Effect Of Preparation Methods On CuSAPO-34Removing NO_x From Diesel Engine Exhaust

In recent years, the traffic-environmental problem is more and more concerned by the government, and the regulation on the harmful constituents contained in the exhaust of autos is particularly strict. The diesel engine is being gotten popular depending on its advantage, such as bigger power, longer using life and higher efficiency of fuel utilization. Because of the higher air-fuel ratio, the engine has a strong point of end gas including less CO2and HC contributing to the greenhouse effect, compared with gasoline engine, but the NOx contained in the end gas is much higher than that of gasoline. In order to meet the need of the emission standard established by different states, some researchers has always focused on how to purify the end gas of diesel engine and a considerable progress has been made. Of which the NH3-SCR is considered to be a better method and is successfully used in the denitration process for the stationary pollution source, such as thermal power plant. The NOx conversion rate could be as high as about90%. Ffor the mobile resource, such as autos, the NH3-SCR method has its own disadvantages, such as how to supply NH3and how to avoid NH3leaking. Besides, which kind of catalyst should be picked up is also a hot potato. As we all know, plenty of hydrocarbon (HC) is contained in the end gas and its content is more than that of NOx. So in order to explore the feasibility of denitration by HC contained in the exhaust, the CuSAPO-34, in our study, is supposed to be the catalyst depending on its high hydrothermal stability and some low carbon HC, such as C3H6or CH4, as the reductant. During the experiment process, the effect of crystallization time and preparation method on the structure and activity of CuSAPO-34were investigated. The HC-SCR results showed that the NOx conversion could not be satisfied and so we change the Cu content and introduce Pd using pore volume impregnation during the preparation process to optimize the CuSAPO-34catalyst. The results revealed that, after optimized by Pd, the NOx conversion was sharply increased. The main conclusions derived from our experiments are shown as follows:(1) Crystallization time has an obvious effect on the crystal form of catalyst and CuSAPO-34can be successfully prepared by changing the time. On the basis of adding proper amount of HF, the crystallization course is completed when the time is long as72h.(2) Preparation method is a key factor on the activity of CuSAPO-34by changing the crystal pattern, pore structure and the degree of crystallinity. During the three methods, the ion-exchanged (IE) sample has the highest NOX conversion in both NH3-SCR and HC-SCR, and the pore volume impregnation (PVI) one has the lowest one. However, the PVI sample has a stronger anti-aging property.(3) The effect of Cu content on the de-NOx activity of CuSAPO-34prepared by the hydrothermal synthesis (HS) was investigated. The results show that the highest NOX conversion rate could be available when the mole ratio of Si:Cu is5and the Cu addition has no obvious effect on the CuSAPO-34crystal pattern.(4) The sample prepared by HS was modified by noble metal Pd through PVI method. The results indicate that the NOx conversion over all samples with different Cu content, optimized by Pd, largely increases.