Construction Of Co₃O₄-MMT Catalyst And Its N₂O Decomposition Performance

Nitrous oxide（N₂O）is a widely available greenhouse gas,its life in the atmosphere is as long as 110～150 years,and it can react with ozone in the stratosphere,thereby causing an ozone layer hole.The massive emission of N₂O has led to a series of serious environmental problems and posed a serious threat to the earth’s living systems.Therefore,emission control and elimination of N₂O is urgent.Direct catalytic decomposition is known as the most ideal N₂O emission reduction technology,and a variety of noble metal and transition metal oxide catalysts have been used for direct catalytic N₂O decomposition.Among them,Co₃O₄ has a unique spinel structure,and contains high concentration of oxygen vacancies,weak Co-O bonds,and strong redox electron pairs(Co³⁺/Co²⁺),which makes it show relatively excellent catalytic activity in the direct decomposition reaction of N₂O.However,since the N₂O decomposition process usually occurs at the gas-solid two-phase interface,the comprehensive utilization rate of the active phase in the Co₃O₄ catalyst is relatively low,and a single Co₃O₄ catalyst also has problems such as easy sintering,poor high temperature stability and insufficient ability to resist impurity gases,which seriously limits its practical application.Therefore,how to effectively solve the above problems has become the focus of current research.Montmorillonite（MMT）is the most deeply studied cationic clay mineral at present,because of its unique layered structure and interlayer cation exchangeable characteristics,it shows a broad application prospect as a catalyst or carrier.In this paper,montmorillonite was selected as the carrier material.Firstly,a series of Co-MMT（CD）catalysts with different Co content were prepared by in-situ polymerization-coordination deposition method.By investigating the catalytic decomposition activity of these catalysts for N₂O,the optimal Co loading amount of MMT carrier was obtained.Subsequently,the effect of different calcination heating rates on catalytic activity was studied,and the optimal preparation conditions for the catalyst were obtained.At the same time,Co-MMT（DP）catalyst was prepared under this condition using traditional deposition and precipitation methods as a comparison.Through a series of characterization methods,the impact of preparation methods on the structure and performance of the catalyst was emphatically analyzed,with the aim of clarifying the structure-activity relationship between the texture structure and surface properties of the catalyst and its N₂O catalytic decomposition activity.The main conclusions are as follows:1.The N₂O catalytic decomposition activity and impurity gas tolerance of Co-MMT catalysts were investigated in the presence of N₂O at 1000 ppm and GHSV of 10,000 h^-1,or in the presence of impurity gases of 3%O₂,200 ppm NO,and/or 3.3%H₂O.The results showed that the Co（0.015）-MMT-2（DP）catalysts prepared by in situ polymerization-coordination deposition method had higher catalytic activity,stability and impurity gas tolerance compared with the Co（0.015）-MMT-2（DP）catalysts prepared by deposition-precipitation method as well as pure Co₃O₄,which were characterized by XRD and N₂-physisorption to yield Co（0.015）-MMT-2（CD）catalysts exhibit more excellent structural weave properties by XRD and N₂-physisorption characterization.2.The structural and surface properties of Co-MMT catalysts prepared by different methods were characterized by FT-IR,Raman,TEM,XPS,H₂-TPR,and O₂-TPD.The results showed that compared with the Co（0.015）-MMT-2（DP）catalyst prepared by the deposition-precipitation method,the Co（0.015）-MMT-2（CD）catalyst not only achieved a high dispersion of high content Co₃O₄ active phase on MMT,but also this catalyst has a weaker Co-O bond and better low-temperature reduction ability,while the surface of this catalyst contains more Co_Oh²⁺and abundant oxygen vacancies on the surface of this catalyst.Further DFT calculations show that Co_Oh²⁺has higher catalytic activity for N₂O decomposition.