Experimental and modeling studies on catalysis for photocatalytic reactions and detection of trace gases.

摘要

The first part of this thesis focuses on the accelerating effects of water on formic acid photocatalytic oxidation (PCO) and decomposition (PCD) rates on TiO2 and Pt/TiO2. Density functional theory (DFT) calculations indicated that formic acid adsorbed molecularly on a dry anatase (101) surface, but dissociated to monodentate formate when water adsorbed, depending on formic acid and water coverages. For ¼ monolayer (ML) formic acid coverage, O-H dissociation required a 1:1 ratio of water to formic acid, and for 1 ML formic acid coverage, 2 monolayers of water were required to stabilize the adsorbed formate species. The 2nd layer of water also induced dissociation of the 1st layer water creating OH groups. DFT calculations also showed that water co-adsorption increased the reactivity by decreasing the adsorbate's effects on the surface through hydrogen bonding. Details of how adsorbates altered the electronic structure though bond breaking and electron transfer were examined.;FTIR spectroscopy and TPD studies indicated that the addition of water to TiO2 displaced adsorbed formic acid. However, FTIR spectroscopy also showed that water addition caused a change in the adsorbed structure of formate that may be associated with the higher reactivity. These transformations can have an important influence on elementary steps in PCD and PCO of formic acid on TiO2 and Pt/TiO2.;The second part of this thesis focuses on the effect of the metal gate composition in metal-insulator-semiconductor (MIS) devices on acetylene response in hydrogen/acetylene mixtures. A number of bimetallic compositions were tested at different temperatures, and the largest reproducible response was observed for a 15% Ag/Pd sensor at 398 K. Kinetic modeling of the relevant surface reactions on Pd and PdAg provided insights into how temperature, feed concentration, and percent Ag in the bimetallic affected response. The accumulation of carbon species influenced the final response, and appeared to be responsible for dynamic trends in response. Response increased with carbon species fouling until a critical concentration of carbon species, where response decreased due to a lower hydrogen consumption rate.