X-ray Absorption Fine Structure Spectroscopic Interrogation of Catalytic Reaction Kinetics from the Substrate Perspective

Coupling catalyst characterization with reactivity measurements for studying mechanisms is state of the art in catalysis research. X-ray absorption (XAS) and other spectroscopies are limited in their ability to directly link the structure of catalytically active sites with the transformation of reactants that interact with the catalyst surface. We demonstrate that the substrate could play an additional role as a probe of the surface structure of the catalyst. From this, a substrate-centric view on catalytic reactions could be obtained using the same characterization methodology as that exploited for interrogating the catalyst. For demonstration, brominated 4-nitrophenol was probed by Br K-edge XAS at different stages of catalytic nitro reduction. Its reactivity was correlated with both the Pt-Au catalyst structure, probed by Pt- and Au-centric XAS, and electrostatic interactions between the substrate and the peptides covering the nanoparticle surfaces. This concept can be extended to operando studies of a large class of catalysts in which surface exposure can be optimized to drive the reaction.