Mechanochemical Synthesis Of New CeO₂-Based Catalysts For Study On Catalytic Degradation Of 1,2-DCBz

In recent years,the urbanization process in China has gradually accelerated the scale of domestic waste incineration disposal,which brings the problem that it is more and more difficult to control the waste incineration smoke pollutants,especially the highly toxic,carcinogenic and refractory dioxins.Therefore,under the increasingly strict emission standards,effective control of dioxins appears more urgent.Among the typical dioxin terminal control technologies,catalytic degradation technology has many advantages in terms of less secondary pollution,low energy consumption and high efficiency compared with other technologies,thus becoming a method with good development prospects.In view of this technology,the current exploration lies in the development of catalysts with high activity and stability,few by-products and low price.CeO₂catalyst has been proved to be more effective in catalytic degradation of Cl-VOCs.In addition,compared with the catalysts prepared by traditional methods,the mechanochemical method shows better catalytic performance,and its green and sustainable characteristics make it become a research hotspot.Based on the above background,pure CeO₂,a series of binary Mn-Ce-O and multiple Mn-Ce-Z-O（Z=Sn,Ru,Cr,V）catalysts were synthesized by mechanochemical in this paper.1,2-dichlorobenzene was used as the experimental reactant model for dioxins,focusing on the activity and stability of the catalysts.Combined with characterization analysis,the changes of preparation method,Mn precursor,Mn Ce component proportion and active component diversity on the physical and chemical properties of the catalyst were studied.In the end,the key factors that are more advantageous for mechanized synthesis of catalysts,such as the mechanism of Mn doping to improve the low temperature activity of CeO₂-based catalysts,and the mechanism of Cr addition to improve the high temperature stability of CeO₂-based catalysts,are proposed.The main conclusions are as follows:（1）Compared with Mn CeO_x-CP catalyst prepared by traditional coprecipitate method,it was found that Mn CeO_x-BM catalyst prepared by mechanochemical had higher catalytic activity in the temperature range of 150～350℃,and almost realized the complete transformation of1,2-dichlorobenzene at 250℃.The conversion rate of 1,2-dichlorobenzene for Mn CeO_x-CP is only 60%at the corresponding temperature.This is mainly because the catalysts synthesized by mechanochemical method have higher porosity and larger specific surface area,so that their catalytic performance shows obvious advantages.（2）The doping of Mn contributes to the improvement of the activity of CeO₂catalyst,and the Mn precursor and content of Mn has a significant impact on the performance of catalyst synthesized by mechanochemical:Mn CeO_x-MN catalyst prepared with manganese nitrate as precursor shows better catalytic activity than Mn CeO_x-MC catalyst prepared with manganese acetate as precursor,which is mainly attributed to stronger surface acidity,higher content of Mn⁴⁺and reducible oxygen.For a series of Mn_yCe_1-yO_xcatalysts with different component ratios,their catalytic activity increased with the increase of Mn doping content,because with the increase of Mn content,the surface defects of the catalyst became larger and larger,Ce^3+/4+became higher and higher,and the REDOX performance became stronger and stronger,resulting in a positive effect.（3）Based on the low temperature activity of catalytic degradation of 1,2-dichlorobenzene,the best preparation formula for mechanized synthesis of binary mangane-cerium composite oxide catalyst is as follows:Based on mechanochemical,Mn（NO₃）₂·4H₂O was used as manganese precursor and Mn_0.85Ce_0.15O_xcatalyst with Mn/（Mn+Ce）mole ratio of 0.85 was adjusted.Its activity is as follows:T_50%=152℃,T_90%=193℃,T_100%=250℃.The embedment of Mn ions into CeO₂crystal leads to lattice distortion and the formation of"Mn-O-Ce"solid solution structure,which contributes to the release of more oxygen vacancies and greatly improves the catalytic activity.（4）The addition of Sn,Ru,Cr and V further improves the physical and chemical properties of the catalysts,which is mainly reflected in the smaller particle size in the microstructure,which improves the dispersity of the catalysts.The third metal ion in crystal structure may also be embedded in the cerium fluorite lattice like Mn ion,which contributes to the stability of the active component.More surface reactive oxygen species and lower temperature reducibility enhance the REDOX capacity of the catalyst.The surface acidity also increased to some extent.（5）Synthesis of catalytic degradation of 1,2-dichlorobenzene activity and stability experimental results,Mn-Ce-Cr-O is a catalyst with high activity at low temperature and high temperature stability.Raman,XPS and H₂-TPR characterization results confirm each other,indicating that Cr⁶⁺species with strong oxidation capacity exist in Mn-Ce-Cr-O catalyst,and participate in the catalytic oxidation of 1,2-dichlorobenzene in the stability test experiment.The enhancement mechanism of Cr on catalyst activity stability lies in the Deacon reaction on the catalyst surface,which realizes the deep oxidation of 1,2-dichlorobenzene on multiple catalysts and accelerates the removal of Cl species on the surface.The enhancement of Cl resistance improves the stability of the catalyst.