Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

Hemelsoet, Karen; Ghysels, An; Mores, Davide; Wispelaere, Kristof De; Speybroeck, Véronique Van; Weckhuysen, Bert M.; Waroquier, Michel

doi:10.1016/j.cattod.2011.05.040

Cited by 44 publications

(43 citation statements)

References 114 publications

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“…The difference in acidity was quantified both experimentally and theoretically by measuring the shift in OH stretching frequency upon adsorption of CO 63. 65 The difference in acidity of both materials is also reflected in the calculated deprotonation energies of H‐SAPO‐34 and H‐SSZ‐13, which differ by approximately 20 kJ mol −1 (Table S2). The previous set of simulations enables the evaluation of the reactivity of the {B n } H‐SSZ‐13/H‐SAPO‐34 cage toward methylation.…”

Section: Resultsmentioning

confidence: 99%

Mechanistic Studies on Chabazite‐Type Methanol‐to‐Olefin Catalysts: Insights from Time‐Resolved UV/Vis Microspectroscopy Combined with Theoretical Simulations

Speybroeck¹,

Hemelsoet²,

Wispelaere³

et al. 2012

ChemCatChem

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125

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The formation and nature of active sites for methanol conversion over solid acid catalyst materials are studied by using a unique combined spectroscopic and theoretical approach. A working catalyst for the methanol‐to‐olefin conversion has a hybrid organic–inorganic nature in which a cocatalytic organic species is trapped in zeolite pores. As a case study, microporous materials with the chabazite topology, namely, H‐SAPO‐34 and H‐SSZ‐13, are considered with trapped (poly)aromatic species. First‐principle rate calculations on methylation reactions and in situ UV/Vis spectroscopy measurements are performed. The theoretical results show that the structure of the organic compound and zeolite composition determine the methylation rates: 1) the rate increases by 6 orders of magnitude if more methyl groups are added on benzenic species, 2) transition state selectivity occurs for organic species with more than one aromatic core and bearing more than three methyl groups, 3) methylation rates for H‐SSZ‐13 are approximately 3 orders of magnitude higher than on H‐SAPO‐34 owing to its higher acidity. The formation of (poly)aromatic cationic compounds can be followed by using in situ UV/Vis spectroscopy because these species yield characteristic absorption bands in the visible region of the spectrum. We have monitored the growth of characteristic peaks and derived activation energies of formation for various sets of (poly)aromatic compounds trapped in the zeolite host. The formation–activation barriers deduced by using UV/Vis microspectroscopy correlate well with the activation energies for the methylation of the benzenic species and the lower methylated naphthalenic species. This study shows that a fundamental insight at the molecular level can be obtained by using a combined in situ spectroscopic and theoretical approach for a complex catalyst of industrial relevance.

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Section: Resultsmentioning

confidence: 99%

Mechanistic Studies on Chabazite‐Type Methanol‐to‐Olefin Catalysts: Insights from Time‐Resolved UV/Vis Microspectroscopy Combined with Theoretical Simulations

Speybroeck¹,

Hemelsoet²,

Wispelaere³

et al. 2012

ChemCatChem

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125

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“…As further evidence that ethanol has displaced water, a range of C-H stretching signals are now present between 3000 and 2870 cm -1 . [23][24][25][26][27] The first two features (2982 and 2938 cm -1 ) are ascribed to asymmetric stretches of the CH 3 and CH 2 species respectively, whereas the latter two signals (2903 and 2875 cm -1 ) are the corresponding symmetric stretches. [24] These species are diagnostic of ethanol interactions with Brønsted acid sites, and have been observed for a range of solid-acid materials, confirming the interactions between ethanol and the SAPO-34 catalyst.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic investigation into the design of solid–acid catalysts for the low temperature dehydration of ethanol

Potter

Aswegen

Gibson

et al. 2016

Phys. Chem. Chem. Phys.

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The increased demand for bulk hydrocarbons necessitates research into increasingly sustainable, energy-efficient catalytic processes. Owing to intricately designed structure-property correlations, SAPO-34 has become established as a promising material for the low temperature ethanol dehydration to produce ethylene. However, further optimization of this process requires a precise knowledge of the reaction mechanism at a molecular level. In order to achieve this a range of spectroscopic characterization techniques are required to probe both the interaction with the active site, and also the wider role of the framework. To this end we employ a combination of in situ infra-red and neutron scattering techniques to elucidate the influence of the surface ethoxy species in the activation of both diethyl ether and ethanol, towards the improved formation of ethylene at low temperatures. The combined conclusions of these studies is that the formation of ethylene is the rate determining step, which is of fundamental importance towards the development of this process and the introduction of bio-ethanol as a viable feedstock for ethylene production.

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“…Jeanvoine et al 25,26 also suggest that the H- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 6 CHA acidic bands are associated with HO1 and HO2 proton positions and in H-SAPO-34 that HO4 protons might contribute to them, as well. Hemelsoet et al 27 The interpretation of the respective 3677 cm -1 and 3662 cm -1 bands of H-SAPO-34 and H-CHA is more controversial than that of the named Brønsted acidic sites. 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.…”

Section: Introductionmentioning

confidence: 98%

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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Experimental and theoretical IR study of methanol and ethanol conversion over H-SAPO-34

Cited by 44 publications

References 114 publications

Mechanistic Studies on Chabazite‐Type Methanol‐to‐Olefin Catalysts: Insights from Time‐Resolved UV/Vis Microspectroscopy Combined with Theoretical Simulations

Mechanistic Studies on Chabazite‐Type Methanol‐to‐Olefin Catalysts: Insights from Time‐Resolved UV/Vis Microspectroscopy Combined with Theoretical Simulations

Spectroscopic investigation into the design of solid–acid catalysts for the low temperature dehydration of ethanol

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

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