Silicoaluminophosphate Na-SAPO-34 was studied with regard to the decomposition of tetraethylammonium (TEA + ) and its effect on the ion exchange of Sr 2+ and subsequent CO 2 adsorption. TEA + is the template used during the synthesis of the material. X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma mass spectrometry (ICP-MS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and pure component gas adsorption were used to characterize the materials' structural and textural properties. Coupled thermal gravimetric analyses (TGA)/Fourier transform infrared (FT-IR) spectroscopy results indicate that the decomposition of the TEA + in Na-SAPO-34 follows a three-step mechanism and is faster in air when compared to tests performed in helium. The transient spectroscopy and DRIFT methods also indicate that a detemplation temperature of about 430 °C gives formation to ammonium cations and possibly to other organic small fractions. Ion exchange of the resulting SAPO-34 materials with Sr 2+ followed by calcination at 500 °C resulted in materials with good textural properties for CO 2 adsorption, including surface area. Compared to materials detemplated straightforwardly at 500 °C, the two-step method treatment resulted in an increase of ca. 70% in CO 2 uptake at low partial pressure because of an increase in the amount of Sr 2+ cations in the SAPO-34 framework. Traditional one-step detemplation methods produce protons that occupy cation sites that are forbidden or inaccessible to divalent species during the ion exchange, which is the principal limitation to increase the concentration of particular adsorption sites in zeolitic adsorbents.

Two related metal-organic frameworks (MOFs) based on trinuclear copper-pyrazolato structural building units (SBUs) connected by bipyridine linkers have been prepared and studied. A small chemical modification to the supporting pyrazolato ligands of a [Cu 3 ]-SBU results in two vastly different (three-fold vs eight-fold interpenetrated) MOF structures. The gas sorption properties of the two MOFs have been determined experimentally in the 0 to 10 atm pressure range. Both MOFs sorb CO 2 selectively over N 2 and H 2 , showing hysteretic sorption−desorption profiles. The hysteretic behavior is attributed to the structural flexibility of the lattices, probed by powder X-ray diffraction before and after CO 2 sorption. As the metal centers and hydroxy groups of the MOF surfaces are sterically hindered, the sorbed dipolar CO 2 molecules are attached with low sorption enthalpy to the organic groups, as determined by theoretical calculations.

A titanium silicate variant named UPRM-5 was prepared using tetraethylammonium hydroxide as a structure-directing agent (SDA). Characterization of the material by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques showed a homogeneous and crystalline solid powder phase, with unit cell dimensions of a = 6.8 Å, b = 11.7 Å, c = 13.4 Å, α = 102.9°, β = 92.8°, and γ = 91.1°. Successful detemplation was achieved via ion exchange with NH4Cl as evidenced by thermal gravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy data. Effective functionalization was obtained after ion exchanging the detemplated material using SrCl2 and BaCl2. These ion exchanged variants were also characterized using XRD and porosimetry techniques. Thermal-vacuum activation of Sr-UPRM-5 at 90 °C resulted in a material with a surface area of ca. 240 m2/g, while activation at higher temperatures resulted in low surface areas and plausible structural distortion. On the other hand, the barium variant exhibited the best thermal stability, with an average surface area on the order of 250 m2/g after employing activation temperatures up to 180 °C. The differences in thermal stability may be a result of structurally coordinated water. Adsorption of CO2 at 25 °C in Sr- and Ba-UPRM-5 materials activated at different temperatures also co-corroborated the aforementioned thermal stability observations in addition to what appears to be cation relocation. Fitting of the CO2 adsorption data with the Dubinin−Astakhov model revealed a heterogeneous surface, which was corroborated by isosteric heats of adsorption estimated from the uptake data. For low partial pressures, the observed CO2 adsorption capacities increased as follows: NH4-UPRM-5 < Sr-UPRM-5 < Ba-UPRM-5. Both the Sr- and Ba-UPRM-5 materials exhibited outstanding selectivity for CO2 over CH4, N2, and O2.

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