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  Nonequilibrium Catalyst Materials Stabilized by the Aerogel Effect: Solvent Free and Continuous Synthesis of Gamma-Alumina with Hierarchical Porosity

Hagedorn, K., Bahnmüller, U., Schachtschneider, A., Frei, M., Li, W., Schmedt auf der Günne, J., et al. (2017). Nonequilibrium Catalyst Materials Stabilized by the Aerogel Effect: Solvent Free and Continuous Synthesis of Gamma-Alumina with Hierarchical Porosity. ACS Applied Materials and Interfaces, 9(13), 11599-11608. doi:10.1021/acsami.6b16721.

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 Creators:
Hagedorn, Kay1, Author
Bahnmüller, Ulrich1, Author
Schachtschneider, Andreas1, Author
Frei, Maren2, Author           
Li, Wenyu1, Author
Schmedt auf der Günne, Jörn1, Author
Polarz, Sebastian1, Author
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1External Organizations, ou_persistent22              
2Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society, ou_1863425              

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 Abstract: Heterogeneous catalysis can be understood as a phenomenon which strongly relies on the occurrence of thermodynamically less favorable surface motifs like defects or high-energy planes. Because it is very difficult to control such parameters, an interesting approach is to explore metastable polymorphs of the respective solids. The latter is not an easy task as well because the emergence of polymorphs is dictated by kinetic control and materials with high surface area are required. Further, an inherent problem is that high temperatures required for many catalytic reactions can also induce the transformation to the thermodynamically stable modification. Alumina (Al2O3) was selected for the current study as it exists not only in the stable a-form but also as the metastable gamma-polymorph. Kinetic control was realized by combining an aerosol-based synthesis approach and a highly reactive, volatile precursor (AlMe3). Monolithic flakes of Al2O3 with a highly porous, hierarchical structure (micro-, meso-, and macropores connected to each other) resemble so-called aerogels, which are normally known only from wet solgel routes. Monolothic aerogel flakes can be separated from the gas phase without supercritical drying, which in principle allows for a continuous preparation of the materials. Process parameters can be adjusted so the material is composed exclusively of the desired gamma-modification. The gamma-Al2O3 aerogels were much more stable than they should be, and even after extended (80 h) high-temperature (1200 degrees C) treatment only an insignificant part has converted to the thermodynamically stable a-phase. The latter phenomenon was assigned to the extraordinary thermal insulation properties of aerogels. Finally, the material was tested concerning the catalytic dehydration of 1-hexanol. Comparison to other Al2O3 materials with the same surface area demonstrates that the gamma-Al2O3 are superior in activity and selectivity regarding the formation of the desired product 1-hexene.

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Language(s): eng - English
 Dates: 2017-03-142017-03-14
 Publication Status: Published in print
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 Rev. Type: -
 Identifiers: ISI: 000398764100031
DOI: 10.1021/acsami.6b16721
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Title: ACS Applied Materials and Interfaces
  Abbreviation : ACS Appl. Mater. Interfaces
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 9 (13) Sequence Number: - Start / End Page: 11599 - 11608 Identifier: ISSN: 1944-8244
CoNE: https://pure.mpg.de/cone/journals/resource/1944-8244