STEADY-STATE CATALYTIC C-C BOND FORMATION ON REDUCED TIO2 SURFACES

Previous temperature programmed desorption (TPD) experiments on reduce d TiO2 (001) surfaces have demonstrated that alkynes are converted to the corresponding aromatic products with high selectivity. This reacti on also represents the first example of catalytic assembly of carbon-c arbon 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 r eactions 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 significan t catalyst deactivation at temperatures between 290 and 500 K. A four- step kinetic model is proposed, which contains three nonactivated step s for alkyne adsorption/reaction to form the aromatic, followed by the final step, aromatic desorption. This model captures the measured tem perature and pressure dependence of the reaction rate. (C) 1997 Americ an Vacuum Society.