Synthesis Strategies for Ultrastable Zeolite GIS Polymorphs as Sorbents for Selective Separations

Abstract

What is the most significant result of this study? In this study,w ed iscovered that subtle differences in crystal poly-morph structure can have ap rofound influence on material properties. The remarkable aspect of the two polymorphs in this particular study-GIS types P1 and P2-is the fact that their topology is nearly identical, yet as light rotation in the framework along with the replacement of one aluminum atom in the unit cell with as ili-con atom is sufficient to change the thermal stability of the material by more than af actor of two. This unexpected result could potentially impact the design of zeolites for ah ost of applications requiring (hydro)thermally robust isostructures. What was the inspiration for this cover design? When designing the cover,w ew anted to accomplish two objectives. The first was to highlight the hierarchical nature of our col-laborative research that spanned multiple length scales:t hat is, from macroscopic adsorption studies and microscopic materials characterization to atomistic modeling. The cover image highlights bulk sorbents that can be used for separations, am icroscopic image of az eolite crystal framework, and an individual pore operating as as ize-exclusion sieve. As econd aspect that we wanted to emphasize was the relevance of our findings to applications in the energy and chemicals industries. In our study,w eu sed ac ommer-cially viable approach to prepare GIS-type zeolites. To this end, their performance as selective sorbents may prove beneficial for expanding this work beyond the benchtop to be of practical use in industrial separations or adsorption technologies. What other topics are you working on at the moment? The research programs of the three principal investigators-Grabow,M otkuri, and Rimer-all fall under the general umbrella of nanoporous materials. Each of us studies zeolites, but for different applications-Grabow and Rimer focus on catalysis, whereas Mot-kuri, in addition to zeolites, is also interested on metal-organic frameworks for their sorption/separation applications. We are continuing to investigate aw ide range of open framework materials for these applications. An underlying theme of our work is the elu-cidation of structure-performance relationships, and the design of novel pathways to generate new/improved materials in pursuit of advancing these fields of research beyond current state-of-the-art technologies. Invited for the cover of this issue are the groups of R. K. Motkuri and J. D. Rimer at the Pacific Northwest National Laboratory and University of Houston, respectively.T he image depicts bulk sorbents that can be used for separations, am icroscopic image of az eolite crystal framework,a nd an individualp ore operating as as ize-exclusion sieve. Read the full text of the ar

Organic‐Free Interzeolite Transformation in the Absence of Common Building Units

“…Developing predictive models of interzeolite transformation is challenging since the correlations between free energy of formation and zeolite composition or crystal structure are not well understood. There are instances where both parent and daughter zeolites exhibit nearly identical composition, such as the transformation between FAU (Si/Al=1.5–2.5) and GIS (Si/Al=1.5–2.0) . For the system in this study, the Al content of zeolites, as measured by energy‐dispersive X‐ray spectroscopy (EDX), increases with each interzeolite transformation: USY (Si/Al=30–40)→ZSM‐5 (SI/Al=16)→MOR (Si/Al=6).…”

“…There are instances where both parenta nd daughter zeolitese xhibit nearly identical composition, such as the transformation between FAU( Si/Al = 1.5-2.5) and GIS (Si/ Al = 1.5-2.0). [27] For the system in this study,t he Al content of zeolites,a sm easured by energy-dispersive X-ray spectroscopy (EDX),i ncreases with each interzeolite transformation:U SY (Si/ Al = 30-40)!ZSM-5 (SI/Al = 16)!MOR (Si/Al = 6). There is also as tark differencei nt he elemental compositiono fm ordenite (Si/Al = 6) and ZSM-5 (Si/Al = 16) obtainedf rom growth mix- tures S2 and S3.…”

Framework flexibility-driven CO2 adsorption on a zeolite

“…7,8 Theoretical calculations using rigid, all-silica models have suggested this small-pore zeolite as a most promising candidate for CO2 adsorption among known zeolites. 9 However, GIS zeolites, typically synthesized with framework Si/Al ratios below 2.0, 10,11 show negligible CO2 uptake (< 0.03 mmol g -1 at 25 °C and 1.0 bar). 11 We hypothesized that this may be due to the high number of charge compensating extra-framework cations blocking access to the 8-ring windows for CO2 adsorption.To first synthesize isostructural zeolites with lower number of extra-framework Na + ions and thus higher framework Si/Al…”

“…ratios under wholly inorganic conditions, we carefully decreased the alkalinity of the synthesis mixture reported to give pure GIS materials with Si/Al ratios below 2.0, 10,11 as well as increased crystallization temperature. This included the use of aluminosilicate gels with the composition xNa2O•yAl2O3 •10SiO2•220H2O, where x and y are varied between 1.0 ≤ x ≤ 10.0 and 0.5 ≤ y ≤ 2.0, respectively (Table S1, ESI †).…”

Design of Organic Structure‐Directing Agents for the Controlled Synthesis of Zeolites for Use in Carbon Dioxide/Methane Membrane Separations

“…Natural zeolites with the GIS framework are gismondine, amicite, garronite, and gobbinsite, [30] while synthetic SiÀ Al zeolites are referred to as P zeolites. [31] GIS was predicted to have favorable CO 2 adsorption properties in a series of other studies, [33,34,35] in addition to, [12] but experimental structures have shown very limited CO 2 uptake [36] The discrepancy between the predicted and experimental CO 2 uptake was attributed to the experimental aluminosiliate zeolites containing Na + as non-framework neutralizing charges. [36] No syntheses of all-Si GIS zeolite have been reported.…”