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A novel core–shell species for the adsorption-based separation of carbon dioxide (
CO2) from methane (
CH4) is introduced
by hydrothermal synthesis of Ni-MOF-74 on mesoporous spherical Al2O3
carrier substrate. The material was characterized
and the shell thickness determined by means of optical and scanning electron microscopy as well as volumetric
adsorption and fluid displacement experiments. Kinetic experiments with Ni-MOF-74@Al2O3 core–shell composites carried
out at 303.15 K and at pressures up to 10 bar expose remarkably dominating uptake rates for CO2
over CH4.
In the
contrary Ni-MOF-74@Al2O3 appears to be unselective according to equilibrium data at the same conditions. Dynamic
breakthrough experiments of binary CH4/
CO2-mixtures (at 303.15 K and 5 bar) prove the prevailing effect of adsorption
kinetics and the storage function of the mesoporous core. This statement is supported by a considerable boost in
CO2-
selectivity and capacity compared to adsorption equilibria measured on pure Ni-MOF-74 by the factor of 55.02 and
up to 2.42, respectively.
Sorption measurements of water vapor on an isoreticular series of Imidazolate Frameworks
Potsdam (IFP), based on penta-coordinated metal centers with secondary building units (SBUs)
connected by multidentate amido-imidate-imidazolate linkers, have been carried out at 303.15 K. The
isotherm shapes were analyzed in order to gain insight into material properties and compared to
sorption experiments with nitrogen at 77.4 K and carbon dioxide at 273.15 K. Results show that water
vapor sorption measurements are strongly influenced by the pore size distribution while having a
distinct hysteresis loop between the adsorption and desorption branch in common. Thus, IFP-4 and
-8, which solely contain micropores, exhibit H4 (type I) isotherm shapes, while those of IFP-1, -2 and
-5, which also contain mesopores, are of H3 (type IV) shape with three inflection points. The choice
of the used linker substituents and transition metals employed in the framework has a tremendous
effect on the material properties and functionality. The water uptake capacities of the examined IFPs
are ranging 0.48 mmol g????1 (IFP-4) to 6.99 mmol g????1 (IFP-5) and comparable to those documented for
ZIFs. The water vapor stability of IFPs is high, with the exception of IFP-8.