Mechanism of Preferential Hydrogenation of Hydroxymethyl Group to Aldehyde Group in 5-Hydroxymethylfurfural over W2 C-Based Catalyst

Abstract

A W₄ C₂ cluster was used to model a W₂ C catalyst with the armchair model of activated carbon support, noted as W₄ C₂ /AC. Over W₄ C₂ /AC, the mechanism for the hydrogenation of both -H₂ OH and -CHO groups in 5-hydroxymethylfurfural (HMF) was theoretically studied in tetrahydrofuran at GGA-PBE/DNP level. 5-Methylfurfural was the major product from only hydrodehydration of the -CH₂ OH group, whereas 2,5-dihydroxymethylfuran was the minor product from the hydrogenation of both -CH₂ OH and -CHO groups. The rate-determining steps were concerned with the -C(H)₂ -H bond formation for the hydrodehydration of -CH₂ OH group, and the -(OH)(H)-H bond formation for the hydrogenation of -CHO group. Kinetically, W-sites promoted the hydrodehydration of -CH₂ OH group and inhibited the hydrogenation of -CHO group. This stemmed from the strong Lewis acidity of W-sites, which easily accepted the lone-pair electrons of the oxygen atom in the -C(OH)(H)- group, making -C(OH)(H)-H bond formation hard, and hampering the hydrogenation of the -CHO group.

Keywords: 5-hydroxymethylfurfural; 5-methylfurfural; W2C; biomass conversion; hydrogenation.