Non-magic angle spinning NMR - an approach to determine the chemical shift tensors in char particles

Conference · Thu Jan 01 04:00:00 EST 1987 · Prepr. Pap., Am. Chem. Soc., Div. Fuel Chem.; (United States)

OSTI ID:5931957

Sethi, N K; Pugmire, R J; Grant, D M

Carbon-13 NMR spectroscopy has been widely accepted as a major analytical technique for studying fossil fuels. Magic angle spinning (MAS) experiments produce narrow lines in solids but valuable structural information is lost; i.e., the chemical shift anisotropy (CSA) which is a manifestation of the three-dimensional shielding of the nucleus by the surrounding electrons. The CSA is a second rank tensor having three principal elements /sigma//sub 11/, /sigma//sub 22/, and /sigma//sub 33/ characterized by unique resonance frequencies. These three tensor components taken together with the isotropic shielding value (the MAS value which is the average of the three tensor components) provide valuable data regarding the local electronic environment. The tensor can be obtained from the /sup 13/C NMR spectrum of a finely powdered sample and the tensor elements are extracted by analysis of the line shape. This technique provides not only tensor components but population values as well. Only for isolated carbons, or for simple compounds where break-points in the powder pattern are discernible, is it possible to obtain unique fits of the line shape. Tensor information can be extracted by other techniques such as analysis of the spinning side bands from slow spinning MAS experiments and variable angle sample spinning (VASS). In this study we have used the static and VASS methods to study pertinent model compounds and have used these data as a guide to analyze line shapes and extract CSA tensor values and population as well as coals. The experimental techniques are applicable to chars as well as coals. The data permit us to estimate the size of the polycondensed aromatic structure that is the main structural component in chars. The aromatic structure of coal chars should provide valuable information regarding their reactivity.

• Research Organization: Univ. of Utah, Salt Lake City (USA)
• DOE Contract Number: FG02-86ER13510
• OSTI ID: 5931957
• Report Number(s): CONF-870802-
• Conference Information: Journal Name: Prepr. Pap., Am. Chem. Soc., Div. Fuel Chem.; (United States) Journal Volume: 32:4
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010600* -- Coal
Lignite
& Peat-- Properties & Composition
CARBONACEOUS MATERIALS
CHARS
CHEMICAL SHIFT
COAL
DATA
ENERGY SOURCES
EXPERIMENTAL DATA
FOSSIL FUELS
FUELS
INFORMATION
MAGNETIC RESONANCE
MATERIALS
NMR SPECTRA
NUCLEAR MAGNETIC RESONANCE
NUMERICAL DATA
PARTICLES
PYROLYSIS PRODUCTS
RESONANCE
SPECTRA
STRUCTURAL CHEMICAL ANALYSIS