Time-dependent CO2 sorption hysteresis in a one-dimensional microporous octahedral molecular sieve |
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Authors: | Espinal Laura Wong-Ng Winnie Kaduk James A Allen Andrew J Snyder Chad R Chiu Chun Siderius Daniel W Li Lan Cockayne Eric Espinal Anais E Suib Steven L |
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Institution: | Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA. laura.espinal@nist.gov |
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Abstract: | The development of sorbents for next-generation CO(2) mitigation technologies will require better understanding of CO(2)/sorbent interactions. Among the sorbents under consideration are shape-selective microporous molecular sieves with hierarchical pore morphologies of reduced dimensionality. We have characterized the non-equilibrium CO(2) sorption of OMS-2, a well-known one-dimensional microporous octahedral molecular sieve with manganese oxide framework. Remarkably, we find that the degree of CO(2) sorption hysteresis increases when the gas/sorbent system is allowed to equilibrate for longer times at each pressure step. Density functional theory calculations indicate a "gate-keeping" role of the cation in the tunnel, only allowing CO(2) molecules to enter fully into the tunnel via a highly unstable transient state when CO(2) loadings exceed 0.75 mmol/g. The energy barrier associated with the gate-keeping effect suggests an adsorption mechanism in which kinetic trapping of CO(2) is responsible for the observed hysteretic behavior. |
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