Investigating Single-Atom Pt Catalysts on Metal Oxide Supports via 195Pt Solid-State NMR

Objective

Heterogeneous catalysts are essential to both the chemical industry and the green energy transition. Pt1/MOx materials represent a promising class of single-atom catalysts (SACs), where atomically dispersed Pt is bound to a reducible metal oxide support (MOx, e.g., CeO2, TiO2). However, conventional spectroscopic methods typically provide only an averaged picture of Pt environments and often fail to explain differences in reactivity between catalysts. SAC-NMR aims to utilise 195Pt solid-state nuclear magnetic resonance (ss-NMR) techniques developed at ETH Zürich to directly observe Pt sites. Notably, 195Pt ss-NMR yields chemical shift anisotropy (CSA) parameters that correlate with Pt geometry and electronic structure and can reveal the distribution of Pt sites. A systematic approach is adopted: (1) Model molecular Pt complexes are analysed to understand how CSA parameters respond to changes in local geometry. (2) Well-defined molecular Pt complexes are grafted to MOx-supports via a surface organometallic strategy, producing materials with controlled site environments suitable for validating spectroscopic models. Further, well-defined synthetic protocols for Pt1/MOx catalysts are developed. (3) Using the insights from (1) and (2), Pt1/MOx catalysts for CO oxidation and propane dehydrogenation will be studied. This includes the analysis of precatalysts, Pt1/MOx during and after catalysis and substrate-bound Pt sites (e.g., CO, propene). Changes in CSA parameters will be examined to understand differences in Pt geometry and distribution, and how they correlate to differences in reactivity. These insights are expected to guide rational design of improved Pt1/MOx catalysts and enable rapid prediction of reactivity, including through in silico screening. By applying molecular insights to investigate solid-state catalysts, SAC-NMR advances catalysis and facilitates the applicant's expansion into the study of heterogeneous catalysis and related spectroscopies.