Acidic O Dopants Collaborating with Oxidized Pd Centers to Promote Hydrodeoxygenation of Vanillin

Abstract

Hydrodeoxygenation is the key technology for realizing the conversion of biomass into high value-added chemicals, but usually encounters low efficiency and harsh conditions due to the rich electron density and strong C-O bonds of O-containing groups. Herein, an efficient catalyst is precisely constructed with abundant acidic O dopants and well-exposed oxidized Pd centers for hydrodeoxygenation of vanillin. Through a tannic acid-assisted strategy, it is precisely constructed on alumina that electron-deficient O species doped as ether types in carbon along with ultra-small PdO nanoparticles. The collaboration of acidic sites from O dopants and oxidized Pd centers on PdO boosts hydrodeoxygenation of vanillin into valuable 2-methoxy-4-methylphenol in 99% yield with a turnover frequency value of 752 h-1 under mild conditions (80 oC, 0.5 MPa H2), significantly surpassing similar catalysts without oxidized Pd centers or O dopants as well as commercial Pd heterogeneous and homogeneous catalysts. Further theoretical calculation studies disclose that oxidized Pd centers are superior to metallic Pd centers for hydrogenating vanillin aldehyde group, and acidic O dopants are important for promoting the subsequent alcohol-based deoxygenation process.

Keywords: Acidic O dopants, Oxidized Pd centers, Hydrodeoxygenation, Biomass, Tannic acid