Spectroscopic Characterization of Adsorbed Carbon Monoxide on Supported Isolated, Single Atom Catalysts

Supported atomically dispersed metal catalysts are at the frontier of catalysis research, promising the combined advantages of well-defined sites and high selectivity with high stability and easy separation characterizing solid catalysts. To fully exploit the potential for commercial applications of such materials, the development of scalable and facile synthesis methods that can produce high loadings of isolated active sites with high stability is required. The chelate fixation (CheFi) method is a simple, scalable approach for preparing high-density, single-atom catalysts (SACs). 8-hydroxyquinoline (8-HQ) is used as the chelating agent due to its high affinity for metal ions and support surfaces. The 8-HQ allows the metal ions to adhere to the support and be reduced with H2, while hindering their aggregation to form clusters and/or nanoparticles. In this REU project, Fourier-transform infrared spectroscopy (FTIR) was used to characterize isolated platinum sites prepared by CheFi on a model diamond support. Carbon monoxide (CO) is a sensitive probe of the structure of metallic sites, being able to distinguish between particles, clusters, and single atoms via the effect of its surface adsorption on the C-O vibrational frequency. Additionally, the IR signal of 8-HQ can be tracked to mark its decomposition and evaporation during reduction. Results show that at a reduction temperature of 300°C, the 8-HQ signal disappears, the diamond support is chemically altered, and sintering of the single atom catalytic sites occur. The results suggest that activation treatment conditions must be optimized to achieve complete 8-HQ removal while maintaining site isolation.