Direct conversion of biomass components to the biofuel methyl levulinate catalyzed by acid-base bifunctional zirconia-zeolites

A series of metal-zeolite hybrids was prepared by impregnation and deposition-precipitation methods and charaterized with different techniques. Catalytic performance of these catalysts on microwave-assisted conversion of selected carbohydrates to the fuel component methyl levulinate (ML) in methanol was studied. It was demonstrated that metal oxide content/type and acid-base bifunctionality were closely correlated with substrate conversion and ML yield, respectively. Among various as-prepared catalysts, zirconia-zeolite hybrid ZrY6(0.5) with moderate acid-base site content (0.97 & 0.08   mmol   g −1 ), high stability and porosity (average mesopore diameter: 6.2   nm) exhibited superior catalytic activity. At 180   °C, around 67–73%, 78%, 53% and 27% yields of ML could be achieved from monosaccharides (e.g., glucose, mannose and galactose), sucrose, starch and cellulose, respectively. The Zr-Y6(0.5) hybrid exhibited good stability, and could be reused for five times with ML yields of ≥63% from glucose.