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Zhang, Lixiong; Wang, Huanting

doi:10.1023/a:1014951523668

Cited by 8 publications

(3 citation statements)

References 26 publications

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“…It crystallizes in the chabazite framework type (CHA), which contains only one unique T-site, reducing the number of potential surface sites compared to, e.g., H-ZSM-5. The crystals of H-SSZ-13 and some other zeolites with CHA structure, such as H-SAPO-34, commonly have a cubic or almost cubic form. ,, While the shape of the crystals is known, the surface orientations haveto the best of our knowledgebeen sparsely investigated. Based on the CHA structure and the common finding that low-index facets are often most stable, we initially investigated the (101), (110), (001), and (100) surfaces, focusing on purely silicious surfaces to determine their stability.…”

Section: Resultsmentioning

confidence: 99%

Reactivity of Surface Lewis and Brønsted Acid Sites in Zeolite Catalysis: A Computational Case Study of DME Synthesis Using H-SSZ-13

2022

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The stability and reactivity of Lewis and Brønsted acid sites at the H-SSZ-13 surface are investigated for the (101) and (001) surfaces. We focus on the conversion of methanol to dimethyl ether (DME) as a probe reaction that is prototypical for the reactivity of acidic zeolites, for example, in the methanol-to-olefins process. We use periodic density functional theory (DFT) calculations in combination with highly accurate DLPNO-CCSD(T) calculations on cluster models. At Brønsted acid sites, DME can be formed via concerted and stepwise mechanisms. The barriers for acid sites located at the surface are comparable to those located in the bulk. DME formation on a Lewis acid site is similar to the concerted mechanism since two adsorbed methanol molecules react with each other directly. However, the oxygen of the adsorbed methanol is bound to the Al atom and an analogy can therefore also be drawn with a methoxy group and thus the second step of the stepwise mechanism on Brønsted acid sites. The barriers for DME formation on a Lewis acid site are more similar to the concerted mechanism of the Brønsted acid sites and are therefore at 400 °C significantly higher than the stepwise mechanism at Brønsted acid sites.

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Section: Resultsmentioning

confidence: 99%

Reactivity of Surface Lewis and Brønsted Acid Sites in Zeolite Catalysis: A Computational Case Study of DME Synthesis Using H-SSZ-13

2022

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“…The substrates were cleaned by boiling in acetone for 2 h, treated in ultrasonic for 5 min, rinsed with distilled water and dried at 100°C overnight before use. The detailed procedures of preparing the hydrogel for the synthesis of ZnAPSO-34 film and membranes were similar to those reported in the literature for the synthesis of ZnAPO-34 molecular sieve [35 ].The α porous alumina tubes substrates, were installed vertically in teflon holders so that no crystals formed in the solution could deposit on the substrates. The film was prepared on the outer surface of the porous alumina tube since an upside-down T-shaped teflon rod was inserted into the tube and was installed at the bottom of the autoclave.…”

Section: Membrane Preparationmentioning

confidence: 99%

Synthesis and Characterization of ZnAPSO-34 Membrane on Porous α- Al<sub>2</sub>O<sub>3</sub> Support

Brahim

Lounis

Condom³

et al. 2013

AMM

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Zeolites and other inorganic molecular sieve membranes have shown potential for separation based on molecular size and shape because of their small pore sized, typically less than 1nm, and their narrow pore size distribution. The in situ synthesis of ZnAPSO-34 films supported on alumina substrates is reported in this paper. Organic and water contents, alumina source, and supports have important roles in the syntheses of ZnAPSO-34 film. Traditionally, the role of organic molecules in the synthesis of these materials has been associated to their structure-directing and their protonation abilities. In our work, we were interested in a new family of materials; the alumino-phosphate, which are similar to zeolites. This work concerns the in-situ preparation of films of ZnAPSO-34 on porous α -alumina tubes. These films of ZnAPSO-34 corresponding to the structure Chabazite (CHA) have an effective intracrystal nanopore diameter of 0.38 nm. The hydrothermal synthesis was made in an autoclave under autogenous pressure. The membrane used was characterized by thermo-gravimetric analysis (TGA) and differential thermal analysis, X-ray diffraction and scanning electron microscopy after calcination.

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“…Mintova et al demonstrated the microwave synthesis of nanosized AlPO 4 -5 crystals and their use in preparation of thin films on gold substrates by seeded growth. The same technique was employed for synthesis of AlPO 4 -18 films, where colloidal AlPO 4 -18 crystals were deposited on Si wafers by spin-coating, and AlPO 4 -18 films were subsequently grown by hydrothermal treatment using the initial precursor solution. , Zhang and Wang , prepared in situ a variety of aluminophosphate molecular sieve films (AlPO 4 -14, CoAPO- 44, ZnAPO-34) on porous or dense alumina substrates using different mixture compositions and hydrothermal growth conditions. Following a novel seeding approach, Yates and co-workers synthesized fibrous AlPO 4 -5 using microemulsions, which then deposited on glass substrates by sequential deposition, under an applied electric field that provided control over film thickness and orientation.…”

Section: Introductionmentioning

confidence: 99%

Continuous c-Oriented AlPO₄-5 Films by Tertiary Growth

et al. 2007

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c-Oriented AlPO 4 -5 films were synthesized by seeded growth on silicon substrates. Secondary hydrothermal treatment of the seeded substrates under conditions that favor c-out-of-plane growth yielded non-intergrown, highly oriented columnar crystals with a length of 7 µm. Modifying the conditions so that in-plane growth is favored and executing yet another ("tertiary") growth, the crystals obtained by secondary treatment were grown in-plane, along the a-, b-directions, filling the gaps between the columnar grains and yielding well-intergrown, highly oriented, continuous AlPO 4 -5 films. The oriented films obtained by the technique presented here can be potentially useful for separations and catalysis as well as electronic and electrochemical applications.

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Untitled

Cited by 8 publications

References 26 publications

Reactivity of Surface Lewis and Brønsted Acid Sites in Zeolite Catalysis: A Computational Case Study of DME Synthesis Using H-SSZ-13

Reactivity of Surface Lewis and Brønsted Acid Sites in Zeolite Catalysis: A Computational Case Study of DME Synthesis Using H-SSZ-13

Synthesis and Characterization of ZnAPSO-34 Membrane on Porous α- Al<sub>2</sub>O<sub>3</sub> Support

Continuous c-Oriented AlPO₄-5 Films by Tertiary Growth

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Untitled

Cited by 8 publications

References 26 publications

Reactivity of Surface Lewis and Brønsted Acid Sites in Zeolite Catalysis: A Computational Case Study of DME Synthesis Using H-SSZ-13

Reactivity of Surface Lewis and Brønsted Acid Sites in Zeolite Catalysis: A Computational Case Study of DME Synthesis Using H-SSZ-13

Synthesis and Characterization of ZnAPSO-34 Membrane on Porous α- Al<sub>2</sub>O<sub>3</sub> Support

Continuous c-Oriented AlPO4-5 Films by Tertiary Growth

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About

Continuous c-Oriented AlPO₄-5 Films by Tertiary Growth