Study On The Ternary Oxide Catalysts CuMnCeO Used For CO Preferential Oxidation

A series of CuMnCeO catalysts with 10% CuO?weight loading? and variable atomic ratios of Mn/Ce+Mn were synthesized by one step co-precipitation and employed for CO preferential oxidation?CO PROX?. Multiple techniques such as N₂ sorption?BET?, XRD, UV-Raman, ICP-AES, TEM/HRTEM, H₂-TPR, XPS, Cu K-edge XAFS?including EXAFS and XANES? were used for catalyst characterization. The catalyst with Mn/Ce+Mn ratio of 0.05?CuMnCe-0.05?shows the best performance, exhibiting not only the lowest temperature for 50% conversion of CO?T50=73 ?? but also the widest temperature window of full CO conversion?108-149 ??. In addition, it also exhibits the 100% selectivity of oxygen to CO₂ below 117 ?. As revealed by XRD and UV-Raman, the presence of appropriate amount of Mn cannot only enhance the formation of Ce-Cu-Mn-O ternary oxide solid solution with fluorite structure, inhibiting the growth of CeO₂ crystallite size, but also increase the oxygen vacancies. The results of H₂-TPR and XPS indicate that the reducibility and amount of surface oxygen species of CuMnCe-0.05 are also improved, both of which are beneficial to catalytic performance. The Cu K-edge XAFS shows that the bulk copper species of the fresh catalysts remains as CuO. Above characterization results suggest that the more oxygen vacancy and surface lattice oxygen species along with the best reducibility and oxidation performance result in the better performance in CO PROX.The effect of copper loadings on catalytic performance was also studied on the y-CuMnCe catalysts.Many techniques such as BET, TEM, XRD, H₂-TPR, in situ DRIFTS and in situ XANES were used for catalyst characterization. The catalyst with 10 wt.% CuO exhibits the best catalytic performance. The results of characterizations show that the catalyst possesses the largest surface area and the best reducibility performance. In situ XANES results suggest that the bulk copper species still remain as Cu²⁺ ions below 200 ? even in H₂-rich CO PROX atmosphere, besides, the copper species are sensitive to the atmospheres; however, the in-situ DRIFTS spectra indicate that during CO PROX below 120 ? the surface copper species are Cu+ ions which are regarded as the main active sites for CO PROX; above 120 ? CuO species appear, which enhance the oxidation of H₂, decreasing the oxygen to CO₂ selectivity. In addition, the stability and the effect of H₂ O and CO₂ on 10-CuMnCe catalyst in the feed gas were also investigated. The catalyst shows extremely high stability under 100 ?. However, the addition of H₂O and CO₂ exhibits obvious negative influence on the catalytic performance, which not only increases the initial temperature of full CO conversion, but also narrows the complete CO conversion window.