FORMATION OF STABLE ALKYL AND CARBOXYLATE INTERMEDIATES IN THE REACTIONS OF ALDEHYDES ON THE ZNO(0001) SURFACE
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Stable alkyl and carboxylate intermediates were formed by oxidation of higher aldehydes on the zinc polar surface of zinc oxide at low temperatures. Adsorbed acetaldehyde and propionaldehyde underwent nucleophilic attack by lattice oxygen to form dioxyalkylidene species (RCH2CH02). Decomposition proceeded via two separate pathways: hydride elimination to form the corresponding surface carboxylate and alkyl elimination to form surface formate. The alkyl elimination pathway also resulted in the formation of stable surface alkyl species. The selectivity of these two competing elimination reactions was found to be a strong function of the surface temperature, with low temperatures favoring alkyl elimination. TPD and XPS provided the clearest evidence for alkyl elimination and the corresponding formation of surface formates; UPS and XPS provided spectroscopic evidence for the existence of stable surface alkyls. The observation of alkyls as stable surface intermediates in the decomposition of aldehydes on zinc oxide has implications for a variety of catalytic processes, including the synthesis of higher alcohols and oxygenates on oxide surfaces. 1989, American Chemical Society. All rights reserved.
