Thorough investigation of varying template combinations on SAPO-34 synthesis, catalytic activity and stability in the methanol conversion to light olefin

Sedighi, Mehdi; Bahrami, H A; Towfighi, Jafar

doi:10.1039/c4ra08607d

Cited by 25 publications

(13 citation statements)

References 31 publications

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“…When TEAOH and Mor were combined as the binary OSDAs for the synthesis of SAPO-34, the obtained catalyst had a smaller crystal size and a larger surface area, thereby improving the performance of SAPO-34 catalyst in the methanol conversion reaction [17]. A similar behavior was reported by Sedighi et al [18] who used different combinations of TEAOH and Mor to synthesize SAPO-34 and obtained the catalyst with the most extended lifetime with optimal crystal size and acidity for MTO reaction. TEA is reported to favor the formation of a SAPO-5 impurity phase, although it costs considerably lower compared to TEAOH.…”

Section: Introductionsupporting

confidence: 76%

Synthesis of SAPO-34 Using Different Combinations of Organic Structure-Directing Agents

Doan

Nguyen

Dam

et al. 2019

Journal of Chemistry

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The effects of different mixtures of organic structure-directing agents (OSDAs) on the formation of SAPO-34 structure have been investigated. Different OSDAs, namely, triethylamine (TEA), tetraethylammonium hydroxide (TEAOH), and morpholine (Mor) and their combinations were used to synthesize SAPO-34 by a hydrothermal method. The template concentration was optimized by eliminating the competing phases to obtain the purest form of SAPO-34 phase. The as-synthesized samples were analyzed by XRD, FE-SEM/EDS, FT-IR, surface area/pore volume measurements, NH3-TPD, TG/DTA, and 29Si NMR MAS. The selection of template notably impacts the crystal size and physicochemical characteristics of as-synthesized SAPO-34. The sample prepared with 3 Mor : 3 TEA : 1 TEAOH exhibited the highest total acidity, smallest crystal size below 3 µm, and high surface area up to 697 m2/g.

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Section: Introductionsupporting

confidence: 76%

Synthesis of SAPO-34 Using Different Combinations of Organic Structure-Directing Agents

Doan

Nguyen

Dam

et al. 2019

Journal of Chemistry

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“…They do not show up in the computer models of these molecular sieves, i.e., they seem not to be associated with the structural Brønsted acidic sites. In the course of our literature survey we have found that those researchers who use DRIFT technique [31][32][33][34][35][36][37][38][39][40] generally find these bands more intense than those who use TR technique [41][42][43][44][45][46][47][48][49][50][51][52][53][54] . In case of the H-SAPO-34 most researchers assign the band near ~3680 cm -1 to surface P-OH vibration, following Peri's 55 early empirical assignment from the TR spectra of an amorphous AlPO 4 .…”

Section: Introductionmentioning

confidence: 99%

Delicate Distinction between OH Groups on Proton-Exchanged H-Chabazite and H-SAPO-34 Molecular Sieves

et al. 2015

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We observed surprising difference in the FTIR (Fourier transform infrared) hydroxyl spectra of the structurally isomorphous, proton exchanged H-CHA and H-SAPO-34 molecular sieves when measured by transmission (TR) or diffuse reflectance (DRIFT) techniques. Experimental and density functional theory (DFT) based model evidence is presented in this paper to prove that the essential reason for this spectral difference is that DRIFT emphasizes the vibrations of surface hydroxyl sites. Vibrations of the bulk Brønsted acidic hydroxyls shift to higher frequencies when they become surface species, the IR beam is reflected from approximately the top ~15 to 20 Å thick layer of the particles, hence the proportion of surface related IR bands becomes significant compared to the bulk related ones in the DRIFT spectra while the opposite is valid for the TR spectra. We demonstrate that the surface hydroxyls are Brønsted acidic both on the H-CHA and the H-SAPO-34 particles and the upshifted vibrations noticed primarily in the DRIFT spectra are Al-OH vibrations on the surface even of H-SAPO-34, not P-OH groups as most researchers believe. We also show that the bulk Brønsted sites might involve HO1, HO2 and HO4 type hydroxyls associated with the known geometrically different oxygen positions on both molecular sieves, but only HO1 surface hydroxyls are associated with the red-shifted vibration intensified in the DRIFT spectra. Moreover, a single surface model cannot account for every vibration observed in DRIFT spectra. From the combination of IR vibrations of three adequate surface models one can as properly match the experimental DRIFT spectra as the TR spectra from the combination of the calculated bulk HO1…HO4 vibrations of these molsieve crystals.

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“…The large external surface area of the extremely small particles limits the inner surface areas and reduces the number of available acid sites in the micropores that act as active sites. 38 Accordingly, the rapid deactivation of S6 might be related to its small particles with a higher external surface area observed in FESEM and BET analyses. It is noteworthy to mention that using industrial feed condition (72% methanol in water) resulted in the earlier catalyst deactivation as well as lower olens production.…”

Section: Catalytic Performance In the Mto Reactionmentioning

confidence: 94%

Investigation of synthesis time and type of seed along with reduction of template consumption in the preparation of SAPO-34 catalyst and its performance in the MTO reaction

Akhgar

Towfighi

Hamidzadeh³

2020

RSC Adv.

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Thorough investigation of varying template combinations on SAPO-34 synthesis, catalytic activity and stability in the methanol conversion to light olefin

Abstract: Crystals of SAPO-34 molecular sieves were synthesized under hydrothermal conditions by using tetraethylammonium hydroxide, morpholine and a mixture of them as structure-directing agents.

Cited by 25 publications

References 31 publications

Synthesis of SAPO-34 Using Different Combinations of Organic Structure-Directing Agents

Synthesis of SAPO-34 Using Different Combinations of Organic Structure-Directing Agents

Delicate Distinction between OH Groups on Proton-Exchanged H-Chabazite and H-SAPO-34 Molecular Sieves

Investigation of synthesis time and type of seed along with reduction of template consumption in the preparation of SAPO-34 catalyst and its performance in the MTO reaction

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