| Diesel vehicles are highly efficient and economical in terms of fuel consumption compared to the gasoline vehicles, which is being gotten popular in the automotive field. But as is the case of all lean combustion processes, the NOx produced is difficult to eliminate due to the unreacted O2 in the product stream, NOx is a major source of air pollution and can cause a serious of environmental issues, such as photochemical smong, acid rain, and fine particle pollution (haze). More and more strict regulation requirements for diesel engine emissions (or high air/fuel ratio lean-burn gasoline engines) have prompted the development of various catalytic aftertreatment technologies. Nowdays, the abatement of from diesel engines in oxygen-rich conditions remains a challenge in the field of environmental catalysis. Selective catalytic reduction (SCR) is now the preferred technology to achieve the large NOx reductions, especially that ammonia-selective catalytic reduction (NH3-SCR) is an effective technology for the reduction of NOX gases in mobile applications, and catalyst is the key factor of SCR technology. Recently, Cu/zeolite catalysts with chabazite (CHA) crystal structure became a promising candidate for NH3-SCR reaction, such as Cu-SAPO-34 and Cu-SSZ-13. Cu-SSZ-13 prepared by an ion-exchange method showed the improved activity, N2 selectivity, and hydrothermal stability compared with Cu-zeolite catalysts. At present, monolith catalysts are used in DeNOx catalysis for both mobile and stationary source. Cordierite (2Al2O3-5SiO2-2MgO) is widely used as catalyst support for the cleaning up of exhaust gases because of its superior hydrothermal stability, high mechanical strength, low thermal expansivity and especially the low cost. Based on these, Cu-SSZ-13/cordierite monolithic catalyst was synthesized via one step in-situ hydrothermal method. Copper-amine complex was used as the template as well as the direct source of the catalytic active component of copper species. The crystal morphology and crystal structure were analyzed by using various techniques for different samples, the following conclusions are drawn:(1) Crystallization time has an obvious effect on the crystal form of catalyst and Cu-SSZ-13 can be successfully prepared by changing the time. When the time was long as 72 h, Cu-SSZ-13 crystallization completely underwent. At this point, the loading rate, coating thickness, content of active component and silica alumina ratio of Cu-SSZ-13 molecular sieve reached maximum.(2) Cu-SSZ-13/cordierite catalyst has a good hydrothermal stability. Under harsh hydrothermal aging conditions, it still maintained a good catalytic activity. Cu-SSZ-13 degrades mainly according to two possible mechanisms:On the one hand, aging treatment makes some Cu-SSZ-13 molecular sieve falls off from the surface of cordierite, lead to decrease of loading rate, coating thickness and specific surface area. On the other hand, the dealumination and agglomeration of isolated Cu2+ species eventually results in the part collapes of the structure of molecular sieve.(3) The effect of HF content on the DeNOx activity of Cu-SSZ-13/cordierite prepared by the one step in-situ hydrothermal method was investigated. The results show that the highest NOx conversion rate could be available when the mole ratio of HF:A12O3 is 0.05 and the HF addition has no obvious effect on the Cu-SSZ-13/cordierite crystal pattern. However, increased its activity of high temperature and water thermal stability in a certain degree were increased. |
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