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Collective action of water molecules in zeolite dealumination

Author
Organization
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.
Keywords
METHANOL, DEACTIVATION, HYDROCARBONS, HZSM-5, E2

Citation

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Chicago
Nielsen, Malte, Anders Hafreager, Rasmus Yding Brogaard, Kristof De Wispelaere, Hanne Falsig, Pablo Beato, Veronique Van Speybroeck, and Stian Svelle. 2019. “Collective Action of Water Molecules in Zeolite Dealumination.” Catalysis Science & Technology: 3721–3725.
APA
Nielsen, M., Hafreager, A., Brogaard, R. Y., De Wispelaere, K., Falsig, H., Beato, P., Van Speybroeck, V., et al. (2019). Collective action of water molecules in zeolite dealumination. Catalysis Science & Technology, 3721–3725.
Vancouver
1.
Nielsen M, Hafreager A, Brogaard RY, De Wispelaere K, Falsig H, Beato P, et al. Collective action of water molecules in zeolite dealumination. Catalysis Science & Technology. 2019;3721–5.
MLA
Nielsen, Malte et al. “Collective Action of Water Molecules in Zeolite Dealumination.” Catalysis Science & Technology (2019): 3721–3725. Print.
@article{8625322,
  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.},
  author       = {Nielsen, Malte and Hafreager, Anders and Brogaard, Rasmus Yding and De Wispelaere, Kristof and Falsig, Hanne and Beato, Pablo and Van Speybroeck, Veronique and Svelle, Stian},
  issn         = {2044-4753},
  journal      = {Catalysis Science & Technology},
  keywords     = {METHANOL,DEACTIVATION,HYDROCARBONS,HZSM-5,E2},
  language     = {eng},
  pages        = {3721--3725},
  title        = {Collective action of water molecules in zeolite dealumination},
  url          = {http://dx.doi.org/10.1039/c9cy00624a},
  year         = {2019},
}

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