HYDROGENATION OF OLEFINS AND POLYMERIZATION OF ETHENE OVER CHROMIUM OXIDE-SILICA CATALYSTS .1. PREPARATION AND STRUCTURE OF THE CATALYST

The structure, texture, degree of dispersion, and valency of Cr were investigated for CrOx/SiO2 catalysts as a function of the method of impregnation, calcination, and subsequent reduction. The catalysts were characterized by analytical methods, by uv-visible spectroscopy, and by EPR and paramagnetic susceptibility measurements. Impregnation with or adsorption from CrO3 solutions leads in the first instance to binuclear chromate complexes adsorbed on the silica surface. Reduction with H2 or C2H4 results in catalysts containing both Cr2+ and Cr3+ ions, the latter in various states of clustering. In agreement with the literature it was found that the removal of produced water was crucial, higher efficiencies in water removal leading to higher Cr2+/Cr3+ ratios and less tendency to Cr3+ clustering. Surprisingly, reoxidation of Cr2+ occurred also when the catalyst was reduced with CO. This reoxidation was found to be caused by silanol groups. © 1979 Academic Press, Inc. All rights reserved.