期刊
MOLECULES
卷 24, 期 24, 页码 -出版社
MDPI
DOI: 10.3390/molecules24244466
关键词
density functional theory; zeolite; isomorphous substitution; distribution of Zr; structural stability; Bronsted acidity
资金
- National Natural Science Foundation of China [51172154]
Systematic periodic density functional theory computations including dispersion correction (DFT-D) were carried out to determine the preferred location site of Zr atoms in sodalite (SOD) and CHA-type topology frameworks, including alumino-phosphate-34 (AlPO-34) and silico-alumino-phosphate-34 (SAPO-34), and to determine the relative stability and Bronsted acidity of Zr-substituted forms of SOD, AlPO-34, and SAPO-34. Mono and multiple Zr atom substitutions were considered. The Zr substitution causes obvious structural distortion because of the larger atomic radius of Zr than that of Si, however, Zr-substituted forms of zeolites are found to be more stable than pristine zeolites. Our results demonstrate that in the most stable configurations, the preferred favorable substitutions of Zr in substituted SOD have Zr located at the neighboring sites of the Al-substituted site. However, in the AlPO-34 and SAPO-34 frameworks, the Zr atoms are more easily distributed in a dispersed form, rather than being centralized. Bronsted acidity of substituted zeolites strongly depends on Zr content. For SOD, substitution of Zr atoms reduces Bronsted acidity. However, for Zr-substituted forms of AlPO-34 and SAPO-34, Bronsted acidity of the Zr-O(H)-Al acid sites are, at first, reduced and, then, the presence of Zr atoms substantially increased Bronsted acidity of the Zr-O(H)-Al acid site. The results in the SAPO-34-Zr indicate that more Zr atoms substantially increase Bronsted acidity of the Si-O(H)-Al acid site. It is suggested that substituted heteroatoms play an important role in regulating and controlling structural stability and Bronsted acidity of zeolites.
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