性能优异的SrO改性Pd-Rh双金属催化剂的制备

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

摘要:

在浸渍到Al₂O₃载体材料上之前，通过将Sr的前驱体引入到贵金属Pd和Rh的混合盐溶液中，即采用共浸渍法制备了一系列SrO改性的Pd-Rh/Al₂O₃催化剂。结果表明，由于SrO的扩散障碍效应，适量SrO（1%~2%，质量分数）的引入有利于促进Pd，Rh的分散，并且能提高催化剂的水热稳定性。水热老化之后，催化剂能保持更高的Pd，Rh分散度，并且Pd，Rh能稳定在活性更好的氧化态。因此，适量SrO改性的Pd-Rh/Al₂O₃催化剂具有更好的还原性能和三效催化活性。然而，当向催化剂中引入过量的SrO，由于SrO占据了过量的Al₂O₃的表面，而且老化后会出现新的物相SrAl₂O₄，反而会对催化剂的性能产生不利的影响。总的来说，2% SrO改性的催化剂具有最优异的三效催化活性，水热老化之后，相比于空白的Pd-Rh/Al₂O₃催化剂，2%SrO改性的催化剂使CO，HC和NO的起燃温度分别降低了23，15和27 ℃。

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.