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.