Hydrogenation of levulinic acid to γ-valerolactone over bifunctional Ru/(AlO)(ZrO)n catalyst: Effective control of Lewis acidity and surface synergy

A bifunctional Ru/(AlO)(ZrO) n catalyst was reported for efficient hydrogenation of levulinic acid to γ-valerolactone, an important and environmental-benign upgrading process of bio-platform compound. The optimal Ru/(AlO)(ZrO) 0.1 catalyst showed 100% yield to γ-valerolactone in water at 120 °C under 1 MPa H 2 , one of the best performances among Ru catalysts under mild conditions. And this catalyst also presented good stability and reusability. PXRD, TEM, XPS, CO chemisorption, CO adsorption DRIFT-IR, NH 3 -TPD and pyridine adsorption IR gave insights into the acidic property and surface synergy of the catalysts. Highly active electron-rich Ru 0 sites stabilized by strong metal-support interaction (SMSI) can effectively adsorb and activate molecular H 2 and C O bond in levulinic acid. Varying Zr/Al ratio and calcination temperature can rationally control the acid strength and acid sites distribution of support, and (AlO)(ZrO) 0.1 calcined at 400 °C exhibited the maximal proportion of Lewis acid sites. Ru 0 species and Lewis acid sites synergistically enhanced the conversion of levulinic acid and facilitated the intramolecular dehydration of 4-hydroxypentanoic acid as intermediate to γ-valerolactone ( i.e. , the rate-limiting step).