Long- and Local-Range Structural Changes in Flexible Titanium Silicates with Variable Faulting upon Thermal Treatment and Corresponding Adsorption and Particle Size Polydispersity-Corrected Diffusion Parameters for CO₂/CH₄ Separation

Abstract

Sr 2+ -UPRM-5 is a titanosilicate containing adjustable structural faulting that prescribes changes in textural properties with temperature. In this work, we studied thermally induced structural changes in Sr 2+ -UPRM-5 variants prepared using tetrapropylammonium (TPA + ) and tetrabutylammonium (TBA + ) and their correlation to the diffusion of CO 2 and CH 4 at 25°C. Both Sr 2+ -UPRM-5 materials contained different amounts of structural faulting that are correlated to the formation of 12-MR pores. In situ high-temperature X-ray diffraction revealed structural changes corresponding to orthorhombic phases up to 300°C. Analysis of in situ high-temperature 29 Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy revealed new silicon environments surrounding the archetypical Si(2Si, 2Ti oct ) and Si(3Si, 1Ti semioct ) coordination centers. MAS NMR data analysis indicated that the Si environment in Sr 2+ -UPRM-5 (TPA) appears to be more susceptible to changes upon thermal treatment. A phenomenological volumetric transport model corrected for particle size polydispersity was used to estimate diffusion constants at 25°C in adsorbents preactivated at different temperatures. At the optimal conditions, the CO 2 / CH 4 kinetic selectivities were 41 and 30 for Sr 2+ -UPRM-5 (TBA) and (TPA), respectively.

Data Mining for Binary Separation Materials in Published Adsorption Isotherms

“…A further material that appears to show good performance according to both predictors is Sr-UPRM-5, a flexible titanium silicate templated either with tetrapropylammonium (TPA) or tetrabutylammonium (TBA), originally reported by Marcano-Gonzaĺez et al 40 and labeled as TPA-activated or TBAactivated in the ISODB, respectively.…”

Can the NIST Adsorption Database Be Used to Highlight Potential Materials for Gas Separation?

“…One further material which appears to show good perfor-301 mance according to both predictors is Sr-UPRM-5, a flexible 302 titanium silicate templated either with tetrapropylammonium 303 (TPA) or tetrabutylammonium (TBA), originally reported by 304 Marcano-González et al 36 and herein referred to as TPA-305 Activated or TBA-Activated, respectively. Here, we can highlight three materials which are selective 311 towards propylene: CuBTC, TO-MOF and ZnBuPBDC.…”