CYCLOTRIMERIZATION OF ACETYLENE TO BENZENE OVER SINGLE-CRYSTAL PALLADIUM AND GOLD PALLADIUM SURFACES AND OVER SUPPORTED PALLADIUM CATALYSTS

Kinetic and spectroscopic studies of ethyne cyclisation to benzene over and Pd/Au yield detailed information about the reaction mechanism. The existence of a critical ethyne coverage threshold for reaction is dramatically demonstrated by experiments using coadsorbed NO which compresses the reactant surface phase without itself participating in the reaction. Results obtained from both single crystal model systems and supported Pd catalysts clearly show that C4H4 is the crucial surface intermediate in the cyclisation reaction. Data obtained with well characterised Pd/Au single crystal systems reveal the sensitivity of this reaction to the electronic structure, atomic composition and morphology of the metal surface.