Catalytic Hydrodehydroxylation of Biomass-Related Chemicals via Water-Mediated Hydrogen Heterolysis over a Pd-S Interface

Traditionally partial sulfur-poisoned Pd is used to enhance selectivity in hydrogenation reactions. Herein, we report that this type of catalyst can also display ultraselective hydrodehydroxylation of the C-OH group, which is important in synthesizing biomass-based fine chemicals. A series of thiol (i.e., 4-fluorobenzenethiol, 2,3,4,5,6-pentafluorobenzenethiol, and 1-hexanethiol)-modified Pd catalysts were fabricated and showed a high yield of 5-methyl furfural product formed from 5-hydroxymethyl furfural in H-2/H2O at 100 degrees C. Furthermore, the catalysts also exhibit excellent catalytic performance in hydrogenative ring-opening reactions of furan alcohols (i.e., 5-methylfuran alcohol and furan alcohol) to the corresponding ketones (i.e., 2,5-hexanedione and cyclopentanone, respectively). Elucidation of the catalytic mechanism indicates that H-2 is heterolytically activated on Pd-S as a frustrated Lewis pair to form H--Pd-S-H3O+ via a water-mediated pathway, which can selectively dehydroxylate the C-OH group and substantially promote these bifunctional catalytic reactions at the lowest reaction temperature compared to the literature. This study presents exciting bifunctional catalysis for challenging substrates by generating a transient H+-H- pair using thiol-modified metal catalysts in water.

Automated summary

This study demonstrates the ultraselective hydrodehydroxylation of C-OH groups and excellent catalytic performance in hydrogenative ring-opening reactions using partially sulfur-poisoned Pd catalysts. The elucidation of the catalytic mechanism reveals the heterolytic activation of H-2 on Pd-S and the promotion of bifunctional catalytic reactions.