Studies On Cerium And Wolfram Series Catalysts Formulations And Coating Process For Selective Catalytic Reduction

Nitrogen oxides are one of the main pollutants of diesel engines, and selective catalytic reduction(SCR) is the mainstream NO_x control technology of diesel enginenow. However, because current commercial vanadium-based SCR catalysts are toxic and in poor low-temperature performance, low-temperature and nontoxic SCR catalyst will be important in future research. The solution combustion synthesis(SHS) has good prospects since it is simple, and the catalyst prepared has nano-structure.This experiment made SCR catalyst through SHS, which selected cerium and tungsten as the active ingredients.And then influence of the pH, fuel type and fuel amounts on the physical and chemical properties of catalyst were studied.This article also studied the influence of coating method on the catalytic properties. The main works and conclusions in this paper are stated as followed.(1) The effect of cerium and tungsten formula and fuel type are investigated. TiCe0.2O_x catalyst has very excellent low-temperature activity and TiW0.2O_x catalyst has high thermal stability and high-temperature activity, while TiCe0.2W0.2O_x retained low temperature activity as TiCe0.2O_x and high temperature activity increased due to the addition of W. The two elements formed a good synergy. A urea preparation had the highest NO conversion, and the catalytic activity can reach 80% at 150 ℃.The glycine preparationcan significantly enhance the catalytic performance in high temperature.The citric acidpreparation had similar activity to the glycine, but the high temperature activity is slightly lower. BET and SEM results showed that the urea could effectively increased surface area and pore numbersto improve the microstructure.The urea preparation had the bestmicroscopic performance.(2) The effect of fule consumption is investigated. 1:0.5 ratio of glycine has the best catalytic activity and the widest temperature window. With the fuel increasing, NO conversion gradually decreased.Citric acid fuel ratio does not affect the low-temperature catalytic activity, but increasing fuel amounts slightly improved the high-temperature activity. Urea preparation had the highest catalytic activity in 1:0.5 ratio, and the activity can reach more than 80% at 150℃. The activity is the lowest in 1:1.5 urea ratio and the temperature window did not significantly change. BET and XRD results showed that 1:0.5 glycine preparation product has the greatest surface area and desorption pore volume, better microstructure. Citric acid is more moderate; microstructure has no change with fuel consumption. 1:0.5 urea product had largest surface area, the more fuel will result in a larger sintering proportion, grain growth, smaller surface area and the reduction of pores.(3) This experiment studied the impact of the precursor pH environment on the products catalytic properties. The results showed that the acidic environment did more favor to low-temperature performance of glycine preparation, alkaline environment could promote the citric acid preparation’s high temperature activity; the impact of acid-base environment on urea catalytic performance is very small. Acidic environment can significantly improve the surface area of the catalyst prepared in glycine. Additional catalyst is sensitive to pH changes.(4) The traditional dip coating, combustion coating and the new dip coating were tested, and individual research had been done for the new dip coating.The findings are as follows: The new dip coating method has the highest NO conversion rate and N2 selectivity, activity can be maintained over 80% during 230-450℃. BET, SEM, XRD characterization analysis showed novel dip coating has better microstructure. Most of the active ingredient was uniformly dispersed on the surface.The coating layer combined with the support more compactly, difficult to fall off.This article also did research on airspeed, powder catalysts, coating rate and particle size.The results showed that the new dip coating completely preserved SCR catalyst activity of the powder; it has good resistance to high air-speed. Low temperature activity will increase with the higher coating rate, while the coating particle size had no effect on the catalytic activity.