Ce Modified Molecular Sieve In Hc Cold Start The Research And Application Of Motor Vehicles

In recent years, with the increasingly stringent emission regulating, HC pollutant treatment in motor vehicle cold-start becomes a hot research topic. The traditional catalysts in the presence of HC low temperature processing ability is poor, light-off temperature higher. Molecular sieve has a developed pore structure, centralized pore size distribution, large specific surface area, good heat resistance is widely used in purification of motor vehicle exhaust gas, so as to it improves the HC low temperature adsorption capacity of HC, and solves the cold start problem. But molecular sieve belonging to microporous materials in water resistant heat capacity is difference, and supported noble metal duing to pore structure restriction, It is not uniformly distributed in precious metals, so that the modified molecular sieve in order to improve the water resistance, heat capacity enlargement of pore structure and increase the catalytic activity of motor vehicle cold-start exhaust gas treatment technology development has important significance.This paper, It is fist from modification of rare earth of Ce in molecular sieve, and also review the various performance, picking out the best condition of the modified zeolite. Afterwards,It loads the noble metal Pd on the modified zeolite and finished products catalust. Through the contrast experiment and the various methods of characterization of the modified zeolite in load Pd materials of detailed research, and engine test bench tests in the modification of the practical application of molecular sieve catalyst materials made a preliminary investigation. The following conclusions can be drawn.1. The three different types molecular sieve Hβ,NaY, HZSM-5are researched in surface area, High temperature thermal aged and hydrothermal thermal aged surface area than attenuation and pore size distribution. The results show that Hβ hydrothermal thermal aged surface area than attenuation often severe, NaY high temperature thermal aged surface area than attenuation is very serious, And HZSM-5molecular sieve in high temperature thermal aged and hydrothermal thermal aged surface area than have declined, but still keep good specific surface area, so we choose HZSM-5molecular sieve as a modification of the material. 2. The ion-exchange method to HZSM-5was modified zeolite, this under the condition of different factors modified molecular sieve of various performance changes, and screened the best ion exchange conditions. The results show that different switching frequency and calcining temperature for molecular sieve modification of various performance are significant, the exchange of best times is four times, best calcining temperature is550℃, and through the characterization of the experiment proves, Ce elements in the main molecular sieve in two forms exist. One is in the researches of surface adhere CeO2, one kind is in the researches of internal amorphous Ce-O.3. Under the same conditions preparate the Pd/HZSM-5, Pd/Al2O3and Pd-Ce/HZSM-5catalytic materials, through the contrast experiment investigation modified the advantage and disadvantage of molecular sieve performance. The experimental results show that under the same conditions can be modified zeolite on load more Pd, low temperature on the adsorption of HC showed a significant activity, in the modification of molecular sieve metal Pd can better distribution, pore structure more uniformly. And through the experiment proves, Pd in main molecular sieve modified existing form is attached to the molecular sieve surface, a small amount will be formed within the molecular sieve into the amorphous Pd-O.4. Investigating to engine test bench for practical application of Pd/HZSM-5, Pd/Al2O3and Pd-Ce/HZSM-5, test bench experiment results show that:the modification of the molecular sieve tail gas CO, THC and NOx conversion rate highest, air/fuel ratio window is the largest, four successive after test for conversion of tail gas basic not too big change, catalytic activity, thermal resistance to water and heat capacity were greatly improved. Test bench oxygen storage capacity showed that the modification of molecular sieve bench oxygen storage ability best that Ce elements for the catalyst materials of oxygen storage capacity has played a significant role, the main reason is that exists and precious metals synergy happens the CeO2, CeO2with variable Ce4+/Ce3+, and has the unique oxygen storage performance.