Utilization of Ni as a Non-Noble-Metal Co-catalyst for Ceria-Supported Rhenium Oxide in Combination of Deoxydehydration and Hydrogenation of Vicinal Diols

Removal of vicinal diols by combination of deoxydehydration and hydrogenation (DODH + HG) was carried out over the mixture of ReO x /CeO2 and CeO2-supported base metals with H2 as the reducing agent, in order to replace expensive Pd in the ReO x –Pd/CeO2 catalyst used in previous studies for the same reaction. Similar high activity and selectivity of the mixture catalysts of ReO x /CeO2 and pre-reduced Ni/CeO2 were observed for DODH + HG as those of Pd-based catalysts (co-loaded ReO x –Pd/CeO2 or mixture catalysts of ReO x /CeO2 + Pd/CeO2), while co-loaded ReO x –Ni/CeO2 catalyst showed almost no activity. The ReO x /CeO2 + Ni/CeO2 catalyst system gave 99% yield of tetrahydrofuran from 1,4-anhydroerythritol and could be applied to DODH + HG of other diols and polyols such as glycerol, erythritol, and xylitol. Unlike ReO x –Pd/CeO2, the activity of the ReO x /CeO2 + Ni/CeO2 catalyst decreased in the reuse test, especially before second or later reuses, even when the recovered catalyst was calcined as regeneration. The catalysts were characterized by various methods such as thermal gravimetry–differential thermal analysis, temperature-programmed reduction with H2, and X-ray absorption fine structure spectroscopy. The deactivated ReO x /CeO2 + Ni/CeO2 catalyst after use and the inactive ReO x –Ni/CeO2 catalyst after reduction had Re–Ni direct bonds, suggesting that the strong interaction between Re and Ni species decreased the activity of ReO x /CeO2 in the DODH reaction.