Capture of nitrogen dioxide and conversion to nitric acid in a porous metal–organic framework

Air pollution by nitrogen oxides, NOx, is a major problem, and new capture and abatement technologies are urgently required. Here, we report a metal–organic framework (Manchester Framework Material 520 (MFM-520)) that can efficiently confine dimers of NO2, which results in a high adsorption capacity of 4.2 mmol g–1 (298 K, 0.01 bar) with full reversibility and no loss of capacity over 125 cycles. Treatment of NO2@MFM-520 with water in air leads to a quantitative conversion of the captured NO2 into HNO3, an important feedstock for fertilizer production, and fully regenerates MFM-520. The confinement of N2O4 inside nanopores was established at a molecular level, and the dynamic breakthrough experiments using both dry and humid NO2 gas streams verify the excellent stability and selectivity of MFM-520 and confirm its potential for precious-metal-free deNOx technologies. Nitrogen oxides are major air pollutants; capture and abatement technologies exist but they typically involve toxic species or precious-metal catalysts. Now, a metal–organic framework has been shown to store NO2 dimers selectively, and to separate NO2 from other gases under wet conditions. Treatment with water in air leads to conversion of NO2 into HNO3—an important feedstock for fertilizer production—with full recovery of the host.