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Treating hydrated Na75-Y with Na2S(aq) results in the formation of a cationic sodium sulfide cluster within the zeolite
Source publication
The extraframework sodium sulfide cationic cluster, Na4S2+, has been introduced into zeolite Y (FAU, Si/Al = 1.56). A single crystal of |Na73(Na4S2+)1.0|[Si117Al75O384]-FAU was prepared by allowing aqueous 0.1 M Na2S solution to flow past a |Na75|[Si117Al75O384]-FAU crystal, and followed by vacuum dehydration at 723 K. Its structure was determined...
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The Cd4S6+ and Cd2S2+ clusters in the sodalite cavities were synthesized by reaction of the fully Cd2+-exchanged zeolite Y (Si/Al = 1.56) and 0.1 M Na2S(aq) solution at 294 K for 2 days. The single-crystal structure was determined at 100(1) K by synchrotron X-ray diffraction techniques in the cubic space group Fd\(\overline{3}\)m. The structure was...
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Citations
... The average number of diamines per supercage was calculated by dividing the moles of amine in the zeolite by the moles of supercages in FAU zeolite (details in Supporting Information Section S4). [38][39][40] Before pre-treatment, approximately 0.5, 1.2, 2.1, and 1.8 molecules of 44TMDP were loaded per supercage for the nominal loadings of 5, 10, 25, 40 wt% from wet impregnation (Figure 3c). The difference in number of 44TMDP per supercage for nominal loadings of 25 and 40 wt% is within experimental error. ...
Dehydration of methyl lactate to acrylic acid and methyl acrylate was experimentally evaluated over Na-FAU zeolite catalyst impregnated with multifunctional diamines. 1,2-bis(4-pyridyl)ethane (12BPE) and 4,4-trimethylenedipyridine (44TMDP), at a nominal loading of 40 wt% or two molecules per Na-FAU supercage, afforded a dehydration selectivity of 96+3% over 2000 min time on stream, exceeding the selectivity target of 90% for commercial viability. During continuous reaction at 300 °C, the amine loadings in Na-FAU remained constant for 12BPE but decreased as much as 83% for 44TMDP. Although 12BPE and 44TMDP have van der Waals diameters approximately 90% of the Na-FAU window opening diameter, both flexible diamines interact with internal active sites of Na-FAU as characterized by infrared spectroscopy. Tuning the weighted hourly space velocity (WHSV) from 0.9 to 0.2 h-1 afforded a yield as high as 92% at a selectivity of 96% with 44TMDP impregnated Na-FAU, resulting in the highest yield reported to date.
Dehydration of methyl lactate to acrylic acid and methyl acrylate was experimentally evaluated over a Na-FAU zeolite catalyst impregnated with multifunctional diamines. 1,2-Bis(4-pyridyl)ethane (12BPE) and 4,4'-trimethylenedipyridine (44TMDP), at a nominal loading of 40 wt % or two molecules per Na-FAU supercage, afforded a dehydration selectivity of 96 ± 3% over 2000 min time on stream. Although 12BPE and 44TMDP have van der Waals diameters approximately 90% of the Na-FAU window opening diameter, both flexible diamines interact with internal active sites of Na-FAU as characterized by infrared spectroscopy. During continuous reaction at 300 °C, the amine loadings in Na-FAU remained constant for 12BPE but decreased as much as 83% for 44TMDP. Tuning the weighted hourly space velocity (WHSV) from 0.9 to 0.2 h-1 afforded a yield as high as 92% at a selectivity of 96% with 44TMDP impregnated Na-FAU, resulting in the highest yield reported to date.
