Mechanisms of Mo2C(101)-Catalyzed Furfural Selective Hydrodeoxygenation to 2-Methylfuran from Computation

The selective formation of 2-methylfuran (F-CH3) and furan from furfural (F-CHO) hydrogenation and hydrodeoxygenation on clean and 4H precovered Mo2C(101) surfaces has been systematically computed on the basis of periodic density functional theory including dispersion correction (PBE-D3). The clean Mo2C(101) surface has two distinct surface sites: unsaturated C and Mo sites for the adsorption of H and furfural, respectively. The selectivity comes from the different preference of furfural hydrogenation and dissociation (F-CHO + H = F-CH2O vs F-CHO = F-CO + H) under the variation of H-2 partial pressure. On the basis of the computed minimum energy path on the clean surface, microkinetics shows that high H-2 partial pressure can promote 2-methylfuran formation and suppress furan formation. To verify this proposed selectivity trend of 2-methylfuran at high H-2 partial pressure, the 4H precovered Mo2C(101) surface (0.25 monolayer hydrogen coverage), which provides neighboring hydrogens for promoting furfural hydrogenation and blocks the active sites for suppressing furfural dissociation, has been used. The computed results are in full agreement with the experimentally observed selective formation of 2-methylfuran and the H-2 reaction order of one half as well as rationalize the need for a high H-2/furfural ratio (400/1). On the basis of these results, a new two-step protocol for experiments is proposed: i.e., the first step is the pretreatment of the catalyst with hydrogen, and the second step is furfural hydrogenation on H precovered catalysts.