Study On Automobile Exhaust Catalysts Under Lean-burn Conditions

The design and application of lean-burn petrol engine and diesel engine are rising now in the world for the advantages of higher output power, more effective burning, more economy and less emission of CO and HC. The traditional three-way catalyst is ineffective under lean-burn conditions. Though the lean-burn automobile exhaust molecular sieves catalysts being studied now are active and selective, they are very easy to be inactive in the presence of vapor at high temperature for the destroy of crystal structure. A new type of silicoaluminophosphates SAPO-34 is very suitable as support of automobile exhaust catalysts under lean-burn conditions due to its suitable structure of pore, adjustable acidity and good hydrothermal stability. According to the disadvantages of molecular sieve catalysts above, SAPO-34 has been synthesized first and then Ion-Exchanged Ag-SAPO-34 and Cu-SAPO-34 catalysts as well as biflinctional catalysts of Ag-SAPO-34 + CeO₂, Cu-SAPO-34 + CeO₂ and Ce/Cu/SAPO34 have been prepared to aim to solve the following three problems:Based on the study and optimum of synthesized technology parameters, such as crystallizing temperature, crystallizing time, template, the source of Si and Al, the content of Si and etc., high purity and crystalline silicoaluminophosphates SAPO-34 has been synthesized successfully, and there is no by-product SAPO-5. The synthetic SAPO-34 is proved much hydrothermal stable and very suitable as support of automobile exhaust catalysts under lean-burn conditions.The activities, preparation technology, hydrothermal stability and reaction mechanism of Ion-Exchanged Ag-SAPO-34 and Cu-SAPO-34 catalysts have been studied in details. The Ag-SAPO-34 catalyst which is active at low temperature and much hydrothermal stable has been prepared, on which the highest conversion of NO to N₂ is 73.6% at the temperature of 336℃. And the conversion only decreases by 2.3-5.5 percents after being treated hydrothermally. The Cu-SAPO-34 catalyst which has high activity, wide operating temperature range and excellent hydrothermal stability has been prepared too, on which the highest conversion of NO to N₂ is 75.4% at the temperature of 430℃. And the conversion only decrease by 2-5 percents after being treated...