Zeolite HZSM-5 at variable Si/Al ratios were titrated by water from both vapor and liquid phases and investigated by solid state NMR. Water loading is qualitatively controlled from 0 to 0.06 molecule / acid site, and quantitatively controlled from 0.06 molecule / acid site to excess amounts. A model of multiple-site chemical exchange between free water, acid sites, and bonded water is proposed. The reactivity of HZSM-5 at different water loadings is evaluated via H/D exchange reactions using isobudane-d10 and benzene-d6. Water is found to both enhance (at trace amounts, i.e., 0.1 molecule / acid site) and reduce (large amounts, i.e., &gt; 0.5 molecule / acid site) the reactivity of HZSM-5. The role of EFAl (extra-framework aluminum) and aluminols, as well as acid site heterogeneity, is discussed. Relevance to reactions occurring at higher temperatures, and involving carbon-carbon bond rearrangements, will be introduced.

Investigation of water interactions with HZSM-5 and impacts on catalyst reactivity

2019 Fall National Meeting

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