Reactions of maleic anhydride over TiO2 (001) single crystal surfaces

The reactions of maleic anhydride (MA) have been investigated on the "near" stoichiometric and substoichiometric surfaces of TiO2 by temperature programmed desorption (TPD). Moreover, self-consistent field semiempirical PM3 calculations of MA over relaxed and unrelaxed Ti13O45H38 rutile clusters [simulating the rutile TiO2(011) surface] were conducted on two modes of adsorption. The dissociation of one C-O-C bond following adsorption on a Ti-5c(4+) - O2- Site results in a more stable adsorbed species (by 0.5 eV) than the nondissociatively adsorbed molecule. Desorption of a wide range of products in several temperature domains was observed during MA-TPD. In addition to the decomposition pathway to carbon monoxide (CO), carbon dioxide (CO2), acetylene (HC = CH), and ketene (H2C = C = O), the desorption of several coupling products is also seen: vinylacetylene (HC = CCH = CH2), butene, traces of butadiene (H2C = CHCH= CH2), and benzene (C6H6). Over the substoichiometric surfaces these coupling products are more accentuated while the decomposition pathway to ketene decreased. (C) 2000 American Vacuum Society. [S0734-2101(00)17404-4].