Mechanism and Kinetics of Isobutene Formation from Ethanol and Acetone over ZnxZryOz

Isobutene is a specialty chemical used in the production of fuel additives, polymers, and other high-value products. While normally produced by steam cracking of petroleum naphtha, there is increasing interest in identifying routes to isobutene from biomass-derived compounds, such as ethanol and acetone. Recent work has shown that zinc-zirconium mixed oxides are effective and selective catalysts for producing isobutene from ethanol. We report here investigations of the mechanism and kinetics of the acetone and ethanol conversion to isobutene with the aim of elucidating the reaction pathway, the roles of active acidic and basic sites, and the role of water in promoting stability and selectivity. Zinc-zirconium mixed oxide catalysts with varying zinc loadings were synthesized and characterized with XRD, Raman, BET, CO2-TPD, NH3-TPD, and DRIFTS IR of adsorbed pyridine. The observed reaction kinetics suggest that the reaction of ethanol to isobutene proceeds via a five-step sequence. Ethanol first undergoes d...