Controlling the selectivity of catalytic oxidation of styrene over nanocluster catalysts

Abstract

Atomically precise Au₂₅ and Ag₄₄ as well as alloy nanoclusters (Au_25−xAg_x and Au₁₂Ag₃₂) are investigated for catalytically selective oxidation of styrene. Distinct synergistic effects of Au–Ag bimetallic nanoclusters are identified. In addition, the addition of H₂O (a few vol%) to the reaction solvent is found to drastically affect the product selectivity. Based upon Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements, a possible mechanism for the nanocluster-catalyzed styrene selective oxidation is proposed. Specifically, H₂O could change the surface composition of Au on the Au₂₅ nanocluster and the valence state of Ag on the Ag₄₄ nanocluster. Such effects are also present on the bimetallic Au_25−xAg_x, but not on the bimetallic Au₁₂Ag₃₂ nanocluster because for the latter Au exclusively acts as kernel atoms. This work provides insights into the different functional roles of water in the nanoclusters based upon their different atomic structures.