HYDROGENATION OF OLEFINS AND POLYMERIZATION OF ETHENE OVER CHROMIUM OXIDE-SILICA CATALYSTS .2. INTERACTION WITH HYDROGEN

The hydrogen uptake of chromium oxide/silica catalyst shows a partial similarity with that of α-Cr2O3 as reported by Weller and Voltz [J. Amer. Chem. Soc. 76, 4695 (1954)]. At low temperatures a heterolytic dissociative adsorption of H2 occurs at a site consisting of two Cr3+ ions and two oxygen anions. At high temperatures a subsequent reaction occurs leading to reduction of Cr3+ to Cr2+ followed by a dissociation of water. The Cr2O/silica catalyst differs from the α-Cr2O3 sample of Weller and Voltz because water is not expelled but reacts with silica under formation of silanol groups. At still higher temperatures this reaction is reversed by an interaction of the silanol groups with Cr2+ producing Cr3+ and H2. © 1979 Academic Press, Inc. All rights reserved.