Role of Weakly Adsorbed Molecules in Catalytic Reactions

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Weakly adsorbed water has been observed to dramatically increase the rates of photocatalytic decomposition of organics on platinum/titania (Pt/TiO2) catalysts, but chemisorbed water, which is more strongly adsorbed, does not. The objective of this research is to understand how weakly adsorbed molecules accelerate the rate of these catalytic reactions. Understanding these observations may be important in many catalytic reactions. These studies will also contribute to understanding photocatalytic oxidation, which is used to oxidize low concentrations of VOC pollutants in air. A combined experimental and theoretical approach will be used to elucidate the mechanisms that are involved in acceleration of these catalytic reactions. Photocatalytic decomposition, which takes place on Pt/TiO2 at room temperature, is a particularly effective means to study such behavior. The use of UV light to start and stop the reaction isothermally provides a unique means to study intermediates and mechanisms. The experimental studies will use continuous-flow isothermal reaction, infrared spectroscopy of adsorbed species and intermediates, and temperature-programmed desorption. Transient isothermal reaction will be combined with isotope labeling as a major component of the experimental studies. Adsorption isotherms of water will be used to determine the amounts of adsorbed water during reaction conditions. The theoretical modeling will use ab initio computational chemistry to test reaction mechanisms, determine the effect of weakly adsorbed molecules on adsorbed organics, and do trajectory calculations to investigate the reaction coordinate for photocatalytic decomposition. The infrared spectra of optimized intermediate structures will also be computed from first principles for comparison to the experimental results. The modeling and experiments will be coordinated so that each helps guide the other.