Nanometer scale spectroscopic visualization of catalytic sites during a hydrogenation reaction on a Pd/Au bimetallic catalyst

Understanding the mechanism of catalytic hydrogenation at the local environment requires chemical and topographic information involving catalytic sites, active hydrogen species, and their spatial distribution. Here we used tip-enhanced Raman spectroscopy (TERS) to study the catalytic hydrogenation of chloronitrobenzenethiol on a well-defined Pd(submonolayer)/Au(111) bimetallic catalyst ( $$p_{\rm{H}_{2}}$$  = 1.5 bar, 298 K), where the surface topography and chemical fingerprint information were simultaneously mapped with nanoscale resolution (~10 nm). TERS imaging of the surface after catalytic hydrogenation confirms that the reaction occurs beyond the location of Pd sites. The results demonstrate that hydrogen spillover accelerates hydrogenation at Au sites as far as 20 nm from the bimetallic Pd/Au boundary. Density functional theory was used to elucidate the thermodynamics of interfacial hydrogen transfers. We demonstrate TERS to be a powerful analytical tool that provides a unique approach to spatially investigate the local structure–reactivity relationship in catalysis. Visualizing catalytic processes at the nanoscale is crucial to establish structure–activity relations, but remains very challenging. Here, hydrogen spillover is revealed with a 10 nm spatial resolution during hydrogenation of chloronitrobenzenethiol on a bimetallic Pd/Au catalyst by means of tip-enhanced Raman spectroscopy.