Hydrogenation of chemisorbed ethylene on clean, hydrogen, and ethylidyne covered platinum (111) crystal surfaces

Catalysis with Supported Size-selected Pt Clusters

“…peratures above 450 − 500 K. At higher concentrations a graphite layer forms and the organic deposits become immobile, consequently the active sites on the metal are poisoned [5,98]. At even higher temperatures (∼ 700 K) ethene rapidly forms a monolayer of graphene.…”

“…For Pt (111), but also for other d-metals, in the absence of hydrogen, ethane is formed and can be detected when studying thermal desorption of ethene, thus the formation of ethane occurs via a self-hydrogenation [98].…”

Bonding and chemistry of hydrocarbon monolayers on metal surfaces

“…In this mechanism, ethylene conversion to ethylidyne is initiated by hydrogenation to form C 2 H 5 followed by sequential ~ehy drogenation at the a-carbon to give CCH 3 . The mechanism and its associated -17-energetics derived based on a combination of theory [39a] and experiment [50] are shown in Figure 18A and are compared with those for a previously proposed mechanism for ethylidyne formation Figure 18B. It should be noted that one hydrogen atom is needed to initiate our proposed mechanism of ethylidyne formation.…”

“…Such a reaction is implicated, for example, by the formation of methane in ethanol decomposition on Ni(lll) [48], methane formation in acetaldehyde decomposition on a stepped platinum surface (49], ethylene hydrogenation to ethane on Pt(lll) [50], and ethylidyne H,D exchange on Rh(lll) (10]. While it is possible that some of the products mentioned above are formed by a mechanism other than hydrogenation {for example, an intramolecular hydrogen shift), we favor elementary hydrogenation/dehydrogenation steps to explain the observed surface chemistry based on the prevalence of these reactions in organometallic chemistry.…”

“…Two possible mechanisms which have been proposed -22-are shown in Figure 26. Both mechanisms utilize the observation that ethylidyne-covered surfaces are found to be capable of dissociating hydrogen under high pressures of hydrogen [50]. In the upper mechanism, this surface hydrogen is then transferred up to gas phase ethylene via formation of ethylidene (CHCH 3 ) speci_es on the surface.…”