Improved CO Oxidation via Surface Stabilization of Ceria Nanoparticles Induced by Rare-Earth Metal Dopants

Abstract

Rare earth (RE) metals have often been used as dopants to improve the catalytic activity of ceria. However, their exact role in the activity of ceria catalyst has not been clearly identified. Combining experimental and theoretical approaches, we extensively investigate CO oxidation as a model reaction on RE-doped ceria (REC). The apparent activity is linearly proportional to the specific surface area (A S), which is enlarged by RE dopants as a consequence of surface stabilization. To decouple the effect of each RE dopant on the surface inherent activity, we set A S of REC to be almost constant by adjusting the pH during synthesis. In this case, however, pure ceria shows higher activity than any REC. We therefore conclude that although the RE dopants have lower intrinsic activity than that of Ce, they have an important effect of increasing A S to a level that pure ceria can never attain synthetically, thereby increasing their catalytic activity.

Design of Ceria Catalysts for Low‐Temperature CO Oxidation

“…Deactivation of catalysts suggests loss of active surface due to metal sintering (coalescence of particles, and particle growth), phase transformation, and pore elimination . As mentioned above, RE dopants lower surface energy, leading to smaller particle sizes . In addition, the excellence of the co‐doping system has been established in previous studies.…”

“…Studies showed that RDC catalysts form a higher number of defect sites on the catalyst surface than pure CeO 2 , and these defect sites are directly related to catalytic activity . Therefore, regardless of the dopant, it is true that CO oxidation is affected by defect sites, but specifically, RDC catalysts create high density of defect sites by the increased surface area, thereby enhancing the CO oxidation activity . As shown in Figure a, the catalytic activity of RDC increases linearly with the increase in specific surface area.…”

“…RE dopants dramatically increase the specific surface areas. Thanks to a significant increase in specific surface area, the density of defective sites can be increased by generating additional chemisorption sites (Figure a) . Studies showed that RDC catalysts form a higher number of defect sites on the catalyst surface than pure CeO 2 , and these defect sites are directly related to catalytic activity .…”

“…Thanks to a significant increase in specific surface area, the density of defective sites can be increased by generating additional chemisorption sites (Figure 4a). [17] Studies showed that RDC catalysts form a higher number of defect sites on the catalyst surface than pure CeO 2 , and these defect sites are directly related to catalytic activity. [30,[81][82] Therefore, regardless of the dopant, it is true that CO oxidation is affected by defect sites, but specifically, RDC catalysts create high density of defect sites by the increased surface area, thereby enhancing the CO oxidation activity.…”

“…The performance of metal doping depends on dopant ratio, combination of co-dopants as well as factors such as surface area, morphology, and reducibility. [16][17] Besides, the activity of metal catalysts supported by CeO 2 is controlled by several factors including metal particle size, metal-support interaction, support morphologies and OSC. In this sense, the activity is controlled by a combination of physical and intrinsic properties of CeO 2 -based catalysts, mainly depending on the choice of metal and synthetic method among other factors.…”