Revealing the Facet\nDependence of Carbon Monoxide\nOxidation Catalyzed by Pd Nanoparticles via Single-Molecule Nanocatalysis

It is a challenge for ensemble measurements to understand\nthe effect\nof the nanocatalyst structure on the reactivity and stability. Using\nsingle-molecule techniques, the facet-dependent catalytic properties\nand dynamics of nanocatalyst were revealed for the CO oxidation on\nindividual palladium nanoparticles (Pd NPs) in two types (Pd-100 with\nhigh proportion of (100) facets and Pd-111 with low proportion of\n(100) facets) at the single nanoparticle level. It is discovered that\nPd-100 possesses higher intrinsic catalytic activity per site than\nPd-111, indicating remarkable activity of Pd-100 for catalyzing the\noxidation of CO. Based on the Langmuir–Hinshelwood (L-H) mechanism\nwith competitive adsorption on two adjacent sites, the facet-dependent\nadsorption properties of substrate molecules on Pd (111) and (100)\nfacets are revealed by a single-molecule fluorescence spectrum. For\nthese two types of Pd NPs, it was found that the catalytic kinetics\nor heterogeneities in the reaction of CO oxidation could be mainly\nattributed to the different activity heterogeneity in product formation\nand the desorption process on different crystal faces. Furthermore,\ndensity functional theory calculations confirmed the L-H mechanism,\nwhich indicates that the obtained unique crystal-plane-dependent properties\nof Pd NPs could be attributed to the stronger binding of the reactant\non (100) facets than those on (111) facets. Such results provide fundamental\ninsights into the structure–activity relationship of nanocatalysts\nand guide the design of highly efficient catalysts.