Unraveling the multi-pollutant removal using M-MoWTi (M = Fe, Mn, Cr) catalyst: experiment and mechanistic study of competition for active sites

Multi-pollutant removal (MPR) of NO and VOCs simultaneously is efficient of flue gas treatment in coal-fired power plants. But reducing the competition for active sites between NH3, NO, C6H6, and C7H8 remains challenging. Herein, Cr, Mn, and Fe were respectively doped to MoWTi catalyst via wet impregnation. The Fe3+ + Mo5+ ↔ Fe2+ + Mo6+ redox cycle led to an increased proportion of low valence ions (Mo5+ and W5+) and facilitated the creation of active oxygen vacancies with several active sites. It also possessed plentiful mild to strong acid sites with ideal ratio. These factors enhanced catalytic activity of Fe-MoWTi. Remarkable MPR efficiencies of NO, C6H6, and C7H8 were achieved under industrial SCR condition, characterized by low oxygen but high SO2 levels at 340 °C, with removal rates reaching 89.85%, 97.57%, and 86.30% respectively. Theory calculations further revealed that Fe-MoWTi favor NH3 and O2 adsorptions. NO elimination was found to follow both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) processes, supported by in situ DRIFTS analysis. The reactions involving NO/NO2/nitrite/nitrate occurred with NH3(ads)/ NH4+(ads)/NH2 (ads). C6H6 and C7H8 underwent gradual oxidation, formatting alcohols, aldehydes, acids, and maleic acids, before eventually being mineralized to gaseous CO2 and H2O. Findings hold significant potential for application, providing guidance for the development of catalysts with improved resistance against SO2 poisoning and enhanced MPR capabilities.

Removal of multi-pollutant from flue gas utilizing ammonium persulfate solution catalyzed by Fe/ZSM-5

A nano-sized iron loaded ZSM-5 zeolite (Fe/ZSM-5) catalyst was firstly used to activate (NH₄)₂S₂O₈ solution for the simultaneous removal of multi-pollutant from flue gas. The simultaneous removal efficiencies 100% of SO₂, 72.6% of NO and 93.4% of Hg° were achieved under the condition that the catalyst dose was 0.8 g/L, concentration, pH and temperature of (NH₄)₂S₂O₈ solution were 0.03 mol/L, 5 and 65 °C, respectively. The stability of catalyst was checked by a continuous test, proving that the catalytic activity was maintained for 4 h and the leached iron reached low levels. Based on the catalyst characterizations, product analysis and literatures, the removal mechanism was speculated preliminarily, during which, OH and SO₄^- played key roles for oxidizing NO and Hg° into NO₃^- and Hg²⁺.