Bridging the materials and pressure gaps: Catalytic oxidation of carbon monoxide and propylene on a stepped platinum surface

The catalytic oxidation of carbon monoxide (CO) and propylene on platinum catalysts has gained considerable attention due to the importance of these reactions in technological areas including environmental emissions abatement, reduction of CO in fuel cell streams and hydrocarbon sensing. Although platinum catalysts have been widely used for these applications, the fundamental understanding of molecular-level reaction mechanisms remains incomplete. Practical platinum oxidation catalysts are complex because they are generally based on oxide-supported platinum nanoparticles with multiple exposed surface orientations, significant concentrations of defect sites and the possibility of metal-support interactions. In this context, correlations between surface structure and reactivity are vitally important for the optimization of these practical catalysts. Establishing these correlations remains challenging because of the complex interactions between multiple reaction pathways and a range of reaction sites. This work focuses on the deep oxidation of CO and propylene on the stepped Pt(411) single crystal surface. To develop a robust understanding of dominant oxidation pathways, these two model oxidation reactions were studied over an extended temperature (100–000 K), pressure (10−10 to 0.01 Torr) and coverage range using a combination of conventional and synchrotron-based soft X-ray surface science techniques. The ideal Pt(411) surface consists of alternating 2- and 3-atom wide (100) terraces separated by (111) monotomically high step sites. The research reported represents a pioneering effort to establish the properties of this complex and reactive model catalyst surface. Complex adsorption and reaction behavior has been observed during all of these mechanistic studies. Oxygen adsorbs in a thermally activated process above 300 K and two types of atomic oxygen are formed. On this complex stepped surface, the dominant complete oxidation processes studied show unexpected increases in rate with increasing oxygen pressure. A wide range of reaction temperatures were observed for both carbon monoxide and propylene oxidation. Oxidation of terrace CO plays an important role in low temperature oxidation processes. By studying these model reactions on a complex stepped single crystal surface over an extended pressure range, this research provides a unique perspective which bridges the well-documented materials and pressure gap between fundamental mechanistic studies and practical catalysis.