Abstract
We report the reversible adsorption of ammonia (NH3) up to 9.9 mmol g–1 in a robust Al-based metal–organic framework, MFM-303(Al), which is functionalized with free carboxylic acid and hydroxyl groups. The unique pore environment decorated with these acidic sites results in an exceptional packing density of NH3 at 293 K (0.801 g cm–3) comparable to that of solid NH3 at 193 K (0.817 g cm–3). In situ synchrotron X-ray diffraction and inelastic neutron scattering reveal the critical role of free −COOH and −OH groups in immobilizing NH3 molecules. Breakthrough experiments confirm the excellent performance of MFM-303(Al) for the capture of NH3 at low concentrations under both dry and wet conditions.
Highlights
Over 150 million tonnes of NH3 are produced each year primarily as fertilizer, consuming 2% of the world’s energy.[1]
Agricultural activities have led to significant emissions of NH3, making it one of the five most damaging air pollutants, along with particulate matters, NOx, SO2, and non-methane volatile organic compounds.[2]
Several prerequisites need to be fulfilled for any practical use, including safe and efficient storage media with high volumetric uptakes, a facile cracking process, and an effective capture and removal system since even 1 ppm of NH3 can poison proton exchange membrane fuel cells.[6]
Summary
Over 150 million tonnes of NH3 are produced each year primarily as fertilizer, consuming 2% of the world’s energy.[1]. A variety of materials have been investigated as storage and capture media for NH3, such as activated carbons,[7] zeolites,[8,9] mesoporous silica,[10,11] and organic polymers.[12,13] porous materials as regenerable NH3 capture systems have been demonstrated, many are limited by factors such as low storage capacity, irreversible uptake, and/or low packing density of stored NH3, which restrict their on-board applications due to the additional volume required for the storage system
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