Steady-state catalytic C–C bond formation on reduced TiO2 surfaces

Abstract

Previous temperature programmed desorption (TPD) experiments on reduced TiO2 (001) surfaces have demonstrated that alkynes are converted to the corresponding aromatic products with high selectivity. This reaction also represents the first example of catalytic assembly of carbon–carbon bonds on a metal oxide surface in ultrahigh vacuum. Although the catalytic formation of carbon–carbon bonds on single crystal surfaces is a rarity, many important catalytic processes involve carbon–carbon bond formation, and it is therefore worthwhile to consider how such reactions might be studied directly using the tools of surface science. Steady-state experiments involving the production of trimethylbenzene from methylacetylene at low pressure (10−9–10−5 mbar) conditions have demonstrated multiple turnovers of the catalyst and no significant catalyst deactivation at temperatures between 290 and 500 K. A four-step kinetic model is proposed, which contains three nonactivated steps for alkyne adsorption/reaction to form the aromatic, followed by the final step, aromatic desorption. This model captures the measured temperature and pressure dependence of the reaction rate.