Effect of Fe2O3 nanoparticles on combustion of coal surrogate (Anisole): Enhanced ignition and formation of persistent free radicals

This contribution explores the effect of nanoparticles of iron (III) oxide (Fe2O3) on the combustion of coal surrogate, i.e., anisole, identifying the changes in ignition features as well as the occurrence of persistent organic pollutants in the initiation channels. The method applies packed-bed reactor coupled with Fourier transform infrared (FTIR) spectroscopy to quantitate the ignition temperature under typical fuel-rich conditions, in-situ electron paramagnetic resonance (EPR) to elucidate the formation of environmentally-persistent free radicals (EPFR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to monitor the chemisorption of organic substrates on the nanoparticles, as well as X-ray diffraction for particles characterisation (PXRD). We employ cluster-based quantum mechanical calculation to map the reaction pathway within the scope of the density functional theory. The results of Fe2O3-mediated combustion of anisole depict an excessive reduction in ignition temperature from 500 degrees C around 220 degrees C at lambda = 0.8. As confirmed both from EPR and DRIFTS measurements, the chemisorption of anisole on alpha-Fe2O3 surfaces follows the direct dissociation of the O-CH3 (and OCH2-H), leading to the formation of surface-bound phenoxy radicals at temperatures as low as 25 degrees C and incurring an estimated energy barrier of E-a = 18 kJ mol(-1) and a preexponential factor of A = 2.7 x 10(12) M-1 s(-1). This insight applies to free-radical chain reactions that induce spontaneous fires of coal, as coal comprises ferric oxide nanoparticles, and equally to coexistence of aromatic fuels with thermodynamically reactive Fe2O3 surface, e.g., in fly ash, at the cooled-down tail of combustion stacks. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.