Highly Efficient and Reversible Absorption and Oxidation of Low-Concentration Nitric Oxide by Functionalized Ionic Liquids

Abstract

A novel method of using anion-functionalized ionic liquids (ILs) with high NO absorption capacity and reversibility for the capture and in situ oxidation of low-concentration NO was established. For the mixed gas containing 0.25% NO, the accumulation rate of nitric acid in these ILs was significantly higher than that in the conventional ILs; after absorption and oxidation reached equilibrium, the molar ratio of HNO₃ to [P₄₄₄₆][PhSO₃] was 0.86, which was 5 times as high as that of the conventional IL. Therefore, the problems of low efficiency and poor reversibility of traditional ILs in the absorption and oxidation process were solved. Through absorption and oxidation experiments, quantum chemical calculation, NMR, and time-resolved in situ ATR-FTIR spectroscopic investigation, the results demonstrated that such a high accumulation rate of HNO₃ originated from high uptake of NO through multiple-site interaction. Moreover, high reversibility is attributed to low volatility of conjugated acid of anions and decreased basicity of O sites on anions. We believe that such highly efficient and reversible conversion of low-concentration NO to HNO₃ by ILs provides a new strategy for improving atomic economy of fossil fuel combustion, that is, converting post-combustion pollutants to good valuable chemicals.