One-Step Conversion of Ethanol to Isobutene: Catalyst Optimization and Reaction Mechanism

Generations of high-value biojet and chemicals through isobutene have prominent advantages as isobutene can be prepared via the catalytic conversion of ethanol from biomass fermentation, thus making the process sustainable by using renewable feedstock. The synthesis of ethanol into isobutene is crucial for the whole process, as the reaction pathway and mechanism for isobutene-rich C4 olefins, together with the corresponding catalyst system, remain to be elucidated. In this study, a ZnO-ZrO2 catalyst was prepared and employed for the single-step conversion of ethanol, which led to a complete transformation of ethanol with a performance yielding 65.7% isobutene. Moreover, the reaction pathway was elucidated with SVUV-PIMS and DRIFTS, revealing the significant involvement of acetone, which originates from acetic acid produced via ethanol oxidation, and diacetone alcohol intermediates in the formation of isobutene. Subsequently, an integrated reaction network from ethanol to isobutene was proposed, identifying deleterious side reactions, including the formation of vinyl ketone and pentene, which were responsible for catalyst deactivation and loss of selectivity. This study offers valuable insights into the reaction mechanism of ethanol to isobutene, which is crucial for the controlled catalytic reaction of bioethanol to C4 olefins, with potential applications in sustainable fuels and chemicals.