X-Ray Absorption Spectroscopy Investigation of the Activation Process of Raney Nickel Catalysts

Author： Rothe J. Hormes J. Schild C. Pennemann B.

ISSN： 0021-9517

Source： Journal of Catalysis, Vol.191, Iss.2, 2000-04, pp. : 294-300

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Abstract

The formation of highly reactive Raney Nickel catalysts, which are commonly used in hydrogenation reactions, has been studied using X-ray absorption spectroscopy (XAS) with synchrotron radiation. Various samples representing different “frozen” states of the activation reaction have been prepared. The process has been quenched after different reaction times by neutralizing the alkaline solution leaching the aluminium from the two alloys used as educts. XANES spectra taken at the Ni K edge of the catalysts derived from an Ni/Al alloy and an Ni/Al/Fe alloy reveal that the transformation starts with a very rapid change of the electronic structure followed by a much slower change of the geometric structure of the alloys. Most noticeable is the sharp increase of the density of empty d band states, which partially redevelop when the reaction products slowly relax to an electronic as well as a lattice structure similar to that of fcc-Ni metal. Thus at least a well-defined local order is preserved in the final catalysts. The presence of Fe (6 wt%) in the starting alloy slows down the reaction, while the Fe K-XANES points to the oxidation of this component.