Recent advances in coal characterization by 13C and 1H n.m.r.

Abstract Ultralarge magic-angle spinning (MAS) systems (2.4–6.5 cm 3 ) provide a sufficiently large increase in signal-to-noise ratio that 13 C MAS experiments without cross-polarization (CP), as well as time-domain 13 C CP/MAS studies, can be carried out expeditiously. The non-CP approach allows one to circumvent the uncertainties in quantitation by 13 C CP/MAS techniques; however, a more direct determination of T H 1 ϱ values than by variable contact-time experiments yields promising results on 13 C spin counting in coal. The 1 H combined rotation/multiple-pulse spectroscopy technique, based on multiple-pulse dipolar line narrowing and MAS, provides a useful complement to 13 C MAS techniques, typically yielding poorly resolved 1 HC sp2 and 1 HC sp3 peaks from which deconvolution nevertheless provides at least a semiquantitative assessment of amounts. A dipolar-dephasing approach and imbibing with perdeutero-pyridine, employed either separately or together, dramatically improve resolution and provide strategies for examining the mobilities of individual coal components.