Preparation Of Copper Modified Manganese Oxide Catalysts With Different Structure And Their Performance For Catalytic Combustion Of Toluene

In recent years,volatile organic compounds（VOCs）emitted during industrial and commercial processes have caused great harm to human health and the environment.Therefore,it is imperative to effectively remove VOCs pollutants.Catalytic combustion technology has a good effect on the removal of low-concentration VOCs,which can be converted into harmless CO₂ and H₂O.Catalyst is the key of catalytic combustion,and noble metal catalysts with high activity are limited in industrial applications due to their high cost,stability,and poor water resistance.The non-noble metal manganese oxide catalysts are inexpensive and have high stability,however,the catalytic performance still needs to be improved.In this paper,the preparation conditions of copper-modified manganese oxide catalysts and the activity of catalytic oxidation for toluene were studied.In addition,the effect of copper on the structure and properties of manganese oxide catalysts were also discussed.In this paper,manganese oxide catalysts with different structures were prepared by controlling the pH of hydrothermal synthesis under the conditions of doped copper and undoped copper.The structural and physical-chemical properties were analyzed by XRD,SEM,TEM,N₂-AD,H₂-TPR and XPS and the catalytic performance of these catalysts were studied by catalytic combustion of toluene.It was found that the catalytic activity of catalysts with different structures for catalytic combustion of toluene are absolutely different,and the copper-manganese oxide catalyst prepared under the same preparation conditions showed better catalytic activity for toluene.The catalyst prepared under acidic conditions had a one-dimensional tunnel structure,the catalyst prepared under alkaline conditions had a two-dimensional layered structure,and the catalyst prepared under neutral conditions had a transition structure.Among them,the tunnel structure catalyst Cu-Mn-4 showed the best activity among these Cu-Mn catalysts.Abundant surface oxygen species,good low temperature reducibility,low average oxidation state of manganese and high specific surface area lead to remarkable catalytic performance（T50=138°C,T90=169°C）of this catalyst.The unique copper states existing in the tunnel-structure play a key role in promoting the cyclic redox process,which promotes the catalytic oxidation reaction.Additionally,the catalytic performance of Cu-Mn-4 catalyst for toluene under water vapor condition was investigated.It was resulted that the catalyst Cu-Mn-4 exhibited excellent water resistance and stability.In this paper,the effect of copper doping ratio on the structure and properties of manganese oxide catalysts were studied.The results suggested that the catalytic oxidation activity of copper-manganese catalysts for toluene was in the following order:Cu_0.25-Mn-4>Cu_0.1-Mn-4>Cu_0.4-Mn-4>Cu₀-Mn-4.At a lower copper-manganese ratio,it can be found that the low temperature reducibility has been improved with the increase of the copper-manganese ratio,which promoting the catalytic activity.Additionally,the accumulation of copper on the surface of catalyst,the surface oxygen species,oxygen vacancies were increased.And the Cu-Mn redox interaction force was enhanced.However,when the copper to manganese ratio increases to 0.4,the catalytic activity of the catalyst Cu_0.4-Mn-4 was reduced,due to the reduction of oxygen species and oxygen vacancies on the catalyst surface.