A comparative first principles study on trivalent ion incorporated SSZ-13 zeolites

Abstract

The dispersion-corrected density functional theory has been used to study the trivalent ions B, Al, Ga, and Fe incorporated SSZ-13-type zeolites. The associated structure and Brønsted/Lewis acidity change caused by the incorporation ions were comparatively studied. It was found that the smaller the radius differences of the incorporation ions are, the smaller the changes in the structure will be and the less acidity will be enhanced for the Brønsted sites. The trivalent Al is found to be the most favorable trivalent incorporation ion and Na is found to be the most favorable charge balanced ion for the synthesis of SSZ-13-type zeolites due to size comparability, which are in line with the experimental observation. The substitution energies which show the relative synthesis difficulty level were also applied for B, Al, Ga, and Fe incorporated zeolites and found that the difficulty decreases with order of Fe > B > Ga ≫ Al, also in good agreement with the experimental observations. Adsorption studies for the NH3 and pyridine molecules indicate that adsorption on the Brønsted acid sites is more stable than on the Lewis acid sites. The Brønsted acidity was found to follow the order of HAl-SSZ-13 > HGa-SSZ-13 ≈ HFe-SSZ-13 > HB-SSZ-13 where the Lewis acidity was found to follow the order of HGa-SSZ-13 ≈ HFe-SSZ-13 > HAl-SSZ-13 > HB-SSZ-13. Our results provide new insights for the synthesis of the SSZ-13-type zeolites and fundamental information for the zeolitic catalyst designation to enhance the catalytic performance.

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

“…Lewis acidity decreases in the order of Sn-MTW > Zr-MTW > Ti-MTW > Ge-MTW. Sn-MTW and Zr-MTW have stronger acidity than Ti-MTW and Ge-MTW, which is consistent with previous studies. ,,− It is worth noting that Ti-MTW and Ge-MTW have similar adsorption energies for NH 3 .…”

Molecular Structure and Confining Environment of Sn Sites in Single-Site Chabazite Zeolites

“…Periodic DFT studies of metal-substituted zeolites have estimated Ti heteroatom stability in CHA, 31 and compared adsorbate (water, ammonia, pyridine) binding energies at various heteroatom sites in CHA. [32][33][34][35] Such studies have also estimated ammonia binding energies, 36 and developed linear scaling relationships for O-and S-containing compounds, 37 bound at different heteroatoms in CHA. Theoretical studies of metalsubstituted CHA frameworks continue to proliferate, yet experimental progress to prepare and characterize such model catalysts has not been commensurate.…”

“…In contrast to most molecular sieves, chabazite (CHA) is a high-symmetry framework containing only one crystallographically unique T-site, which promises to clarify interpretations of experimental characterization data and provide model structures that can be described more accurately by theory. Periodic DFT studies of metal-substituted zeolites have estimated Ti heteroatom stability in CHA and compared adsorbate (water, ammonia, and pyridine) binding energies at various heteroatom sites in CHA. − Such studies have also estimated ammonia binding energies and developed linear scaling relationships for O- and S-containing compounds, bound at different heteroatoms in CHA. Theoretical studies of metal-substituted CHA frameworks continue to proliferate, yet experimental progress to prepare and characterize such model catalysts has not been commensurate.…”

Selective catalytic reduction of nitric oxide with ammonia over high-activity Fe/SSZ-13 and Fe/one-pot-synthesized Cu-SSZ-13 catalysts

“…Some researchers have reported that Fe-SSZ-13 showed high-temperature (>500 °C) SCR activity and better N 2 /N 2 O selectivity. 15,17,23,[41][42][43] Fe-SSZ-13 was prepared by conventional ion exchange (I.E.) using aqueous solutions of Fe precursor salts.…”