Concave Cubes as Experimental Models of Catalytic Active Sites for the Oxygen-Assisted Coupling of Alcohols by Dilute (Ag)Au Alloys

A major challenge in understanding structure–function relationships in heterogeneous catalysis is bridging the materials complexity gap between the well-ordered surfaces used in fundamental experimental and computational studies and the more complex and dynamic materials that exist under catalytic operating conditions. In this work, we utilized (Ag)Au concave cube nanoparticles as experimental models to test a prediction made by theory regarding a potential bimetallic active site for the dissociation of molecular oxygen, which is a key initiating step in the selective oxygen-assisted coupling of alcohols. As a consequence of their method of synthesis, the concave cubes have surfaces that are rich in Ag-stabilized Au step edges, which is the active site proposed by theory, and thus we predicted that they would have high activity for the methanol coupling reaction. Indeed, in addition to 99% selectivity toward the desired coupling product, methyl formate, the concave cubes show a major increase in activity compared to ozone-activated nanoporous gold, a comparable dilute (Ag)Au alloy catalyst for the same reaction, even without an activating ozone pretreament. Further, the well-defined surfaces of these concave cubes open up opportunities for in-situ microscopy and spectroscopy experiments that can provide a better understanding of (Ag)Au active sites. More broadly, this work highlights how nanoparticles with controlled shapes and well-defined surfaces can be rationally tailored to experimentally validate predictions from theory.