TY - JOUR
T1 - Distribution of Aluminum over the Tetrahedral Sites in ZSM-5 Zeolites and Their Evolution after Steam Treatment
AU - Holzinger, Julian
AU - Beato, Pablo
AU - Lundegaard, Lars Fahl
AU - Skibsted, Jørgen
N1 - doi: 10.1021/acs.jpcc.8b05277
PY - 2018/7/12
Y1 - 2018/7/12
N2 - Zeolite ZSM-5 is one of the most widely used zeolites, in particular in heterogeneous catalysis. This work investigates the incorporation of Al in the silica framework of monoclinic ZSM-5 and the Al speciation during steam treatment for four ZSM-5 samples with different Si/Al ratios, using ultrahigh field
27Al NMR (22.3 T),
29Si NMR, X-ray diffraction, and IR spectroscopy.
27Al MQMAS NMR at 22.3 T allows identification and quantification of 10 distinct tetrahedral framework resonances which are assigned to the crystallographic sites by their average T-O-T angles, determined from powder XRD patterns for the same samples. A clear Al site preference is observed and found to be dependent on the Si/Al ratio of the parent zeolite. The framework sites facing the intersections in ZSM-5 are found to be most prone to dealumination, whereas Al in the straight and sinusoidal-shaped channels are more stable toward steam treatment at high temperatures. Extra-framework Al species with 5- and 6-fold coordination and two distorted tetrahedral AlO
4 sites have also been identified. The spectroscopic data are supported by catalytic activities from α-test cracking experiments which are in accordance with a reinsertion of Al in the framework at mild steaming and the onset of dealumination at higher temperatures.
AB - Zeolite ZSM-5 is one of the most widely used zeolites, in particular in heterogeneous catalysis. This work investigates the incorporation of Al in the silica framework of monoclinic ZSM-5 and the Al speciation during steam treatment for four ZSM-5 samples with different Si/Al ratios, using ultrahigh field
27Al NMR (22.3 T),
29Si NMR, X-ray diffraction, and IR spectroscopy.
27Al MQMAS NMR at 22.3 T allows identification and quantification of 10 distinct tetrahedral framework resonances which are assigned to the crystallographic sites by their average T-O-T angles, determined from powder XRD patterns for the same samples. A clear Al site preference is observed and found to be dependent on the Si/Al ratio of the parent zeolite. The framework sites facing the intersections in ZSM-5 are found to be most prone to dealumination, whereas Al in the straight and sinusoidal-shaped channels are more stable toward steam treatment at high temperatures. Extra-framework Al species with 5- and 6-fold coordination and two distorted tetrahedral AlO
4 sites have also been identified. The spectroscopic data are supported by catalytic activities from α-test cracking experiments which are in accordance with a reinsertion of Al in the framework at mild steaming and the onset of dealumination at higher temperatures.
UR - https://www.scopus.com/pages/publications/85048523081
U2 - 10.1021/acs.jpcc.8b05277
DO - 10.1021/acs.jpcc.8b05277
M3 - Journal article
SN - 1932-7447
VL - 122
SP - 15595
EP - 15613
JO - The Journal of Physical Chemistry Part C
JF - The Journal of Physical Chemistry Part C
IS - 27
ER -