Surface Studies of Ceria and Mesoporous Ceria Powders by Solid-State ¹H MAS NMR

Abstract

Herein is described the first detailed study of ceria surfaces using 1 H MAS NMR techniques to probe the nature of hydroxyl species formed after exposure to water. The 1 H MAS NMR signal deriving from adsorbed hydroxyl species was used to probe the surface of ceria and crystalline mesoporous powders as a function of calcination temperature. It was found that the signals from all samples were well-resolved and of high intensity and showed easily observed chemical shifts depending on their environment. High surface areas were evidenced by large hydroxyl-derived 1 H peak integrals for the mesoporous samples compared to that of ceria prepared by traditional precipitation techniques. It is suggested that surface-adsorbed hydroxyl species generally occupy two distinct structural environments (on-top and bridge) on ceria surfaces. Hydroxyl groups assigned to ontop positions were found to be more mobile and desorbed at lower temperatures than those held in bridging positions. In addition, the mesoporous surface appears to comprise of two distinct regions assigned to external surfaces and internal pore and cavity surfaces. We also highlight a more general point that adsorbate probe MAS NMR techniques can provide important analysis of surface chemistry in favorable circumstances. Ceria is an ideal example in which very well-resolved intense 1 H signals from adsorbed hydroxyl species are observed, and consequently MAS NMR methods provide unique details of the surface chemistry. The relevance of these data is discussed in the context of current knowledge of the properties of ceria.

A First-Principles Analysis for Sulfur Tolerance of CeO2in Solid Oxide Fuel Cells

“…[31][32][33][34]36 We used U and J of 7.0 and 0.7 eV, respectively, which are consistent with those reported by Jiang and co-workers. 37 For the surface model, we examined only CeO 2 (111) to characterize the H 2 S-CeO 2 interactions because CeO 2 (111) is energetically the most stable [38][39][40] among the low-index CeO 2 (111), (110), and (100) surfaces. As shown in Figure 1, the CeO 2 (111) surface model with 12 atomic layerssa p( 3 × 2) lateral cellswas constructed.…”

Eco-friendly and morphologically-controlled synthesis of porous CeO2 microstructure and its application in water purification

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Study of flowerlike CeO2 microspheres used as catalyst supports for CO oxidation reaction

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