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

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. © 1997 American Vacuum Society.