Platinum/Gold Alloy Nanoparticles-Supported Hydrotalcite Catalyst for Selective Aerobic Oxidation of Polyols in Base-Free Aqueous Solution at Room Temperature

As-prepared platinum/gold alloy nanoparticles-supported hydrotalcites (PtxAuy-starch/HTs) by using a soluble starch as a green reducing and a stabilizing agent are found to be truly effective heterogeneous catalysts for the selective aerobic oxidation of glycerol (GLY) and 1,2-propanediol (PG) in base free aqueous solution using molecular oxygen in atmospheric pressure at room temperature. The PtxAuy-starch/HTs exhibited higher selectivities for oxidation of the primary hydroxyl group in GLY and PG toward glyceric acid (GA) and lactic acid (LA), respectively, with molecular oxygen in aqueous solution than those reactions over monometallic Pt-starch/HT or Au-starch/HT. Pt60Au40-starch/HT was found to be the most active catalyst for selective aerobic oxidation of polyols. It showed 73% GLY conversion with 57% GA yield and 63% PG conversion with 47% LA yield and retained high selectivity in recycling experiments. XRD patterns of the PtxAuy-starch NPs indicated the d-spacing of Pt atoms was changed by alloying with Au atoms. XPS and XANES analyses suggested that Pt atoms gained more electrons than Au atoms in PtxAuy-starch/HTs as a result of the two types of electron transfers: (1) from the starch ligand to both Au and Pt atoms and (2) from Au to Pt atoms. We concluded that the high activity and selectivity of PtxAuy-starch/HT can be explained in terms of alterations of geometric and electronic states of the catalytically active surface Pt sites by Au atoms and starch ligand.