Experiments were combined with atomically detailed simulations and density functional theory (DFT) calculations to understand the effect of incorporation of an ionic liquid (IL), 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF]), into a metal organic framework (MOF with a zeolitic imidazolate framework), ZIF-8, on the CO separation performance. The interactions between [BMIM][PF] and ZIF-8 were examined in deep detail, and their consequences on CO/CH, CO/N, and CH/N separation have been elucidated by using experimental measurements complemented by DFT calculations and atomically detailed simulations. Results suggest that IL-MOF interactions strongly affect the gas affinity of materials at low pressure, whereas available pore volume plays a key role for gas adsorption at high pressures. Direct interactions between IL and MOF lead to at least a doubling of CO/CH and CO/N selectivities of ZIF-8. These results provide opportunities for rational design and development of IL-incorporated MOFs with exceptional selectivity for target gas separation applications.

Metal-organic frameworks (MOFs) have been widely studied for different applications owing to their fascinating properties such as large surface areas, high porosities, tunable pore sizes, and acceptable thermal and chemical stabilities. Ionic liquids (ILs) have been recently incorporated into the pores of MOFs as cavity occupants to change the physicochemical properties and gas affinities of MOFs. Several recent studies have shown that IL/MOF composites show superior performances compared with pristine MOFs in various fields, such as gas storage, adsorption and membrane-based gas separation, catalysis, and ionic conductivity. In this review, we address the recent advances in syntheses of IL/MOF composites and provide a comprehensive overview of their applications. Opportunities and challenges of using IL/MOF composites in many applications are reviewed and the requirements for the utilization of these composite materials in real industrial processes are discussed to define the future directions in this field.

Zeolites are aluminosilicate materials that contain regular three-dimensional arrays of molecular-scale pores, and they can act as hosts for catalytically active metal clusters. The catalytic properties of such zeolites depend on the sizes and shapes of the clusters, and also on the location of the clusters within the pores. Transmission electron microscopy has been used to image single atoms and nanoclusters on surfaces, but the damage caused by the electron beam has made it difficult to image zeolites. Here, we show that aberration-corrected scanning transmission electron microscopy can be used to determine the locations of individual metal atoms and nanoclusters within the pores of a zeolite. We imaged the active sites of iridium catalysts anchored in dealuminated HY zeolite crystals, determined their locations and approximate distance from the crystal surface, and deduced a possible cluster formation mechanism.

Highly dealuminated Y zeolite-supported mononuclear iridium complexes with reactive ethylene ligands were synthesized by chemisorption of Ir(C2H4)2(C5H7O2). The resultant structure and its treatment in He, CO, ethylene, and H2 were investigated with infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The IR spectra show that Ir(C2H4)2(C5H7O2) reacted readily with surface OH groups of the zeolite, leading to the removal of C5H7O2 ligands and the formation of supported mononuclear iridium complexes, confirmed by the lack of Ir−Ir contributions in the EXAFS spectra. The EXAFS data show that each Ir atom was bonded to four carbon atoms at an average distance of 2.10 Å, consistent with the presence of two ethylene ligands per Ir atom and in agreement with the IR spectra indicating π-bonded ethylene ligands. The EXAFS data also indicate that each Ir atom was bonded to two oxygen atoms of the zeolite at a distance of 2.15 Å. The supported iridium−ethylene complex reacted with H2 to give ethane, and it also catalyzed ethylene hydrogenation at atmospheric pressure and 294 K. Treatment of the sample in CO led to the formation of Ir(CO)2 complexes bonded to the zeolite. The sharpness of the υCO bands indicates a high degree of uniformity of these complexes on the support. The iridium−ethylene complex on the crystalline zeolite support is inferred to be one of the most nearly uniform supported metal complex catalysts. The results indicate that it is isostructural with a previously reported rhodium complex on the same zeolite; thus, the results are a start to a family of analogous, structurally well-defined supported metal complex catalysts.