Catalytic Oxidation Of Toluene With Modified Nickel-cobalt Spinel And Its Mechanism

NiCo₂O₄ catalyzes oxidation of VOCs has the advantages of green,safety,and no secondary pollution,so it has been widely concerned in the field of VOCs degradation.However,NiCo₂O₄has problems such as low oxygen conversion efficiency,low proportion of high-valence metals,small specific surface area,and poor adsorption capacity,which limits its practical application.The purpose of this paper is to prepare high-performance NiCo₂O₄catalysts by doping non-precious metals to increase the oxygen migration rate,adjust the crystal plane to change the surface chemical properties and composition,modify the alkaline environment,and adjust the hydrothermal time to regulate the physical structure of the material.The research contents are as follows:1)In order to increase the active oxygen migration rate of NiCo₂O₄catalyst,NiCo₂O₄spinel catalyst of doping Ce with high oxygen conversion rate was prepared by impregnation,coprecipitation and hydrothermal method.By changing the doping of Ce,the effect of oxgen transfer rate on the catalyst of toluene was expored.When the toluene concentration was 2538ppm,the space velocity was 10000h^-1,and the catalyst volume was0.5m L,the 15%Ce/NiCo₂O₄catalyst prepared by one hydrothermal method,the catalyst had the best performance in degrading toluene(T₉₉=267°C),and catalytic oxidation at267°C for 72h,there was no significant change in catalyst performance.2)The exposure of different crystal faces has an important effect on the surface chemical composition and chemical properties of materials,so as to study the influence of crystal faces on the catalytic activity of materials.NiCo₂O₄spinel catalysts with specific exposed crystal faces were successfully prepared by hydrothermal method,and the effects of different crystals on catalytic oxidation performance were investigated.The preparation conditions are hydrothermal temperature 170°C,hydrothermal time 17h,calcination temperature 300°C,roasting time 200min,NiCo₂O₄sheet exposure{110}crystal plane,with lager valence metal concentration was large,better redox properties and the higher concentration of surface adsorption oxygen,has the best catalytic performance.When the toluene concentration was 2538ppm,the space velocity was 10000h^-1,and the catalyst volume was 0.5m L,the catalytic performance of NiCo₂O₄flake catalyst was the best(T₉₉=256°C).After catalytic oxidation at 256°C for 72h,the catalyst performance does not change significantly.3)On the basis of certain chemical composition and surface chemistry,the influence of different physical structures on the catalytic performance of NiCo₂O₄was studied.NiCo₂O₄spinel catalysts with different physical structures were prepared by hydrothermal method.The effect of specific surface area on its catalytic performance was also investigated.The results show that the material has the largest specific surface area and the best catalytic toluene performance when the preparation conditions were hydrothermal temperature 170°C,hydrothermal time 8h,calcination temperature 300°C,roasting time200min.When the toluene concentration was 2538ppm,the space velocity was 10000h^-1,and 8h NiCo₂O₄catalyst has the best catalytic performance for toluene oxidation(T₉₉=199℃).