Selective surface reactions of single crystal metal carbides: Alkene production from short chain alcohols on titanium carbide and vanadium carbide

The adsorption and reaction of ethanol and 2-propanol on the (100) surface of single crystal vanadium carbide (VC) and titanium carbide (TiC) have been studied using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy. A mixture of molecular and dissociative adsorption is observed at cryogenic temperatures on both of the carbide surfaces. Dissociative adsorption of the short chain alcohols leads to the formation of an alkoxy intermediate at 153 K on both VC(100) and TiC(100). With increasing temperature, the alkoxy intermediate selectively reacts with the carbide surfaces to produce an alkene. A comparison of TPD intensities indicates that dissociative adsorption occurs to a greater extent on TiC; however, the reaction yield for dehydration of the alkoxy surface species is ̃20% greater on VC(100) as compared to TiC(100). Specific isotopic labeling studies of the ethanol reaction identify γ-hydride elimination as a key step in alkene formation on VC(100). This pattern of reactivity on metal carbide surfaces significantly differs from the decomposition reactions, producing carbon monoxide and hydrogen, or the β-hydride elimination reactions, producing an aldehyde and hydrogen, that are observed on most transition metal surfaces.