(100) facets of γ-Al2O3: The active surfaces for alcohol dehydration reactions

Ja Hun Kwak, Donghai Mei, Charles H F Peden, Roger Rousseau, János Szanyi

Research output: Contribution to journalArticle

65 Citations (Scopus)

Abstract

Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al2O 3 in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Brønsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al3+ ions on the (100) facets of γ-Al 2O3 and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al2O3, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al3+ ions on both hydrated and dehydrated surfaces: penta-coordinate Al3+ ions (Lewis acid sites), and their corresponding -OH groups (Brønsted acid sites), depending on the calcination temperature.

Original languageEnglish
Pages (from-to)649-655
Number of pages7
JournalCatalysis Letters
Volume141
Issue number5
DOIs
Publication statusPublished - May 2011

Fingerprint

Dehydration
Alcohols
Ethanol
Desorption
Ethylene
Ions
Temperature programmed desorption
Methanol
Adsorption
Lewis Acids
Temperature
Acids
Titration
Calcination
Thermodynamic properties
Molecules
Water
ethylene
Experiments

Keywords

  • (100) facets
  • Alcohol
  • Dehydration reactions
  • Penta-coordinate Al ions

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

Cite this

(100) facets of γ-Al2O3 : The active surfaces for alcohol dehydration reactions. / Kwak, Ja Hun; Mei, Donghai; Peden, Charles H F; Rousseau, Roger; Szanyi, János.

In: Catalysis Letters, Vol. 141, No. 5, 05.2011, p. 649-655.

Research output: Contribution to journalArticle

Kwak, Ja Hun ; Mei, Donghai ; Peden, Charles H F ; Rousseau, Roger ; Szanyi, János. / (100) facets of γ-Al2O3 : The active surfaces for alcohol dehydration reactions. In: Catalysis Letters. 2011 ; Vol. 141, No. 5. pp. 649-655.
@article{241b97060a264c95a9048d390d430ee0,
title = "(100) facets of γ-Al2O3: The active surfaces for alcohol dehydration reactions",
abstract = "Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al2O 3 in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Br{\o}nsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al3+ ions on the (100) facets of γ-Al 2O3 and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al2O3, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al3+ ions on both hydrated and dehydrated surfaces: penta-coordinate Al3+ ions (Lewis acid sites), and their corresponding -OH groups (Br{\o}nsted acid sites), depending on the calcination temperature.",
keywords = "(100) facets, Alcohol, Dehydration reactions, Penta-coordinate Al ions",
author = "Kwak, {Ja Hun} and Donghai Mei and Peden, {Charles H F} and Roger Rousseau and J{\'a}nos Szanyi",
year = "2011",
month = "5",
doi = "10.1007/s10562-010-0496-8",
language = "English",
volume = "141",
pages = "649--655",
journal = "Catalysis Letters",
issn = "1011-372X",
publisher = "Springer Netherlands",
number = "5",

}

TY - JOUR

T1 - (100) facets of γ-Al2O3

T2 - The active surfaces for alcohol dehydration reactions

AU - Kwak, Ja Hun

AU - Mei, Donghai

AU - Peden, Charles H F

AU - Rousseau, Roger

AU - Szanyi, János

PY - 2011/5

Y1 - 2011/5

N2 - Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al2O 3 in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Brønsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al3+ ions on the (100) facets of γ-Al 2O3 and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al2O3, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al3+ ions on both hydrated and dehydrated surfaces: penta-coordinate Al3+ ions (Lewis acid sites), and their corresponding -OH groups (Brønsted acid sites), depending on the calcination temperature.

AB - Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al2O 3 in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523-533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Brønsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al3+ ions on the (100) facets of γ-Al 2O3 and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al2O3, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al3+ ions on both hydrated and dehydrated surfaces: penta-coordinate Al3+ ions (Lewis acid sites), and their corresponding -OH groups (Brønsted acid sites), depending on the calcination temperature.

KW - (100) facets

KW - Alcohol

KW - Dehydration reactions

KW - Penta-coordinate Al ions

UR - http://www.scopus.com/inward/record.url?scp=79958786334&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=79958786334&partnerID=8YFLogxK

U2 - 10.1007/s10562-010-0496-8

DO - 10.1007/s10562-010-0496-8

M3 - Article

AN - SCOPUS:79958786334

VL - 141

SP - 649

EP - 655

JO - Catalysis Letters

JF - Catalysis Letters

SN - 1011-372X

IS - 5

ER -