Acidity of aluminophosphate structures. Part 1.—Incorporation of sillicon into chabazite-like structure 44

Lohse, U.; Parlitz, B.; Altrichter, B.; Jancke, K.; Löuffler, Elke; Schreier, E.; Vogt, F.

doi:10.1039/ft9959101155

Cited by 23 publications

(13 citation statements)

References 15 publications

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“…69 In the SAPO-34 framework, Si can be distributed in two types of domains, SAPO and aluminosilicate (AS). 70,71 In SAPO domains, only SM II occurs and gives rise to a 29 Si signal in a Si(OAl) 4 (OP) 9 environment at around −90 ppm. On the other hand, in AS domains, Si(OAl) 4 (OSi) 9 and Si islands are formed via SM II and III.…”

Section: Resultsmentioning

confidence: 99%

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New Insights into Formation of Molecular Sieve SAPO-34 for MTO Reactions

Zhang

Huang

2016

J. Phys. Chem. C

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Small-pore molecular sieve SAPO-34 is well-known as the most promising and effective catalyst for the conversion of methanol to olefins (MTO). In this paper, we have investigated the formation of SAPO-34 under different dry gel conversion (DGC) conditions using two types of synthesis gels with one containing hydrofluoric acid (HF) and the other not. Particular attention was paid to the Si incorporation and distribution in final SAPO-34 products. The results indicate that under DGC (with HF) conditions SAPO-34 is formed from the transformation of a highly crystalline, layered prephase that is held by covalent bonds. The final SAPO-34 product is a mixture of triclinic and trigonal phases containing six framework Si species. The Si distribution in triclinic and trigonal SAPO-34 is drastically different. The majority of Si species are located in the aluminosilicate domains in trigonal phase. Conversely, under DGC (without HF) conditions, the crystallization of SAPO-34 involves three transformational stages. Initially, a layered, crystalline intermediate forms and then transforms to a semicrystalline phase. The structures of both intermediates are held by weak noncovalent bonding interactions. The final SAPO-34 product is in pure trigonal form and contains two major Si species. Despite the difference in Si distribution, the SAPO-34 products prepared by using different gels have similar bulk Si contents. MTO reaction tests show that before 50 min of time-on-stream the DGC (with HF) product gives lower ethylene and propylene selectivity but higher propane selectivity than the DGC (without HF) product. After 50 min on stream, similar light olefin and propane selectivities are observed over the two SAPO-34 samples.

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Section: Resultsmentioning

confidence: 99%

“…Formation of AS domains was previously observed in SAPO-44, which also has CHA topology. 70,71 This implies that under DGC (with HF) conditions, AS domain can form next to the SAPO domain. Thus, we attribute the 54 ppm signal to the Al site in the AS domain in trigonal SAPO-34.…”

Section: Resultsmentioning

confidence: 99%

New Insights into Formation of Molecular Sieve SAPO-34 for MTO Reactions

Zhang

Huang

2016

J. Phys. Chem. C

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“…The catalytic activities of other MeAPO-5 materials have been reported and the strong acidity of CoAPO-5 and MnAPO-5 has been ascribed to equilibrium between Brønsted and strong Lewis sites. 20,21 Following this, it seems likely that the catalytic activity of CuAPO-5 is also governed by the number of acid sites. In another study, we have investigated the oxidation state of copper in CuAPO-5 during the selective catalytic reduction of NOx using an in-situ cell.…”

Section: Nox Conversionmentioning

confidence: 97%

“…The Brønsted sites often co-exist with Lewis acid sites. [20][21][22] Including a source of silicon in the reaction mixture yields SAPO's, where silicon substitutes for phosphorus or a combination of both phosphorus and aluminium. 23 The resulting framework now has a net charge that makes possible ion exchange and the creation of catalytically active sites.…”

Section: Introductionmentioning

confidence: 99%

Selective catalytic reduction of NOx over microporous CuAPO-5: structural characterisation by XAS and XRD

et al. 2005

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“…Induction period in the early time on stream (TOS) leads to incomplete conversion of methanol ,, that can be explained through hydrocarbon pool (HP) mechanism. Haw and Kolboe reported that cyclic organic species, such as hexamethylbenzene (HMB), play the role of the reaction centers for light olefins production as the MTO reaction proceeds by a HP mechanism. , Accordingly, the time for the formation of these cyclic organic species causes the induction period, i.e., an increase in activity before maximum conversion. However, the small cage size of the SAPO-34 molecular sieve causes the HMB to form in the cages working as a diffusion barrier for methanol and lower olefins.…”

Section: Catalyst Performancementioning

confidence: 99%

Beneficial Use of Ultrasound in Rapid-Synthesis of SAPO34/ZSM-5 Nanocomposite and Its Catalytic Performances on MTO Reaction

Moradiyan

Halladj

Askari

2018

Ind. Eng. Chem. Res.

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SAPO-34 is highly selective and hydrothermally stable for MTO reactions but it is rapidly deactivated by the formation of coke through its micropores. The promising SAPO-34/ZSM-5 nanocomposite catalyst with a different ratio was synthesized by the ultrasonic-assisted hydrothermal method and it obtained products that were characterized to further investigate their catalytic performance. Utilization of the ultrasound method led to a faster synthesis time, a decrease of crystallite size, an increase of surface area, and a dominant mesopore structure. The physicochemical properties of the product were extensively investigated by XRD, FESEM, TEM, FT-IR, N2 adsorption–desorption techniques, and NH3-TPD. Results indicate that the composite had high conversion and selectivity compared to that of the original ZSM-5 and SAPO-34. When composite structures due to the synergic effect between ZSM-5 and SAPO-34 acted as promoted catalysts, they improved catalytic properties of composite catalysts. Moreover, the SAPO-34/ZSM-5 nanocomposite catalyst with 50% ratio synthesized by the ultrasonic-assisted hydrothermal method (U–S/Z (50%)) showed 100% conversion and 90% selectivity to light olefin at 450 °C.

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Acidity of aluminophosphate structures. Part 1.—Incorporation of sillicon into chabazite-like structure 44

Cited by 23 publications

References 15 publications

New Insights into Formation of Molecular Sieve SAPO-34 for MTO Reactions

New Insights into Formation of Molecular Sieve SAPO-34 for MTO Reactions

Selective catalytic reduction of NOx over microporous CuAPO-5: structural characterisation by XAS and XRD

Beneficial Use of Ultrasound in Rapid-Synthesis of SAPO34/ZSM-5 Nanocomposite and Its Catalytic Performances on MTO Reaction

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