Computer modelling of trace SO2 and NO2 removal from flue gases by utilizing Zn(ii) MOF catalysts

Abstract

SO₂ and NO₂ capture and conversion have been investigated via density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations using a novel hydrogen-bonded 3D metal–organic framework (MOF) containing a Zn(II) centre and a partially fluorinated (polar –CF₃) long-chain dicarboxylate ligand with a melamine (basic –NH₂) co-ligand. Initially, computational single-component isotherms have been determined for SO₂ and NO₂ gases. These simulations have shown exothermic adsorption enthalpies of −36.4 and −28.6 kJ mol⁻¹ for SO₂ and NO₂, respectively. They have also indicated that SO₂ has a high affinity for polar –CF₃ and basic –NH₂ binding sites of the ligand in the framework pore walls. The lower adsorption capacity of NO₂ compared with SO₂ is due to weaker electrostatic interactions with the framework. Furthermore, MOF adsorbent selectivity for removing trace amounts of SO₂ and NO₂ in flue gases has been estimated through the co-adsorption of ternary gas mixtures (SO₂/CO₂/N₂ and NO₂/CO₂/N₂). Together with DFT, the climbing image nudged elastic band (CI-NEB) method has been used for investigating the plausible mechanisms for HbMOF1 catalyzed cycloadditions of SO₂ and NO₂ with epoxides leading to the formation of cyclic sulphites and nitrates, respectively.