Preparation Of The Pd-only Three Way Catalysts And Recovery Of Pd From Spent Catalysts

Catalytic removal technology is one of the most effective ways to eliminate the automobile exhaust emission and the development of highly active and durable catalysts is the key. In comparison with the traditional three-way catalysts containing platinum, rhodium and palladium, the Pd-only three way catlalysts have drawn more considerable interests in recent years because of their higher catalytic activities and lower cost.In this paper, Pd-only catalysts were prepared with honeycomb ceramic monolith as carriers, Ce-Zr composite oxides as additives andγ-Al₂O₃ as coatings. The activities are evaluated on simulated automobile exhaust catalytic purification equipment. The factors that effect the catalytic activities including different additives, different loading ways, different Pd mass, second evaluation and aging on high temperature have been studied. The ways of recovrery of Pd from automobile exhaust spent catalysts have been studied.The powder materials includingγ-Al₂O₃, Ce-Zr-La composite oxides, Ce-Zr-Fe-Mn complex oxides have been prepared by precipitation technique, characterized by XRD, BET, TPR and other analysis methods. The results showed that Ce-Zr-La and Ce-Zr-Fe-Mn composite oxides remained solid solution structure with cubic phase after calcinations on high temperture, and applied to additives.The catalysts with Ce-Zr-Fe-Mn composite oxides as additive and loading different Pd mass have been prepared by the electroless plating method. The catalyst with Pd mass 2g/L had the best activity. The catalysts with Ce-Zr-La composite oxides as additive with Pd loading 2g/L has been prepared by the electroless plating and traditional impregnation method. The characterization results showed that catalytic properties of the catalyst prepared by electroless plating were superior to that of the catalyst prepared by impregnation; the catalytic performance of catalyst prepared by electroless plating was decreasing after characterized twice; after the catalyst aged at 1000℃for 4h, it has had good catalytic activity of CO oxidation.Pd was leached by mixed HCl-H₂O₂ solutions with extraction rate 97%, precipitated and purificated by Pd(NH₃)Cl₂ and reduced by hydration combined amine. Pd total recovery >96%, purity>99%.