(670d) Toward in-Situ Studies of Catalyst Surfaces: High-Pressure STM and Ambient Pressure XPS

In-situ information of surfaces structure of catalysts is crucial for understanding catalytic mechanisms. STM and XPS are two of the important techniques providing structural and chemical information of catalysts. A new high-pressure STM operating inside a small volume reaction cell (19 cm^3) was designed and built in our laboratory recently. This unique design allows studying surfaces of catalysts in environments of reactants with a wide pressure range (10^-10 torr to ~10 bars) and a realtively high temperature. The design of this STM will be presented. This high pressure STM revealed pressure-dependent surface structure and formation of nanoclusters of Pt model catalysts in reactant gases with a wide pressure range, suggesting the importance of studying structures of catalyst surfaces under reaction conditions for understanding catalytic mechanisms. The ambient pressure X-ray photoelectron spectroscopy (AP-XPS) has been extensively used to obtain in-situ chemical information about surface regions of catalysts. Using AP-XPS, we observed restructuring of Rh0.5Pd0.5 core-shell bimetallic catalysts driven by oxidizing, reducing, and catalytic reactions, indicating a new approach to design catalysts by a combination of the tunable syntheses of nanomaterials and the followed restructuring of the as-synthesized nanomaterials with controllable chemical reactions.