Reaction pathways and intermediates in the decomposition of acetic and propionic acids on the polar surfaces of zinc oxide

Abstract

The decomposition of acetic and propionic acids on the (0001)-Zn and (000 1)-O polar surfaces of ZnO was investigated using temperature programmed desorption, and X-ray and ultraviolet photoelectron spectroscopies. On the (0001)-Zn surface the carboxylic acids adsorbed dissociatively to form the corresponding surface carboxylate species. At temperatures greater than 500 K, these surface carboxylates underwent either net dehydration to form unsaturated aldehydes (i.e. ketene and acrolein) or net total oxidation to carbon oxides and water. In contrast to the (0001)-Zn polar surface, the (000 1)-O polar surface was found to be inactive for the decomposition of these carboxylic acids; only molecularly adsorbed species, which desorbed intact at low temperature, were observed on this surface. These results provide further evidence for the pronounced structural dependence of acid-base reactions on the polar surfaces of zinc oxide.