Preparation and characterization of palladium-based composite membranes by electroless plating and magnetron sputtering

Pd and Pd-Ag (24 wt.%) alloy composite membrane were prepared by electroless plating and magnetron sputtering, respectively. The membranes were characterized by scanning electron microscopy (SEM) and H-2 permeation measurement. Commercial microfiltration ceramic membrane were coated with gamma-Al2O3-based layer by the sol-gel method and used as substrate of Pd and Pd-Ag alloy film. Both the as-prepared membranes were shown: to be He gas-tight at room temperature with a thickness of <1 mu m. Permeation results showed that H-2 permeation through these composite membranes is mainly dominated by the surface chemistry of H-2 on or/and in the membranes. The membranes exhibited a high permeation rate of H-2 and a H-2/N-2 permselectivity of higher than 60 in the optimized operation conditions. (C) 2000 Elsevier Science B.V. All rights reserved.

Thioreduction of cyclopentanone and hydrodesulfurization of dibenzothiophene over sulfided nickel or cobalt-promoted molybdenum on alumina catalysts

Two series of sulfided Ni or Co promoted Mo/alumina catalysts, having different Ni or Co loadings, were characterized by their activities for the transformation of cyclopentanone into cyclopentanethiol (flow reactor, 220 degrees C, atmospheric pressure) and for the hydrodesulfurization of dibenzothiophene (flow reactor, 340 degrees C, 3 MPa hydrogen pressure). The addition of the promoter increased significantly the activity of the Mo/alumina catalyst for both reactions, up to a maximum obtained with the catalysts having a (promoter)/(promoter+Mo) molar ratio equal to 0.3-0.4. This increase in activity was due in part to an increase in the hydrogenating properties of the Mo/alumina catalyst. However, an additional modification of the catalyst (basic and nucleophilic properties) must be considered to account for the spectacular effect of the promoter on the rate of the dibenzothiophene direct desulfurization reaction. (C) 1999 Elsevier Science B.V. All rights reserved.

Epoxidation of styrene with NaOCl and catalyzed by nickel(II) complexes

Epoxidation of styrene was catalyzed by some nickel(II) complexes, with NaOCl as the oxygen donor. The catalyst Ni(PA)(2). 2H(2)O has been found to be stable for the epoxidation of styrene. Some additives were introduced in the reaction to improve the "micro-environment" of the catalyst. Radical trap had little influence on styrene epoxidation. It was interesting to find that phase-transfer agent had negative influence on epoxidation in this biphase reaction. A possible mechanism of styrene epoxidation catalyzed by Ni(PA)(2). 2H(2)O has been proposed.

Partial oxidation of ethane to syngas over nickel-based catalysts modified by alkali metal oxide and rare earth metal oxide

The catalytic activity, thermal stability and carbon deposition of various modified NiO/gamma-Al2O3 and unmodified NiO/gamma-Al2O3 catalysts were investigated with a flow reactor, XRD, TG and UVRRS analysis. The activity and selectivity of the NiO/gamma-Al2O3 catalyst showed little difference from those of the modified nickel-based catalysts. However, modification with alkali metal oxide (Li, Na, K) and rare earth metal oxide (La, Ce, Y, Sm) can improve the thermal stability of the NiO/gamma-Al2O3 and enhance its ability to suppress carbon deposition during the partial oxidation of ethane (POE). The carbon deposition contains graphite-like species that were detected by UVRRS. The nickel-based catalysts modified by alkali metal oxide and rare earth metal oxide have excellent catalytic activities (C2H6 conversion of similar to 100%, CO selectivity of similar to 94%, 7x 10(4) l/(kg h), 1123 K), good thermal stability and carbon-deposition resistance.