Effect of Stabilizing Polymers on Catalysis of Hydrotalcite-Supported Platinum Nanoparticles for Aerobic Oxidation of 1,2-Propanediol in Aqueous Solution at Room Temperature

The effect of stabilizing polymers such as starch, PVP, and PVA on catalysis of hydrotalcite-supported platinum nanoparticles (Pt–polymer/HT) for the base-free aerobic oxidation of 1,2-propanediol (PG) in aqueous solution using molecular oxygen under atmospheric pressure at room temperature (RT), electronic state, and hydrophilicity was investigated. The particle size of supported Pt naoparticles (NPs) was controlled to be the same (ca. 2.2 nm) by changing polymer amount during the preparation of Pt NPs. The Pt–starch/HT exhibited the higher activity than the Pt–PVP/HT and Pt–PVA/HT for oxidation of the primary hydroxyl group of PG toward lactic acid (LA). Pt 4f XPS and Pt L 3 -edge XANES analyses suggested that Pt atoms in Pt NPs stabilized by starch and PVA were more negative than that stabilized by PVP. Furthermore, the measurement of water contact angle suggested that Pt–starch/HT and Pt–PVA/HT had less hydrophilic nature than that of Pt–PVP/HT. These results indicate that the polymer plays an important role in determining not only the electronic charge on the Pt surface atoms but also wettability of water solvent, and these are strongly attributed to their catalysis. Starch was found to be an appropriate ligand for stabilized Pt NPs in which preserved the abundance of negatively charged to active surface and provided the suitable wettability for water solvent (hydrophilicity), bringing about the high catalytic activity of Pt–starch/HT.