Structure–Activity Relationships of WOx-Promoted TiO2–ZrO2 Solid Acid Catalyst for Acetalization and Ketalization of Glycerol towards Biofuel Additives

WO x -promoted TiO 2 –ZrO 2 solid acid catalyst was prepared and applied in the catalytic acetalization and ketalization of glycerol with carbonyl compounds to produce biofuel additives. The presence of WO x promoter and TiO 2 remarkably improved the catalytic activity of ZrO 2 . Approximately, 100% glycerol conversion was evidenced with non-bulky aliphatic aldehydes and ketones like, propanol and cyclohexanone. The physical characterization of WO x -promoted TiO 2 –ZrO 2, revealed a higher formation of tetragonal crystalline phase of ZrO 2 , over monoclinic. The total surface acidity and the ratio of Brønsted to Lewis acidic site concentrations were determined by NH 3 -TPD and pyridine-chemisorbed FTIR spectroscopy, respectively. A considerably higher concentration of Lewis acidic sites, ~ 213.29 μmol/gm, was evidenced on the WO x -promoted TiO 2 –ZrO 2 catalyst surface. Catalytic activity study revealed a direct correlation between the surface Lewis acidic site concentration and the activity of catalyst. This significant observation indicated the key role of Lewis acidic sites in this catalytic process. The WO x -promoted TiO 2 –ZrO 2 catalyst was also considerably stable and showed good performance in the acetalization/ketalization of glycerol with other substituted carbonyl compounds. Graphic Abstract The WO x -promoted TiO 2 –ZrO 2 solid acid catalyst exhibits superior catalytic performance for acetalization and ketalization of glycerol with carbonyl compounds to produce biofuel additives.