Role of Weakly Adsorbed Molecules in Catalytic Reactions

在铂/二氧化钛催化剂上，弱吸附水能显著提高有机物的光催化分解速率，而吸附较强的化学吸附水不能显著提高光催化降解有机物的速率。这项研究的目的是了解弱吸附分子如何加速这些催化反应的速度。了解这些观察结果在许多催化反应中可能很重要。这些研究还将有助于理解光催化氧化，光催化氧化用于氧化空气中低浓度的VOC污染物。实验和理论相结合的方法将被用来阐明加速这些催化反应的机理。在室温下在铂/二氧化钛上进行的光催化分解是研究这种行为的一种特别有效的手段。利用紫外光等温启动和停止反应为研究中间体和反应机理提供了一种独特的手段。实验研究将使用连续流动等温反应、吸附物种和中间体的红外光谱以及程序升温脱附。瞬时等温反应将与同位素标记相结合，作为实验研究的主要组成部分。水的吸附等温线将被用来确定在反应条件下吸附的水量。理论模型将使用从头计算化学来测试反应机理，确定弱吸附分子对吸附有机物的影响，并进行轨迹计算来研究光催化分解的反应坐标。为了与实验结果进行比较，还将从第一性原理计算优化的中间结构的红外光谱。建模和实验将相互协调，相互指导。

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.