Synthesis of an Advanced Pd–Rh Bimetallic Three-Way Catalyst by Adjusting the Distribution of Noble Metals

Abstract—In recent years, the substantial increase in the prices of Pd and Rh brings about increasingly greater cost pressure for the exhaust gas aftertreatment industry, thus development of advanced Pd–Rh bimetallic catalysts with lower noble metal loading is of great significance. In this work, an advanced Pd–Rh catalyst was obtained by adjusting the synthesis procedure of the reference catalyst prepared by conventional step impregnation method. That was, during the impregnation process, the volume of the salt solutions of noble metals was controlled to be smaller than the calculated required value, and meanwhile, the ratio between that of Pd solution and Rh solution was adjustable. By this means, the distribution of Pd and Rh on Al₂O₃ support could be effectively adjusted. As revealed by the various characterization results, for Pd–Rh catalyst with appropriate ratio between the volume of Pd solution and Rh solution, the distribution and oxidation states of Pd and Rh species are efficiently modified, especially after hydrothermal aging treatment. Consequently, after hydrothermal aging, prominent reduction capability and higher conversion efficiency for CO, HC and NO are achieved for the modified catalyst.