Hydrogenation of olefins and polymerization of ethene over chromium oxide/silica catalystsII. Interaction with hydrogen

Abstract

The hydrogen uptake of chromium oxide/silica catalyst shows a partial similarity with that of α -Cr 2 O 3 as reported by Weller and Voltz [ J. Amer. Chem. Soc. 76 , 4695 (1954)]. At low temperatures a heterolytic dissociative adsorption of H 2 occurs at a site consisting of two Cr 3+ ions and two oxygen anions. At high temperatures a subsequent reaction occurs leading to reduction of Cr 3+ to Cr 2+ followed by a dissociation of water. The Cr 2 O/silica catalyst differs from the α -Cr 2 O 3 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 Cr 2+ producing Cr 3+ and H 2 .