Preparation of Highly Active Monometallic Rhenium Catalysts for Selective Synthesis of 1,4-Butanediol from 1,4-Anhydroerythritol.

1,4-Butanediol can be produced from 1,4-anhydroerythritol through the co-catalysis of monometallic mixed catalysts (ReO /CeO +ReO /C) in the one-pot reduction with H . The highest yield of 1,4-butanediol was over 80 %, which is similar to the value obtained over ReO -Au/CeO +ReO /C catalysts. Mixed catalysts of CeO +ReO /C showed almost the same performance, giving 89 % yield of 1,4-butanediol. The reactivity trends of possible intermediates suggest that the reaction mechanism over ReO /CeO +ReO /C is similar to that over ReO -Au/CeO +ReO /C: deoxydehydration (DODH) of 1,4-anhydroerythritol to 2,5-dihydrofuran over ReO species on the CeO support with the promotion of H activation by ReO /C, isomerization of 2,5-dihydrofuran to 2,3-dihydrofuran catalyzed by ReO on the C support, hydration of 2,3-dihydrofuran catalyzed by C, and hydrogenation to 1,4-butanediol catalyzed by ReO /C. The reaction order of conversion of 1,4-anhydroerythritol with respect to H pressure is almost zero and this indicates that the rate-determining step is the formation of 2,5-dihydrofuran from the coordinated substrate with reduced Re in the DODH step. The activity of ReO /CeO +ReO /C is higher than that of ReO -Au/CeO +ReO /C, which is probably related to the reducibility of ReO /C and the mobility of the Re species between the supports. High-valent Re species such as Re on the CeO and C supports are mobile in the solvent; however, low-valent Re species, including metallic Re species, have much lower mobility. Metallic Re and cationic low-valent Re species with high reducibility and low mobility can be present on the carbon support as a trigger for H activation and promoter of the reduction of Re species on CeO . The presence of noble metals such as Au can enhance the reducibility through the activation of H molecules on the noble metal and the formation of spilt-over hydrogen over noble metal/CeO , as indicated by H temperature-programmed reduction. The higher reducibility of ReO -Au/CeO lowers the DODH activity of ReO -Au/CeO +ReO /C in comparison with ReO /CeO +ReO /C by restricting the movement of Re species from C to CeO .