The Research On Au-Pd Bimetallic Catalyst For Catalytic Property Of CO Oxidation

Noble metal catalysts have a wide range of applications, of which the catalytic activity is determined by many factors, including particle size, property of support. Thus lots of synthesis methods have been developed and applied. For CO oxidation, Au and Pd have good catalytic activity; however defects exist for single-component catalyst. Au nanoparticles easily move and agglomerate at high temperature for its low melting temperature while Pd is prone to be oxidized under oxygen-rich conditions, leading to a worse catalytic activity. Therefore new structures and multi-component catalysts are good solutions. We have systematically studied single- and multi-component Au-Pd catalysts. The results are as follows:For Au catalyst, the modified impregnation methods are applied resulting in a catalytic conversion of CO at room temperature. Catalysis of Au is influenced by a combination of factors. Factors of calcination temperature and shape of support as well as the CO catalysis mechanism on Au have been studied with TEM and XRD characterization. To prevent agglomeration of Au, Au@SiO₂ core-shell structure is developed which is proved to be effective. For Pd support catalyst, sequential tests under oxidation-rich condition verify its instability. All above provide research support for the study of Au-Pd bimetallic catalyst in the following part.For bimetallic Au-Pd catalyst with wet synthesis method, it is synthesized through the multi-step deposition of Au and Pd on amine group modified Si O2 support, which leads to nanoparticles of smaller size. The phase of samples is identified to be alloy and the Au/Pd weight ratio has significant influence on CO catalytic activity. For Au/Pd is 1/3, the catalytic activity is better than pure Pd, while for Au/Pd is 3/1, it is the opposite. This indicates that Au has promoting effect on Pd in a limited amount range, which shows a synergistic effect. More Pd exists as metallic state with appearance of Au leading to a better stability for catalysis.For bimetallic Au-Pd catalyst with atomic layer deposition method, different reductants, H2 and formalin are used to deposit Pd. The results show that H2 leads to a better selective growth of Pd on Au nanoparticles. Through the adjustment of Pd ALD cycles, the CO conversion temperature increases with the gain of cycles. Particle size remains the same after calcination indicating a better thermal stability. Tests under simulated exhaust condition for cyclic tests shows a better anti-oxidized property in comparison with pure Pd catalyst.