Catalytic oxidation of dichloromethane over phosphate-modified Co3O4: Improved performance and control of byproduct selectivity by Co3O4 defects and surface acidity

• Phosphoric acid etching created more oxygen vacancies on Co 3 O 4 . • Phosphate modification on Co 3 O 4 generated strong surface acid sites. • Phosphate modified Co 3 O 4 were highly active and stable for CH 2 Cl 2 oxidation. • Phosphate modified Co 3 O 4 produced negligible Cl-containing organic byproducts. The catalytic oxidation of chlorinated volatile organic compounds (CVOCs) is an important topic in environmental catalysis, but the design of highly effective catalysts remains challenging. In this work, phosphate – modified Co 3 O 4 oxides gave higher activity, better durability and much lower selectivities to Cl-containing byproducts (e.g., CH 3 Cl and CHCl 3 ) compared to the pristine Co 3 O 4 in the catalytic oxidation of dichloromethane (CH 2 Cl 2 ). Such phosphate modification created more oxygen vacancies on the Co 3 O 4 and thus enhanced reducibility. On the other hand, the presence of phosphate generated abundant surface Brønsted acid sites and suppressed surface basicity. The improved performance was related to the promoted adsorption/activation of CH 2 Cl 2 on the surface acid sites, and synergistically facile oxidation of the reactive intermediates by the oxygen species activated on the oxygen vacancies. Moreover, on the modified catalyst, the fast oxidation of the reaction intermediate (i.e., CH 3 O-) inhibited the formation of CH 3 Cl. Meanwhile, the low surface basicity of the catalyst was probably responsible to the low selectivity to CHCl 3 .