EPR (Electron Paramagnetic Resonance) Study of Nitroxide Spin Probe Doped IIllinois No. 6 Coal from the Premium Coal Sample Program: Reactive Site Distribution

摘要

Recently, we reported a method to determine the relative pore (accessibility) size and number distribution in selected high-volatile bituminous coal samples by diffusing nitroxide spin probes of different shapes, varying in diameter or length from 0.47 nm to 3.5 nm, into the swellable pores of the coal samples. The relative spin probe concentration was measured by Electron Paramagnetic Resonance (EPR) methods for each sized spin probe. EPR spectra obtained from coal samples containing spin probes gave rise to a spectrum similar to that shown in Figure 1, consisting of an intense central line due to undoped coal (curve B) and, at high gain (curve A), resolved powder EPR lines at high and low magnetic fields due to the z tensor component of the nitrogen hyperfine coupling (A/sub zz/) arising from the nitroxide spin probe dopant. The separation between the high and low field component equals 2A/sub zz/. The relative spin concentrations were determined by integrating the low field peak. The relative spin probe concentration is given in table I for probe I (reacts with amines), probe IV (reacts with acids and phenols), probe V (hydrogen bonding only to the nitroxyl group) and probe VI (hydrogen-bonding to ketone and nitroxyl groups). Notably, the ratio of pores containing acid or phenolic groups to those containing amine groups is 1/3; 6.7/1; 0.5/1; and 12/1 for Mary Lee, Black Creek, Illinois No. 5 and Illinois No. 6 respectively. (ERA citation 12:049249)