Oxygenate reaction pathways on transition metal surfaces

The importance of various oxygenates as fuels and as chemical intermediates and products continues to grow. Alcohols and aldehydes have also been the subjects of numerous surface reactivity studies. We review here the decomposition mechanisms of oxygenates on transition metal surfaces focusing primarily on metals of Groups VIII and IB. Common pathways as well as deviations from these serve to illustrate the patterns of oxygenate reactions. Several major divisions in the preferred pathways can be rationalized in terms of the affinities of metals for making metal-oxygen and metal-hydrogen bonds. Other important factors determining oxygenate reactivities include surface crystallographic structure and the detailed molecular structure of the oxygenate. Differences in product distribution between metals are frequent, even in cases where many of the reaction steps are common, primarily because of the plethora of elementary reaction steps usually involved in oxygenate decomposition on transition metal surfaces. As a result, differences late in the reaction sequence can obscure important similarities in the overall reaction network. Spectroscopic identification of common surface reaction intermediates including alkoxides, acyls, and oxametallacycles, has become increasingly important in revealing the underlying similarities in seemingly diverse oxygenate reaction pathways on transition metal surfaces. (C) 1998 Elsevier Science B.V.