Production of γ-valerolactone via selective catalytic conversion of hemicellulose in pubescens without addition of external hydrogen†
γ-Valerolactone (GVL) is an important chemical, whereas its synthesis directly from raw biomass is challenging because of its complex structure. A three-step method was developed for the selective conversion of hemicellulose in pubescens to GVL without addition of external hydrogen in the present work. We achieved a high yield of 20.0 wt% GVL based on the weight of pubescens with a high selectivity of 90.5% based on the amount of carbohydrates converted. The Pt/C catalyst was prepared by an impregnation method and characterized by XRD, TEM, XPS, Boehm titration and H2 chemisorption. It was indicated that platinum existed in the form of metal Pt0 and the GVL yield was improved on Pt/C catalytic reduction with H2. Our work also suggested that the platinum species interacted with the carboxylic and lactonic groups of activated carbon, and the Pt (220) surface might exhibit high activity for the conversion of LA and FA to GVL (TON = 1229.4). Particularly, the Pt/C catalyst was effective for the in situ generation of hydrogen by high selective decomposition of FA, and for the conversion of an aqueous mixture of monomers and oligomers derived from pubescens to GVL without separation of AlCl3, the catalyst for the dissolution of hemicellulose in the first step. The cross-enhancement of different kinds of reactions in the system was significant, which showed evidence of synergetic effects for the selective production of GVL from multiple reactions.