Post modification of Oxo-clusters in robust Zirconium-Based metal organic framework for durable SO2 capture from flue gas

Abstract

The efficient capture of SO2 after the combustion of fossil fuels is of great challenge as the low SO2 concentration (<500 ppm) and coexisting with CO2, water, O2 in flue gas. Robust zirconium-based MOFs possessing accessible polar sites usually have high SO2 adsorption capacity but poor durably in adsorption desulfurization due to the acidic sulfate deposition on the Zr-O cluster. Herein, a Zr-O cluster post-modification method was introduced in a Zr-MOF (MOF-808) to form EDTA-MOF-808 (EDTA, ethylene diaminetetraacetic acid) for selective and durable removal of SO2. The introduction of EDTA not only improve their SO2 adsorption capacity, but also sharply increase their SO2/CO2 selectivity (57.2 vs 8.9) and SO2/N2 selectivity (1915.8 vs 292.7) at low SO2 partial pressure. Moreover, the synergistic effects of dipole and hydrogen bonding interaction between SO2 and EDTA in EDTA-MOF-808 make the capture of SO2 in a reversible manner, which can prevent the formation of S(VI) species in Zr-MOF. DFT calculation confirmed that SO2 was interacted with EDTA through moderate dipole–dipole interaction (S(SO2) with N(EDTA)) and hydrogen bonds (H(–COOH) with O(SO2)). Systematic investigations including thermodynamic SO2 adsorption, dynamic breakthrough experiments, stability tests and DFT-calculations in both MOF-808 and EDTA-MOF-808 confirmed the efficient performance of post modification of Zr-O clusters with EDTA in Zr-MOFs for durable SO2 capture.