Abstract

We present detailed ONIOM(omega B97X-D:PM6) calculations for the formation mechanism of novel composites combining protonic mordenites (H-MOR) with various ionic liquids: 1,3-dimethyl-imidazolium chloride [MMIm] Cl, 1-ethyl-3-methyl-imidazolium chloride [EMIm]Cl; 1-methyl-3-propyl-imidazolium chloride [PMIm]Cl; 1-butyl-3-methyl-imidazolium chloride [BMIm]Cl, 1-(2-hydroxyethyl)-3-methyl-imidazolium chloride [HEMIm] Cl, 1,3-dimethyl-1,3,2-diazasilolium chloride [MMSiN]Cl, and 1,3-dimethyl-1,3-diphospholium chloride [MMPP]Cl. The most feasible [M]-MOR formation mechanism ([M](+) = [MMIm](+), [EMIm](+), [PMIm](+), [BMIm](+), [HEMIm](+), [MMSiN](+) [MMPP](+)) involves an ion exchange at the T4O10 position favoring the isolation of a minimal number of [M](+) isomers (i.e., conformational traps). The interaction of these [M]-MOR composites with pollutant gases has afterward been evaluated. Among the studied sytems, [EMIm]-MOR and [HEMIm]-MOR present electronic and steric conditions for potential applications in gas separation, capture, and storage (H-2 and H2S). The H-MOR framework exhibits two structural conformers with the [HEMIm](+) cation in the confined space. Both, the MOR-T4O10-[HEMIm] and MOR-T4O10-[HEMIm](HB) conformers, interconvert by a dynamic equilibrium with a transition state MOR-T4O10-TS1 acting as a conformational switch (ON-OFF) that selectively recognizes and captures H2S through a plier-like conformation.