Conversion of NO_X/SO_X in fossil fuel flue gas to fertilizers via nanocomposite Co/Mn@Silica catalyst

Nitrogen oxides and sulfur oxides (NO_X/SO_X) are the main concern for the emission of toxic air pollutants from fossil fuels combustion causing many health and environmental concerns. Environmental regulations demand low emission concentrations. Existing technologies used to decrease the NO_X/SO_X content are FGD (Flue-Gas Desulfurization) and SCR (Selective Catalytic Reduction).^1,2 However, these technologies use expensive catalysts and need high working temperatures (350-400^oC).

Recently, new wet scrubbing processes use ozone or hydrogen peroxide as oxidation reagents and produce fertilizers (ammonium sulfate and ammonium nitrate) from the SO_x/NO_x upon injection of ammonia.

In a previous study Co(OH)₂)/Silica nanocomposites has been found as an efficient water oxidizer.³ We adopted this catalyst for the oxidation of SO_x/NO_x as the main catalyst in wet scrubber reactors to reduce toxic gases by using atmospheric oxygen as the oxidation reagent.

In this work we have developed a new nanocomposite Co/Mn@Silica oxidation catalyst to produce NO₃^- and SO₄^2- using atmospheric oxygen as the oxidizing agent. The Co and the Mn formed lies at the surface of the larger silica nanoparticles forming a nanocomposite catalyst. The process was studied in a scrubber pilot system at the temperature range 60-80^oC. The conversion of the SO_x/NO_x emissions at 60˚C are >99%/88%, respectively. The production of the catalyst and the wet scrubbing process are discussed in detail.

References

1. Busca, G., Lietti, L., Ramis, G., & Berti, F. (1998). Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review. Applied Catalysis B: Environmental, 18(2), 1–36.
2. Srivastava, R. K., & Jozewicz, W. (2001). Flue gas desulfurization: The state of the art. Journal of the Air and Waste Management Association, 51(12), 1676–1688.
3. Zidki, T., Zhang, L., Shafirovich, V., & Lymar, S. V. (2012). Water oxidation catalyzed by cobalt(II) adsorbed on silica nanoparticles. Journal of the American Chemical Society, 134(35), 14275–14278.