TY - CHAP
T1 - Influence of the lanthanum exchange degree on the concentration and acid strength of bridging hydroxyl groups in zeolites La,Na-X
AU - Huang, J.
AU - Jiang, Y.
AU - Hunger, M.
PY - 2007
Y1 - 2007
N2 -
1H MAS NMR spectroscopy was applied for the quantitative investigation of the concentration of hydroxyl groups in zeolites La,Na-X with different lanthanum-exchange degrees as a function of the dehydration temperature. A maximum concentration of Brønsted acidic bridging OH groups (SiOHAl) corresponding to ca. 1 OH per lanthanum cation was reached upon dehydration of zeolites La,Na-X at 423 to 473 K. Further raise of the dehydration temperature led to a dehydroxylation of the above-mentioned zeolites, while the dealumination of the framework was negligible. By adsorption of deuterated acetonitrile as probe molecule, a significant increase of the acid strength of bridging OH groups was found with increasing lanthanum exchange degree. This finding is explained by the polarizing effect of the multivalent lanthanum cations, which leads to a withdrawal of electrons from the O-H bonds of Brønsted acid sites in zeolites La,Na-X possessing a high concentration of these multivalent extra-framework cations.
AB -
1H MAS NMR spectroscopy was applied for the quantitative investigation of the concentration of hydroxyl groups in zeolites La,Na-X with different lanthanum-exchange degrees as a function of the dehydration temperature. A maximum concentration of Brønsted acidic bridging OH groups (SiOHAl) corresponding to ca. 1 OH per lanthanum cation was reached upon dehydration of zeolites La,Na-X at 423 to 473 K. Further raise of the dehydration temperature led to a dehydroxylation of the above-mentioned zeolites, while the dealumination of the framework was negligible. By adsorption of deuterated acetonitrile as probe molecule, a significant increase of the acid strength of bridging OH groups was found with increasing lanthanum exchange degree. This finding is explained by the polarizing effect of the multivalent lanthanum cations, which leads to a withdrawal of electrons from the O-H bonds of Brønsted acid sites in zeolites La,Na-X possessing a high concentration of these multivalent extra-framework cations.
UR - http://www.scopus.com/inward/record.url?scp=35348868633&partnerID=8YFLogxK
U2 - 10.1016/S0167-2991(07)80900-1
DO - 10.1016/S0167-2991(07)80900-1
M3 - Chapter
AN - SCOPUS:35348868633
SN - 0444530681
SN - 9780444530684
SN - 9780444531858
SN - 9780444531865
VL - 170
T3 - Studies in Surface Science and Catalysis
SP - 622
EP - 628
BT - From zeolites to porous MOF materials
A2 - Xu, Ruren
A2 - , Zi Gao
A2 - Chen, Jiesheng
A2 - Yan, Wenfu
PB - Elsevier
CY - Amsterdam; Oxford
ER -