Study Of The Monolithic Cu-SAPO-34/Cordierite Catalyst For Diesel Exhaust Gas Purification

As global energy crisis intensifying, the amounts of vehicles with stronger motive power and better economic performance increase gradually. The addition of excess O2 not only improve the efficiency of fuel but also significantly reduce the emissions of HC and CO. But NOx, which is the main environmental pollutant, is purified difficultly by the conventional three-way catalysts in the rich oxygen conditions. Recently, the catalytic conversion of NO in the presence of excess O2 has been intensively studied to decrease the NOX in the exhaust gas from diesel engines and lean-burn facilities.The catalyst for NOX-SCR needs to meet the demands of resist-thermal and long-life but also exhibits high activity for the selective reduction of NO under an atmosphere containing water vapor and rich O2. Catalyst carrier properties have the great effect on catalyst activity and service-life. Due to the influence of actual conditions of engine, vehicle exhaust catalyst carrier must have the traits of small resistance, warming faster, high temperature resistance, high mechanical strength, light quality, convenient installation, and et al.Based on these, the cordierite monoliths were used as the catalyst carriers, CuO was used as the copper source and Cu-SAPO-34/cordierite samples were synthesized via one-step hydrothermal procedure. The samples were characterized by XRD, SEM, TG-DTG, ICP, XPS techniques. The performance of Cu-SAPO-34/cordierite monolithic catalysts for removal NO in simulated diesel-engine exhaust conditions was explored using propane and ammonia as the reducing agent, respectively. The main results and conclusion obtained from experiments and studies were given as follow:(1) The method of one-step hydrothermal procedure can make the metal active components directly synthesize on the molecular sieve and obviously increasing the content of miscellaneous atoms of molecular sieve. The loading amount is more than 22% after one synthesis operation. The Cu-SAPO-34 coatings obtained by the in situ synthesis are firm and compact. The loss of the catalysts is lower than 1% after ultrasonic treatment.(2) For the C3H8-SCR process, Cu- SAPO-34/cordierite catalyst shows a high conversion of NO. NO conversion decreases with the increase of space velocity and the decrease of concentration of O2. The NOx conversion decreases after the addition of 10% water vapor to the feed gas but the deactivation caused by water vapor is not permanent. For the NH3-SCR process, the active Cu component prepared through in situ synthesis can significantly improve the activity of selective catalytic reduction. The conversion of NO is decreased slightly with the increase of space velocity. The H2O in the feed gas decreases the NO conversion and the coexistence of SO2 and H2O have the slight promoting influence on the NO reduction activity. (3) The aging experiments clearly show that almost no changes of the characteristic diffraction peaks can be recognized in XRD patterns of catalysts before and after the heat treatment. Cu-SAPO-34/cordierite shows the good thermal and chemical stability. The conversion of NOX is more than 80% in the entire experimental periods.