Study On Non-thermal Plasma Assisted Cu-Mn/SAPO-34 Selective Catalytic Reduction Of NO_x From Diesel Engine Exhaust

Nitrogen oxides(NOx)are harmful to environment and human health.Diesel engine exhaust is one of the main sources of NOx.Ammonia-selective catalytic reduction(NH3-SCR)is the most important technology to remove NO,from diesel engine exhaust.Although the developed NH3-SCR catalysts have wide active temperature window,high hydrothermal stability and hydrocarbon resistance,they still exhibit low catalytic activity below 200 ?.When these catalysts are used on the light-duty diesel vehicles as well as diesel vehicles during cold start,the concentration of NOx in the exhaust is unable to meet the emission standard.The "PPC" method was used to combine non-themal plasma with NH3-SCR to enhance removal efficiency of NOx from diesel engine exhaust under low temperature(<200 ?).The Cu-Mn/SAPO-34 catalyst was synthesized by the one-pot hydrothermal synthesis method and showed the highest catalytic activity when Cu/Mn was 2.The impact factors were studied,including the reaction temperature,energy density,concentrations of NH3,H20 and C3H6.It was found that the promotional effect of plasma on reaction was due to the active substances produced.There was no NH3 slip problem when the ratio of NOx/NH3 was 1,achieving high NOx removal efficiency.The addition of H20 and C3H6 did not negatively affect the NOx removal,and no by-products were found during the reaction.After continuous operation for 35 hours and 5 times regeneration of the catalysts,the reaction system still showed high NOx removal efficiency.Subsequently,the reaction process of plasma assisted SCR system was analyzed by in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS).It was found that the NH3-SCR reaction through the L-H pathway occurred only on the surface of catalyst could also occur in gas phase after combining plasma with SCR.After the reaction between NH3 with NO2 in gas phase,the reaction products would be further decomposed into N2 and H20 on the surface of the catalyst.When C3H6 existed in the system,it did not inhibit the reaction through L-H pathway on the catalyst,whereas increased the concentration of NO2,and further promoted the reaction between NH3 and N02 in gas phase.Simultaneously,C3H6 also activated the NH3-SCR reaction through the E-R pathway.