Impoved Palladium Only Three Way Catalysts Using Phosphorus Modified Alumina Support

Fundamental studies of the three-way catalysts (TWCs) are highly demanded tomeet the increasingly stringent regulations for automotive exhaust emissions. Due tothe higher exhaust temperature of automobile exhaust, the surface area of the TWCssupport was prone to decreased dramatically, which led to the embedding andsintering of the precious metals. Improving hydrothermal aging-resistant ability of thesupport has been one of the hot spots for studying TWCs.This article based on sol-gel synthesis of different doped content of phosphorusin alumina, respectively, non-phosphorus-containing alumina and aluminumphosphate treated as the blank and phosphorus-rich references. Studyingphosphorus-containing alumina used in palladium only three-way catalystsystematically, focusing on the interaction between the phosphorus and the preciousmetals, furthermore, corresponding with the TWC catalytic activity.Sol-gel synthesis of phosphorus-containing alumina owns high specific surfacearea (SBET) and shows an excellent resistant hydrothermal ability. After the harshhydrothermal treatment, P-doped alumina most maintains activate alumina crystal andpretty high SBET, crystalline aluminum phosphates appears in5wt.%P-dopedalumina. The TWC activity for fresh P-doped samples improving with the increase ofphosphorus content. The T50of the5wt.%P-doped catalyst in CO oxidation, NOreduction and HC oxidation compared to the no P-doped catalyst significantlyreduced around20°C.For aged samples, due to the phosphorus, the precious metals in the P-dopedsupport can maintain small particles sizes and high precious metals dispersions. Theability of phosphorus anchoring the precious metals as the mount of P increasingsignificantly improves. After hydrothermal treatment, the catalyst with5wt.%phosphorus maintained around3nm Pd particle sizes and the metal dispersion can bekept close to the50%. For strong anchoring role of precious metals, P-doped catalystsshowed superior catalytic activity after the aging. Compared to the no P-dopedcatalyst, T50of the P-doped catalysts reduced about30°C.Aluminum phosphate as a phosphorus-rich support, the catalytic activity of freshsamples is not ideal, might due to its small surface areas. But after high-temperaturehydrothermal aging, its catalytic activity compared to the other samples whose the level of reducing is the minimum. Especially in the oxidation of CO and HC, which isequivalent to5wt.%of P-doped catalyst.