A W 4 C 2 cluster was used to model a W 2 C catalyst with the armchair model of activated carbon support, noted as W 4 C 2 /AC. Over W 4 C 2 /AC, the mechanism for the hydrogenation of both À H 2 OH and À 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 À CH 2 OH group, whereas 2,5-dihydroxymethylfuran was the minor product from the hydrogenation of both À CH 2 OH and À CHO groups. The rate-determining steps were concerned with the À C(H) 2 À H bond formation for the hydrodehydration of À CH 2 OH group, and the À (OH)(H)À H bond formation for the hydrogenation of À CHO group. Kinetically, Wsites promoted the hydrodehydration of À CH 2 OH group and inhibited the hydrogenation of À 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 À C(OH)(H)À group, making À C(OH)(H)À H bond formation hard, and hampering the hydrogenation of the À CHO group.