In-situ studies of catalysts for understanding of catalytic reactions

Catalysis plays important roles in society. In particular, heterogeneous catalysis has proven to be the cornerstone of chemical and energy transformation, e.g. petroleum refining, chemical production, and plays a significant role in the development of new technology for pollution control. Understanding of catalysis requires in-situ/operando studies of catalysts in their working condition. This requirement is non-trivial hence there exist a "materials gap" and "pressure gap" in fundamental studies of heterogeneous catalysis. Attempt to narrow this "pressure gap" is described in this thesis. Through development of in-situ surface characterization techniques: high temperature near ambient scanning tunneling microscopy (HT-NAP STM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS), in-situ studies of catalysts are realized. Examples of insitu studies using these techniques, including visualization and surface chemistry characterization of model catalysts (mono-metalic and alloy) at atomic level under CO environment, and during CO oxidation, are described. The results reveal a dynamic atomic packing at the step edge of the Pt(111) surface which suggests restructuring of step edges of metal catalysts under reaction conditions and during catalysis. For Pt/Cu/Pt(111) near-surface alloy, In situ studies using HP-STM suggest formation of nanoclusters-like features at a relatively high pressure of CO (2 Torr) at room temperature with the restructured surface being active for CO oxidation at room temperature. In addition, Rh(110) surface restructures from the (1 x 2) phase to (1 x 1) phase under CO oxidation environment at Torr regime. These results overall demonstrate the necessity of in-situ surface characterization of catalysts for comprehensive understanding of heterogeneous catalysis.