Journal: Science Advances

Article Title: Identification of different oxygen species in oxide nanostructures with 17 O solid-state NMR spectroscopy

doi: 10.1126/sciadv.1400133

Figure Lengend Snippet: ( A ) 17 O NMR spectra for ceria nanoparticles enriched at different temperatures and acquired at different external fields compared with the 17 O NMR spectra of micrometer-sized ceria (bulk ceria) and the summary of the chemical shifts predicted using a structural model shown in (B). The spectra obtained at 14.1 and 9.4 T were acquired with spinning speeds of 55 and 20 kHz, respectively. Short pulse lengths of 0.1 to 0.4 μs corresponding to π/72 to π/18 pulses for H 2 17 O and optimized recycle delays from 1 to 100 s to ensure quantitative observations of all the resonances were used. Detailed experimental parameters are summarized in table S9. ( B ) The structural model of ceria used in the DFT calculations. Red and white spheres represent oxygen and cerium ions, respectively. The exposed surface is (111), and the calculated chemical shift of 17 O in each layer is shown on the right.

Article Snippet: Bulk ceria (typically 200 mg, Sinopharm Chemical Reagent Co. Ltd.) and nanosized ceria (typically 200 mg) were first heated at 573 K for 10 hours (except the ceria nanoparticles that were later enriched at 523 K; this particular sample was heated at 523 K) and then enriched by heating the powders in a 70% 17 O-enriched O 2 gas (Cambridge Isotope Laboratories) atmosphere at various temperatures (523 to 1073 K) for 10 hours (for bulk ceria sample, 17 O enrichment was performed at 1073 K for 10 hours).

Techniques:

Journal: Science Advances

Article Title: Identification of different oxygen species in oxide nanostructures with 17 O solid-state NMR spectroscopy

doi: 10.1126/sciadv.1400133

Figure Lengend Snippet: ( A , bottom to top) 17 O MAS NMR spectra of nonenriched ceria nanoparticles adsorbed with nonenriched water; ceria nanoparticles enriched in 17 O 2 at 573 K and then exposed to air; ceria nanoparticles enriched in 17 O 2 at 573 K and then adsorbed with nonenriched water (water was added dropwise); the previous sample dried under vacuum at room temperature and at 573 K; and ceria nanoparticles enriched in 17 O 2 at 573 K. ( B , bottom to top) 17 O NMR spectra of liquid H 2 17 O; 17 O MAS NMR spectra of bulk ceria adsorbed with H 2 17 O (bulk-H 2 17 O); the previous sample dried under vacuum at 373 K; nonenriched ceria nanoparticles adsorbed with H 2 17 O by adding water dropwise [nano-H 2 17 O(D)]; the previous sample dried under vacuum at 373 K; and nonenriched ceria nanoparticles adsorbed with H 2 17 O by adsorbing water through a vacuum line and then dried under vacuum at 373 K [nano-H 2 17 O(A)]. The samples of H 2 17 O, bulk-H 2 17 O, and nano-H 2 17 O(D) in (B) were packed into the rotors in air. All the spectra were acquired at 9.4 T. Detailed experimental parameters are summarized in table S10. Asterisks denote spinning sidebands.

Article Snippet: Bulk ceria (typically 200 mg, Sinopharm Chemical Reagent Co. Ltd.) and nanosized ceria (typically 200 mg) were first heated at 573 K for 10 hours (except the ceria nanoparticles that were later enriched at 523 K; this particular sample was heated at 523 K) and then enriched by heating the powders in a 70% 17 O-enriched O 2 gas (Cambridge Isotope Laboratories) atmosphere at various temperatures (523 to 1073 K) for 10 hours (for bulk ceria sample, 17 O enrichment was performed at 1073 K for 10 hours).

Techniques:

Journal: Science Advances

Article Title: Identification of different oxygen species in oxide nanostructures with 17 O solid-state NMR spectroscopy

doi: 10.1126/sciadv.1400133

Figure Lengend Snippet: ( A ) 17 O NMR spectra of bulk ceria enriched in 17 O 2 at 1073 K (bottom) and reduced in H 2 atmosphere at 1073 K (top). ( B ) 17 O NMR spectra of nanosized ceria enriched in 17 O 2 at 773 K (bottom), reduced in H 2 atmosphere at 773 K (top), and reoxidized in air reduced ceria (middle). Inset shows the full width of the three 17 O spectra. A rotor-synchronized Hahn-echo sequence (π/6 - τ - π/3- τ - acquisition) was used. Data were obtained at 9.4 T under a MAS rate of 20 kHz. One hundred thousand (A, bulk), 300,000 (A, reduced), 1024 (B), and 40,000 scans (B, inset) were averaged, and recycle delays of 0.1 s (A), 1 s (B), and 0.01 s (B, inset) were used. Asterisks denote spinning sidebands.

Article Snippet: Bulk ceria (typically 200 mg, Sinopharm Chemical Reagent Co. Ltd.) and nanosized ceria (typically 200 mg) were first heated at 573 K for 10 hours (except the ceria nanoparticles that were later enriched at 523 K; this particular sample was heated at 523 K) and then enriched by heating the powders in a 70% 17 O-enriched O 2 gas (Cambridge Isotope Laboratories) atmosphere at various temperatures (523 to 1073 K) for 10 hours (for bulk ceria sample, 17 O enrichment was performed at 1073 K for 10 hours).

Techniques: Sequencing