Mechanism of ketonization of acetic acid on anatase TiO2 surfaces

Abstract

The interaction of CH₃COOH with anatase TiO₂ surfaces has been studied and the results analysed in connection with those previously obtained for HCOOH on this and other oxides. The electron-donor properties of the carboxylate species formed at the surface were found to enhance the thermal elimination of surface hydroxyls, thus determining the actual state of the surface under catalytic conditions. Formation of ketene was detected by i.r.; a mechanism, involving this ketene and molecularly adsorbed acid in equilibrium with the gas phase, has been put forward for catalytic ketonization on TiO₂ at T < 350°C. Decomposition of the adsorbed acetate at T > 350°C in the absence of gas phase produces alkyl-metal species (Ti—CH₃) which, at T > 400°C, give C₂H₆ and CH₄ leading to irreversible coke poisoning of the surface.