Development And Engine Bench Testing On DeNO_x Catalysts For NO_x Removal In Heavy Duty Diesel Emission

Ammonia selective catalytic reduction（NH₃-SCR）is the most effective NO_X purification technology for diesel exhaust.The key technology of SCR is the catalyst including vanadium-and zeolite-based catalysts.With the emission regulations getting more and more strict,the problems of SCR catalyst including the narrow temperature window,the poor hydrothermal aging resistance and coating durability have become a critical issue in application.In this thesis,two types of vanadium-and zeolite-based catalysts were fully studied in the catalyst preparation and modification,hydrothermal aging mechanism,the catalyst coating and engine bench testing.The conclusions are as follows:（1）For V-W/Ti catalyst,the 2.5%vanadium content has the better low temperature performance and thermal stability;The modification of SO₄^2-could improve NO_X activity at the low temperature and thermal stability of V-W/Ti catalyst;The catalysis activity window moved to the high temperature after doped with Fe/Ni,and the Cu and SiO ₂ could improve the low temperature performance.For Ce-W/Ti catalyst,CeO₂ could prevent the crystallization of WOx species and phase transformation of TiO₂,while maintaining high Lewis acidity after hydrothermal aging,which show excellent hydrothermal aging performance.The SiO₂ Sol-gel is best binder,and the coating loss rate is 2.2%.Through the optimization of V-W/Ti catalysts coated process,the monolithic catalysts has good catalytic activity.（2）The mesoporous ZSM-5 zeolite was prepared with duel-template method,which has the specific surface area of 608 m²/g,and the crystallinity is 84.1%.The mesoporous structure promotes the disperision of active Cu species.At the same time,the mesoporous ZSM-5 zeolite has large amounts of Br?nsted acid sites and high degree of Cu ion exchange.As a result,the Cu/ZSM-5 catalyst exhibits high De-NOx activity.In the simulated atmosphere containing 5%H₂O,the catalysis activity window(T₉₀)is 225-550℃.The addition of Fe on the Cu/ZSM-5 could improve high temperature NO_X activity,and Ce and Zr can improve the NO_X catalytic activity at low temperature.（3）For Cu-Ce/SAPO-34 catalyst,the addition of Co could not only enhance the NO_X activity at low temperature,but also broaden the temperature window.At 30,000h^-1,the light-off temperature(T₅₀)of NO_X is 152℃,and the temperature window(T₉₀)of NO_X activity is 175-550℃.（4）In the engine bench testing,for fresh V-W/Ti and Cu/ZSM-5 catalysts,at30,000 h^-1,the light-off temperature(T₅₀)of NO_X is 270 and 175℃.After the rapid aging at 550℃,200 h on engine bench,the performance of V-W/Ti catalyst decreased about 10%,and in the ESC and ETC testing cycle,the NO_X emissions are1.44 and 1.59 g/kW·h,which could still meet the China V standard,meanwhile the performance of the Cu/ZSM-5 catalyst almost keep the same performance with the fresh sample,and the NO_X emissions are 0.63 and 0.69 g/kW·h.At the same time,the ammonia leakage is less than 10 ppm.The results of NOx emission on Cu/ZSM-5catalyst have been close to the China VI standard for WHSC and WHTC cycle（0.40and 0.46 g/kW·h）...