The extra-framework zinc sulfide cationic clusters, Zn4S⁶⁺ and Zn2S²⁺, have been introduced into zeolite Y (FAU, Si/Al = 1.56). The |Zn24.5Na12(Zn4S⁶⁺)0.5(Zn2S²⁺)5.5|[Si117Al75O384]-FAU was prepared by allowing aqueous 0.1 M Na2S solution to flow past a |Zn37.5|[Si117Al75O384]-FAU at 294 K for 2 days. Its structure was determined by single-crystal synchrotron X-ray diffraction techniques. The crystallographic study showed that one sulfide ion at the center of the sodalite cavity coordinates to four Zn²⁺ ions at site I’ to give a centered-tetrahedral cationic cluster, Zn4S⁶⁺, and the other sulfide ion opposite 6-ring in the sodalite cavity bridges between two Zn²⁺ ions at site I’ to give a cationic cluster with bent arrangement, Zn2S²⁺, in 6.3% and 68.8% of the sodalite cavity of zeolite Y, respectively. Through high-resolution transmission electron microscope image, zinc sulfide quantum dots (QDs) group with the size of one unit cell (ca. 3 nm) in which hundreds were distributed was identified. By using UV–vis diffuse reflectance spectroscopy, it was confirmed that the zinc sulfide QDs occupied in the structure of zeolite Y exhibited enhanced optical activity because of the quantum size effect compared with that of bulk zinc sulfide. In this study, a method for quantizing semiconducting compounds in the cavity of zeolite Y was presented more easily, and its properties were investigated in more depth. The results proved that zeolite could be applied and used as a quantum container for the quantization of semiconductor compounds.
The Cd4S6+ and Cd2S2+ clusters in the sodalite cavities were synthesized by reaction of the fully Cd2+-exchanged zeolite Y (Si/Al = 1.56) and 0.1 M Na2S(aq) solution at 294 K for 2 days. The single-crystal structure was determined at 100(1) K by synchrotron X-ray diffraction techniques in the cubic space group Fd\(\overline{3}\)m. The structure was refined using all intensities to the final error index R1/wR2 = 0.048/0.156 (for Fo > 4σ(Fo)). Approximately 13 Cd2+ and 53 Na+ ions per unit cell were found at two and four crystallographically distinct positions, respectively: two site-Iʹ positions (in the sodalite cavities opposite double 6-rings (D6Rs)) are occupied by 5 and 7.5 Cd2+ ions, respectively, per unit cell. The 0.5 Cd2+ ions per unit cell are at site IIʹ in the sodalite cavity. The 2 Na+ ion is located at the center of the D6R (site I). The 15.5 Na+ ions per unit cell are located at site Iʹ. Site-II position is occupied by 31.5 Na+ ions per unit cell. The remaining 4 Na+ ions per unit cell are located at sites IIIʹ near triple 4-rings in the supercage. Finally, 0.5 and 1.5 S2− ions per unit cell, associated with Cd2+ ions, were found at the center of sodalite cavity and opposite 6-ring in the sodalite cavity, respectively. The 1 S2− ion at the center of the sodalite cavity is coordinated to 4 Cd2+ ions at site Iʹ to give a centered-tetrahedral cationic cluster, Cd4S6+, and the other S2− ion opposite 6-ring in the sodalite cavity bridges between two Cd2+ ions at site Iʹ to give a cationic cluster with a bent arrangement, Cd2S2+, in 6.3% and 18.8% of the sodalite cavities of zeolite Y (Si/Al = 1.56), respectively.
Co-feeding an inert and site-selective chemical titrant provides desirable selectivity tuning when titrant adsorption is favored over side reaction pathways on a solid acid catalyst. Here, a selectivity enhancement from 61 to 84 C % was demonstrated for methyl lactate dehydration to methyl acrylate and acrylic acid over a NaY zeolite catalyst using amines as the co-fed titrants to suppress side reactions on in situ-generated Brønsted acid sites (BASs). The effectiveness of BAS titration was evaluated by considering both the basicity and steric properties of the titrant molecule with the goal to maximize the selectivity enhancement. The presence of electron-donating alkyl functional groups not only enhances amine basicity but also introduces additional steric constraints to the molecule with respect to the pore dimensions of the NaY zeolite. While higher basicity of titrant amines favors stronger adsorption on BASs, steric limitations hinder site binding through contributions from internal diffusion limitations and local steric repulsion between the titrant and the zeolite wall around the BAS. Titrant bases with proton affinities above ∼1040 kJ/mol and sizes below 85% of the NaY supercage window or pore diameter are predicted to afford dehydration selectivities above 90 C % to acrylate products.
