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 SO2 by urea, then residual NO and SO2 could be oxidized by the vaporized H2O2/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 H2O2 catalysis. Further, 95.2% SO2 and 88.6% NO were removed from flue gas under the operation conditions where SO2 concentration was 2000 ppm, NO concentration was 500 ppm, O-2 concentration was 7%, CO2 concentration was 10%, catalytic temperature was 140 degrees C, H2O2 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, H2O2 generally decompose not only into the (OH)-O-center dot free radical by iron oxide but also into (HOO)-H-center dot 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 H2O2 on the protonated surface of the low-acid catalyst. Furthermore, the rational catalytic mechanism of catalyst/H2O2 at low and high temperatures (corresponding to 140 and 200 degrees C) was proposed by transient response experiments.