Thermodynamics of Hydrogen Bonding between CO and the Supercage Brønsted Acid Sites of the H-Y Zeolite − Studies from Variable Temperature IR Spectrometry

Areán, C. Otero; Manoilova, O. V.; Цыганенко, А. А.; Palomino, Gemma Turnes; Mentruit, M. Peñarroya; Geobaldo, Francesco; Garrone, Edoardo

doi:10.1002/1099-0682(200107)2001:7<1739::aid-ejic1739>3.0.co;2-m

Cited by 36 publications

(6 citation statements)

References 27 publications

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“…Δ E ads is the relative energy of the adsorption complex with respect to the free model and the probe in the gas phase (Δ E ads = E ads – E model – E probe ). For the faujasite (FAU) models, the adsorption heats (−Δ E ads ) increase in the sequence CO < CH 3 CN < NH 3 < N(CH 3 ) 3 < C 5 H 5 N. The experimentally reported adsorption heat of CO on a faujasite-type H–Y zeolite (Si/Al = 5.6) is 26 kJ/mol, which is close to our calculated value of 30 kJ/mol for FAU-7 model with a similar Si/Al ratio. Expectedly, due to its very low basicity, Δ E ads (CO) does not vary significantly for the different FAU models, predicting that the CO molecular probe is not sufficiently sensitive to discriminate acidity variations.…”

Section: Resultssupporting

confidence: 82%

Scaling Relations for Acidity and Reactivity of Zeolites

Liu¹,

Tranca²,

Santen³

et al. 2017

J. Phys. Chem. C

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Zeolites are widely applied as solid acid catalysts in various technological processes. In this work we have computationally investigated how catalytic reactivity scales with acidity for a range of zeolites with different topologies and chemical compositions. We found that straightforward correlations are limited to zeolites with the same topology. The adsorption energies of bases such as carbon monoxide (CO), acetonitrile (CH3CN), ammonia (NH3), trimethylamine (N(CH3)3), and pyridine (C5H5N) give the same trend of acid strength for FAU zeolites with varying composition. Crystal orbital Hamilton populations (COHP) analysis provides a detailed molecular orbital picture of adsorbed base molecules on the Brønsted acid sites (BAS). Bonding is dominated by strong σ donation from guest molecules to the BAS for the adsorbed CO and CH3CN complexes. An electronic descriptor of acid strength is constructed based on the bond order calculations, which is an intrinsic parameter rather than adsorption energy that contains additional contributions due to secondary effects such as van der Waals interactions with the zeolite walls. The bond order parameter derived for the CH3CN adsorption complex represents a useful descriptor for the intrinsic acid strength of FAU zeolites. For FAU zeolites the activation energy for the conversion of π-adsorbed isobutene into alkoxy species correlates well with the acid strength determined by the NH3 adsorption energies. Other zeolites such as MFI and CHA do not follow the scaling relations obtained for FAU; we ascribe this to the different van der Waals interactions and steric effects induced by zeolite framework topology.

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Section: Resultssupporting

confidence: 82%

Scaling Relations for Acidity and Reactivity of Zeolites

Liu¹,

Tranca²,

Santen³

et al. 2017

J. Phys. Chem. C

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“…Transmission IR spectra were recorded at 3 cm Ϫ1 resolution on a Bruker IFS66 instrument. Thin self-supporting wafers of the metal oxide samples were prepared and outgassed at 673 K in a dynamic vacuum (residual pressure < 10 Ϫ2 Pa) for 2 h inside an IR cell [47] which allowed in situ high temperature outgassing, gas dosage, and low or room temperature measurements to be carried out.…”

Section: Sample Characterizationmentioning

confidence: 99%

Infrared Spectroscopic Studies on the Surface Chemistry of High‐Surface‐Area Gallia Polymorphs

Delgado

Areán

2005

Zeitschrift anorg allge chemie

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Polymorphs α, β, and γ of Ga 2 O 3 having hexagonal (corundum-type), monoclinic and cubic (spinel-type) structure, respectively, were prepared in a high-surface-area form, and characterized by powder X-ray diffraction. Nitrogen adsorption at 77 K showed these gallia samples to have specific surface areas of 77 (α-Ga 2 O 3 ), 40 (β-Ga 2 O 3 ) and 120 m 2 g Ϫ1 (γ-Ga 2 O 3 ). Fourier transform infrared spectroscopy of adsorbed carbon monoxide (at 77 K) and pyridine (at room temperature) showed that the three gallia polymorphs have a very similar surface Lewis acidity, regardless of their different crystal structures. This Lewis acidity was assigned, mainly, to coordinatively unsaturated tetrahedral Ga 3ϩ ions situated on the surface of the small crystallites which constitute the different metal 2115 oxide varieties. Ga 3ϩ ···CO adducts formed after CO adsorption gave (in all cases) a characteristic CϪO stretching band at 2195Ϫ2200 cm Ϫ1 , while Lewis-type adducts formed with adsorbed pyridine were characterized by IR absorption bands at 1610Ϫ1612 and 1446Ϫ1450 cm Ϫ1 . The three (partially hydroxylated) gallia polymorphs showed also a very weak Brønsted acidity, which they manifested by forming hydrogen-bonded adducts with both CO and pyridine; however no protonation of adsorbed pyridine occurred.

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“…Transmission IR spectra were recorded, at 3 cm Ϫ1 resolution, on a Bruker IFS66 instrument. For these measurements, thin self-supported wafers of the oxide samples were prepared and activated (outgassed) at 673 K for 2 h inside an IR cell [55] which allowed in situ high-temperature outgassing, gas dosage, and low-temperature measurements to be carried out.…”

mentioning

confidence: 99%

Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

Areán

Delgado

Montouillout

et al. 2005

Zeitschrift anorg allge chemie

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By precipitation with ammonia of ethanolic solutions containing the appropriate proportions of gallium and aluminium nitrate, following by calcination of the resulting gels at 773 K, mixed Ga 2 O 3 /Al 2 O 3 oxides having Ga:Al ratios of 9:1, 4:1, 1:1, 1:4 and 1:9 were obtained. Powder X-ray diffraction showed that these mixed metal oxides form a series of solid solutions having the spinel-type structure; also shown by γ-Al 2 O 3 and γ-Ga 2 O 3 . The specific surface area (determined by nitrogen adsorption at 77 K) was found to range from 160 m 2 g Ϫ1 for the mixed oxide having Ga:Al ϭ 9:1 up to 370 m 2 g Ϫ1 for that having Ga:Al ϭ 1:9. High resolution MAS NMR showed that Ga 3ϩ and Al 3ϩ ions occur at both tetrahedral and octahedral sites in the spinel-type structure of

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Thermodynamics of Hydrogen Bonding between CO and the Supercage Brønsted Acid Sites of the H-Y Zeolite − Studies from Variable Temperature IR Spectrometry

Cited by 36 publications

References 27 publications

Scaling Relations for Acidity and Reactivity of Zeolites

Scaling Relations for Acidity and Reactivity of Zeolites

Infrared Spectroscopic Studies on the Surface Chemistry of High‐Surface‐Area Gallia Polymorphs

Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

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