Investigation on chemical structure of minerals in coal using 27Al MQMAS NMR

High-resolution two-dimensional 27Al multiple-quantum magic-angle-spinning (MQMAS) NMR, being capable of averaging the second-order quadrupolar interaction, was applied in order to characterize the mineral matter in coals that have been spotlighted recently in new approach to the coal utilization. Octahedral aluminum compounds which consist of kaolin and other mineral phases could be clearly distinguished by 27Al MQMAS method. As the total carbon percent increases, octahedral aluminum species tend to vary from kaolin. A combination of cross polarization and MQMAS, it being called as 1H→27Al CP/MQMAS, was also employed to evaluate chemical bonding between aluminum atom and hydrogen atom. As a result, the octahedral components containing the linkage of Al–O–H such as kaolin and excluding the Al–O–H bond were separated by this technique. MQMAS and CP/MQMAS are very effective in characterization of inorganic matter including quadrupolar nuclei, which are particularly well suited to the analysis of clay minerals with noncrystalline materials and present in coals while XRD is difficult to analyze the amorphous compounds.