Greenhouse Gas N₂O Catalytic Decomposition-Investigation On Composite Metal Oxide Catalyst Preparation And Performance

Global warming has seriously affected the sustainable development of human beings and the ecological environment.As the third largest greenhouse gas after CO2 and CH4,N2O pollution has attracted wide attention of all countries.N2O can stay in the atmosphere for about 150 years.Although the concentration of N2O in the atmosphere is far lower than CO2,its ability to produce greenhouse effect is about 310 times than CO2,and its contribution to greenhouse effect is about 6-10%.Researchers generally believe that catalytic decomposition technology is an effective way to reduce N2O emissions,and the core of this technology is the performance of catalyst.In recent years,scientists mainly focus on molecular sieve catalysts,metal oxide catalysts and composite metal oxide catalysts.In this paper,based on the previous studies,the composite metal oxide catalysts were selected to explore the influence of active component selection and preparation methods of catalysts on the performance of catalysts.Developed countries have developed the technology of N2O decomposition and emission reduction,but the technology is highly monopolized and the cost of introduction is very expensive.The research of this topic will face great challenges.Based on the principle of mass conservation before and after the reaction,the main influencing factors on catalytic N2O decomposition reaction,such as reaction temperature,pressure,reaction gas compositions,have been detailedly analyzed and calculated for the first time,which provides the theoretical basis for the further experimental researches.For N2O catalytic decomposition,the key factor to accelerate the chemical reaction process is the acidity and basicity of the active center.Therefore,acid-base theory is applied to guide the selection and preparation of active components of catalysts.The N2O molecule is a linear polar molecule(N-N-O).The central N atom forms two ? bonds and two three-center four electron ? bonds through SP hybridization.The oxidation number of N is+1.According to the molecular characteristics of N2O and the acidity and basicity of metal oxides,Mg,Al,Cu,Zn,La,Ru and other oxides may have N2O decomposition activity.Firstly,the composite metal oxide catalysts of MgAlO?CuMgAlO?ZrMnZnO and LaMgAlO were prepared.The performance of the catalysts was evaluated under the experimental conditions,and the catalysts and precursors were characterized.The results show that the catalyst has the ability of catalyzing N2O decomposition,and the selectivity of the catalyst is 100%.The change law of the surface alkalinity and the characterization results are basically the same,which is consistent with the change law of the acid-base characteristics of metal ions.The LaMgAlO(MexOy)catalyst prepared by coprecipitation method was used as the support to study the Ru modified catalyst.Ru2O/MexOy catalyst was prepared by impregnation method.TEM result showed that the active component Ru was well dispersed on the surface of the catalyst and the particle size was in nanometer level.The evaluation results show that the effect of different Ru loading amounts is different:when the Ru loading amount is less than 2%(wt),the number of active centers is not enough,and the activity of catalysts increases with the increase of Ru content.When the Ru content is higher than 2%(wt),the active centers cover each other and the activity of catalysts does not increase significantly.Considering the cost of catalyst manufacturing,the ideal loading amount of Ru is 2.0%(wt).The evaluation results show that Ru can improve the decomposition performance of N2O,but Ru modified catalyst is sensitive to H2O(g).The surface of catalyst becomes rough and dry after use.The activity of catalyst disappears after the reaction reaches a certain time.However,the catalyst's activity was still above 60%after 100 hours reaction under experimental conditions.The study prepared Ce/Cu/Mn/Zn composite metal oxide catalyst by coprecipitation method.The catalyst was characterized by XRF?FT-IR?XRD?CO2/O2-TPD?H2-TPR?SEM-EDSn TGA analysis and its performance was evaluated.The results show that the addition of Ce improves the dispersion of the active components of the catalyst,improves the reducibility of the catalyst,plays a good role in the synergy between the active components,and accelerates the diffusion speed of O on the catalyst surface.The continuous evaluation of Ce1.0/Cu/Mn/Zn catalyst for 200 hours showed that the decomposition rate of N2O remained above 92%,and the catalyst had good N2O decomposition activity,selectivity and stability.On the basis of the above study,CeMeOy/?-Al2O3 catalysts were prepared by impregnation method.BET?XRD?CO2/O2-TPD?H2-TPR?SEM-EDS characterization and performance evaluation were carried out.The results showed that when the Ce/Cu molar ratio reached 1.2,the catalyst activity was the best.Under the experimental condition,the catalyst activity remained above 95%and the selectivity is 100%in the 200h reaction.The surface morphology and structural characteristics of the catalyst have not changed before and after the reaction.which provides theoretical and experimental basis for further pilot test and industrial experimental research.