Cu-SAPO-34 Catalyst Prepared By One-pot Synthesis And Its Selective Catalytic Reduction Of NO_x

NH₃-SCR technology using ammonia as reducing agent is an important technology to control NO_x emission of diesel engine at present.Considering the actual operating conditions of the engine and DPF regeneration upstream of SCR system,NH₃-SCR catalyst should have wide active temperature window,high nitrogen selectivity and great hydrothermal aging stability.Molecular sieve catalyst Cu-SAPO-34 has attracted wide attention due to its excellent low temperature activity and high temperature hydrothermal aging stability.However,the low temperature hydrothermal aging stability of Cu-SAPO-34 is the key problem to be solved.In order to find the catalysts with excellent NH₃-SCR performance and low-temperature hydrothermal aging stability,the Cu-SAPO-34 zeolite catalyst was prepared by one-pot synthesis method,and its SCR performance and physical and chemical characteristics were tested.Firstly,the conditions of one-pot synthesis method were optimized.By setting different calcination temperatures and heating rates,Cu-SAPO-34catalysts with different calcination temperatures and heating rates were prepared.Then SCR performance tests and characterization including BET and XRD were carried out.The results show that calcination temperature and heating rate have significant effects on SCR performance of the catalysts.When the calcination temperature is 700?and the heating rate is 5?/min,the catalyst has larger surface area and pore volume,and the crystallinity of CHA is relatively high,which makes the catalyst have better NH₃-SCR performance.The effect of Si/Al ratio on the performance of catalyst and the stability of hydrothermal aging at low temperature was studied.Based on the optimum calcination temperature and calcination heating rate,Cu-SAPO-34catalysts with Si/Al ratios of 0.3,0.4,0.5,0.6,0.7 and 0.8 were prepared by one-pot synthesis method,and their SCR performance were tested and characterized.The results show that the CHA structure of the catalyst with a Si/Al ratio of 0.4 is more complete,its surface area and pore volume are larger,and it has more abundant acidic sites and SCR reaction active sites,so it has relatively excellent SCR performance.And because of the more stable structure,no obvious deterioration occurred after low-temperature hydrothermal aging,indicating that the catalyst with a Si/Al ratio of 0.4 has better low-temperature hydrothermal aging stability.The effect of loading active element Ce on the performance of catalysts and the stability of hydrothermal aging at low temperature was studied.Three kinds of CuCe_x-SAPO-34 catalysts were prepared by one-pot synthesis method with different Ce loading.The results of performance evaluation show that when the Ce/Al ratio is 0.06,the improvement of NO_x conversion is the most remarkable.Through the characterization of CuCe_0.06-SAPO-34 and Cu-SAPO-34 catalysts,it is found that loading proper amount of Ce can promote the formation of porous structure of the catalyst,make the catalyst have better distribution of copper ions and acidic sites,enhance the stability of its surface structure and pore structure,reduce the deterioration in the aging process,make the catalyst have abundant acidic sites and SCR activity before and after aging,and maintain excellent SCR performance.