Effective Electroregeneration of the Oxidized Iron(II) Thiochelate Absorbent in the Wet NO_X Absorption Process

Abstract

The ever-increasing air pollution has brought the treatment of nitrogen oxides (NO X ) to the forefront of flue gas purification. Wet absorption achieves outstanding NO X removal efficiency, but it suffers from an oxidative deactivation of the NO X absorbent, iron­(II) thiochelate, by the residual O2 in flue gases. To address this critical issue, we demonstrate a regeneration process to electrochemically reduce the oxidized iron thiochelate into the original form to effectively bind nitric oxide (NO). A series of voltammetric techniques were adopted to define the redox potentials of Fe­(III)/Fe­(II) thiochelate, represented as 2,3-dimercapto-1-propanesulfonate (DMPS). The electrochemical reduction of the oxidized iron thiochelate led to the transformations of disulfide (S–S) to a thiol (R–SH) and Fe­(III) to Fe­(II). Both the rate and Faradaic efficiency of electroregeneration could be enhanced through the adsorption between iron­(II) thiochelate and a copper catalyst as revealed by X-ray photoelectron spectroscopy. At an optimal condition, recovery efficiencies of 99.8 and 96.1% for thiol and Fe­(II) concentrations were obtained, respectively, on a Cu electrode at −1.3 V vs Ag/AgCl, thereby restoring 97.9% of NO absorption capacity. Our findings offer routes to complement the wet scrubbing NO X treatment technology while preventing the abuse of chemical absorbents.