Noble-metal-free heterogeneous catalysts for deoxydehydration (DODH) using H2 as a reductant were developed. Among various transition metals examined as additives to modify the MoOx/TiO2 catalyst, Cu showed good conversion and selectivity in the transformation of 1,4-anhydroerythritol (1,4-AHERY) to 2,5-dihydrofuran (2,5-DHF). The performance of the MoOx–Cu/TiO2 catalysts was comparable to those modified with either Ag or Au instead of Cu. Upon the combination of two Mo precursors, i.e. (NH4)6Mo7O24 and Na2MoO4, the selectivity of the catalyst (MoOx–Cu–Na/TiO2) was further enhanced to achieve 81% yield of 2,5-DHF. This catalyst also exhibited broad substrate scope including cyclic and linear alkyl vicinal diols and tartaric ester. Furthermore, MoOx–Cu–Na/TiO2 was reusable at least three times after its calcination as regeneration. The reaction was almost zero-order with respect to the H2 pressure and 1,4-AHERY concentration, suggesting that the release of the alkene is the rate-determining step. The comprehensive characterization using STEM, XRD and XAFS provided insights into the surface structure of the catalyst, revealing that H2 is activated over Cu particles and subsequently transferred to Mo cluster species on the TiO2 surface via the spillover effect to proceed with the DODH reaction.
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