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.