Oxygen vacancy engineering by La-incorporation into Co3O4 matrix for boosting catalytic oxidation of vinyl chloride: experimental and DFT evidences

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The development of high-performance transition metal oxides catalysts is one of the promising topics in the application field of chlorinated volatile organic pollutants abatement. Herein, La-incorporated Co 3 O 4 catalysts with variable lanthanum contents were prepared by using ZIF-67 as the sacrificial template, giving rise to successful oxygen vacancies engineering and the construction of a hollow-cage structure. Experimental results revealed that La-incorporation into Co 3 O 4 structure remarkably improved the catalytic activity for vinyl chloride (VC) oxidation with a close dependence on the lanthanum content. Among all catalysts, 5La-Co (the molar ratio of La in the total metal was 5 %) exhibited an optimal catalytic activity achieving 90 % of VC conversion at 276 °C in comparison with the pristine Co 3 O 4 (0La-Co in this work) at 290 °C. Moreover, this catalyst presented an adequately high catalytic stability under complex humid conditions. Characterization results and DFT calculations revealed the modulation of the intrinsic electronic structure and spinel lattice parameters on the Co 3 O 4 matrix by La incorporation, leading to the valence states redistribution of Co 3+ /Co 2+ , more oxygen vacancy generation originating from the lower formation energy (1.86 eV), and more abundant surface oxygen species originating from the lower gas-phase oxygen adsorption energy (−1.59 eV). All these properties enabled the observable catalytic activity enhancement of La-incorporated Co 3 O 4 catalysts. In addition, the formation of enol groups and carboxylic acid as key organic intermediates during the VC oxidation process was highlighted by the in-situ DRIFT spectroscopy. The more plentiful surface oxygen species available on La-incorporated Co 3 O 4 catalyst surface were favorable to the formation and further oxidation of these organic intermediates.