Size effects of Pd nanoparticles supported over CeZrPAl for methane oxidation
The size of Pd nanoparticles is considered to be critical for the cost and performance of methane oxidation catalysts. Herein, Pd/CeZrPAl catalysts with different Pd sizes from 3.4 to 110.9 nm were prepared by an impregnation method to identify the effects of the size of Pd nanoparticles on the methane oxidation activity. The measurement of TOF under lean burn conditions showed that the methane oxidation reaction catalyzed by Pd/CeZrPAl is structure-sensitive. TOF showed a positive linear relationship with Pd size. Based on the structural analysis, the dependence of the intrinsic activity (TOF) on size is due to the distortion of the morphology of Pd nanoparticles to create more active sites. However, the evaluation of methane conversion activity under lean burn conditions showed that the overall conversion performance of methane oxidation catalyzed by Pd/CeZrPAl has nothing to do with the size of Pd nanoparticles but mainly rests with the valence distribution of Pd species. These results provide a scientific basis for the design and application of high-performance catalysts for the after-treatment of natural gas vehicle exhaust.