Water coordination, proton mobility, and Lewis acidity in HY nanozeolites: A high-temperature 1H and 27Al NMR study

Marios S. Katsiotis, Michael Fardis, Yasser Al Wahedi, Samuel Stephen, Vasilios Tzitzios, Nikolaos Boukos, Hae Jin Kim, Saeed M. Alhassan, Georgios Papavassiliou

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12 Scopus citations

Abstract

A nanosized HY zeolite was synthesized and studied by means of 1H and 27Al NMR during thermal dehydration in the temperature range 20-600 °C. The nanozeolite is comprised of a mixture of well-crystallized ultrathin platelets and octahedral nanocrystals, dressed with pentacoordinated extraframework Al(V). 1H NMR spin-lattice (T1) and spin-spin (T2) relaxation measurements in combination with 27Al 3Q-MAS NMR reveal two different interaction paths between water molecules and the nanozeolite solid matrix: (i) water molecules strongly interacting with Al(V) cations, indicated by the high T1/T2 ratio, and (ii) water molecules with amply smaller T1/T2 ratio, interacting moderately with Al(IV) and Al(VI) cations. Relevant measurements on bulk HY rich in extraframework Al(VI) show the presence of the second relaxation channel only, indicating that the enhanced water adsorption observed for the nanozeolite originates partly from its extended surface and partly from the Al(V) decoration. Al(IV) sites in the nanozeolite appear to be highly resilient during heating, even while the framework starts to collapse and Al(VI) transforms to Al(V). Finally, 1H NMR shows that water protons interact particularly strongly with the Al sites in the nanozeolite at temperatures as high as 500 °C, unveiling the important role of the Al(V) decoration on this nanocatalyst.

Original languageBritish English
Pages (from-to)3428-3438
Number of pages11
JournalJournal of Physical Chemistry C
Volume119
Issue number6
DOIs
StatePublished - 12 Feb 2015

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