Aqueous-Phase Hydrogenation of Succinic Acid to γ-Butyrolactone and Tetrahydrofuran over Pd/C, Re/C, and Pd-Re/C Catalysts

Monometallic Pd/C and Re/C and bimetallic Pd-Re/C catalysts with different Re/Pd molar ratios were prepared by incipient-wetness impregnation and characterized by temperature-programmed reduction, X-ray diffraction, CO chemisorption, and transmission electron microscopy. The results indicated that there is a strong interaction between Pd and Re species and that Pd can significantly promote the reduction of rhenium oxide. The hydrogenation of succinic acid to gamma-butyrolactone and tetrahydrofuran was investigated over the as-prepared Pd/C, Re/C, and Pd-Re/C catalysts. Pd/C showed a low conversion of succinic acid and a high selectivity to gamma-butyrolactone. Adding a small amount of Re evidently enhanced the hydrogenation activity of succinic acid and improved the yield of gamma-butyrolactone, whereas more Re increased the yield of tetrahydrofuran. The main reaction pathway for the conversion of succinic acid in aqueous solution on Pd-Re/C catalysts is proposed through hydrogenation of the intermediates, including gamma-butyrolactone, 1,4-butanediol, and tetrahydrofuran as the substrates.