No abstract

Sulfur dioxide (SO2) is an acidic and toxic gas and its emission from utilizing energy from fossil fuels or in industrial processes harms human health and environment. Therefore, it is of great interest to find new materials for SO2 sorption to improve classic flue gas desulfurization. In this work, we present SO2 sorption studies for the three different metal–organic frameworks MOF-177, NH2-MIL-125­(Ti), and MIL-160. MOF-177 revealed a new record high SO2 uptake (25.7 mmol·g–1 at 293 K and 1 bar). Both NH2-MIL-125­(Ti) and MIL-160 show particular high SO2 uptakes at low pressures (p < 0.01 bar) and thus are interesting candidates for the removal of remaining SO2 traces below 500 ppm from flue gas mixtures. The aluminum furandicarboxylate MOF MIL-160 is the most promising material, especially under application-orientated conditions, and features excellent ideal adsorbed solution theory selectivities (124–128 at 293 K, 1 bar; 79–95 at 353 K, 1 bar) and breakthrough performance with high onset time, combined with high stability under both humid and dry SO2 exposure. The outstanding sorption capability of MIL-160 could be explained by DFT simulation calculations and matching heat of adsorption for the binding sites Ofuran···SSO2 and OHAl‑chain···OSO2 (both ∼40 kJ·mol–1) and Ofuran/carboxylate···SSO2 (∼55–60 kJ·mol–1).

Crystal structures of two metal-organic frameworks (MFU-1 and MFU-2) are presented, both of which contain redox-active Co(II) centres coordinated by linear 1,4-bis[(3,5-dimethyl)pyrazol-4-yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert-butyl hydroperoxide and the solid catalysts are easily recovered from the reaction mixture. Whereas heterogeneous catalysis is unambiguously demonstrated for MFU-1, MFU-2 shows catalytic activity due to slow metal leaching, emphasising the need for a deeper understanding of structure-reactivity relationships in the future design of redox-active metal-organic frameworks. Mechanistic details for oxidation reactions employing tert-butyl hydroperoxide are studied by UV/Vis and IR spectroscopy and XRPD measurements. The catalytic process accompanying changes of redox states and structural changes were investigated by means of cobalt K-edge X-ray absorption spectroscopy. To probe the putative binding modes of molecular oxygen, the isosteric heats of adsorption of O(2) were determined and compared with models from DFT calculations. The stabilities of the frameworks in an oxygen atmosphere as a reactive gas were examined by temperature-programmed oxidation (TPO). Solution impregnation of MFU-1 with a co-catalyst (N-hydroxyphthalimide) led to NHPI@MFU-1, which oxidised a range of organic substrates under ambient conditions by employing molecular oxygen from air. The catalytic reaction involved a biomimetic reaction cascade based on free radicals. The concept of an entatic state of the cobalt centres is proposed and its relevance for sustained catalytic activity is briefly discussed.

Herein, we report ap re-synthetic pore environment design strategy to achieve stable methyl-functionalized metalorganic frameworks (MOFs) for preferential SO 2 binding and thus enhanced low (partial) pressure SO 2 adsorption and SO 2 / CO 2 separation. The enhanced sorption performance is for the first time attributed to an optimal pore sizeb yi ncreasing methyl group densities at the benzenedicarboxylate linker in [Ni 2 (BDC-X) 2 DABCO] (BDC-X = mono-, di-, and tetramethyl-1,4-benzenedicarboxylate/terephthalate;D ABCO = 1,4-diazabicyclo[2,2,2]octane). Monte Carlo simulations and first-principles density functional theory (DFT) calculations demonstrate the key role of methyl groups within the pore surface on the preferential SO 2 affinity over the parent MOF. The SO 2 separation potential by methyl-functionalized MOFs has been validated by gas sorption isotherms,i deal adsorbed solution theory calculations,s imulated and experimental breakthrough curves,and DFT calculations.