Highly Selective Synthesis of 1,4-Butanediol via Hydrogenation of Succinic Acid with Supported Cu–Pd Alloy Nanoparticles

Hydroxyapatite (HAP)-supported Cu–Pd catalysts, denoted as Cu–Pd/HAP, have been discovered to be the efficient catalysts for hydrogenation of bioderived succinic acid in which the products are selectively tunable by adjusting the mixing ratio of Cu and Pd. Optimal performance toward 1,4-butanediol (BDO) is observed with Cu–Pd/HAP prepared with 8 wt %-Cu and 2 wt %-Pd, affording a selectivity of 82% at quantitative conversion. In contrast, the monometallic Cu and Pd catalysts are unable to produce BDO as the major product, but only γ-butyrolactone (GBL) with a low yield of 16% and butyric acid (BA) with a considerable yield of 78%, respectively, is formed. The formation of well-dispersed bimetallic alloy nanoparticles is revealed by transmission electron microscopy with energy-dispersive spectroscopy, H₂-temperature programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy studies. It is concluded that the fine alloying structure with high Cu contents is significant in favoring the formation of BDO via the ring-opening step of GBL rather than the hydrogenation of GBL to the nontarget product of BA. In addition, the CuPd alloy catalyst exhibits good recycling ability in four consecutive runs without significant loss in its activity.