An investigation of coal by means of e.s.r., 1H n.m.r., 13C n.m.r. and dynamic nuclear polarization |
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Affiliation: | 1. Instituto Ciencia de Materiales de Sevilla (CSIC-US), Avda. Américo Vespucio, 49, 41092 Sevilla, Spain;2. Laboratorio de Rayos-X. CITIUS, Avda. Reina Mercedes, 4, 41012 Sevilla, Spain;3. Center for the Development of Nanoscience and Nanotechnology, CEDENNA, 9170124 Santiago, Chile;4. Escuela de Ciencias Químicas, Universidad Pedagógica y Tecnológica de Colombia UPTC, Avda. Central del Norte, Vía Paipa, Tunja, Boyacá 39-115, Colombia. |
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Abstract: | Sixty coal samples of different rank and origin have been investigated by means of e.s.r., 1H n.m.r. and 13C n.m.r., the last two in combination with dynamic nuclear polarization (DNP). The following parameters have been determined: the number of free radicals, the e.s.r. linewidth, the 1H Zeeman relaxation rate, the 1H relaxation rate in the rotating frame, the 1H DNP enhancement, the 13C DNP enhancement, the 13C Zeeman relaxation rate and the 13C aromaticity, observed via 1H13C cross-polarization (CP), both with and without magic-angle spinning (MAS). The relations between these parameters and coal rank have been investigated. Moreover, with DNP special experiments have been performed which provide information about the localization and the mobility of the unpaired electrons present in these coals. Finally, DNP has been used to investigate various features of the quantitative analysis of coal via 13C n.m.r. MAS was found to reduce the measured 13C aromaticity, and for three coals it was shown that even without MAS only ≈ 50% of the aromatic 13C nuclei are detected by the CP technique. |
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