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

Abstract

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 H₂ partial pressure. On the basis of the computed minimum energy path on the clean surface, microkinetics shows that high H₂ partial pressure can promote 2-methylfuran formation and suppress furan formation. To verify this proposed selectivity trend of 2-methylfuran at high H₂ 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 H₂ reaction order of one half as well as rationalize the need for a high H₂/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