Construction Of Micronano Structure Of Cobalt-based Oxide Catalyst And Its Catalytic Purification Of N₂O

As the third largest global greenhouse gas,nitrous oxide(N2O)has a higher global warming benefit per unit concentration than CO2 and CH4,and continues to deplete stratospheric ozone.With the continuous advancement of industrial processes,the concentration of N2O in the atmosphere is increasing,and the elimination and purification of N2O is imminent.As the most promising N2O elimination technology,direct catalytic decomposition method has attracted much attention.However,traditional preparation methods and simple additive doping modes are difficult to improve the comprehensive performance of catalysts,so as to meet the harsh requirements of N2O purification catalysts in the complex environment of industrial waste gas(such as NOx,O2,H2O,SO2,CO2 and other impurities).In this paper,a series of Co3O4-based metal oxide catalysts with high catalytic activity and impurity gas resistance were synthesized based on sol-gel method with different surfactants as structural and crystallographic control agents and supplemented with auxiliaries,and a detailed investigation was carried out to investigate the connection between the physicochemical structure of the catalysts and the activity of catalytic decomposition of N2O,as follows:1.A series of xS-Co3O4 catalysts were synthesized by combining sol-gel method with Co3O4 as the active component and selecting cationic,anionic and nonionic surfactants as catalyst structure and crystalline surface control agents,respectively,and their catalytic decomposition activity of N2O were tested.It was shown that the addition of nonionic surfactants promoted the performance of Co3O4 catalytic decomposition of N2O.(1)During the catalyst preparation,the introduction of the nonionic surfactant F127 gave the 3.0F-Co3O4 catalyst a unique "Yardang Landform" microstructure,while exposing mainly the highly active(400)and(511)crystalline facets of the resulting catalyst.Based on this unique microstructure,the surface active site density of the 3.0FCo3O4 catalyst is 7.62 μmol m-2,which is about 9 times higher than that of the Co3O4(P)catalyst prepared by the conventional precipitation method.In addition,the 3.0F-Co3O4 catalyst can maintain a conversion of N2O above 60%in the feed stream of 2000 ppmv N2O/Ar with 5 vol%O2,100 ppmv NO and 2 vol.%H2O at 400℃ and GHSV=20,000 h-1.(2)Similar to F127,the addition of P123 can also change the microstructure of the Co3O4 catalyst,and the obtained optimal 8.0P-Co3O4 catalyst has many defects visible at the grain edges,exposing more highly active crystalline surfaces.Compared with the Co3O4(P)catalyst prepared by the conventional precipitation method,the 8.0P-Co3O4 catalyst not only has a significantly higher number of oxygen vacancies on its surface(about 4.7 times more than that of Co3O4(P)),but also has a weakened Co-O bond on its surface,which corresponds to a significantly lower reaction activation energy Ea.In addition,it was able to maintain a high activity(N2O conversion～72%)in the coexistence of three impurity gases at 400℃ for a reaction time of up to 24 h.2.Based on the above research work,3.0F-BiyCo(y=0-0.04)series catalysts were synthesized by sol-gel method in one step.The modification of Co3O4 by using the large radius metal Bi as an additive weakens the Co-O bond on the surface of the 3.0F-Co3O4 catalyst and enhances the reactivity of the individual active sites of the catalyst.The study showed that the doping of additive Bi did not change the unique"Yardang Landform" microstructure and crystal surface exposure of 3.0F-Co3O4 catalyst,and more active crystal surface was exposed on the basis of the original.More importantly,the doping of the additive Bi not only increases the specific surface area of the catalyst to a certain extent,but also further weakens the Co-O bond on the catalyst surface.The optimum 3.0F-Bi0.015Co catalyst achieves more than 88%N2O conversion(2000 ppmv N2O/Ar,GHSV=20,000 h-1)at 300℃,and its corresponding TOF value increases from 1.50×10-3 s-1 for 3.0F-Co3O4 to 3.63×10-3 s-1.In addition,the catalyst has good resistance to O2 and H2O.Under the harsh condition that 100 ppmv NO,5 vol.%O2 and 2 vol.%H2O coexist,the conversion rate of N2O on the 3.0F-Bi0.015Co catalyst can be stable above 90%at 400 ℃.