Synthesis of an advanced Pd-Rh bimetallic catalyst for gasoline engine emission control

Abstract

• An advanced Pd-Rh bimetallic catalyst was obtained by adjusting the Rh distribution. • The aggregation of Pd upon aging is suppressed owing to the diffusion barrier effect. • More PdO and Rh 2 O 3 species are kept due to the synergistic effect between Pd and Rh. • After aging, the modified catalyst shows superior catalytic conversion efficiency. In recent years, the dramatic increase of the prices of Pd and Rh brings about increasingly heavier cost pressure for the exhaust gas after-treatment industry, thus it is of great significance to develop advanced Pd-Rh bimetallic catalysts with low metal loading. In this work, on the basis of conventional catalyst composed of Al 2 O 3 -supported Pd and CZ (ceria-zirconia-based oxide)-supported Rh, an advanced Pd-Rh catalyst was obtained by adjusting the synthesis procedure. That was, a small portion of Rh was co-impregnated with Pd on Al 2 O 3 , while the other portion was still supported on CZ. In this way, the co-impregnated Rh may act as an auxiliary for Pd/Al 2 O 3 component. As revealed by the various characterization results, the agglomeration of Pd species is well suppressed, and larger amount of PdO species is maintained for the modified catalyst after hydrothermal aging treatment. On the other hand, the state of Rh species also appears to be somewhat modified. Consequently, after hydrothermal aging treatment, the modified catalyst behaves much better for the catalytic conversions of CO, HC and NO.