Catalytic oxidation of dibromomethane over Ti-modified Co₃O₄ catalysts: Structure, activity and mechanism

Ti-modified Co₃O₄ catalysts with various Co/Ti ratios were synthesized using the co-precipitation method and were used in catalytic oxidation of dibromomethane (CH₂Br₂), which was selected as the model molecule for brominated volatile organic compounds (BVOCs). Addition of Ti distorted the crystal structure and led to the formation of a Co-O-Ti solid solution. Co₄Ti₁ (Co/Ti molar ratio was 4) achieved higher catalytic activity with a T₉₀ (the temperature needed for 90% conversion) of approximately 245°C for CH₂Br₂ oxidation and higher selectivity to CO₂ at a low temperature than the other investigated catalysts. In addition, Co₄Ti₁ was stable for at least 30h at 500ppm CH₂Br₂, 0 or 2vol% H₂O, 0 or 500ppm p-xylene (PX), and 10% O₂ at a gas hourly space velocity of 60,000h^-1. The final products were CO_x, Br₂, and HBr, without the formation of other Br-containing organic byproducts. The high catalytic activity was attributed to the high Co³⁺/Co²⁺ ratio and high surface acidity. Additionally, the synergistic effect of Co and Ti made it superior for CH₂Br₂ oxidation. Furthermore, based on the analysis of products and in situ DRIFTs studies, a receivable reaction mechanism for CH₂Br₂ oxidation over Ti-modified Co₃O₄ catalysts was proposed.