported catalysts and decreased as a function of catalyst calcination temperature. The effect was probably due to the formation of mixed surface compounds between Co3O4 and Al2O3 at higher calcination temperatures, which hinder cobalt reduction. Promotion with platinum spectacularly increased the rate of cobalt reduction; the promotion seemed to reduce the activation energy of the formation of cobalt metallic phases. Analysis of the magnetization data suggests that the presence of Pt led to the reduction of smaller cobalt oxide particles, which could not be reduced at the same conditions in the cobalt monometallic catalysts. Promotion of cobalt alumina-supported catalysts with small amounts of Pt resulted in a significant increase in Fischer–Tropsch cobalt time yield. The efficient control of cobalt reducibility through catalyst calcination and promotion seems to be one of the key issues in the design of efficient cobalt alumina-supported Fischer–Tropsch catalysts.

Stable V-MCM-41 mesoporous materials have been synthesized by hydrothermal method, using hexadecyl-trimethyl-ammonium bromide as template, and industrial Na2o (3.3-3.5)SiO2 as the source of much cheaper silica instead of conventional expensive organic precursors. Several modern techniques like XRD, N2 adsorption, FT-IR, UV-vis and SEM have been utilized to characterize the framework structure and texture of the samples. The results of N2 adsorption and X-ray diffraction showed that the synthesized samples had a high ordered hexagonal structure, good hydrothermal stability and thermal stability. The selective oxidation of styrene using hydrogen peroxide as oxidant over V-MCM-41 samples showed a good catalytic performance of partial oxidation, the phenylacetic acid was the principal product (the selectivity value was 49.4%). Even after a thermal treatment at 900 0C in air for 12 h or a hydrothermal treatment in boiling water for 8 days, each of the two resultant materials could retain the ordered channels and a high BET surface area. UV-vis spectra provided strong evidences that most of vanadium ions were incorporated into the framework of siliceous MCM-41 sample.

For the selective hydrogenation of acetylene, the novel Pd/ -Al2O3 catalysts prepared by plasma method were investigated. The inuence of the preparation method, content of Pd active component, catalyst promoter and reaction temperature has been investigated. It was found that the conversion and selectivity of the catalysts prepared by glow discharge plasma were superior to those obtained from the conventional catalysts. The acetylene conversion of 100% and the selectivity of 71.3% in C2H4 were obtained at 50℃ over the plasma-prepared sample (0.15 wt.% Pd), while the plasma-prepared catalyst was stable during the long-time test for more than 20 h. 2003 Elsevier B.V. All rights reserved.