Trimetallic Cu–Ni–Zn/H-ZSM-5 Catalyst for the One-Pot Conversion of Levulinic Acid to High-Yield 1,4-Pentanediol under Mild Conditions in an Aqueous Medium

The one-pot direct conversion of levulinic acid (LA) to 1,4-pentanediol (1,4-PDO) was investigated over a trimetallic Zn-promoted Cu–Ni alloy on a H-ZSM-5 (Cu–Ni–Zn/H-ZSM-5) catalyst. Under mild reaction conditions at 130 °C and a H2 pressure of 2.5 MPa for 6 h in an aqueous medium, almost complete conversion of LA to high-yield 1,4-PDO (93.4%) was achieved. The presence of the Zn promoter effectively suppressed the growth of the Cu–Ni alloy nanoparticles (NPs) on the surface of H-ZSM-5. Consequently, the reducibility of the Cu–Ni–Zn alloy was much higher than that of the Cu–Ni alloy. The numerous Lewis acid sites of the Cu–Ni–Zn/H-ZSM-5 catalyst enhanced the adsorption of LA, and the adsorbed LA was converted to γ-valerolactone (GVL) at the Brønsted acid sites of H-ZSM-5 followed by hydrogenation at the Cu–Ni alloy sites. Subsequently, the readsorption of GVL was activated at the Lewis acid sites and GVL underwent ring opening, followed by hydrogenation to form 1,4-PDO at the Cu–Ni alloy sites. The H2 spillover on the Zn-promoted Cu–Ni alloy NPs enhanced the hydrogenation of LA to 1,4-PDO. Because of the mild reaction conditions, the formation of coke and active site sintering was highly suppressed. In addition, metal leaching did not occur over the trimetallic Cu–Ni–Zn/H-ZSM-5 catalyst. Consequently, the Cu–Ni–Zn/H-ZSM-5 catalyst could be used for up to five cycles with minimal activity loss.