Potassium-containing coal-pellets for NOx reduction under gas mixtures of different composition Original Research Article

Potassium-containing coal-pellets, with a catalyst content of 16.8% w/w, prepared from a high volatile bituminous coal and humic acid were tested for NOx abatement under complex gas mixtures. The activity and selectivity for NOx reduction as opposed to other oxidant gas consumption shown by these pellets were investigated in a fixed bed reactor under several gas mixtures (NOx/O2/N2, NOx/O2/CO2/N2, NOx/O2/H2O/N2 and NOx/O2/CO2/H2O/N2). TPRs, isothermal reactions for 2 h and lifetime tests (isothermal reactions prolonged until complete carbon consumption) were performed. Also, TPDs after some isothermal reactions were carried out. For comparative purposes, a catalyst-free sample was also checked. In all the gas mixtures tested, potassium-containing coal-pellets showed a reactivity window at moderate temperatures (e.g. 600–750 K, for NOx/O2/N2) where NOx reduction occurred without significant O2 consumption. The presence of CO2 decreases the reactivity and selectivity of potassium-containing sample. Conversely, the presence of H2O increases sample reactivity but diminishes the selectivity for NOx reduction. The catalyst-free sample exhibits lower activity and selectivity than those observed for potassium-containing pellets under all the conditions studied.