Cascade Reactions for the Continuous and Selective Production of Isobutene from Bioderived Acetic Acid Over Zinc-Zirconia Catalysts

Bio-oil (obtained from biomass fast pyrolysis) contains a high concentration of acetic acid, which causes problems related to its storage and handling. Acetic acid was upgraded directly to isobutene over a ZnxZryOz binary metal oxide. The reaction proceeds via a three-step cascade involving ketonization, aldol condensation, and CC hydrolytic bond cleavage reactions, which was corroborated by isotopic labeling studies. Separately, ZnO and ZrO2 are incapable of producing isobutene from either acetic acid or acetone. In contrast, under optimal conditions, a Zn2Zr8Oz catalyst generates a ca. 50% isobutene yield, which corresponds to 75% of the theoretical maximum. Spectroscopic investigations revealed that a balanced concentration of acid and base sites is required to maximize isobutene yields.