Probing the evolution of water clusters during hydration of the solid acid catalyst H-ZSM-5

Abstract

A technique developed recently for in situ solid-state ¹H NMR studies of adsorption processes has been used to probe hydration of the solid acid catalyst H-ZSM-5, yielding information on the interaction between the adsorbed water molecules and Brønsted acid sites on the H-ZSM-5 host material. Quantitative analysis of the results from the in situ experiment allows the average size of water clusters associated with the Brønsted acid sites to be determined directly, and suggests that there is a preference to form clusters comprising five–six water molecules. The in situ ¹H NMR data also provide insights into kinetic aspects of the adsorption process.

Keywords:

• adsorption
• NMR
• solid-state chemistry
• zeolites

Acknowledgements

We are grateful to Cardiff University for financial support.

Notes

Note

1. The ¹H NMR signal from ice is too broad (ca. 50 kHz [20]) to be observable using normal conditions for recording ¹H MAS NMR spectra of the type employed in the present work.