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).