Oxygen vacancy mediated La1-xCexFeO3-δ perovskite oxides as efficient catalysts for CWAO of acrylic acid by A-site Ce doping

Abstract

The influence of Ce amount on catalytic behaviour of perovskite catalysts La1-xCexFeO3-δ, prepared by coprecipitation was examined in catalytic wet air oxidation (CWAO) of high concentrated acrylic acid pollutant. The catalysts with the molar ratio of Ce/ (La + Ce) upper than 0.4 exhibit high catalytic activity, and outstanding stability. Because Ce doping into the skeleton of LaFeO3 could cause the change of iron valence state as well as the change of the reactive oxygen species and oxygen vacancies of the catalyst. Three ways of O2 involved in this reaction were considered, a synergistic mechanism of oxygen vacancies, the reversible electronic transition Fe3+↔ Fe2+, and direct oxidization of acrylic acid. First-principles calculations revealed that the oxygen vacancy is more easily to form in the case of Ce content increasing in La1-xCexFeO3-δ, and oxygen would adsorb on oxygen vacancy to form reactive oxygen species. Consequently, the reactive oxygen species (O*) could oxidize acrylic acid. In this process, Fe ions of higher valence sate which would attack organic compounds and itself was reduced to Fe2+ to achieve catalytic cycles. Finally, the reaction was verified as first order, which was well explained by a proposed generalized kinetic model, in good accordance with our experimental data.