The Reaction Of CO Oxidation Over The Supported Pt/MOx Catalysts

Catalysts for the oxidation of CO at low temperature were found practical application in many aspects.They are used in closed-spaceship and offices,in closed-cycle CO₂ lasers,in gas sensor for detection trace amount of CO in air,in industrial and automobile emissions and in CO safety masks,etc.On the other hand,for the application of fuel cell,it is important to remove the CO from the system.However,the commercial catalysts for CO oxidation are not stable in water environment and have a low activity around room temperature.The supported Au catalysts have the high activity at low temperature,but a common problem is that most of the supported gold catalysts are not stable under long-term reaction conditions and upon storage,especially at relative low temperature in the presence of water vapor.Compared with gold catalysts,it was found that the activity of Pt catalysts is much lower in the low-temperature CO oxidation, although the supported Pt catalysts are well known efficient catalysts for selective catalytic oxidation of CO at relatively high temperature.Therefore,it would be an attractive subject to develop highly active catalyst with super long-term stability for low-temperature CO oxidation.In this work,various supported platinum catalysts(Pt/MeO_x,Me=Fe,Zn,Al,Ni,Mn,Ca,Ti,Si,Co,Cu)were prepared by colloid deposition method,and their catalytic properties for the low-temperature CO oxidation were investigated.It was found that the type of support has considerable effect on the activity of the catalysts.And we have investigated the structure of Pt/Fe₂O₃ by X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),temperature programmed reduction(TPR), ⁵⁷Fe M(?)ssbauer spectroscopy(MBS),Gravimetric-differential thermal analysis (TG-DTA),and carried out the Fourier transform infrared(FTIR)measurement on the Pt/Fe₂O₃ in suit,the goal of the work was to study the nature of the active sites, and the reaction mechanism for CO oxidation on Pt/Fe₂O₃ catalyst prepared by colloid deposition method.1,Catalytic performance of CO oxidation over Pt/MO_xVarious supported platinum catalysts(Pt/MeO_x,Me=Fe,Zn,Al,Ni,Mn, Ca,Ti,Si,Cu)were prepared by colloid deposition method,which have the higher activity for the CO oxidation.1%Pt/Fe₂O₃ can completely transform CO into CO₂ at room temperature in the presence of water vapor.2,Catalytic performance of CO oxidation over Pt/Fe₂O₃The preparation method has effect on the activity of the Pt/Fe₂O₃ catalysts for the CO oxidation,the Pt/Fe₂O₃ catalysts synthesized by the colloid-deposition have the high activity compared with the catalysts prepared by the deposition-precipitation and the coprecipitation,1%Pt/Fe₂O₃ calcination at 200℃can completely transform CO into CO₂ at room temperature in the presence of water vapor for more than 3000 h.Further more,the 1%Pt/Fe₂O₃ have been stored in a vial under ambient atmosphere for about one year at room temperature and catalytically tested again,we found that the activity of the catalyst for CO oxidation was almost unchanged compared to the original catalyst.The detailed investigation on the Pt/Fe₂O₃ catalysts shows that the calcinations temperature have considerable effect on the catalytic performance of the CO oxidation reaction,and the suitable calcinations temperature is 200℃.Integrating the results of catalyst characterization,we suppose that the calciantion has an effect on the interaction between the Pt species and the support, bring the changes in the states and the compose of the Pt species and the support。For the 1%Pt/Fe₂O₃-200 catalyst,the Pt and Pt²⁺coexist in the catalyst,mostly in Pt²⁺state,the support is composed by the amorphous ferrihydrite,Fe²⁺,Fe₂O₃ and Fe₃O₄,and these Fe²⁺may be formed by a stronger interaction between Pt species and the support,this interface may be related to catalytic activity of CO oxidation. The addition of water vapor in feed stream has the positive influence on the activity of the catalysts.The reason may be that the water participate the activation of oxygen directly and then considerably enhances the reaction activity.The Pt loading has considerable effect on the activity of CO oxidation for the Pt/Fe₂O₃,the influence becomes more strong as increasing the Pt loading,and the property of the support gradually betray off the property of it's own.The catalytic activity can be increased by increasing the Pt loading at a certain extent.For the Pt/Fe₂O₃—200,Pt²⁺is the adsorption site for CO,defect sites and the Fe species maybe could active oxygen.In the reaction,the adsorption/dissociation of oxygen is the rate-determining step.The water participate the activation of oxygen directly.At the high space velocity,carbonates formed in the reaction gradually accumulate on the surface of the catalyst,resulting in a decay of oxygen adsorption/dissociation rate,so that,the activity of the catalyst decreases.