Researchers from the National Engineering Research Center of Fine Petrochemical Intermediates, Lanzhou Institute of Chemical Physics (LICP), Chinese Academy of Sciences (CAS), have invented an anti-sulfur poisoning three-way catalyst for the reduction of gasoline engine exhaust. The corresponding Chinese invention patent has been authorized on May 4, 2012.
Gasoline engine exhaust contains a great quantity of CO, HC, SOX and NOX, among which SOX is mainly from sulfide in gasoline. Sulfide will partly turn into SO2 and SO3 after being burned in engine. The combined action of SO2 and SO3 can lead to toxication and deactivation of catalysts, which will in turn cause catalysts to be inefficient in transforming pollutants in exhaust, such as CO, HC, NOX, etc.
As it is known, hydrogenated and isomerized gasoline which contains a small amount of sulfide is mainly used abroad. The content of sulfide in gasoline exerts little influence on the use of gasoline engine catalysts. Thus, the research on anti-sulfur poisoning three-way catalyst for gasoline engine exhaust is relatively rare. However, gasoline containing sulfur from the Middle East is mainly used in China and thereby the content of sulfur in catalytic cracked gasoline is relatively high. That’s why the stability of catalysts is weaker when catalysts are used in China.
In this invention the three-way catalyst uses cordierite honeycomb ceramics as a matrix, and noble metals, namely Pd, Pt, and Rh as main active constituents.A compound aluminum oxide coating layer composed of aluminum oxide powder, rare earth metal, alkali earth metal, transitional metal and La-Y-Ce-Zr solid solution is coated on the surface of the matrix. A presoaking layer composed of rare earth metal and transitional metal is further impregnated on the compound aluminum oxide coating layer. Then soluble salt solution containing the noble metal active constituents of Pd, Pt, and Rh is utilized to impregnate catalyst carrier to get the three-way catalyst. The presoaking layer can prevent active sties of noble metals from being bound or covered with sulfur. In this way the service life of catalysts can be prolonged. This catalyst has excellent anti-sulfur poisoning performance on the basis of maintaining unchanged transform rates of CO, HC and NOx.
