Defect-induced channel blockage drives propene and propane separation in PCR zeolites

Abstract PCR zeolites display an unusually high kinetic selectivity in propene/propane separation. However, both propene and propane should diffuse freely through the ideal PCR framework, according to our molecular simulations. This discrepancy may be explained by foreign species introduced to the PCR channel system during thesynthesis. To test this hypothesis, we synthesized 10 × 8-ring PCR zeolites by Assembly-DisassemblyOrganization-Reassembly (ADOR) and assessed propene/propane adsorptive separation on these small-porezeolitic materials using experimental (volumetric and spectroscopic measurements) and computationalmethods (Density Functional Theory (DFT) and Force Field (FF) calculations). Whether by in-situ FTIR with thepivalonitrile probe or by MAS NMR with the shift reagent, we detected a particularly high concentration ofhydroxyl groups specifically in PCR micropores. These defects partly block the 10-ring channels, forcing masstransport through the smaller 8-ring channels, which becomes the rate-determining step. As a result, PCRmicroporous adsorbents match the performance of other zeolites, such as DDR, IHW, and ITE, contradictingcomputational predictions. These findings highlight adsorption on PCR zeolites as a sustainable alternative toenergy-intensive separations of light hydrocarbon mixtures. Moreover, a comprehensive approach to controllingimpurity location in pores during synthesis may yield adsorbents with optimal properties for real-world applications in the petroleum industry.