Role of MoO3 on a Rhodium Catalyst in the Selective Hydrogenolysis of Biomass-Derived Tetrahydrofurfuryl Alcohol into 1,5-Pentanediol

Selective hydrogenolysis of biomass-derived tetrahydrofurfuryl alcohol (THFA) to produce 1,5-pentanediol (1,5-PeD) is accomplished by a binary catalyst consisting of MoO3 and supported Rh nanoparticles; a 1,5-PeD selectivity up to 80% is achieved in the present work. Moreover, a very interesting phase-transfer behavior for MoO3 during the reaction is observed with the assistance of different characterization techniques. In this process, MoO3 dissolves partially in the liquid phase under the reaction conditions and is transformed into the soluble hydrogen molybdenum oxide bronzes (HxMoO(3)) in the presence of H-2, which are recognized as the genuinely active sites for the CO bond breaking of THFA. Density functional theory (DFT) calculations were then carried out to simulate the plausible mechanisms and highlight the role of Mo in the ring-opening process of THFA in more detail. We propose that the formation of 1,5-PeD takes place in a two consecutive reactions. THFA first undergoes acid-catalyzed ring-opening process to form the key intermediate 5-hydroxypentanal with the homogeneous catalysis of dissolved HxMoO(3). The intermediate is then quickly hydrogenated into 1,5-PeD under the heterogeneous catalysis of Rh. The concerted hydrogen-transferring-opening mechanism plausibly explains the high reaction selectivity toward 1,5-PeD in the hydrogenolysis of THFA and is verified by the reactivity trends of related substrates.