Adsorption of Nitrogen-Containing Compounds from Model Fuel over Sulfonated Metal–Organic Framework: Contribution of Hydrogen-Bonding and Acid–Base Interactions in Adsorption

Adsorptive denitrogenation (ADN) was carried out by adsorption of indole (IND) and quinoline (QUI) over metal–organic frameworks (MOFs) including acidic UiO-66SO₃H for the first time. The adsorbed amount of IND increased with increasing content of SO₃H in UiO-66. The favorable effect of the SO₃H group on the adsorptive removal of IND could be explained by hydrogen bonding between the O of SO₃H and the H of IND, which was firmly supported by the adsorption of pyrrole and methylpyrrole and by theoretical calculations. The application of an SO₃H group in the adsorptive removal of neutral IND is meaningful since neutral nitrogen-containing compounds are not easy to remove and since UiO-66SO₃H is reusable after simple washing with ethanol. The expected increase in QUI adsorption (due to acid–base interaction) with acidic SO₃H was observed when QUI was present at low concentrations (<∼400 ppmw). This favorable contribution of acidic SO₃H to the adsorption of basic QUI was also supported by calculations for the adsorption of one QUI molecule on the SO₃H group of UiO-66. Interestingly, the adsorbed amount of QUI decreased with increasing content of SO₃H in UiO-66 when the QUI concentration was high (initial concentration of 1000 ppmw). One of the reasons for the negative effect of acidic SO₃H on QUI adsorption might be the presence of only one H atom in SO₃H or steric hindrance (due to decreased pore space), although detailed works are needed to support this

Pressure-Dependent Structural and Chemical Changes in a Metal–Organic Framework with One-Dimensional Pore Structure

Pressure-dependent structural and chemical changes of the metal–organic framework (MOF) compound MIL-47­(V) have been investigated up to 3 GPa using different pore-penetrating liquids as pressure transmitting media (PTM). We find that at 0.3(1) GPa the terephthalic acid (TPA) template molecules located in the narrow channels of the as-synthesized MIL-47­(V) are selectively replaced by methanol molecules from a methanol–ethanol–water mixture and form a methanol inclusion complex. Further pressure increase leads to a gradual narrowing of the channels up to 1.9(1) GPa, where a second irreversible insertion of methanol molecules leads to more methanol molecules being inserted into the pores. After pressure release methanol molecules remain within the pores and can be removed only after heating to 400 °C. In contrast, when MIL-47­(V) is compressed in water, a reversible replacement of the TPA by H₂O molecules takes place near 1 GPa. The observed structural and chemical changes observed in MIL-47­(V) demonstrate unique high pressure chemistry depending on the size and type of molecules present in the liquid PTM. This allows postsynthetic nonthermal pressure-induced removal and insertion of organic molecules in MOFs forming novel and stable phases at ambient conditions