REACTIONS OF 1-PROPANOL AND PROPIONALDEHYDE ON RH(111)

Temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS) were used to investigate the reactions of 1-propanol and propionaldehyde on the clean Rh (111) surface. The principal emphasis of this study was to determine the reaction pathways and intermediates involved in alcohol and aldehyde decomposition. Propoxide intermediates were formed by the dissociation of 1-propanol; these were easily isolated in the HREEL spectrum at 147 K. Decarbonylation occurred at ca. 226 K, resulting in the formation of adsorbed hydrocarbon fragments and adsorbed CO. No aldehyde or acyl intermediates were detected during the course of the decomposition of this primary alcohol. 1-Propanol decomposed on the Rh(111) surface to produce CO, H-2, and surface carbon. In contrast, propionaldehyde adsorbed on Rh(111) decomposed to form ethane, as well as CO, H-2, and surface carbon. At 145 K, eta-2(C,O)-propionaldehyde was observed by HREELS. By 251 K, some decarbonylation had occurred to yield bridge-bonded CO and ethyl species. A portion of the ethyl species formed by low temperature decarbonylation of propionaldehyde was hydrogenated to ethane, while the rest dehydrogenated to form ethylidynes, observed at 301 K by HREELS. Ethylidyne species dehydrogenated to acetylides which ultimately decomposed to carbon and hydrogen. The surprising divergence of reaction pathways for propanol and propionaldehyde is consistent with observations for ethanol and acetaldehyde decomposition on Rh(111) and suggests that higher alkoxide decomposition on this surface may involve C-H scission along the alkyl chain, rather than at the alpha-carbon.