Enhanced activity for co preferential oxidation over cuo catalysts supported on nanosized ceo2 with high surface area and defects

“Nanosizedceria (n-CeO2) was synthesized by a facile method in 2-methylimidazolesolution. The characterization results of XRD, N2 adsorption-desorption, Raman and TEM indicate that n-CeO2 shows a regular size of 10 ± 1 nm, a high surface area of 130 m2·g−1 and oxygen vacancies on the surface. A series of CuO/n-CeO2 catalysts (CuCeOX) with different copper loading were prepared for the preferential oxidation of CO in H2-rich gases (CO-PROX). All CuCeOX catalysts exhibit a high catalytic activity due to the excellent structural properties of n-CeO2, over which the 100% conversion of CO is obtained at 120 °C. The catalytic activity of CuCeOX catalysts increases in the order of CuCeO12 < CuCeO3 < CuCeO6 < CuCeO9. It is in good agreement with the order of the amount of active Cu+ species, Ce3+ species and oxygen vacancies on these catalysts, suggesting that the strength of interaction between highly dispersed CuO species and n-CeO2 is the decisive factor for the activity. The stronger interaction results in the formation of more readily reducible copper species on CuCeO9, which shows the highest activity with high stability and the broadest temperature “window” for complete CO conversion (120–180 °C).”

Figure 1A shows the N2 adsorption-desorption isotherm and pore size distribution of n-CeO2 and p-CeO2Table 1 lists the BET surface areas, average pore diameters and lattice parameters of n-CeO2 and p-CeO2. Their N2 adsorption-desorption isotherms both correspond to typical type IV isotherms. n-CeO2 exhibits an H2-type hysteresis loop in the relative pressure (P/P0) range from 0.4 to 1.0, suggesting the existence of mesopores due to the agglomeration of particles [10,17]. p-CeO2 shows an H3-type hysteresis loop in the relative pressure (P/P0) range from 0.8 to 1.0, which indicates the generation of irregular pores in p-CeO2 [16]. From the inset of Figure 1A, we can see that n-CeO2 shows a narrow distribution of pore size between 5 nm and 15 nm. For p-CeO2, the pore size distribution is wider and in the range of 5–50 nm. As listed in Table 1, the pore volumes of n-CeO2 and p-CeO2 are 0.176 and 0.083 m3·g−1, and the average pore diameters are 5.6 and 18.7 nm, respectively. n-CeO2 possesses a large surface area, reaching to 130 m2·g−1, while p-CeO2 exhibits a relatively small surface area of 35 m2·g−1. The larger pore volume and smaller pore size benefit faster diffusion of reactant gas in catalysts. The larger surface area is beneficial to the high dispersion of copper species which can form more potential active sites.
Figure 1. N2 absorption-desorption isotherms combined with the pore size distribution curves (inset) (A), XRD patterns (B) and UV-Raman profiles (C) of n-CeO2 and p-CeO2.

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