Efficient transformation of levulinic acid/esters to γ-valerolactone via a durable catalyst with simply tunable acid-base sites

The xZrO2/TiO2-PMo(y) catalysts were synthesized using a conventional impregnation method with TiO2 as the support. By simply adjusting the loading amount of Zr species and the addition of phosphomolybdic acid, the acid and basic properties of the catalysts were rationally modulated. The synthesized 30%ZrO2/TiO2-PMo(6) catalyst exhibited excellent Meerwein-Ponndorf-Verley (MPV) reduction performance, achieving a 90.8% yield of γ-valerolactone (GVL) from levulinic acid (LA) at 180 °C within 3 h. The total acidity, Lewis and Brønsted acid sites, and basic sites of the xZrO2/TiO2-PMo(y) catalysts were characterized and their effects on the MPV reduction of LA to GVL were detailed discussion. The deactivation of the 30%ZrO2/TiO2-PMo(6) catalyst was mainly due to the carbon deposition instead of leaching, and the catalytic performance could be restored through an effective regeneration method. Additionally, the 30%ZrO2/TiO2-PMo(6) catalyst demonstrated superior universality in the MPV reduction of methyl levulinate (ML), ethyl levulinate (EL), and butyl levulinate (BL) to GVL, with yields of 85.3%, 84.2%, and 83.7% for ML, EL, and BL, respectively. This study presents a sustainable method for the MPV reduction of LA to GVL and provides a potentially valuable reference for other reactions that involve the synergistic catalysis of Lewis and Brønsted sites along with basic sites.