Effects of Biomolecules on the Selectivity of Biosynthesized Pd/MgO Catalyst toward Selective Oxidation of Benzyl Alcohol

Abstract

Catalysts prepared through biosynthesis have aroused wide concern recently, but the detailed role of biomolecules and the identification of the main components have not been figured out yet. In this study, biogenic Pd/MgO catalysts were prepared through sol-immobilization (SI) and absorption-reduction (AR) methods, respectively, using Artocarpus heterophyllus Lam leaves extracts as reductant and stabilizer. The catalyst prepared by SI method showed obviously higher benzaldehyde selectivity than that by AR method under the same conditions. The difference can be attributed to the different oxidation behaviors of phenolic hydroxyls between the two synthetic procedures. In the SI procedure, the phenolic hydroxyls were oxidized to semiquinone, while in the AR procedure, the phenolic hydroxyls were oxidized to hydroxyquinone, resulting in less carboxyls binding onto the surface of the Pd nanoparticles (NPs), thus inhibiting the formation of the byproducts. Moreover, gallic acid, chlorgenic acid, and rutin were ...