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Issue 14, 2019
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Collective action of water molecules in zeolite dealumination

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Abstract

When exposed to steam, zeolite catalysts are irreversibly deactivated by loss of acidity and framework degradation caused by dealumination. Steaming typically occurs at elevated temperatures, making it challenging to investigate the mechanism with most approaches. Herein, we follow the dynamics of zeolite dealumination in situ, in the presence of a realistic loading of water molecules by means of enhanced sampling molecular dynamics simulations. H-SSZ-13 zeolite is chosen as a target system. Monte Carlo simulations predict a loading of more than 3 water molecules per unit cell at representative steaming conditions (450 °C, 1 bar steam). Our results show that a higher water loading lowers the free energy barrier of dealumination, as water molecules cooperate to facilitate hydrolysis of Al–O bonds. We find free energies of activation for dealumination that agree well with the available experimental measurements. Clearly, the use of enhanced sampling molecular dynamics yields a major step forward in the molecular level understanding of the dealumination; insight which is very hard to derive experimentally.

Graphical abstract: Collective action of water molecules in zeolite dealumination

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Publication details

The article was received on 02 Apr 2019, accepted on 05 Jun 2019 and first published on 21 Jun 2019


Article type: Paper
DOI: 10.1039/C9CY00624A
Catal. Sci. Technol., 2019,9, 3721-3725
  • Open access: Creative Commons BY-NC license
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    Collective action of water molecules in zeolite dealumination

    M. Nielsen, A. Hafreager, R. Y. Brogaard, K. De Wispelaere, H. Falsig, P. Beato, V. Van Speybroeck and S. Svelle, Catal. Sci. Technol., 2019, 9, 3721
    DOI: 10.1039/C9CY00624A

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