Investigation of oxygen vacancy effects on acetic acid adsorption on anatase TiO2 (101)

Ketonization is an effective means of eliminating carboxylic acids from bio-oil and increasing the carbon chain. Oxygen vacancy defects in metal oxides affect the catalytic performance. However, few studies have investigated the specific effect of oxygen vacancy defects on carboxylic acid adsorption. In this work, the interaction between acetic acid and defect anatase TiO₂ (101) was analyzed using density functional theory (DFT). Surface oxygen vacancies are more difficult to form than subsurface, but acetic acid is more readily absorbed at the surface defects. The static point potential difference between surface Lewis acid and basic sites promotes the dissociation of acetic acid on both intact and defective surfaces, especially on the surface oxygen vacancies, which decreases the reaction energy barrier for water formation during ketonization. Additionally, surface oxygen vacancies convert the bidentate carboxylates formed on the perfect surface into more active monodentate carboxylates, which reduces the energy barrier for carbon–carbon coupling reactions in the ketonization. These results indicate that the surface oxygen vacancies can enhance the ketonization of acetic acid and demonstrate that the adsorption of macromolecular organics on catalysts is influenced by a combination of Lewis acidic strength, electrostatic site distribution, interfacial structure, and reactant active sites. Our results reveal in detail the effect of acetic acid adsorption on surface oxygen vacancies at the molecular level, which lays the foundation for further studies on the catalytic reaction mechanism as well as the regulation of catalysts.