Theoretical Study of Zirconium Isomorphous Substitution into Zeolite Frameworks

Abstract

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 Brönsted 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. Brönsted acidity of substituted zeolites strongly depends on Zr content. For SOD, substitution of Zr atoms reduces Brönsted acidity. However, for Zr-substituted forms of AlPO-34 and SAPO-34, Brönsted acidity of the Zr-O(H)-Al acid sites are, at first, reduced and, then, the presence of Zr atoms substantially increased Brönsted acidity of the Zr-O(H)-Al acid site. The results in the SAPO-34-Zr indicate that more Zr atoms substantially increase Brönsted 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 Brönsted acidity of zeolites.

Electrochemical Analysis of Polymer Membrane with Inorganic Nanoparticles for High-Temperature PEM Fuel Cells

“…These suggested the relative effects of TiO 2 and ZrO 2 contents on the improvement of the water contents and IEC, respectively. Several studies have been reported on the Lewis acid and Brønsted acid sites of ZrO 2 -TiO 2 and other materials containing Zr or Ti atoms [ 16 , 19 , 20 ]. Lewis acid sites increase as the Ti content increases, whereas the Brønsted acid sites increase as the Zr content increases.…”

Comparative First-Principles Study on Tetravalent Ion-Incorporated MTW-Type Zeolites

“…The mean square deviation parameters (Θ) can be used to represent the deformation of a local regular [MO 4 ] tetrahedron (Figure b) to reflect the local structural deformation of the T location normalΘ = 1 6 ∑ i = 1 6 false( α i − α̅ false) 2 where α i represents the i th ∠O–M–O angle and α̅ is the average of six ∠O–M–O angles. In contrast to the commonly used local geometrical parameters, e.g., bond distances, it is found that the Θ parameter presents a correlation with the relative stabilities for different pure silica zeolite models.…”

“…Tetravalent metal ions (Ti 4+ , Ge 4+ , Zr 4+ , Sn 4+ ) can be incorporated into the zeolite by means of isomorphous substitution to introduce the well-defined Lewis acid center for the zeolite, which can enhance the catalytic activity of the zeolite for a designated reaction. − Mal et al reported Sn-ZSM-12 zeolite with a Si/Sn >70 that could be used as an effective catalyst for the oxidation of phenol, m -cresol, and m -xylene, which performed better than the Sn-free ZSM-12. They also found that Sn-ZSM-12 exhibited better activity than mesoporous Sn-MFI/MEL in the oxidation of naphthalene and 2-methylnaphthalene to naphthol, 2-naphthalenemethanol and 2-naphthaldehyde .…”

“…It is interesting that tetravalent metal ions improve the catalytic performance of zeolites by means of isomorphous substitution into the tetrahedral sites of zeolite. ,− The local coordinated environment around the metal-incorporated site has a great influence on the structure and acidity of zeolite and hence on the catalytic performance. − For example, Curet-Arana et al reported that the incorporation of Sn into BEC and BEA frameworks results in more structural distortion than that of Ti and Ge . If the relationships between the structural properties (e.g., acidity, cell volume, band gap, etc.)…”

Heteroatom Lewis acid zeolites: synthesis, characterization and application in the conversion of biomass-derived oxygenates

“…[24][25][26] Moreover, the different topologies of Lewis acid zeolites provide distinct confinement effects and shape selectivity. [27][28][29][30] Hence, Lewis acid zeolites may play an increasingly important role in developing new catalytic processes that convert raw resources into fuels and chemicals.…”