Supports Effect And Deactivation Mechanism Of Au Catalyst For CO Oxidation

As one of active redox catalysts, gold catalyst has the advantages of excellent low-temperature activity and selectivity, which is also utilized under humid conditions. However, the large-scale production, poor reproducibility and stability hinder gold catalyst from industrial application. Therefore, to further explore the influential factors of catalytic activity, mechanism of reactions and deactivation of catalysts, this paper discusses the interaction between support material and catalytic performance, and the reason of deactivation at low temperature region.Via synthesizing various MnO2support and FeOx support with different crystalline phase and active support and the SiO2structure of the composite supports CeO2/SiO2, the effect of support nature on catalytic activity was investigated. Besides, with deposition precipitation method (DP method) and co-precipitation method (CD method), the relationship between gold nanoparticles and catalytic performance was explored. Furthermore, this paper studied the deactivation of Au/MnO2catalyst at low temperature through temperature programming technology.Using K2S2O8, KMnO4and (NH4)2S2O8as oxidants proving tunnel ions of K+and NH4+, rod-like α-MnO2was prepared under hydrothermal conditions. Then gold nanoparticles were deposited on obtained α-MnO2support with co-precipitation method (CD method). It can be concluded that the tunnel ions have a great influence on the morphology of catalyst supports. The catalytic performance in the following sequence:KMnO4>K2S2O8≈(NH4)2S2O8. In addition, while utilizing KMnO4as oxidant addition, Au/MnO2catalyst exhibits relatively low activity at the range of-10℃and0℃, which is attributed to CO2product block on the active site of gold catalyst.Rhombohedral and spindle shaped α-Fe2O3materials were synthesized through a hydrothermal method assisted with L-lysine and D-asparagine as the structure directing agent. Based on obtained α-Fe2O3, γ-Fe2O3and Fe3O4were prepared via the phase transformation. Interestingly, cross-linking phenomenon occurred in the above process. The H2-TPR results suggest that spindle iron oxide can be reduced easily. Spindle shaped Au/FeOx catalysts obtained by DP method shows catalytic activity in the sequence: Au/L-a-Fe2O3> Au/L-γ-Fe2O3>Au/L-Fe3O4. The performance of Au/FeOx catalysts with rhombohedral morphology are as follows:Au/L-y-Fe2O3>Au/L-a-Fe2O3Au/L-Fe3O4. The XRD pattern of Au/L-FeOx catalysts indicates that y-Fe2O3support partly transforms into α-Fe2O3during reaction process. Via synthesizing with DP method, Au/L-FeOx catalysts containing Au3+exhibit relatively poor low-temperature activity, while prepared by CD method, gold catalysts mainly consist of Au0exhibit excellent activity for CO oxidation. It suggests that the Au0species are beneficial to the low-temperature performance of gold catalysts. After treatment of N2, both Au0and Au3+exist on the Au/L-FeOx catalyst obtained by DP method. Therefore, the appropriate ration of Au0and Au3+is significant to promoting catalytic activity for CO oxidation.