Renewable bio-based routes to γ-valerolactone in the presence of hafnium nanocrystalline or hierarchical microcrystalline zeotype catalysts

Abstract

Different renewable bio-based routes leading to the versatile bioproduct γ-valerolactone (GVL) were studied in integrated fashions, starting from furfural (Fur), α-angelica lactone (AnL) and levulinic acid (LA), in the presence of multifunctional hafnium-containing catalysts, in alcohol media. These routes involved acid and reduction reactions for which multifunctional catalysts were prepared via top-down strategies, namely the nanocatalyst Hf-deAlBeta-n and the hierarchical (intracrystalline micro/mesopores) microcrystalline material Hf-WdeSAlBeta-m. Mechanistic and kinetic modelling studies, molecular-level investigations by solid-state spectroscopic characterization, and catalyst stability studies led to assessments about the catalytic roles and potentialities of the prepared materials for GVL production. The influences of the catalytic reaction conditions and type of transition metal in the catalysts were studied. The best-performing catalyst was the hierarchical zeotype Hf-WdeSAlBeta-m (GVL yields of up to 99% from LA, 91% from AnL, and 73% from Fur, at 180 °C), which correlated with its enhanced acidity and mesoporosity. To the best of our knowledge, this is the first reported hafnium-containing BEA zeotype possessing an intracrystalline hierarchical pore system, and the results highlighted the catalytic potentialities of these types of materials for the integrated production of GVL.