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

Abstract

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 Zn_<i>x</i>Zr_<i>y</i>O_<i>z</i> binary metal oxide. The reaction proceeds via a three-step cascade involving ketonization, aldol condensation, and C–C 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 Zn₂Zr₈O_<i>z</i> 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