Simultaneous removal of NOx and SO2 from coal-fired flue gas based on the catalytic decomposition of H2O2 over Fe2(MoO4)3

Abstract

The purification of flue gas has drawn the increasing attention in recent years. In the present study, a novel oxidation-absorption process was proposed for simultaneous removal of NOx and SO2 from coal-fired flue gas based on the catalytic decomposition of H2O2 over Fe2(MoO4)3, in which gaseous pollutants were first oxidized by OH radicals and then absorbed with ammonia solution. The effects of H2O2 dosage, temperature, gas hourly space velocity (GHSV) and flue gas component on simultaneous removal efficiency were systematically investigated. The results indicated that the removal efficiencies of 91.4% for NOx and 100% for SO2 could be achieved under the optimal conditions. The signal of OH radical was verified by fluorescence test. The OH radicals were essential for NO oxidation and the subsequent NOx removal, while SO2 was primarily removed in absorption process. Moreover, the presence of SO2 was favorable for NOx removal, mainly because the existence of SO2 promoted NO oxidation. X-ray photoelectron spectroscopy (XPS) analysis further confirmed that SO2 could reduce part of Fe3+ to Fe2+ on catalyst surface, thereby reducing the consumption of H2O2 by Fe3+ and promoting the majority of H2O2 to generate OH. The continuity test revealed that the synthesized Fe2(MoO4)3 showed satisfactory stability. The surface morphology and crystal structure of the catalyst exhibit negligible change after 15 h of reaction. Products analysis indicated that NH4NO3 and (NH4)2SO4 were the primary products after removal of NOx and SO2. A three-step mechanism was preliminarily developed to interpret the simultaneous removal process in H2O2/Fe2(MoO4)3 system.