Research Of Catalytic Reduction Of NO With NH₃ Over Modified Cu-SAPO-34

With the rapid increasing of vehicle ownership, nitrogen oxides (NOX) pollution was increasingly serious. In recent years, frequent fog weather has also been proved that is closely related to the NOx emission of motor vehicles. Due to the high thermal efficiency and low emission of CO2, diesel vehicles have attracted much attention. However, the concentration of nitrogen oxides in the exhaust is high, and it is necessary to carry out the purification treatment before emission. NH3-SCR technology has become one of the most efficient approaches of NOx elimination. Cu-SAPO-34 small molecular sieve catalyst, owing to excellent low temperature catalytic activity, wide temperature operating window and remarkable hydrothermal stability, has been draw great attention and is considered to be one of the most application prospect of diesel exhaust NH3-SCR catalysts. For the Cu-SAPO-34 research has just started, it is still lack of a systematic study for the catalyst preparation conditions and the material modification research. So the preparation conditions of Cu-SAPO-34 catalyst were optimized in this paper. Then the effect of Fe introduction on selective catalytic reduction of NO with NH3 of Cu-SAPO-34 was investigated, in order to develop catalyst with efficiency NH3-SCR activity and provide basis and guidance for modification of Cu-SAPO-34 molecular sieve catalysts.In this paper, the preparation conditions of Cu-SAPO-34 catalyst were optimized, including preparation methods, Cu exchange time, concentration of Cu exchange and copper source. The effects of copper sources on selective catalytic reduction of NO with NH3 of Cu-SAPO-34 was discussed by XRD, BET, ICP, H2-TPR, NH3-TPD and XPS characterization technology. The results demonstrate that Cu-SAPO-34 were prepared by ion exchange method, Cu exchange time is 8 h, exchange of Cu concentration is 0.05 mol/L, copper acetate is copper source, performed higher NH3-SCR activity and wider temperature operating window. The Cu-SAPO-34 catalysts with similar Cu content were prepared by different copper source, appeared the almost same high temperature activity, but their low temperature activity had significant difference. Low temperature activity order of catalysts were Cu(copper acetate)-SAPO-34>Cu(copper sulphate)-SAPO-34>Cu(copper nitrate)-SAPO-34. Characterization results indicated that the different copper sources led to the different copper species form and the amount of the catalysts. It can be observed that catalyst made by copper acetate as copper source, its minimum Cu2+ hydrogen reduction temperature; more Cu content; strongest acidity, so its best activity at low temperature. Cu-SAPO-34 catalyst remains excellent activity and has good stability under high speed of 60000h-1.In order to further improve the high temperature activity and broaden the reactive temperature window of Cu-SAPO-34 catalyst, Fe was introducted into Cu-SAPO-34 catalyst by mechanical mixing method and ion exchange method. The research results show that Fe-beta/Cu-SAPO-34 prepared by mechanical mixing method improves the high temperature activity, but low temperature activity is significantly decrease, the modified result is not ideal. Compared with mechanical mixing method, the low Fe exchange concentration of 0.0128 Fe-Cu-SAPO-34 prepared by ion exchange method not noly maintained the excellent low temperature activity of Cu-SAPO-34, but also greatly improves the high temperature activity and has a very wide activity temperature window.