ADSORPTION OF ACETONITRILE ON CERIUM OXIDE - AN INFRARED SPECTROSCOPIC STUDY ACCORDING TO THE REDUCTION STATE OF THE OXIDE

Acetonitrile adsorption on evacuated ceria evidenced the presence of weak Lewis acid sites and strong basic O2- ones leading respectively to the formation of undissociated adsorbed species and to the CH2CN- monoanion. Moreover, the acetamide dianion, [CH3C(N)O]2-, was also observed and well spectroscopically characterized using H --> D and 16O --> 18O substitutions. Results obtained from adsorption of acetonitrile on ceria H2-reduced at different temperatures were correlated to the hydroxylation state of the samples : for reduction temperatures lower than 673K, part of O2- sites were transformed into OH- partially preventing the formation of CH2CN-species ; for higher reduction temperatures, part of O2- sites were recovered explaining the higher amount of CH2CN- species formed. The characteristic frequencies of adsorbed anionic species were slightly dependent of the oxydation state, Ce4+ or Ce3+, of the adsorbing cation.