Study On Deep Catalytic Oxidation Of O-xylene Over Ag/Co-OMS-2 Catalyst

Benzene pollutants do great harm to human production and life,so it is urgent to deal with them.Catalytic combustion is the most effective method for the treatment of benzene pollutants,which can completely catalyze the oxidation of organic matter to CO₂ and H₂O.Based on OMS-2（Cryptomelane type octahedral molecular sieves）catalyst,Ag/Co-OMS-2（OMS-2 doped with Ag and Co species）catalyst was prepared by doping cobalt oxide and silver oxide in this essay,which was used for catalytic combustion of o-xylene.The research contents are as follows:（1）A series of Co-OMS-2 catalysts were prepared by hydrothermal oxidation-reduction method using potassium permanganate,manganese sulfate,cobalt nitrate and sulfuric acid as reactants.The effects of different systems,p H value,Co/Mn molar ratio and calcination temperature on the structure and activity of the catalyst were investigated.The results of catalytic oxidation of o-xylene showed that the best activity of the T₁₀₀（Temperature corresponding to 100%yield of carbon dioxide）,T₅₀（Temperature corresponding to 50%yield of carbon dioxide）and T₂₀（Temperature corresponding to 20%yield of carbon dioxide）of Co-OMS-2-M-3.5-0.4-350 catalyst was respectively 190℃,175℃and 169℃,compared to the T₁₀₀,T₅₀ and T₂₀ of the OMS-2 were 20℃,19℃and 18℃lower,respectively.XRD（X-ray Diffraction）,FT-IR（Fourier Transform Infrared Spectroscopy）,Raman spectroscopy,Physical adsorption and desorption of N₂,SEM（Scanning Electron Microscope）and EDS（Energy Dispersive X-ray Spectroscopy）.The results showed that Co-OMS-2-M-3.5-0.4-350 was a microcrystalline OMS-2 catalyst,which indicated that the Co oxygen species were uniformly doped into the lattice of OMS-2 catalyst,which reduces the crystallinity of the catalyst.The results of H₂-TPR（H₂-Tempreture programmed reduction）,O₂-TPD（O₂-Tempreture programmed desorption）,TPR-TPO（Tempreture programmed reduction-Tempreture programmed oxidation）and CO₂-TPD（CO₂-Tempreture programmed desorption）showed that the oxidation ability,lattice oxygen release ability and reoxidation ability of the catalysts were enhanced,while the CO₂ adsorption ability was weakened.The oxygen species replaced the manganese species in OMS-2 catalyst,which made the catalyst produce lattice distortion,promoted the release of lattice oxygen in the catalyst,and improved the catalytic oxidation ability of the catalyst for o-xylene.The stability test results showed that the activity of Co-OMS-2-M-3.5-0.4-350 catalyst remained unchanged at the temperature of complete catalytic oxidation of o-xylene for 60 h.（2）On the basis of Co-OMS-2-M-3.5-0.4-350 catalyst,Ag/Co-OMS-2-M-3.5-0.4-350catalysts are prepared by deposition precipitation method.The results of catalytic oxidation of o-xylene showed that the best activity of the T₁₀₀,T₅₀ and T₂₀ of5%Ag/Co-OMS-2-M-3.5-0.4-350 catalyst was respectively 180℃,162℃and 152℃,compared to the T₁₀₀,T₅₀ and T₂₀ of the Co-OMS-2-M-3.5-0.4-350 were 10℃,13℃and17℃lower,respectively.The results of XRD,N₂ physical adsorption desorption,EDS and Raman showed that the incorporation of Ag oxygen species into the catalyst at the molecular level,which was improves the contact degree between different metal oxides,enriches the content of active oxygen species,and finally promotes the efficient catalytic oxidation of o-xylene.The results of H₂-TPR,TPR-TPO,O₂-TPD and CO₂-TPD showed that the incorporation of Ag oxygen species was beneficial to the activation of molecular oxygen and the formation of surface oxygen species,and also improved the fluidity and reoxidation ability of lattice oxygen.At the same time,it also weakens the CO₂ adsorption capacity and reduces the formation of carbonate.The results of stability test showed that the activity of5%Ag/Co-OMS-2-M-3.5-0.4-350 catalyst remained unchanged at the temperature of complete catalytic oxidation of o-xylene for 60 h.