Studies On The Zeolite-based Catalysts With High Adsorption Ability Of Alkane For Automobile Exhaust Purification

With the rapid increasing of vehicle ownership in China, automotive exhaust pollution is growing more seriously. In order to reduce automotive exhaust pollution and meet the increasing rigid emission regulations, the key is to reduce the exhaust emission in the cold-start. In this thesis, the catalysts with excellent adsorption and catalytic oxidation performance of C3H8were prepared by supporting transition metals on zeolite molecular sieves. By help of various analytic techniques, the relationship between the composition, the structure and the performance has been understood. And three-way catalyst, which can meet the emission regulation of Eu IV and Eu V, has been developed after optimizing the process of preparation. The main research results were achieved as follows:1. Studies on the adsorption and catalytic oxidation of C3H8over modified zeolite molecular sieves catalysts.Propane adsorption on zeolite molecular sieves with different structure and Si/Al had been investigated, the results indicated that H-ZSM-5with Si/Al=50has excellent C3H8adsorption ability. And the unfavourable influences on the adsorption of C3H8were observed due to the present of H2O, NO, O2and CO, especially the present of H2O. Furthermore, it is found that precious metals (Pt, Pd) and rare-earth metals modified ZSM-5(Si/Al=50) catalysts can improve the C3H8adsorption and catalytic oxidation performances.2. Studies on the influences of additives on the catalytic activity of Pt/ZSM-5catalysts for propane oxidation.The presence of W can obviously improve the catalytic activity and stability of Pt-W/ZSM-5catalysts for propane oxidation. Its high catalytic activity mainly is attributed to the oxidation-resistance of platinum by means of W. The optimal W loading was5wt.%. The T50and T90of propane oxidation over Pt-5W/ZSM-5are195and200℃, respectively. And its reaction rate and turnover frequency (TOF) are more than one order of magnitude higher than that of Pt/ZSM-5. Furthermore, it is found that the present of CO or SO2in the reaction gas can promote the catalytic activity of Pt-5W/ZSM-5to some extent, but the catalytic activity would be descended due to the present of NO.3. Studies on the influences of different metals modification and preparation method on the catalytic activity of Pd/ZSM-5catalyst for propane oxidation.The catalytic activity and hydrothermal stability of the Pd/ZSM-5catalyst are improved obviously by the Ce modification with the two-step method, and its catalytic activity is increased with the Ce loading. The promotional role of Ce for the Pd/ZSM-5catalyst mainly is attributed to the interaction between Pd and Ce. resulting in an increase in the Pd dispersion and higher oxidation state of Pd (PdOx, x≥+2) on the surface of the catalyst. The present of NO or SO2in the reaction gas may lead to the decrease of the catalytic activity of Pd-Ce/ZSM-5.4. Design and development of monolithic three-way catalyst for meeting Eu IV and Eu V emission regulation.The influences of loading ways of precious metal, precursors of precious metal and the process of coating on the catalytic performance of three-way catalyst were investigated. The results indicate that pre-supported precious metal on the coating materials is a better way to manufacture three-way catalyst with high catalytic activity and stability than the methods of traditional impregnation and mixture of precious metal solution with the coating material in the process of ball-milling. The three-way catalysts prepared with Pd(NH3)2(NO2)2and Rh(NO3)3as precursor salts have relatively high catalytic performance comparing with the catalyst prepared with other corresponding precious metals salts. Based on the above optimized results, the three-way catalyst meeting the emission regulation of Eu IV and Eu V has been prepared by optimizing the coating technology.5. Studies on the Co3O4/ZSM-5catalyst with high catalytic performance for the oxidation of C3H8.The Co3O4catalyst supported on ZSM-5shows better catalytic activity than Pd/ZSM-5catalyst for propane oxidation. And its catalytic activity is increased with the Co loading. Furthermore, the preparation method can influence the catalytic activity of the Co3O4/ZSM-5catalysts seriously. The catalytic activity of Co3O4/ZSM-5catalysts prepared by different methods is decreased in the order of hydrothermal method (HT)> deposition precipitation with NH4HCO3(DPNH)> deposition precipitation with NaOH (DPNa)> impregnation method (IM). The Co3O4/ZSM-5catalysts possess excellent catalytic activity and thermal stability, which mainly should be attributed to the higher surface area, surface Co content, surface relative Co3+concentration and surface lattice oxygen concentration. The propane oxidation over Co3O4/ZSM-5occurs through the Mars Van Krevelen redox mechanism.