Simultaneous activation of copper mixed metal oxide catalysts in alcohols for gamma-valerolactone production from methyl levulinate

Abstract

Catalytic transfer hydrogenation (CTH) of biomass-derivatives to value-added chemicals using metal-based catalysts is a promising process in biorefinery since it does not require high pressure of expensive and flammable hydrogen gas (H2). However, an activation of these catalysts using H2 treatment prior to the CTH process limits this advantage. Here, copper mixed metal oxides are introduced as simultaneously activated catalysts (SACs) in the presence of alcohol for a production of gamma-valerolactone (GVL) from methyl levulinate (ML) without requirement of additional H2 gas during both catalyst pretreatment and hydrogenation steps. Different alcohols were selected to function as hydrogen sources for both catalyst activation and ML hydrogenation. All copper mixed metal oxides, especially CuNiO showed significant potential as catalysts for ML conversion to GVL at 200 °C within 3 h. While 2-propanol and 2-butanol exhibited effective roles as hydrogen sources for simultaneous reductions of the catalysts to generate metal active sites and provided hydrogen species for hydrogenation of ML to GVL. Hydrogen temperature programmed reduction (H2-TPR), alcohol-assisted simultaneous reaction (ASR), in situ X-ray diffraction (in situ XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the complementary cooperation between secondary alcohols and catalysts is the important key for the high GVL production in this work.