UC Irvine

With the importance and wide applicability of metal oxides in heterogeneous catalysis, understanding these materials on a fundamental level is paramount for the improvement of existing materials and design of new catalysts. Heterogeneous catalytic reactions occur at the interface; therefore, the surface of the material plays a key role in the reactivity. Thus, the work presented herein employs a number of surface sensitive techniques including temperature programmed desorption (TPD), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) to gain insight into the reactivity of model metal oxide systems of titanium dioxide (TiO2) and tungsten oxide (WO3-x).

The thermal desorption of deuterium oxide (D2O) from oxidized tungsten (100), sulfurized tungsten (100), and mixed sulfurized/oxidized tungsten (100) was investigating using TPD. The relative amounts of sulfur and oxygen on each surface was determined using AES. The results show that increasing the amount of sulfur on the tungsten surface weakens the interaction of D2O within the monolayer. In addition, only the fully sulfurized tungsten (100) resulted in dissociative D2O adsorption and disproportionation.

Different TiO2 heterostructures supported on highly oriented pyrolytic graphite were prepared using physical vapor deposition (PVD) and characterized using AES, SEM, and X-ray photoelectron spectroscopy (XPS). TPD using D2O as a molecular probe reveled that morphological differences in the prepared surfaces lead to pronounced changes in the desorption kinetics.

In addition, a unique systematic TPD investigation was performed on photodeposited platinum nanoparticles supported on TiO2 nanoparticles supported on HOPG. The results revealed that during the photodeposition process, the platinum adsorbs on the oxygen anion sites of the TiO2 particles.

Lastly, D2O thermal desorption was also used to gain insight into the consequences of sample plasma treatments prior to SEM imaging. Argon and oxygen plasma treatments on HOPG were shown to exhibit different D2O desorption behavior attributed to the oxygen functionality induced by the oxygen plasma. Furthermore, oxygen plasma treated TiO2/HOPG resulted in a defect site not observed on non-plasma treated TiO2/HOPG. Moreover, high density TiO2 nanoparticles prepared via argon and oxygen were compared using TPD and SEM in which no major differences could be elucidated.