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Separation of gas molecules with similar physical and chemical properties is challenging but nevertheless highly relevant for chemical processing. By introducing the elliptically shaped molecule, 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane, into the interlayer space of a layered silicate, a two-dimensional microporous network with narrow pore size distribution is generated (MOPS-5). The regular arrangement of the pillar molecules in MOPS-5 was confirmed by the occurrence of a 10 band related to a long-range pseudo-hexagonal superstructure of pillar molecules in the interlayer space. Whereas with MOPS-5 for CO2 adsorption, gate-opening occurs at constant volume by freezing pillar rotation, for CO the interlayer space is expanded at gate-opening and a classical interdigitated layer type of gate-opening is observed. The selective nature of the gate-opening might be used for separation of CO and N2 by pressure swing adsorption. [ABSTRACT FROM AUTHOR]

The influence of the layer charge on the microstructurewas studiedfor a series of three hybrid pillared interlayered clays based onthe organic dication Me2DABCO2+and charge reducedsynthetic fluorohectorites. To get a detailed picture of the localarrangements within the interlayer space, multinuclear solid-stateNMR spectroscopy was performed in conjunction with high-resolution 129Xe MAS NMR, temperature-dependent wide-line 1D and 2D 129Xe NMR, and Ar/Ar(l) and Xe/Xe(l) physisorption measurements.The resulting layer charge (x) for the three samplesare 0.48, 0.44, and 0.39 per formula unit (pfu). The samples exhibitBET equivalent surfaces between 150 and 220 m2/g and porevolumes which increase from 0.06 to 0.11 cm3/g while thelayer charge reduces. 1D and 2D 1H, 13C, 19F, and 29Si MAS data reveal that the postsyntheticcharge reduction induces regions with higher defect concentrationswithin the silicate layers. Although the pillars tend to avoid thesedefect-rich regions, a homogeneous and regular spacing of the Me2DABCO2+pillars is established. Both the Ar/Ar(l)physisorption and 129Xe NMR measurements reveal comparablepore dimensions. The trend of the temperature-dependent wide-line 129Xe spectra as well as the exchange in the EXSY spectra istypical for a narrow 2D pore system. 129Xe high-resolutionexperiments allow for a detailed description of the microstructure.For x= 0.48 a bimodal distribution with pore diametersbetween 5.9 and 6.4 Å is observed. Reducing the layer chargeleads to a more homogeneous pore structure with a mean diameter of6.6 Å (x= 0.39). The adsorption enthalpiesΔHadsdetermined from the temperature-dependent 129Xe chemical shift data fit well to the ones derived fromthe Xe/Xe(l) physisorption measurements in the high-pressure limitwhile the magnitude of ΔHadsinthe low-pressure limit is significantly larger. Thus, the 129Xe data are influenced by adsorbate–adsorbent as well as adsorbate–adsorbateinteractions. [ABSTRACT FROM AUTHOR]

A F-rich potassium hectorite, [K0.48(2)]inter[Mg2.54(8)Li0.43]oct[Si4]tetO10F2, with a layer chargeof x= 0.48 per formula unit (pfu) was synthesizedby hightemperature melt synthesis. After Mg-exchange, the layer charge couldbe reduced significantly post synthesis by annealing (250 °C)as confirmed by alkylammonium exchange and cation exchange capacity.By pillaring this new low charge material with Me2DABCO2+(N,N-dimethyl-1,1-diazabicyclo[2.2.2]octane dication) and Rh(bpy)33+(rhodium-tris-2,2′-bipyridintrication), we observed a remarkable increase in micropore volumeand pore diameter by Ar/Ar(l) physisorption measurements. This methodallows the tailoring of pore sizes of pillared clays by reducing thelayer charge and consequently the pillar density. [ABSTRACT FROM AUTHOR]