A Study Of Automobile Exhaust Purification Catalysts For Cold Start Emission

With the rapid development of Chinese economy, atuomobile possession increases quickly. Correspondingly, auto exhaust becomes one of the most important sources of air pollution, which does serious harm to human health and urban environment. Due to the higher ignition temperature of three-way catalysts, the tail gas produced at the start-up moment can not be cleaned in time. Therefore, to investigate the catalysts with lower light-off temeprature is very important for reducing the air pollution of the cold-start exhaust, improving urban environment, and stimulating the development of economy.1. Preparation of ceria-based catalysts and evaluation of their catalytic performance for methane combustionCeria-based catalysts were prepared by Sol-Gel method and evaluated by methane combustion reaction. Among the ceria-based catalysts herein, Ce0.95Si0.05O2catalyst has the highest activity. Its methane conversion is up to50%at518℃. Meanwhile, Ce0.95Al0.05O2catalyst has the lowest activity because of its large grain size, low surface. Similar reason can be explained for the relatively lower reactivity of Ceo.95Mgo.o502-s. However, Raman spectroscopy indicates that the oxygen vacancy concentration increases compared with ceria support due to the partial substitution of Ce4+with Mg2+. Hence, its activity of CH4combustion is slightly higher than the Ce0.95Al0.05O2-δ catalyst. Different from the Al, Mg doped ceria-based catalysts, Ce1-xSixO2-δ catalyst has small grain size and relatively large surface. Furthermore, after Ce4+in the lattice was partially substituted by Si4+, the oxygen vacancy formed, which can further proved by the Raman spectroscopy that the oxygen vacancy peak is the highest in the three catalysts. Therefore, Ce0.95Si0.05O2has the highest CH4combustion performance.2. Preparation and evaluation of La1-xCexFeO3catalysts for methane combustion A series of La1-xCexFeO3oxides with different Ce ratios were prepared by Sol-Gel method and calcinated at different temperatures, using nitrates as precursor, citric as sol agent, ammonia water as pH adjustor. Catalytic combustion tests showed that the activity of La1-xCexFeO3oxides firstly increases with the increase of Ce content and reaches the maximum when Ce ratio is up to0.3; then decreases with the further increase of x. The calcinated temperature effects on La0.7Ce0.3FeO3catalysts were also systematically investigated. Our results show that the CH4combustion activity of La0.7Ce0.3FeO3catalysts firstly increases, and are up to the maximum at750℃, then decreases with the further increasing calcination temperature. When the methane conversions of the optimized Lao.7Ceo.3FeO3catalyst are up to10%,50%, and90%, the corresponding reaction temperatures are340℃,439℃, and510℃, respectively. On the basis of the catalyst characterization, the active oxygen species might increase when Ce doped into the LaFeO3oxide. This is also the main reason for explaining the best activity of the catalyst.