Alkali-loaded silica, a solid base:: Investigation by FTIR spectroscopy of adsorbed CO2 and its catalytic activity

FTIR spectra (298 K) Of CO2 adsorbed on SiO2-supported Li2O, Na2O, K2O, and Cs2O were studied. An absorption band around 2345 cm(-1) and two sets of bands, one at around 1675 and 1325 cm(-1) and another at around 1640 and 1375 cm(-1), indicate the presence of monodentate and bidentate types of adsorbed CO2 species. These bands are absent in the spectrum Of CO2 adsorbed on pure SiO2. Therefore, it is concluded that both of these species are associated with alkali metal oxides on the SiO2 surface. The characteristic pairs of absorption bands shift to lower wave numbers with increasing basicity of the metal oxide. Isopropanol mainly undergoes dehydrogenation into acetone over the catalysts. In the methylation of phenol by methanol these catalysts exhibit good activity and similar to 100% selectivity for the O-alkylated product, anisole. (C) 2001 Elsevier Science.