Removal of NO from flue gases by absorption to an iron(ii) thiochelate complex and subsequent reduction to ammonia

Abstract

THE combustion of fossil fuels generates SO₂ and NO_X pollutants which cause acid rain and urban smog¹. Existing flue-gas desulphurization scrubbers involve wet limestone processes which are efficient for controlling SO₂ emissions but are incapable of removing water-insoluble nitric oxide. The current technique for postcombustion control of nitrogen oxide emissions, ammonia-based selective catalytic reduction, suffers from various problems^2,3, including poisoning of the catalysts by fly ash rich in arsenic or alkali, disposal of spent toxic catalysts and the effects of ammonia by-products on plant components downstream from the reactor. To circumvent the need for separate schemes to control SO₂ and NO_X, we have developed an iron(ii) thiochelate complex that enhances the solubility of NO in aqueous solution by rapidly and efficiently absorbing NO to form iron nitrosyl complexes. The bound NO is then converted to ammonia by electrochemical reduction, regenerating the active iron(ii) catalyst for continued NO capture. Our results suggest that this process can be readily integrated into existing wet limestone scrubbers for the simultaneous removal of SO₂ and NO_X