Stability Of Supported Gold Catalysts On CO Oxidation At Low-temperature

Gold catalysts, as a novel catalytic material, have been made great progress in chemical industry and environmental applications due to their excellent catalytic performances. Especially for the catalytic oxidation of CO, industrial applications of the supported nano-gold catalyst have emerged. However, gradual deactivation of gold catalysts due to aggregration of nanogold particles with time on stream significantly confined its application in a wider range. Preparation of catalysts with high activity and high stability is therefore still an important challenge.In this paper, on the basis of the original work, usingγ-Al₂O₃ as carrier, a more detailed study of preparation parameters of Au/Al₂O₃ catalyst for CO oxidation by iso-impregnation has been investigated. The activity and stability of Au/MgO/Al₂O₃ and Au/LaFeO₃/Al₂O₃ catalysts treated in different atmospheres were also tested. AAS,N2-physical adsorption, XRD, H₂-TPR, TEM characterization techniques were used to study the structure, chemical state and the reduction/oxidation behavior of these catalysts. The main results are summarized as follows:1,For 1%Au/Al₂O₃ catalyst prepared by iso-volume impregnation method,ammonia immersing pretreatment is helpful to catalytic activity, for the catalysts either calcined in air or reduced in H₂. The appropriate pH value of HAuCl4 solution in preparation is about 8. Reduction of the catalyst precursor in H₂ presents better stability than calcination in air.2,The online and storage stability and of two series of 1.1%Au catalysts were investigated in air and reactant gas respectively, in which the supports of MgO/Al₂O₃ were synthesized by two deposition method and the air/feed were saturated with water vapor. Compared to Au/Al₂O₃ catalyst, Au/MgO/Al₂O₃ catalysts show much better stability and activity.3,A series of gold catalysts 1.1%Au/LaFeO₃/Al₂O₃ have been for the first time prepared by iso-volume impregnation method with an effort in the modification of Al₂O₃ by Fe-La composite. Its composition and preparation conditions were optimized. When total content of Fe₂O₃ and La₂O₃ reaches 2% and atomic ratio Fe:La = 1, the catalyst gives a higher catalytic activity and a best stability. When reacting at 550℃for 10h, the Au/2%LaFeO₃/Al₂O₃ catalysts activated by O₃,which may reinforce the interaction between metal and support as showed by H₂-TPR,can work better than that activated by H₂, and both are much superior than Au/Al₂O₃ catalyst. This may attribute to the accession of Fe and La exists in the form of LaFeO₃ perovskite on the surface of Al₂O₃.4,Au/2%LaFeO₃/Al₂O₃ catalysts, activated by H₂ or O₃ at 300℃were firstly reacted in 1.0vol.% CO at room temperature and 120℃and then tested their retained activity at room-temperature. The results as listed below are quite different with above:(1)at room temperature: Au/LaFeO₃/Al₂O₃-O₃≈Au/Al₂O₃-H₂>Au/LaFeO₃/Al₂O₃-H₂(2)at 120℃:Au/LaFeO₃/Al₂O₃-H₂ > Au/Al₂O₃-H₂ >>Au/LaFeO₃/Al₂O₃-O₃This may be result from the combined effect of catalyst composition, the atmosphere treatment of activation.5,Besides, when continuously reacting in 1.0vol.% CO hydrogen-rich atmosphere at fuel cell operating temperature,1.1%Au/2%LaFeO₃/Al₂O₃-H₂ catalysts are slightly stable than Au/2%LaFeO₃/Al₂O₃ catalyst activated by O₃.