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

Abstract

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 ~100% selectivity for the O-alkylated product, anisole.