Preparation Of Co-based Momolithic Catalysts For VOCs Catalytic Combustion

The massive emissions of volatile organic compounds?VOCs?pose a serious hazard to the environment and human health.Catalytic combustion is the most effective and widely used technique for treating VOCs.The key to the catalytic combustion of VOCs is the choice of catalyst.In this paper,Co₃O₄ nanowires were grown on cordierite and then combined with other active components such as perovskites and MnO₂ to prepare monolithic catalysts for the catalytic combustion of o-xylene.The main work and results are as follows:1.Perovskite?LaBO₃,B=Mn,Co or Ni?/Co₃O₄ with different morphologies were successfully integrated onto the surface of three-dimensional?3-D?cordierite honeycomb ceramics by two-step combination method of hydrothermal synthesis and impregnation.The charavterization results show that the La₂NiO₄/Co₃O₄ composite exhibits a 3D hierarchical hollow microsphere construction assembled by numerous nanowires,which is different from the nanowire structure of LaMnO_3.15/Co₃O₄ and LaCoO₃/Co₃O₄.Compared to LaMnO_3.15/Co₃O₄/cordierite and LaCoO₃/Co₃O₄/cordierite,the La₂NiO₄/Co₃O₄/cordierite catalyst possesses alower light-off temperature and better catalytic performance.The synergistic effect between La₂NiO₄ and Co₃O₄ promotes the oxygen storage capacity of the catalyst,and the strong interaction between La₂NiO₄ and Co₃O₄ promotes the formation of porous hollow microspheres and increases the specific surface area of the catalyst.In addition,when the perovskite-like loading was 11.39 wt%and the catalyst was calcined at 600°C for 4 hours,it exhibited the best catalytic performance for o-xylene oxidation with 90%conversion at 299°C.In addition,the catalyst also has good conversion stability.2.The MnO₂/Co₃O₄/cordierite monolithic catalysts with different morphologies were prepared by hydrothermal synthesis.We studied the effects of cobalt salt types,molar ratio of cobalt nitrate to urea and hydrothermal reaction temperatures on catalyst activities.The characterization results show that the potassium permanganate reacts with the carbon layer to obtain MnO₂ nanoparticles,while maintaining the nanoflower-like structure,the synergistic effect between MnO₂ and Co₃O₄ also enhanced the catalytic performance.Different cobalt precursors result in different morphologies.When cobalt nitrate is used as the cobalt source,a nanoflower-like structure is obtained;when cobalt acetate is used as a cobalt source,a needle-shaped nanowire structure with sharp tips is formed;the catalysts prepared from cobalt chloride as cobalt source are not composed of nanowires,but the uniformly grown fan-shaped sheets.The activity test results show that the MnO₂/Co₃O₄/cordierite catalyst has the best activity when the cobalt nitrate is used as the cobalt source,the molar ratio of cobalt nitrate to urea at 1:2.5,and the hydrothermal reaction temperature at 160°C.This is because the porous nanowire structure is formed,and the catalyst has a larger specific surface area.It is also found that the catalyst always exhibits excellent catalytic performance in the range of space velocity(5000-20000 h^-1)and concentration?500-1500 ppm?.