OXYGENATE REACTION PATHWAYS ON TRANSITION-METAL SURFACES

The importance of various oxygenates as fuels and as chemical intermed iates and products continues to grow. Alcohols and aldehydes have also been the subjects of numerous surface reactivity studies. We review h ere the decomposition mechanisms of oxygenates on transition metal sur faces focusing primarily on metals of Groups VIII and IB. Common pathw ays as well as deviations from these serve to illustrate the patterns of oxygenate reactions. Several major divisions in the preferred pathw ays can be rationalized in terms of the affinities of metals for makin g metal-oxygen and metal-hydrogen bonds. Other important factors deter mining oxygenate reactivities include surface crystallographic structu re and the detailed molecular structure of the oxygenate. Differences in product distribution between metals are frequent, even in cases whe re many of the reaction steps are common, primarily because of the ple thora of elementary reaction steps usually involved in oxygenate decom position on transition metal surfaces. As a result, differences late i n the reaction sequence can obscure important similarities in the over all reaction network. Spectroscopic identification of common surface r eaction intermediates including alkoxides, acyls, and oxametallacycles , has become increasingly important in revealing the underlying simila rities in seemingly diverse oxygenate reaction pathways on transition metal surfaces. (C) 1998 Elsevier Science B.V.