The analysis of three representative premium coals by 13C nuclear magnetic resonance

Abstract The analytical characteristics of the three Argonne premium coals 801, 601 and 501 were examined by magic-angle spinning (MAS) 13 C n.m.r., using large samples (2.5 cm 3 ). Experiments were performed with 13 C magnetization generated by both cross-polarization (CP) and 90 ° pulse, or direct-polarization (DP), approaches. Various 13 C-based relaxation measurements were made. Using the Delrin 13 C signal of the Delrin-zirconia spinner as a built-in intensity reference, spin counting was carried out. The DP-MAS approach appeared to account for ~80%, and the customary CP-MAS technique for only ~50% of the carbon known to be in each sample; however, a CP-MAS approach that incorporated a better T 1 ϱ H determination appeared to account for > 80% of the carbon. It is concluded that, although useful results can be obtained by 13 C CP-MAS experiments (if CP dynamics are properly characterized), the DP-MAS approach with large samples is more straightforward. Dipolar-dephasing 13 C n.m.r. studies provide a measure of the contributions of proton-bearing and non-proton-bearing carbons in the three coals and the fraction of aromatic or aliphatic carbons that are proton-bearing. The attractiveness and utility of large-volume 13 C MAS approaches in the analysis of coal are demonstrated.