Synergy between Pt and Au in Pt-on-Au Nanostructures for Chemoselective Hydrogenation Catalysis

Abstract

Supported Au nanoparticles (Au NPs) have been identified as highly selective catalysts for the chemoselective hydrogenation reaction potential for advanced and greener syntheses of many special and fine chemicals in organic chemistry, but their potential for applications has been hampered by their generally observed low activity arising from the intrinsic nobleness of gold to H2 activation. This work deals with a synergy between Au NPs and their carrying Pt entities in Pt-on-Au nanostructures (coded as Ptm∧Au, m denoting the atomic Pt/Au ratio) for hydrocinnamaldehyde production in the chemoselective hydrogenation of cinnamaldehyde. Ptm∧Au immobilized on a noninteracting SiO2 support (Ptm∧Au/SiO2) showed activity 1–2 orders of magnitude higher than that of monometallic Pt/SiO2 and Au/SiO2 catalysts. The high activity of Ptm∧Au nanostructures also remained distinct on interacting support materials such as Al2O3 and carbon and when varying the reaction temperature, H2 pressure, or both. Kinetic assessments suggest that the hydrogenation reaction could occur according to a Langmuir–Hinshelwood mechanism, in which cinnamaldehyde adsorbed on the Au surface was attacked by hydrogen atoms activated by Pt entities in the nanostructured Ptm∧Au catalysts. Pt dispersion or the size of the Pt entities and Pt–Au boundary, as well, strongly affected this synergic catalysis.