The hydrogenation of levulinic acid to Γ-valerolactone over Cu–ZrO ₂ catalysts prepared by a pH-gradient methodology

A novel pH gradient methodology was used to synthesise a series of Cu–ZrO ₂ catalysts containing different quantities of Cu and Zr. All of the catalysts were highly selective to the desired product, γ-valerolactone, and are considerably more stable than Cu–ZrO ₂ catalysts prepared by other co-precipitation methods for this reaction. Characterisation and further investigation of these catalysts by XRD, BET, SEM and XPS provided insight into the nature of the catalytic active site and the physicochemical properties that lead to catalyst stability. We consider the active site to be the interface between Cu/CuO _x and ZrO _x and that lattice Cu species assist with the dispersion of surface Cu through the promotion of a strong metal support interaction. This enhanced understanding of the active site and roles of lattice and surface Cu will assist with future catalyst design. As such, we conclude that the activity of Cu–ZrO ₂ catalysts in this reaction is dictated by the quantity of Cu–Zr interface sites.