Modified Fe-Rich Palygorskite as an Efficient and Low-Cost Heterogeneous Fenton Catalyst for NOx and SO2 Removal

In this article, the entire removal process was based on a cycle absorption system in which a primary-absorber was used to scrub SO 2 by urea, then residual NO and SO 2 could be oxidized by the vaporized H 2 O 2 /catalysts in the catalytic system, and finally, the soluble gaseous pollutants and the remaining gaseous oxidants were absorbed by ammonium sulfite that was produced from the primary-absorber. The complex catalysts formed by iron recovery from the bauxite residue (red mud) were restructured with adenosine triphosphate (ATP) to generate mesopores with surface-active sites (FeOH) for efficient H 2 O 2 catalysis. Further, 95.2% SO 2 and 88.6% NO were removed from flue gas under the operation conditions where SO 2 concentration was 2000 ppm, NO concentration was 500 ppm, O 2 concentration was 7%, CO 2 concentration was 10%, catalytic temperature was 140 °C, H 2 O 2 feeding rate was 1.5 mL/h, and the total gas flow rate was 1.5 L/min. The results suggested that the catalytic performance is closely related to the structure of support ATP, which was elucidated by a series of experiments in different Fe loadings and BET characterization. From electron spin resonance (ESR) results, H 2 O 2 generally decompose not only into the • OH free radical by iron oxide but also into • HOO and related reactive oxygen species. According to the results of X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR), the content of FeOH and lattice oxygen in the modified ATP catalyst played an important role in the adsorption of H 2 O 2 on the protonated surface of the low-acid catalyst. Furthermore, the rational catalytic mechanism of catalyst/H 2 O 2 at low and high temperatures (corresponding to 140 and 200 °C) was proposed by transient response experiments.