Aqueous-Phase Acetic Acid Ketonization over Monoclinic Zirconia

Heterogeneous catalysis in the aqueous phase is paramount to the catalytic conversion of renewable biomass resources to transportation fuels and useful chemicals. To gain fundamental insights into how the aqueous phase affects catalytic reactions over solid catalysts, vapor- and aqueous-phase acetic acid ketonization over a monoclinic zirconia (m-ZrO2) catalyst had been comparatively investigated using ab initio molecular dynamics (AIMD) simulations and density functional theory (DFT) calculations. The monoclinic zirconia was modeled by the most stable ZrO2(111) surface structure. The aqueous phase consisted of 111 explicit water molecules with a density of 0.93 g/cm3. The AIMD simulation results reveal that the aqueous phase/ZrO2(111) interface is highly dynamic. At the typical reaction temperature of 550 K, ∼67% 6-fold-coordinated Zr6c Lewis acidic sites are occupied by either water molecules or hydroxyls, while all 2-fold-coordinated O2c sites are protonated as hydroxyls. As a result, it is expected ...