Study On The Ternary Oxide Catalysts CuO/CO₃O₄-CeO₂Used For Co Preferential Oxidation

A series of Co3O4-CeO2supports and CuO/Co3O4-CeO2ternary compositecatalysts with7wt.%CuO and variable Ce/Co atomic ratios were prepared byco-precipitation and wet impregnation, which were employed for the preferentialoxidation of CO (CO PROX). Many techniques such as N2-sorption, XRD, H2-TPR,O2-TPO, CO-TPD, O2-TPD, Cu K-edge XAFS (including EXAFS and XANES) andin-situ DRIFTS were used for catalyst characterization. The catalystCuO/Co3O4-CeO2with Ce/(Ce+Co) ratio of0.1exhibits the best performance,showing not only the lowest temperature for complete CO oxidation (98°C) but alsothe broadest operating temperature window for full CO conversion (98173°C). Theresults of N2-sorption and temperature-programmed characterization includingH2-TPR, O2-TPO, CO-TPD and O2-TPD show that the CuCoCe10catalyst possessesthe highest BET surface area, best reducibility/oxidizability and best performance forCO and O2adsorption, which are favorable to the catalytic performance of catalysts.Linear combination fitting of Cu K-edge XANES spectra reveals that multiple Cuspecies including Cu0, Cu+and Cu2+species co-exist in the spent catalyst CuCoCe10and the existence of Cu+in the fresh sample is also benefit for the activity. Stable Cu+carbonyl species are identified as the main intermediates by in-situ DRIFTS. At lowtemperature (≤100oC), the steady Cu+-CO can prevent the dissociation of H2; but athigh temperature (≥120oC) Cu+can be reduced to Cu0, enhancing H2oxidation; as aresult, the selectivity of O2towards CO2is decreased. Based upon in-situ DRIFTSresults, a potential CO PROX mechanism over CuO/Co3O4-CeO2catalysts isproposed.The effect of different calcination temperature on catalytic activity was studied onthe CuCoCe10catalyst with Ce/(Ce+Co)=0.1, and it is found that the samplecalcinated at350oC exhibits the best CO PROX activity, the initial temperature ofcomplete CO conversion is only98oC. The CuCoCe10catalyst owns the largest BETsurface area and best reducibility. Besides, the effect of H2O and CO2in the feed gaswas also investgated. The initial temperature of complete CO conversion on theCuCoCe10catalyst has increased by30oC, which is still better than the CuO/CeO2catalyst. After85h continuous activity measurement in the presence of H2O and CO2, the CuCoCe10catalyst exhibits a CO conversion higher than90%, and a selectivity ofO2to CO2larger than85%.