Defect sites play an essential role in ceria catalysis. In this study, ceria nanocrystals with well-defined surface planes have been synthesized and utilized for studying defect sites with both Raman spectroscopy and O(2) adsorption. Ceria nanorods ({110} + {100}), nanocubes ({100}), and nano-octahedra ({111}) are employed to analyze the quantity and quality of defect sites on different ceria surfaces. On oxidized surfaces, nanorods have the most abundant intrinsic defect sites, followed by nanocubes and nano-octahedra. When reduced, the induced defect sites are more clustered on nanorods than on nanocubes, although similar amounts (based on surface area) of such defect sites are produced on the two surfaces. Very few defect sites can be generated on the nano-octahedra due to the least reducibility. These differences can be rationalized by the crystallographic surface terminations of the ceria nanocrystals. The different defect sites on these nanocrystals lead to the adsorption of different surface dioxygen species. Superoxide on one-electron defect sites and peroxide on two-electron defect sites with different clustering degree are identified on the ceria nanocrystals depending on their morphology. Furthermore, the stability and reactivity of these oxygen species are also found to be surface-dependent, which is of significance for ceria-catalyzed oxidation reactions.

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An infrared study has been conducted on CO 2 sorption into nanoporous CO 2 "molecular basket" sorbents prepared by loading polyethylenimine (PEI) into mesoporous molecular sieve SBA-15. IR results from DRIFTS showed that a part of loaded PEI is anchored on the surface of SBA-15 through the interaction between amine groups and isolated surface silanol groups. Raising the temperature from 25 to 75 °C increased the molecular flexibility of PEI loaded in the mesopore channels, which may partly contribute to the increase of CO 2 sorption capacity at higher temperatures. CO 2 sorption/desorption behavior studied by in situ transmission FTIR showed that CO 2 is sorbed on amine sites through the formation of alkylammonium carbamates and absorbed into the multiple layers of PEI located in mesopores of SBA-15. A new observation by in situ IR is that two broad IR bands emerged at 2450 and 2160 cm -1 with CO 2 flowing over PEI(50)/SBA-15, which could be attributed to chemically sorbed CO 2 species on PEI molecules inside the mesopores of SBA-15. The intensities of these two bands also increased with increasing CO 2 exposure time and with raising CO 2 sorption temperature. By comparison of the CO 2 sorption rate at 25 and 75 °C in terms of differential IR intensities, it was found that CO 2 sorption over molecular basket sorbent includes two rate regimes which suggest two distinct steps: rapid sorption on exposed outer surface layers of PEI (controlled by sorption affinity or thermodynamics) and the diffusion and sorption inside the bulk of multiple layers of PEI (controlled by diffusion). The sorption of CO 2 is reversible at 75 °C. Comparative IR examination of the CO 2 sorption/ desorption spectra on dry and prewetted PEI/SBA-15 sorbent revealed that presorbed water does not significantly affect the CO 2 -amine interaction patterns.