Cascade catalytic transfer hydrogenation–cyclization of ethyl levulinate to γ-valerolactone with Al–Zr mixed oxides

A series of Al–Zr mixed oxides with different molar ratios were prepared by co-precipitation method and utilized to catalyze conversion of ethyl levulinate (EL) to γ -valerolactone (GVL). Those as-prepared catalysts were characterized by XRD, SEM, N 2 adsorption–desorption, XPS, TG, NH 3 -TPD, CO 2 -TPD and pyridine-IR. The introduction of Al into ZrO 2 was demonstrated to enlarge surface areas, as well as increase the number of acid and base sites that were catalytically active for transfer hydrogenation. Effects of Al–Zr molar ratio, calcination temperature, reaction temperature and time, catalyst dosage, and alcohols used as hydrogen donors on the catalytic performance were investigated. A high GVL yield of 83.2% at EL conversion of 95.5% could be achieved at 220   °C in 4   h over Al 7 Zr 3 -300 using 2-propanol as hydrogen donor and solvent. Poisoning experiments verified that acid–base sites played a synergic role in producing GVL from EL. Moreover, the Al–Zr mixed oxide catalyst was able to be reused for several times with a slight loss in its catalytic activity.