Bloch-decay and cross-polarization-magic-angle spinning {sup 13}C NMR study of the Argonne Premium coals: Effects of high-speed spinning
- Battelle Northwest, Richland, WA (United States)
Bloch-decay and variable-contact-time {sup 13}C cross-polarization-magic-angle spinning (CP-MAS) NMR data at a spinning rate of 13 kHz are presented for the Argonne Premium coals. High-field (7.05 T, 75 MHz, 13-kHz MAS) aromaticities are in satisfactory agreement with low-field CP-MAS (2.3 T, 25 MHz, 4-kHz MAS) results, with the exception of the high oxygen containing Wyodak-Anderson coal. Bloch-decay aromaticities obtained at 13-kHz MAS agree with CP-MAS results at 25 MHz (4-kHz MAS) for all of the bituminous coals, but CP-MAS gives significantly lower aromaticities than Bloch decay for the lignite (Beulah-Zap) and subbituminous (Wyodak-Anderson) coals. A bloch-decay and variable-contact-time CP-MAS study of the ratios of protonated, nonprotonated, and isolated aromatic carbons of acenaphthene revealed small systematic errors for individual carbon intensities, but satisfactory average relative intensities for different structural groups. High-speed MAS leads to measured aromaticities within 3-5% of those measured by low-speed MAS for medium- and high-rank coals. However, significant errors in CP-MAS aromaticities of low-rank coals, together with the failure to detect an appreciable fraction of oxygenated and quaternary carbons, suggest that Bloch decay is the method of choice for determination of structural distributions. Sources of disagreement between Bloch decay and CP-MAS aromaticities for Wyodak-Anderson and Beulah-Zap coals are discussed. 35 refs., 5 figs., 5 tabs.
- OSTI ID:
- 441415
- Report Number(s):
- CONF-891206--
- Country of Publication:
- United States
- Language:
- English
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