Solvent-Free Selective Oxidation of Benzyl Alcohol at Atmospheric Pressure Catalyzed by Pd Nanoparticles Supported on g-C3N4 Materials with Tunable Nitrogen Distributions

Solvent-free atmospheric selective oxidation of benzyl alcohol (BZA) by molecular oxygen is a promising and green process for the synthesis of benzaldehyde (BZL). Supported Pd nanoparticles have been widely reported in the catalytic selective oxidation of BZA where the activity depends on the chemical valence and dispersion of the Pd nanoparticles. Herein, a series of thermally exfoliated g-C3N4 (eg-C3N4 ) have been synthesized under various gas conditions (air/N-2) and then applied as catalyst supports to load Pd nanoparticles. The physicochemical properties of the prepared Pd/eg-C3N4 materials have been characterized by N2 adsorption-desorption, XRD, FT-IR, UV-vis, XPS, and TEM. Pd nanoparticles dispersed well on the supports, and the distributions of Pd and nitrogen species of the catalysts were related to the gas conditions of the supports. In the selective oxidation of BZA, 2.5Pd/eg-C3N4-AN catalyst afforded conversion of BZA and the selectivity to BZL of 88 % and 92 %, respectively. The metallic Pd-0 species are considered the catalytic sites of Pd/eg-C3N4 in the catalytic reaction and meanwhile, the basic Nb species of eg-C3N4 were beneficial to the overall activity of the catalyst.