Research On Catalytic Oxidation Of NO And Mechanism Of Sulfur Resistance Over Supported-perovskites

Lean-burn engine was becoming mainstream technology gradually for its economical and environmental potential. But excess O2 in lean-burn vehicle exhaust rendered traditional three-way catalysts ineffectively in reducing NOx, leading to extra emissions of NOx. NOx Storage-Reduction with the advantages of easy operation and small demand of reductant was becoming the best NOx treatment technology. noble metals with high prices are main active component of NSR catalysts. As a cheap metal compound, perovskite owned superior NSR activity, but perovskites were easily poisoned in sulfur atmosphere owning to low specific area. Exploring the sulfur deactivation mechanism of perovskite, seeking the appropriate modification, improving the sulfur resistance of perovskite were the key issues in developing the efficient NSR non-noble metal catalysts.The literature was based on the NO activity experiments under sulfur atmosphere, combined with characterization and adsorption and desorption experiments to analyze the sulfur-poisoning mechanism of pure La0.8Ce0.2CoO3 perovskite and the effect of CeO2 support addition on sulfur-resistance in NO catalytic oxidation reaction. Results showed that the poisoning of La0.8Ce0.2CoO3 was mainly due to destruction of physical-chemical properties and the formation of stable sulfate under sulfur atmosphere. Support CeO2 acted as SO2 trap preferentially, this slowed down the poisoning rate of active component. Meanwhile in the temperature range of NSR reaction, the redox reaction between CeO2 and SO2 produced more oxygen vacancies and improved the activity in sulfur.Then the effect of Ce doping amounts on sulfur-resistance of supported La1-xCexCoO3/CeO2(x=0, 0.1, 0.2, 0.3) was studied. The results indicated that high Ce doping(x= 0.2, 0.3) owned good sulfur-resistance and low Ce doping(x= 0,0.1) had poor. By characterization and adsorption and desorption experiments indicted that the La1-xCexCoO3/CeO2 was poisoned mainly for the changes of physical-chemical properties and the influence of SO2 to NO2. While the increased Ce substitution improved the physical-chemical properties and stability of catalysts, increased the amount of NO2 and then improved the NO conversion, delayed poisoning time.The paper also focused on the influence of different mesoporous supports adding to LaCoO3 in NO catalytic oxidation reaction. Among them, mesoporous ZrO2, CeO2 and Ce1-xZrxO3 promoted the NO catalytic oxidation activity of LaCoO3.While mesoporous TiO2 and SiO2 inhibited the activity. Different preparation methods of CeO2 support did little effect on the NO catalytic oxidation activity of LaCoO3/CeO2, Among them precipitation had the best activity 73.6% at 300℃, and sol-gel method obtained the best low temperature activity. Solid solution Ce0.9Zr0.1O3 supported LaCoO3 and calcined at 600℃gained the best NO catalytic oxidation activity for supported LaCoO3/Ce1-xZrxO2.