A Mechanistic Study on the Selective Hydrogenation of γ-Butyrolactone over the Rationally Designed Bimetallic CuCo Catalysts

A series of bimetallic CuCo supported on SiO2 was synthesized and characterized by temperature-programmed reduction (TPR), X-ray diffraction (XRD), TEM, and X-ray absorption fine structure (XAFS) spectroscopy. The conclusive characterization results revealed the formation of the CuxCo3–xO4 precursor, which led to high reducibility with the increase of the metal surface area, resulting in the prevention of Cu oxidation. The reactivity tests of γ-butyrolactone (GBL) hydrogenation on a series of supported bimetallic CuCo catalysts were investigated at 200 °C and 4 MPa with a weight hourly space velocity (WHSV) of 0.12–1.92 h–1. It is revealed that cobalt significantly affects GBL conversion, while copper plays an important role in improving the selectivity to 1,4-butanediol (BDO). The initial reaction rate had a large influence on the high metal surface area and was found to be as follows: Cu4Co6/SiO2 > Co/SiO2 ≥ Cu2Co8/SiO2 > Cu6Co4/SiO2 ≥ Cu8Co2/SiO2. The mechanistic study elucidates the overall reaction network in which 1,4-butanediol (BDO) is formed as the initial product, with the subsequent formation of secondary products including tetrahydrofuran (THF), 1-butanol (BuOH), and 1-propanol (PrOH). Furthermore, kinetic analysis of GBL hydrogenation based on the proposed reaction network was simulated, and Delplot analysis was applied to verify the reaction network with confirmation of the proposed reaction network.