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

Abstract

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.