Investigation of demineralized coal char surface behaviour and reducing characteristics after partial oxidative treatment under an O₂ atmosphere

Shenhua (SH) demineralized char was employed to determine the relationship between the char conversion ratio and the surface behavior of particles. The amount, distribution and thermal stability of C(O) generated during the combustion process were clarified by temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR). CO₂ was the primary gaseous product released during the TPD process of each partially oxidized sample. Based on the TPD and FTIR deconvolution results, the decomposition temperature of each functional group could be determined as follows: phenol (1000 K) < carboxyl (1150 K) < ether/anhydride (1400 K) < quinone (1600 K) < lactone (1650 K). Partial oxidative treatment promoted the generation of C(O) on the particle surface, with the maximum amount of C(O) existing on the surface of samples with an intermediate conversion ratio (0.33–0.47). Due to the increase in C(O), the reducibility of the partially oxidized sample was also enhanced. The demineralized chars collected in the intermediate stage (0.33–0.47) expressed the strongest reducibility, and the maximum NO was consumed by per unit mass of these samples. Phenol, carboxyl, anhydride and ether were the main forms of C(O) and were involved in the rapid and successive consumption of NO as major reactants, leading to an apparent reduction of the NO released during the char combustion process.