Combined Experimental and Theoretical Study of the Competitive Absorption of CO(2) and NO(2) by a Superbase Ionic Liquid

[Image: see text] A superbase ionic liquid (IL), trihexyltetradecylphosphonium benzimidazolide ([P(66614)][Benzim]), is investigated for the capture of CO(2) in the presence of NO(2) impurities. The effect of the waste gas stream contaminant on the ability of the IL to absorb simultaneously CO(2) is demonstrated using novel measurement techniques, including a mass spectrometry breakthrough method and in situ infrared spectroscopy. The findings show that the presence of an industrially relevant concentration of NO(2) in a combined feed with CO(2) has the effect of reducing the capacity of the IL to absorb CO(2) efficiently by ∼60% after 10 absorption–desorption cycles. This finding is supported by physical property analysis (viscosity, (1)H and (13)C NMR, and X-ray photoelectron spectroscopy) and spectroscopic infrared characterization, in addition to density functional theory (DFT) calculations, to determine the structure of the IL-NO(2) complex. The results are presented in comparison with another flue gas component, NO, demonstrating that the absorption of NO(2) is more favorable, thereby hindering the ability of the IL to absorb CO(2). Significantly, this work aids understanding of the effects that individual components of flue gas have on CO(2) capture sorbents, through studying a contaminant that has received limited interest previously.