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Designing zeolites with tunable physicochemical properties can substantially impact their performance in commercial applications, such as adsorption, separations, catalysis, and drug delivery. Zeolite synthesis typically requires an organic structure-directing agent to produce crystals with specific pore topology. Attempts to remove organics from syntheses to achieve commercially viable methods of preparing zeolites often lead to the formation of impurities. Herein, we present organic-free syntheses of two polymorphs of the small-pore zeolite P (GIS), P1 and P2. Using a combination of adsorption measurements and density functional theory calculations, we show that GIS polymorphs are selective adsorbents for H2O relative to other light gases (e.g., H2, N2, CO2). Our findings refute prior theoretical studies postulating that GIS-type zeolites are excellent materials for CO2 separation/sequestration. We also show that P2 is significantly more thermally stable than P1, which broadens the operating conditions for GIS-type zeolites in commercial applications and opens new avenues for exploring their potential use in processes such as catalysis. [ABSTRACT FROM AUTHOR]

A detailed mechanism, based on densityfunctional theory calculationsand simulation, is presented outlining the formation of the secondarybuilding unit (SBU) of MIL-101, a chromium terephthalate metal organicframework (MOF). Formation of the metal core and of the SBU is keyto MOF nucleation, the rate-limiting step in the synthesis processof many MOFs. A series of reactions that lead to the formation ofthe SBU of MIL-101 is proposed in this work. The highest barrier (∼35kcal/mol) involves the formation of a dimetal-linker intermediateand high to low spin transition as a third Cr-linker moiety joinsto form a three metal-linker group joined by a central oxygen. Theterephthalate linkers play an important, key mechanistic role withthe carboxylates first joining chromium atoms prior to the formationof bridging oxygens. Subsequent to metal core formation, stepwiselinker addition reactions generate different assembly pathways dueto structural isomers that are limited by the removal of water moleculesin the first chromium coordination shell. A simple kinetic model basedon transition state theory gave a rate of SBU formation similar toa reported rate of MOF nucleation. The least energy path was identifiedwith all linkers on the same face of the metal center added first.These first steps in developing a modeling framework for SBU formationwill hopefully lay the groundwork for future comprehensive predictivemodels of the full MOF framework structure assembly and synthesisconditions required to support the self-assembly process. [ABSTRACT FROM AUTHOR]

New approaches to tailor the synthesis of zeolite polymorphs can lead to breakthroughs in applications spanning from separations to adsorption. A comparison of small ‐ pore zeolite GIS polymorphs P1 and P2 revealed marked differences in their thermal stability. Moreover, adsorption experiments and DFT studies collectively showed that GIS polymorphs are promising materials for selective separation of small molecules. More information can be found in the Full Paper by R. K. Motkuri, J. D. Rimer et al. on page 16078 ff. [ABSTRACT FROM AUTHOR]