Acetylene coupling on Cu(111): formation of butadiene, benzene, and cyclooctatetraene.

摘要: Acetylene trimerizes to benzene on the (111) face of copper, as it does (100) and (110) planes. However, Cu(111) also yields butadiene cyclooctatetraene, latter never previously found with Cu or any other material. No coverage threshold is observed for onset these coupling reactions, implying high adsorbate mobility: gaseous formed by a surface reaction rate-limited process, whereas cyclooctatetraene are desorption processes. H/D isotope tracing shows that formation proceeds via statistically random associative mechanism, associated strong kinetic effects, probably C-H cleavage. A pericyclic mechanism involving dimerization C4H4 metallocycles proposed account cyclooctatetraene. We approximately 45 nm alpha-alumina supported copper particles operated under catalytic conditions at atmospheric pressure yield same principal products those vacuum conditions. It therefore seems likely elementary steps describe chemistry model system important practical Comparison structure, bonding, reactivity acetylene Pd(111) indicates effectiveness in promoting cleavage adsorbed greater rehybridization C-C bond concomitant weakening bond.