Solid-state NMR spectroscopy was utilized for investigating the post-synthetic formation of surface acid sites via AlCl3 modification of dealuminated zeolite Y (DeaY) and siliceous mesoporous SBA-15 and subsequent thermal treatment. Upon calcination at 723 K, aluminum atoms introduced by the AlCl3 modification coordinate at Q2 (Si(2Si,2OH)) and Q3 (Si(3Si,1OH)) sites and form tetrahedrally coordinated (AlIV) framework aluminum species. Most of the spectroscopically observed pentacoordinated (AlV) and octahedrally coordinated (AlVI) aluminum atoms are extra-framework species, partially acting as Lewis acid sites (LAC). The aluminum coordination at the framework is accompanied by the formation of Brønsted acidic SiOH groups with weak acid strength. The weak Brønsted acidity of these SiOH groups is explained by neighboring framework aluminum atoms with strongly disturbed tetrahedral oxygen coordination. For zeolite DeaY, in addition to the aluminum incorporation into silanol nests, also the aluminum incorporation via surface reactions of AlCl3 with the intact SiO2 framework occurs. In the case of mesoporous SBA-15, with a fivefold higher density of SiOH groups of the parent material compared with that of the parent zeolite DeaY, the aluminum incorporation into silanol nests is the dominating mechanism. By solid-state NMR spectroscopy of the dehydrated samples loaded with probe molecules, significantly larger densities (factor of 3--8) of LAC compared with those of Brønsted acid sites were determined for the AlCl3-modified and calcined zeolite DeaY and mesoporous SBA-15.
%0 Journal Article
%1 Lang2017
%A Lang, Swen
%A Benz, Michael
%A Obenaus, Utz
%A Himmelmann, Robin
%A Scheibe, Matthias
%A Klemm, Elias
%A Weitkamp, Jens
%A Hunger, Michael
%D 2017
%J Topics in Catalysis
%K
%N 19
%P 1537--1553
%R 10.1007/s11244-017-0837-6
%T Mechanisms of the AlCl3 Modification of Siliceous Microporous and Mesoporous Catalysts Investigated by Multi-Nuclear Solid-State NMR
%U https://doi.org/10.1007/s11244-017-0837-6
%V 60
%X Solid-state NMR spectroscopy was utilized for investigating the post-synthetic formation of surface acid sites via AlCl3 modification of dealuminated zeolite Y (DeaY) and siliceous mesoporous SBA-15 and subsequent thermal treatment. Upon calcination at 723 K, aluminum atoms introduced by the AlCl3 modification coordinate at Q2 (Si(2Si,2OH)) and Q3 (Si(3Si,1OH)) sites and form tetrahedrally coordinated (AlIV) framework aluminum species. Most of the spectroscopically observed pentacoordinated (AlV) and octahedrally coordinated (AlVI) aluminum atoms are extra-framework species, partially acting as Lewis acid sites (LAC). The aluminum coordination at the framework is accompanied by the formation of Brønsted acidic SiOH groups with weak acid strength. The weak Brønsted acidity of these SiOH groups is explained by neighboring framework aluminum atoms with strongly disturbed tetrahedral oxygen coordination. For zeolite DeaY, in addition to the aluminum incorporation into silanol nests, also the aluminum incorporation via surface reactions of AlCl3 with the intact SiO2 framework occurs. In the case of mesoporous SBA-15, with a fivefold higher density of SiOH groups of the parent material compared with that of the parent zeolite DeaY, the aluminum incorporation into silanol nests is the dominating mechanism. By solid-state NMR spectroscopy of the dehydrated samples loaded with probe molecules, significantly larger densities (factor of 3--8) of LAC compared with those of Brønsted acid sites were determined for the AlCl3-modified and calcined zeolite DeaY and mesoporous SBA-15.
@article{Lang2017,
abstract = {Solid-state NMR spectroscopy was utilized for investigating the post-synthetic formation of surface acid sites via AlCl3 modification of dealuminated zeolite Y (DeaY) and siliceous mesoporous SBA-15 and subsequent thermal treatment. Upon calcination at 723 K, aluminum atoms introduced by the AlCl3 modification coordinate at Q2 (Si(2Si,2OH)) and Q3 (Si(3Si,1OH)) sites and form tetrahedrally coordinated (AlIV) framework aluminum species. Most of the spectroscopically observed pentacoordinated (AlV) and octahedrally coordinated (AlVI) aluminum atoms are extra-framework species, partially acting as Lewis acid sites (LAC). The aluminum coordination at the framework is accompanied by the formation of Br{\o}nsted acidic SiOH groups with weak acid strength. The weak Br{\o}nsted acidity of these SiOH groups is explained by neighboring framework aluminum atoms with strongly disturbed tetrahedral oxygen coordination. For zeolite DeaY, in addition to the aluminum incorporation into silanol nests, also the aluminum incorporation via surface reactions of AlCl3 with the intact SiO2 framework occurs. In the case of mesoporous SBA-15, with a fivefold higher density of SiOH groups of the parent material compared with that of the parent zeolite DeaY, the aluminum incorporation into silanol nests is the dominating mechanism. By solid-state NMR spectroscopy of the dehydrated samples loaded with probe molecules, significantly larger densities (factor of 3--8) of LAC compared with those of Br{\o}nsted acid sites were determined for the AlCl3-modified and calcined zeolite DeaY and mesoporous SBA-15.},
added-at = {2019-11-05T13:27:39.000+0100},
author = {Lang, Swen and Benz, Michael and Obenaus, Utz and Himmelmann, Robin and Scheibe, Matthias and Klemm, Elias and Weitkamp, Jens and Hunger, Michael},
biburl = {https://puma.ub.uni-stuttgart.de/bibtex/21811f7ece7590a12aa5ba0d6bf23456b/ingo},
day = 01,
doi = {10.1007/s11244-017-0837-6},
interhash = {cf83431d7d455d55c3ef1027e3a557b9},
intrahash = {1811f7ece7590a12aa5ba0d6bf23456b},
issn = {1572-9028},
journal = {Topics in Catalysis},
keywords = {},
month = dec,
number = 19,
pages = {1537--1553},
timestamp = {2019-11-05T12:27:39.000+0100},
title = {Mechanisms of the AlCl3 Modification of Siliceous Microporous and Mesoporous Catalysts Investigated by Multi-Nuclear Solid-State NMR},
url = {https://doi.org/10.1007/s11244-017-0837-6},
volume = 60,
year = 2017
}
