Small Ligand-Involved Pickering Droplet Interface Controls Reaction Selectivity of Metal Catalysts

Developing efficient methods to improve catalytic selectivity, particularly without sacrificing catalytic activity, is of paramount significance for chemical synthesis. In this work, we report a small ligand-involved Pickering droplet interface as a brand-new strategy to effectively regulate reaction selectivity of metal catalysts. It was found that small ligands such as polar arenes could engineer the surface structure of Pt catalysts that were assembled at Pickering droplet interfaces. Due to the strong hydrogen-bonding interactions with water, the polar arenes preferentially adsorbed with the water adlayer that covered Pt surfaces, forming water-mediated metal-organic interfaces on the Pickering emulsion droplets. Such an interface system displayed a significantly enhanced p-vinylaniline selectivity from 8.7 to 94.2% with an unreduced conversion in p-nitrostyrene hydrogenation. The selectivity was found to follow a negatively linear correlation with the bond length of the interfacial hydrogen bonds. Theoretical calculations revealed that the small arene ligands could closely array at the interface, which modulated the adsorption patterns of reactant/product molecules to prevent the C═C group from approaching Pt surfaces without suppressing their accessibility toward reactant molecules. Such a remarkable interfacial steric effect contributed to the efficient control of the hydrogenation selectivity. Our work provides an innovative strategy to modulate the surface structure of metal catalysts, opening a new venue to tune catalytic selectivity.