Study On Selective Catalytic Reduction Of Nox By Sapo Zeolites

As one of the main components of atmospheric pollutants, NOx has brought great harm to people’s health, and how to eliminate NOx become one of the focuses of research in recent years. Among the NOx control methods at present, selective catalytic reduction (SCR) with its high removal efficiency, less by-products, the advantages of mild reaction conditions become the direction of future development. To prepare catalyst with the high activity, good selectivity and low price become the core and key of SCR research. During this research, through a large number of experiments we get two excellent activity of SCR catalyst Cu/SAPO-35 and Cu/SAPO-34, besides the influence factors of preparing catalysts, the SCR catalytic activities were studied comprehensively.The SAPO-35 zeolites synthesised using HMI as template, with the increase of Si content in the sol the zeolite crystallinity increased. At the same time SM3 substitution reaction of Si gradually happen, eventually lead to a small amount of Si island growed in the zeolites. Acdity of the zeolites firstly increase then decrease with the increase of Si quantity. Preparring Cu/SAPO-35 catalysts by rotating impregnation method and ion exchange method, then evaluate their SCR activities. We found that the Cu/SAPO-35 samples prepared by the rotating impregnation method have a good low temperature activity, while decreace sharply with much N2O by-products when the temperature grew up. The Cu/SAPO-35 samples prepared by the ion exchange method have better SCR activity, especially during the high temperature period kept high catalytic activity and N2 selectivity. We also found that Cu/SAPO-35 catalysts samples prepared by the ion exchange method generate more Cu2+ when the raw zeolites have more B acid sites, thus the catalysts samples have better SCR performance.We prepared two kinds SAPO-34 samples with different templates, one has Si distribute evenly and the other has much Si island. Then we prepared them to Cu/SAPO-34 catalysts using the method of ion exchange, then studied their SCR catalytic activity. The Cu/SAPO-34 catalysts with Si distribute evenly exhibit excellent SCR catalytic activity and selectivity of N2. The Cu/SAPO-34 samples have much Si island have a good low temperature activity, while decrease sharply with much N2O by-products when the temperature grow up. This suggests that the existence of Si island in the Cu based SAPO catalyst is adverse for the SCR reaction.We compared the Cu/SAPO-34 with the Cu/SAPO-35, analyzed the with the Cu/SAPO-35, analyzed the reason of the different SCR performance. The acidity of SAPO-34 is stronger than the SAPO-35. The SCR activity analysis shows that the Cu/SAPO-35 have a poorer SCR performance during the low temperature, while has a superior SCR performance during the high temperature. Studies show that it maybe because the Cu species in the SAPO-35 have a weaker reducibility and a better stability.