| Currently, NH3-selective catalytic reduction (SCR) technology become the main direction of development in the field of diesel exhaust purification. The SCR converter is usually installed in the rear of the desulfurization unit and diesel particulate trap. The exhaust gas will drop at only 100～300℃, when the exhaust gas flowing through the desulfurization unit and diesel particulate trap. Especially, the growth of exhaust flow path. The SCR catalysts with a low temperature and high SCR activity are key to SCR technology. The research and application of catalysts for diesel exhaust purification is important.In this paper, I developed a suitable catalyst for China’s economic and the pressure of low energy according to the properties of the diesel exhaust gas purification. In view of the honeycomb cordierite stucture in the field of automobile exhaust gas purification universality. Palygorskite (PG) was deposited onto cordierite (CC) supports using a simple suspension slurry method. The conditions of solid-liquid ratio, coating methods-time, slurry mixing time, drying method, drying conditions, calcination temperature and pickling cordierite substrate were the most influential parameters determining the coatings’ textural and mechanical properties. The mechanical properties of coating was investigated by means of ultrasonic vibration. Results showed that the PG layer exhibited very bad adhesion even after being subjected to ultrasonic vibration. The cordierite-palygorsikite supports didn’t have the conditions of diesel exhaust purification.Secondly, the best solid-liquid ratio slurry by adding right amount of binders to solve the phenomenon of coating shedding. The effect of different binders, H2O2 treatment, calcination temperature and PG coating particle size on the adhesion of the PG layers to the CC substrates was investigated.the PG coatings were extensively characterized by BET, SEM, Ultrasonic vibration. Results showed that the PG layer, whose surface area and pore volune were drastically increased, exhibited very good adhesion even after being subjected to ultrasonic vibration. the adhesion of the PG layer was improved by the use of appropriate binders. Based on these results, advantages of different binders are discussed.Furthermore, cordierite honeycomb ceramics (CC) coated with Palygorskite (PG) as catalysts’ carrier were prepared by method of immersing CC into a PG-water mixed slurry followed by calcination. The samples were loaded with manganese oxides by wet impregnation to obtain MnOx/PG-CC catalysts used for low temperature NO removal from exhaust gas of diesel engines. The independences of catalyst’s performance on preparation conditions (preparation conditions, manganese loading, PG coating particle size, binders, preparation methods, calcination temperature and calcination atmosphere) and operating conditions (oxygen concentration, space velocity) were investigated. The structural characteristics of catalysts were characterized by BET, SEM-EDS and XRD, thus the connections between catalyst’s structure and its SCR activity were discussed. Results showed that a loading amount of the active ingredient significantly increased from 3% to 13% after the PG coating the catalytic activity for NO conversion increased from 10% to 78% at 100℃. Significant rise in the catalysts’ surface areas was observed after PG coating onto cordierite honeycomb ceramics, which led to the high loading and uniform dispersion of active manganese species on the coating carrier. Additionally, a distinct improvement in surface Mn4+/Mn3+ ratio was also detected. It was suggested that the synergistic interactions between PG and manganese oxides is the key reason for the excellent SCR performance of the catalyst at low temperatures, and that the method of PG coating followed by MnOx loading is effective for promoting the SCR performance of the Cordierite honeycomb ceramics.At the end, the influence of simulated diesel exhaust water vapor on Mn13/PG-CC was studed through activity test experiment. The activity of catalysts were influenced by water vapor more serious at lower temperature. To further improve the SCR activity and water vapor tolerance of catalysts, Ce metal oxides were addied as auxiliaries to modify catalysts. Results indicated that the addition of Ce oxides improved Mn13/PG-CC catalysts’activity for NO reduction at lower temperature to some extend. Meanwhile, the water vapor tolerance of catalysts be up to 15%, when the space velocity was 26000 h-1. And the influence on the catalysts were reversible after heat treatment, which could be restored. |
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