Synthesis of Sr-modified Pd-Rh Bimetallic Catalyst with Advanced Three-Way Catalytic Performance

Abstract:

A series of SrO-modified Pd-Rh/Al₂O₃ catalysts were synthesized by co-impregnation technique, i.e., Sr precursor was introduced into the mixed salt solution of Pd and Rh prior to their impregnation on Al₂O₃ powders. The results reveal that owing to the diffusion barrier effect of SrO, the introduction of appropriate amount of SrO (1wt%~2wt%) can increase the dispersion of Pd and Rh, as well as improve the hydrothermal stability of the catalyst. After hydrothermal aging treatment, higher dispersion and more active oxidation state of Pd and Rh are maintained. Consequently, modified reduction capability and improved three-way catalytic performance can be obtained for the appropriate SrO-modified Pd-Rh/Al₂O₃ catalyst. However, when excessive amount of SrO is introduced, plenty of surface sites on Al₂O₃ support will be occupied, and new SrAl₂O₄ phase is generated, leading to adverse effect instead. To sum up, the catalyst modified by 2wt% SrO exhibits the best three-way catalytic performance, by which after hydrothermal aging treatment, the light-off temperatures of CO, HC and NO are 23, 15 and 27 °C lower than those by bare Pd-Rh/Al₂O₃ catalyst.

Key words:SrO;Pd-Rh/Al₂O₃ catalysts;dispersion;oxidation state;three-way catalytic performance