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The flexibility of the zeolite Rho framework offers great potential for tunable molecular sieving. The fully copper‐exchanged form of Rho and mixed Cu,H‐ and Cu,Na‐forms have been prepared. EPR spectroscopy reveals that Cu2+ ions are present in the dehydrated forms and Rietveld refinement shows these prefer S6R sites, away from the d8r windows that control diffusion. Fully exchanged Cu‐Rho remains in an open form upon dehydration, the d8r windows remain nearly circular and the occupancy of window sites is low, so that it adsorbs CO2 rapidly at room temperature. Breakthrough tests with 10 % CO2/40 % CH4 mixtures show that Cu4.9‐Rho is able to produce pure methane, albeit with a relatively low capacity at this pCO2 due to the weak interaction of CO2 with Cu cations. This is in strong contrast to Na‐Rho, where cations in narrow elliptical window sites enable CO2 to be adsorbed with high selectivity and uptake but too slowly to enable the production of pure methane in similar breakthrough experiments. A series of Cu,Na‐Rho materials was prepared to improve uptake and selectivity compared to Cu‐Rho, and kinetics compared to Na‐Rho. Remarkably, Cu,Na‐Rho with >2 Cu cations per unit cell exhibited exsolution, due to the preference of Na cations for narrow S8R sites in distorted Rho and of Cu cations for S6R sites in the centric, open form of Rho. The exsolved Cu,Na‐Rho showed improved performance in CO2/CH4 breakthrough tests, producing pure CH4 with improved uptake and CO2/CH4 selectivity compared to that of Cu4.9‐Rho. [ABSTRACT FROM AUTHOR]

Abstract: The present work shows the synthesis of nano‐sized hybrid zeolitic imidazolate frameworks (ZIFs) with the rho topology based on a mixture of the linkers benzimidazole (bIm) and 4‐methyl‐5‐imidazolecarboxaldehyde (4‐m‐5‐ica). The hybrid ZIF was obtained by post‐synthetic modification of ZIF‐93 in a bIm solution. The use of different solvents, MeOH and N,N‐dimethylacetamide (DMAc), and reaction times led to differences in the quantity of bIm incorporated to the framework, from 7.4 to 23 % according to solution‐state NMR spectroscopy. XPS analysis showed that the mixture of linkers was also present at the surface of the particles. The inclusion of bIm to the ZIF‐93 nanoparticles improved the thermal stability of the framework and also increased the hydrophobicity according to water adsorption results. N2 and CO2 adsorption experiments revealed that the hybrid material has an intermediate adsorption capacity, between those of ZIF‐93 and ZIF‐11. Finally, ZIF‐93/11 hybrid materials were applied as fillers in polybenzimidazole (PBI) mixed matrix membranes (MMMs). These MMMs were used for H2/CO2 separation (at 180 °C) reaching values of 207 Barrer of H2 and a H2/CO2 selectivity of 7.7 that clearly surpassed the Robeson upper bound (corrected for this temperature). [ABSTRACT FROM AUTHOR]

Abstract: To gain insight into the influence of metal–organic framework (MOF) fillers and polymers on membrane performance, eight different composites were studied by combining four MOFs and two polymers. MOF materials (NH2‐MIL‐53(Al), MIL‐69(Al), MIL‐96(Al) and ZIF‐94) with various chemical functionalities, topologies, and dimensionalities of porosity were employed as fillers, and two typical polymers with different permeability‐selectivity properties (6FDA‐DAM and Pebax) were selected as matrices. The best‐performing MOF–polymer composites were prepared by loading 25 wt % of MIL‐96(Al) as filler, which improved the permeability and selectivity of 6FDA‐DAM to 32 and 10 %, while for Pebax they were enhanced to 25 and 18 %, respectively. The observed differences in membrane performance in the separation of CO2 from N2 are explained on the basis of gas solubility, diffusivity properties, and compatibility between the filler and polymer phases. [ABSTRACT FROM AUTHOR]

Abstract: A fully interpenetrated 8,3‐connected zirconium MOF with the the‐i topology type, STA‐26 (St Andrews porous material‐26), has been prepared using the 4,4′,4“‐(2,4,6‐trimethylbenzene‐1,3,5‐triyl)tribenzoate (TMTB) tritopic linker with formic acid as a modulating agent. In the as‐prepared form STA‐26 possesses Im 3 ‾ m symmetry compared with the Pm 3 ‾ m symmetry of the non‐interpenetrated analogue, NU‐1200, prepared using benzoic acid as a modulator. Upon removal of residual solvent there is a shift between the interpenetrating lattices and a resultant symmetry change to Cmcm which is fully reversible. This is observed by X‐ray diffraction and 13C MAS NMR is also found to be remarkably sensitive to the structural transition. Furthermore, heating STA‐26(Zr) in vacuum dehydroxylates the Zr6 nodes leaving coordinatively unsaturated Zr4+ sites, as shown by IR spectroscopy using CO and CD3CN as probe molecules. Nitrogen adsorption at 77 K together with grand canonical Monte Carlo simulations confirms a microporous, fully interpenetrated, structure with pore volume 0.53 cm3 g−1 while CO2 adsorption at 196 K reaches 300 cm3 STP g−1 at 1 bar. While the pore volume is smaller than that of its non‐interpenetrated mesoporous analogue, interpenetration makes the structure more stable to moisture adsorption and introduces shape selectivity in adsorption. [ABSTRACT FROM AUTHOR]

The trivalent metal cations Al3+, Cr3+, and Fe3+ were each introduced, together with Sc3+, into MIL-100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X-ray diffraction (PXRD) and solid-state NMR, UV/Vis, and X-ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL-100 samples were prepared in which part of the Fe is present as α-Fe2O3 nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed-metal catalysts in Lewis acid catalysed Friedel-Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed-metal Sc,Fe materials give acceptable activity: 40% Fe incorporation only results in a 20% decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α-Fe2O3 nanoparticles were also active Lewis acid species, although less active than Sc3+ in trimer sites. The incorporation of Fe3+ into MIL-100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc3+ and Fe3+. A procedure for using these mixed-metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal. [ABSTRACT FROM AUTHOR]

The understanding of the factors that affect the real pore-network structure for a given bulk material due to different synthetic procedures is essential to develop the material with the best adsorption properties. In this work, we have deeply studied the influence of the crystallinity degree over the adsorption capacity on three new isostructural MOFs with the formula {[CdM(μ4-pmdc)2(H2O)2] ⋅solv} n (in which, pmdc=pyrimidine-4,6-dicarboxylate; solv=corresponding solvent; MII=Cd ( 1), Mn ( 2), Zn ( 3)). Compared with other methods, the solvent-free synthesis stands as the most effective route because, apart from enabling the preparation of the heterometallic compounds 2 and 3, it also renders the adsorbents with the highest performance, which is indeed close to the expected one derived from Grand Canonical Monte Carlo (GCMC) calculations. The structural analysis of the as-synthesised and evacuated frameworks reveals the existence of a metal atom exposed to the pore. The accessibility of this site is limited due to its atomic environment, which is why it is considered as a pseudo-open-metal site. The chemical and physical characterisation confirms that this site can be modified as the metal atom is replaced in compounds 2 and 3. To assess the effect of the metal replacement on the adsorption behaviour, an exhaustive study of CO2 experimental isotherms has been performed. The affinity of the pseudo-open metal sites towards CO2 and the distribution of the preferred adsorption sites are discussed on the basis of DFT and GCMC calculations. [ABSTRACT FROM AUTHOR]