TY - JOUR
T1 - Identification of Distinct Framework Aluminum Sites in Zeolite ZSM-23
T2 - A Combined Computational and Experimental
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Al NMR Study
AU - Holzinger, Julian
AU - Nielsen, Malte
AU - Beato, Pablo
AU - Brogaard, Rasmus Yding
AU - Buono, Carlo
AU - Dyballa, Michael
AU - Falsig, Hanne
AU - Skibsted, Jørgen
AU - Svelle, Stian
PY - 2019
Y1 - 2019
N2 -
ZSM-23 (MTT) is a silicon-rich zeolite with one-dimensional, 10-membered ring channels, which has recently attracted interest as a promising catalyst in aromatic-free methanol-to-hydrocarbons conversion. To obtain a better understanding of the catalytic activity and ultimately to design a better catalyst, it is crucial to locate the active sites in the zeolite framework. This work investigates the tetrahedral aluminum framework sites in two zeolite H-ZSM-23 samples by experimental and computational
27
Al NMR spectroscopy.
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Al MQMAS NMR experiments at six different magnetic fields (4.7-22.3 T) were utilized to resolve distinct Al sites. The detected tetrahedral framework Al sites were assigned to the specific tetrahedral sites in the crystal structure by DFT calculations of the
27
Al chemical shieldings. A comprehensive investigation of the structural model, basis set, and exchange-correlation potential used in the DFT calculations was performed. Two avenues were pursued for calculating the
27
Al isotropic chemical shifts: the isolated-sites approach where clusters are extracted from large supercells with high Si/Al ratios and an approach targeting lower Si/Al ratios with a fully periodic model. It is found that for the ZSM-23 zeolites with Si/Al = 24 and 37 investigated here, the latter approach gives the best agreement with experiment.
AB -
ZSM-23 (MTT) is a silicon-rich zeolite with one-dimensional, 10-membered ring channels, which has recently attracted interest as a promising catalyst in aromatic-free methanol-to-hydrocarbons conversion. To obtain a better understanding of the catalytic activity and ultimately to design a better catalyst, it is crucial to locate the active sites in the zeolite framework. This work investigates the tetrahedral aluminum framework sites in two zeolite H-ZSM-23 samples by experimental and computational
27
Al NMR spectroscopy.
27
Al MQMAS NMR experiments at six different magnetic fields (4.7-22.3 T) were utilized to resolve distinct Al sites. The detected tetrahedral framework Al sites were assigned to the specific tetrahedral sites in the crystal structure by DFT calculations of the
27
Al chemical shieldings. A comprehensive investigation of the structural model, basis set, and exchange-correlation potential used in the DFT calculations was performed. Two avenues were pursued for calculating the
27
Al isotropic chemical shifts: the isolated-sites approach where clusters are extracted from large supercells with high Si/Al ratios and an approach targeting lower Si/Al ratios with a fully periodic model. It is found that for the ZSM-23 zeolites with Si/Al = 24 and 37 investigated here, the latter approach gives the best agreement with experiment.
UR - http://www.scopus.com/inward/record.url?scp=85063935682&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.8b06891
DO - 10.1021/acs.jpcc.8b06891
M3 - Journal article
AN - SCOPUS:85063935682
SN - 1932-7447
VL - 123
SP - 7831
EP - 7844
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 13
ER -