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Sr2+-UPRM-5 is a titanosilicatecontaining adjustablestructural faulting that prescribes changes in textural propertieswith temperature. In this work, we studied thermally induced structuralchanges in Sr2+-UPRM-5 variants prepared using tetrapropylammonium(TPA+) and tetrabutylammonium (TBA+) and theircorrelation to the diffusion of CO2and CH4at25 °C. Both Sr2+-UPRM-5 materials contained differentamounts of structural faulting that are correlated to the formationof 12-MR pores. In situ high-temperature X-ray diffraction revealedstructural changes corresponding to orthorhombic phases up to 300°C. Analysis of in situ high-temperature 29Si magicangle spinning nuclear magnetic resonance (MAS NMR) spectroscopy revealednew silicon environments surrounding the archetypical Si(2Si, 2Tioct) and Si(3Si, 1Tisemioct) coordination centers.MAS NMR data analysis indicated that the Si environment in Sr2+-UPRM-5 (TPA) appears to be more susceptible to changes uponthermal treatment. A phenomenological volumetric transport model correctedfor particle size polydispersity was used to estimate diffusion constantsat 25 °C in adsorbents preactivated at different temperatures.At the optimal conditions, the CO2/CH4kineticselectivities were 41 and 30 for Sr2+-UPRM-5 (TBA) and(TPA), respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] Effect of activation temperature on the adsorption of CH4 and N2 onto UPRM-5 (TEA). [•] Sr2+-UPRM-5 (TEA): selectivity toward N2 at an activation temperature of 180°C. [•] Equilibrium adsorption did not approach saturation in a 7atm range. [•] Selectivity influenced by slow CH4 uptake rates as time approached infinity. [ABSTRACT FROM AUTHOR]