Study On Ag/γ-Al₂O₃ Catalyst For Methanol-Fueled Vehicle Exhaust Purification

Methanol-fueled vehicle is an important method to relief the energy crisis and control the vehicle exhaust pollution. Its development must be of great significance to the automobile industry, energy structure adjustment and other relevant aspects. Developing superior catalysts for purifying the exhaust from methanol-fueled vehicles is one of the basic conditions.With the national emission standard for exhaust pollutants, viz. the nine-mode method, the exhaust pollutants from the 6102 heavy gasoline vehicle engine using methanol, methanol-hydrogen fuels and gasoline fuel were tested through the dais experiments respectively. The results showed: compared with the use of gasoline fuel, the use of methanol fuel could greatly reduce the emission of CO, NOx, CO2 and other conventional pollutants, but the emission of methanol and formaldehyde was increased remarkably. So the purification of the methanol-fueled vehicle exhaust was mainly to control and reduce the emission of methanol and formaldehyde.A series of Ag/γ-Al2O3 catalysts were prepared with different methods using γ-Al2O3 as the carrier and used in the deep oxidation of methanol. Under different preparing methods, different calcination temperatures, different Ag contents, different space velocity and La2O3 and CeO2 modified γ-Al2O3, the performance evaluation for the deep oxidation of methanol over Ag/γ-Al2O3 catalysts were studied and compared in a fixed-bed normal pressure flow reactor. The results showed: the series of Ag/γ-Al2O3 catalysts had excellent performance for the deep oxidation of methanol; the catalysts prepared by coprecipitation method had better performance than those prepared by impregnation-deposition method, and using NaOH as the coprecipitator or basifier had better catalytic activity than using Na2CO3; the Ag/γ-Al2O3 catalysts had the best performance when the calcination temperature was 500℃, the Ag content was 6% and the space velocity was low. The additive of La2O3 could reduce the initiation temperature of methanol and the addition of La2O3 and CeO2 could increase the selectivity of methanol to CO2. The mechanism of methanol deep oxidation was presumed that the deep oxidation of methanol should not include the CO middle step.The activated phase, the surface features and the Ag dispersion were characterized by XRD and TEM. The results showed: there were no obvious changes between the catalysts before and after reaction; only Ag and γ-Al2O3 were in presence; the particle size of Ag was much influenced by the calcination temperature; and the additive of CeO2 could improve the dispersion of Ag on theγ-Al2O3 carrier.