Zeolite and zeolite-like molecular sieves are being used in a large number of applications such as adsorption and catalysis. Achievement of the long-standing goal of creating a chiral, polycrystalline molecular sieve with bulk enantioenrichment would enable these materials to perform enantioselective functions. Here, we report the synthesis of enantiomerically enriched samples of a molecular sieve. Enantiopure organic structure directing agents are designed with the assistance of computational methods and used to synthesize enantioenriched, polycrystalline molecular sieve samples of either enantiomer. Computational results correctly predicted which enantiomer is obtained, and enantiomeric enrichment is proven by high-resolution transmission electron microscopy. The enantioenriched and racemic samples of the molecular sieves are tested as adsorbents and heterogeneous catalysts. The enantioenriched molecular sieves show enantioselectivity for the ring opening reaction of epoxides and enantioselective adsorption of 2-butanol (the R enantiomer of the molecular sieve shows opposite and approximately equal enantioselectivity compared with the S enantiomer of the molecular sieve, whereas the racemic sample of the molecular sieve shows no enantioselectivity). chirality | zeolite | asymmetric catalysis | chiral adsorption

Molecular sieves are crystalline, microporous materials (pores less than 2 nm) that consist of three-dimensional networks of oxide tetrahedra. These materials are used in a wide variety of applications, and at present, over 200 different frameworks have been identified. [1,2] In many applications, only a single structure will give optimal performance. This specificity in the structure-property relationships is one of the major driving forces behind much of the research directed at creating new structures.[3] It is estimated from theory that there are well over a million possible frameworks, [4] but of the 200 that have been synthesized, fewer than 10% are in commercial use. [5,6] As an example of the utility within these possible frameworks, recent studies on carbon capture have identified numerous predicted frameworks with calculated performance superior to known materials. [7] Thus, the motivation to create these structures remains high.

Copper-exchanged zeolite chabazite (Cu-SSZ-13) was recently commercialized for the selective catalytic reduction of NOX with ammonia in vehicle emissions as it exhibits superior reaction performance and stability compared to all other catalysts, notably Cu-ZSM-5. Herein, the 3D distributions of Cu as well as framework elements (Al, O, Si) in both fresh and aged Cu-SSZ-13 and Cu-ZSM-5 are determined with nanometer resolution using atom probe tomography (APT), and correlated with catalytic activity and other characterizations. Both fresh catalysts contain a heterogeneous Cu distribution, which is only identified due to the single atom sensitivity of APT. After the industry standard 135,000 mile simulation, Cu-SSZ-13 shows Cu and Al clustering, whereas Cu-ZSM-5 is characterized by severe Cu and Al aggregation into a copper aluminate phase (CuAl2O4 spinel). The application of APT as a sensitive and local characterization method provides identification of nanometer scale heterogeneities that lead to catalytic activity and material deactivation.

Zeolite SSZ-39 is evaluated for catalyzing the methanol-to-olefins (MTO) reaction. By steaming NH4–SSZ-39, Al can be removed from framework positions, resulting in an increase in framework-Si/AlT and thus a lowered active acid site density. The Si/AlT ratios can be controlled by the steaming temperatures. SSZ-39 steamed at 750 °C, with preserved pore volume and morphology, is an excellent MTO catalyst, as high, stable olefin selectivities, long time-on-stream activity, and low alkane production are observed. Moreover, interesting propylene/ethylene/butylene ratios of 2.8/1/1.1 are obtained, likely related to the shape of the AEI cage. By Cu2+-exchanging SSZ-39, evidence is provided to show that AlT sites in close proximity (high AlT density) produce the unwanted effects (higher alkane-make and carbonaceous deposits) in nonsteamed materials during MTO.