Modification Of Beta Zeolite And Catalytic Performance For Decomposition Of N₂O

In recent years,through in-depth research on N2O,people gradually realized that it belongs to one of the greenhouse gases,and its main contribution to global climate change is about 6%.In 2015,the"Paris Agreement"passed the law concerning the reduction of six types of greenhouse gas emissions including CO₂,CH₄,N₂O,O₃,HCFCs,and peroxycarbides.In addition,it also has serious damage to the ozone layer.Therefore,the research on controlling the emission and decomposition of N₂O is very important to protect the living environment of human beings.Among many N₂O elimination methods,the direct catalytic decomposition method is widely studied.This method is not only a simple process route,but also has a high N₂O conversion rate,no secondary pollution,a lower cost,and is a more effective elimination method.The transition metal ion-modified zeolite molecular sieve catalyst has been extensively studied by researchers,and it has the characteristics of higher N₂O decomposition efficiency and better activity,while the beta molecular sieve exhibits excellent catalytic performance in catalytic N₂O decomposition reaction.In this dissertation,Fe/beta,Co/beta and Co-Fe/beta catalysts were prepared by liquid ion exchange method.The acidity and bimetallic loading of the prepared solution were used to characterize the physical-chemical properties of the zeolite.XRD,FT-IR,N₂-physisorption,DR UV-Vis,NH₃-TPD,ICP-OES and other methods were used to characterize the crystal structure,specific surface area,acid amount,element content,and physical and chemical properties of different element species.The Fe/beta,Co/beta and Co-Fe/beta molecular sieves prepared under different conditions were used to catalyze the decomposition of N₂O,and their catalytic activity and influencing factors were analyzed.The main conclusions are the following:The liquid ion exchange method was used to obtain Fe/beta at pH equal to 1.00,2.00 and 2.60 with Hbeta zeolite as motherboard molecular sieve.The results show that the Fe/beta-2.00 molecular sieve catalyst with pH equal to 2.00 has the lowest N₂O decomposition temperature and the best reaction activity,which is related to the higher content of Fe3+in the active center of the catalyst.Moreover,the addition of appropriate nitric acid removes the non-framework aluminum species of the molecular sieve,increases the crystallinity of the sample,and facilitates the diffusion of N₂O gas molecules into the molecular sieve pores.The stability evaluation results show that the Fe/beta-2.00 catalyst has good stability,and the N₂O conversion rate remains above 60%after 80 h reaction.The synthesis of Co/beta molecular sieves was carried out by liquid ion exchange method with Hbeta molecular sieve as motherboard molecular sieve at pH 1.50,2.00,3.00.The results show that Co/beta-2.00 was obtained at a pH of 2.00.The results showed that the N₂O decomposition activity of Co/beta-2.00 molecular sieve catalyst obtained at a pH of 2.00 was the best.The addition of nitric acid can remove the non-skeletal aluminum species of the molecular sieve and is beneficial to the N₂O gas diffused into the molecular sieve pores.In addition,the Co/beta-2.00 catalyst has good stability,and the N₂O conversion rate remains above 80%after 80 hours of reaction.Using Co?NO₃?₂·6H₂O and Fe?NO₃?₃·9H₂O as the cobalt source and iron source,Co-Fe/beta bimetallic molecular sieves were prepared by liquid ion exchange method,Fe and Co were simultaneously introduced into beta molecular sieves.The characterization results show that when there is a competitive exchange between Fe3+and Co2+in the solution,Fe3+preferentially exchanges ions with H+on the molecular sieve.The N₂O decomposition activity is the best on the Co_1.5Fe_0.5/beta zeolite catalyst,which is mainly related to the active center of Co2+and Fe3+is relatively high.The stability evaluation results show that the Co_1.5Fe_0.5/beta catalyst has good stability,and the conversion rate of N₂O still maintains over 80%after 80hours of reaction.