IR STUDY OF ACETONITRILE ADSORPTION ON HYDROXYLATED ZIRCONIUM DIOXIDE- MECHANISM OF ACETONITRILE HYDROLYSIS

In situ FTIR spectroscopy has been used to investigate the adsorption of acetonitrile at room temperature onto zirconia activated at various temperatures (423, 723 and 873 K), attention being focussed on the sa mple pretreated at 423 K. Two acetamide monoanions (CH3CONH-), called alpha and beta species, were spectroscopically evidenced with main ban ds, respectively, at 1169, 1432, 1590, 3320 cm(-1) and at 1196, 1471, 1557, 3340 cm(-1). The use of O-18- Or D-labelled compounds gave poor results as far as the vibrational mode description was concerned, exce pt for the delta(NH) mode. However, the H --> D substitution was very useful for determining mechanisms. It was proposed that the beta-type acetamide species results from H2O displacement from the surface and C H3CN adsorption in acidic Lewis sites, followed by a hydroxylation of this latter species by H2O readsorption. The formation of the alpha-ty pe acetamide species was thought to be due to a direct interaction of acetonitrile with basic OH groups. Upon heating at a temperature highe r than 373 K and in the presence of water vapour, acetamide species we re hydrolysed into acetate species.