Modified chromium/silica gel catalysts: impregnation of the silica gel with titanylacetylacetonate and comparison with chromium on SiO2 and TiO2

Abstract

TiO2 supported on silica gel was prepared by impregnating silica gel with titanylacetylacetonate—ethanol with different Ti content (0.2, 0.4, 1 and 2 mmol Ti/g SiO2). These samples were investigated and compared with silica gel and titania (P 25). At low concentration the titanium is highly dispersed, and at the highest titanium concentration some 30% of the titanium is present as anatase crystallites. Polymerization measurements showed a lower catalytic activity with titanium present. FTIR spectra of CO adsorbed on chromium(II) at room and low temperature showed that for chromium/titanium/silica gel catalysts the chromium(II)-C surface species (characteristic CO IR bands at 2190 and 2120, 2100, 2045 cm–1) is dominant over the chromium(II)-C surface species (characteristic CO IR bands at 2180, 2185 and 2120, 2100, 2035 cm–1), while for normal chromium/silica gel catalysts the chromium(II)-A species is the major one. This effect is more clearly observed for higher chromium concentrations (0.5% Cr as opposed to 0.074% Cr).