Synthesis of nitro compounds from nitrogen dioxide captured in a metal-organic framework

Increasing levels of air pollution are driving the need for the development new processes that take ‘waste-to-chemicals’. Herein we report the capture and conversion under ambient conditions of a major air pollutant, NO2, using a robust metal-organic framework (MOF) material, Zr-bptc (H4bptc = 3, 3’, 5, 5’-biphenyltetracarboxylic acid), comprising of {Zr6(μ3-O)4(μ3-OH)4(COO)12} clusters linked by 4-connected bptc4− ligands in a ftw topology. At 298 K, Zr-bptc shows exceptional stability and adsorption of NO2 at both low (4.9 mmol g-1 at 10 mbar) and high pressures (13.8 mmol g-1 at 1.0 bar) as measured by isotherm experiments. Dynamic breakthrough experiments have confirmed the selective retention of NO2 by Zr-bptc at low concentrations under both dry and wet conditions. The immobilised NO2 can be readily transformed to valuable nitro compounds relevant to construction, agrochemical and pharmaceutical industries. In situ crystallographic and spectroscopic studies reveal strong binding interactions of NO2 to the {Zr6(μ3-O)4(μ3-OH)4(COO)12} cluster node. This study paves a circular pathway to enable the integration of nitrogen-based air pollutants into the production of fine chemicals.