Kinetics and reaction mechanism of NO removal from simulated flue with peroxymonosulfate solution activated by high temperature and metal ions (Fe2+, Co2+ and Fe3+)

A strategy for removing nitric oxide (NO) from simulated flue gas by transition metal ion (Fe2+, Co2+, and Fe3+)-induced production of sulfate (SO4 center dot-), hydroxyl ((OH)-O-center dot), and singlet oxygen radicals (O-1(2)) from peroxymonosulfate (PMS) at high temperature was investigated, and the catalytic performances of the three metal ions were compared. The nitric oxide radical ((NO)-N-center dot) was detected in solution using electron spin-resonance (ESR) spectroscopy, and a pathway for reaction between NO and the radicals was further explored and refined. The metal ion-catalyzed decomposition of PMS could be considered a pseudo-first order reaction with good reliability (R-2 > 0.97), and the rate constant, k(0), for metal ion-catalyzed PMS degradation followed the sequence: Fe2+ > Co2+ > Fe3+. Specific experiments were optimized to select the optimal experimental parameters (PMS/metal molar ratio and solution pH) for maximizing the NO removal efficiency. ESR was employed to monitor the progress of PMS activation, and it was found that: 1) SO4 center dot-, (OH)-O-center dot, and O-1(2) radicals were mainly produced during the activation of PMS by the three metal ions; 2) the three radicals synergistically removed NO; 3) the generation of O-1(2) was more sensitive to temperature than the generation of the SO4 center dot- and (OH)-O-center dot radicals; 4) the capacity of the metals to catalyze the oxidation reaction followed the order: Fe2+ > Co2+ > Fe3+. These findings provide new insight into PMS activation by transition metal catalysts at high temperature.