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Journal of Materials Science

, Volume 44, Issue 24, pp 6629–6636 | Cite as

Mesoporous silica-aluminas derived from precipitation: a study of the acidity, textural properties and catalytic performance

  • M. Bartoszek
  • R. Eckelt
  • Ch. Jäger
  • H. Kosslick
  • A. Pawlik
  • A. Schulz
Mesostructured Materials

Abstract

Silica-alumina covering broad range of compositions have been obtained by combined hydrolysis precipitation. These materials were characterized mainly by solid-state NMR spectroscopy. Textural properties were investigated by measurements of nitrogen sorption, and the acidity of Brønsted sites was studied by TPD and FTIR spectroscopy using ammonia as probe molecule. The catalytic performance of these materials was studied by the Brønsted acid-catalyzed acetalization reaction. New insights into the nature of the silicate compartment and the acidity of Brønsted sites of amorphous silica-alumina have been obtained. Silica-aluminas of different silica content do not represent a homologous row. They differ mainly in the connectivity of the silicate compartment. The results show that silica-alumina contain a quantitative amount of Brønsted sites. The appearance of tetrahedral Al is closely related to silica. The concentration of tetrahedral Al, and hence Brønsted acid sites, follows a volcano shape. After increasing with SiO2 content, the site concentration reaches a maximum at 20 wt% of silica and decreases again due to the marked decrease in the total alumina content in high silica samples. Surprisingly, the catalytic activity does not follow this trend. It increases especially with high silica samples due to the interplay of acid site concentration and the strength of acid sites. The aluminosilicate compartment of high silica samples shows a high Si/Al ratio. The improved acid strength of the sites overcompensates the lower site concentration, leading to a distinctly enhanced catalytic activity.

Keywords

Boehmite Silicate Network High Silica Content Silicate Content Acid Site Concentration 

Notes

Acknowledgement

The authors thank Dr. M.-M. Pohl for recording the TEM image. The excellent assistance from Dr. U. Bentrup and Mrs. M. Halle in FTIR and ICP measurements is gratefully acknowledged.

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • M. Bartoszek
    • 1
  • R. Eckelt
    • 1
  • Ch. Jäger
    • 3
  • H. Kosslick
    • 1
    • 2
  • A. Pawlik
    • 3
  • A. Schulz
    • 1
    • 2
  1. 1.Leibniz-Institute for Catalysis e. VRostockGermany
  2. 2.Institute of ChemistryUniversity of RostockRostockGermany
  3. 3.BAM – Federal Institute for Materials Research and Testing, Division I.3, Working Group NMR SpectroscopyBerlinGermany

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