Hydrogenation of olefins and polymerization of ethene over chromium oxide/silica catalystsI. Preparation and structure of the catalyst

Abstract

Catalysts containing approx. 2Vertical Bar3< chromium on Davison silica gel 12 were prepared by impregnation with chromic acid, either just enough acid to fill the pore volume or excess acid (Type 1 and Type 2 catalyst, respectively), calcining in air at 500/sup 0/C, and reducing the orange catalyst in a pulse reactor either with carbon monoxide or with hydrogen to either a green or a blue color. The catalysts were characterized by thermal analyses, magnetic susceptibility, and ESR, reflectance, and IR spetroscopy. The results suggested that chromic acid forms binuclear surface complexes on the silica which become stabilized during calcination. During reduction, decomposition of CrO/sub 3/ to Cr/sub 2/O/sub 3/ occurs and two or three-dimensional clusters form on Type 1 catalysts and chromium pairs or two-dimensional clusters form on Type 2 catalyst. In the reduction with hydrogen, product water promotes the formation of clusters; in the reduction with carbon monoxide, the amount of hydroxyl groups determine the degree of reduction that can be obtained.