A DRIFT spectroscopic study of acetylene adsorbed on metal oxides

The interaction of acetylene with surface sites of SiO2, TiO2, CaO, MgO, Al2O3, Ga2O3, La2O3, and ZrO2 oxides was studied. Two main types of acetylene adsorption complexes were found: first, complexes formed by weak reversible adsorption at O2- sites and basic OH groups and, second, stable complexes formed by the dissociative adsorption of acetylene at Medelta+-Odelta- pairs with the formation of acetylide species. The position of the C-H band in weakly adsorbed complexes and C=C bands in strongly adsorbed complexes can be used for the sensitive characterization of oxide basicity. The measurements performed at elevated acetylene pressures (10-20 Torr) give information on the total basicity of oxides, whereas the analysis of the complexes formed at low pressures (similar to0.2 Torr) characterizes the properties of specific absorption sites. The interaction of acetylene with surface sites was mainly reversible; however, the products of acetylene oligomerization could be observed in the long-term experiments.