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

✍ Scribed by Gary E. Maciel; Charles E. Bronnimann; Antoni Jurkiewicz; Robert A. Wind; Vicky H. Pan

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 686 KB
• Volume: 70
• Category: Article
• ISSN: 0016-2361
• DOI: 10.1016/0016-2361(91)90045-c

✦ Synopsis

Ultralarge magic-angle spinning (MAS) systems (2.4-6.5 cm3) provide a sufficiently large increase in signal-to-noise ratio that 13C MAS experiments without cross-polarization (CP), as well as time-domain 13C CP/MAS studies, can be carried out expeditiously. The non-CP approach allows one to circumvent the uncertainties in quantitation by 13C CP/MAS techniques; however, a more direct determination of Ty, values than by variable contact-time experiments yields promising results on 13C spin counting in coal. The 'H combined rotation/multiple-pulse spectroscopy technique, based on multiple-pulse dipolar line narrowing and MAS, provides a useful complement to 13C MAS techniques, typically yielding poorly resolved lH-CSpZ and 'H-Csp3 p eaks from which deconvolution nevertheless provides at least a semiquantitative assessment of amounts. A dipolar-dephasing approach and imbibing with perdeuteropyridine, employed either separately or together, dramatically improve resolution and provide strategies for examining the mobilities of individual coal components.