Abstract
Hierarchical zeolites containing both micro- (<2 nm) and mesopores (2-50 nm) have gained increasing attention in recent years because they combine the intrinsic properties of conventional zeolites with enhanced mass transport rates due to the presence of mesopores. The structure of the hierarchical self-pillared pentasil (SPP) zeolite is of interest because all-silica SPP consists of orthogonally intergrown single-unit-cell MFI nanosheets and contains hydrophilic surface silanol groups on the mesopore surface while its micropores are nominally hydrophobic. Therefore, the distribution of adsorbed polar molecules, like water and ethanol, in the meso- and micropores is of fundamental interest. Here, molecular simulation and experiment are used to investigate the adsorption of water and ethanol on SPP. Vapor-phase single-component adsorption shows that water occupies preferentially the mesopore corner and surface regions of the SPP material at lower pressures (P/P0 < 0.5) while loading in the mesopore interior dominates adsorption at higher pressures. In contrast, ethanol does not exhibit a marked preference for micro- or mesopores at low pressures. Liquid-phase adsorption from binary water-ethanol mixtures demonstrates a 2 orders of magnitude lower ethanol/water selectivity for the SPP material compared to bulk MFI. For very dilute aqueous solutions of ethanol, the ethanol molecules are mostly adsorbed inside the SPP micropore region due to stronger dispersion interactions and the competition from water for the surface silanols. At high ethanol concentrations (CEtOH > 700 g L-1), the SPP material becomes selective for water over ethanol.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 79-88 |
| Number of pages | 10 |
| Journal | ACS Physical Chemistry Au |
| Volume | 2 |
| Issue number | 2 |
| DOIs | |
| State | Published - Mar 23 2022 |
Bibliographical note
Funding Information:This work is supported in part by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC0001004 (for experimental measurements and molecular simulation of unary adsorption) and the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Award DE-FG02-17ER16362 (for molecular simulations of binary mixtures). The authors acknowledge the Minnesota Supercomputing Institute at the University of Minnesota for providing computational resources that contributed to this work. Equipment at the Facility for Adsorbent Characterization and Testing was purchased through Advanced Research Project Agency – Energy (ARPA-E) Interagency AgreementNo. 1208-0000.
Funding Information:
This work is supported in part by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DE-SC0001004 (for experimental measurements and molecular simulation of unary adsorption) and the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences under Award DE-FG02-17ER16362 (for molecular simulations of binary mixtures). The authors acknowledge the Minnesota Supercomputing Institute at the University of Minnesota for providing computational resources that contributed to this work. Equipment at the Facility for Adsorbent Characterization and Testing was purchased through Advanced Research Project Agency - Energy (ARPA-E) Interagency AgreementNo. 1208-0000.
Publisher Copyright:
© 2021 The Authors. Published by American Chemical Society.
Keywords
- Adsorption Selectivity
- Liquid Adsorption
- Micro/Mesoporous Materials
- Monte Carlo Simulation
- Sorbate Siting
- Vapor Adsorption