Details
| Originalsprache | Englisch |
|---|---|
| Seiten (von - bis) | 11599-11608 |
| Seitenumfang | 10 |
| Fachzeitschrift | ACS Applied Materials & Interfaces |
| Jahrgang | 9 |
| Ausgabenummer | 13 |
| Publikationsstatus | Veröffentlicht - 5 Apr. 2017 |
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 (Al 2O 3) was selected for the current study as it exists not only in the stable α-form but also as the metastable γ-polymorph. Kinetic control was realized by combining an aerosol-based synthesis approach and a highly reactive, volatile precursor (AlMe 3). Monolithic flakes of Al 2O 3 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 sol-gel 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 γ-modification. The γ-Al 2O 3 aerogels were much more stable than they should be, and even after extended (80 h) high-temperature (1200 °C) treatment only an insignificant part has converted to the thermodynamically stable α-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 Al 2O 3 materials with the same surface area demonstrates that the γ-Al 2O 3 are superior in activity and selectivity regarding the formation of the desired product 1-hexene.
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in: ACS Applied Materials & Interfaces, Jahrgang 9, Nr. 13, 05.04.2017, S. 11599-11608.
Publikation: Beitrag in Fachzeitschrift › Artikel › Forschung › Peer-Review
}
TY - JOUR
T1 - Nonequilibrium Catalyst Materials Stabilized by the Aerogel Effect: Solvent Free and Continuous Synthesis of Gamma-Alumina with Hierarchical Porosity
AU - Hagedorn, Kay
AU - Bahnmüller, Ulrich
AU - Schachtschneider, Andreas
AU - Frei, Maren
AU - Li, Wenyu
AU - Günne, Jörn Schmedt auf der
AU - Polarz, Sebastian
N1 - Publisher Copyright: © 2017 American Chemical Society. Copyright: Copyright 2018 Elsevier B.V., All rights reserved.
PY - 2017/4/5
Y1 - 2017/4/5
N2 - 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 (Al 2O 3) was selected for the current study as it exists not only in the stable α-form but also as the metastable γ-polymorph. Kinetic control was realized by combining an aerosol-based synthesis approach and a highly reactive, volatile precursor (AlMe 3). Monolithic flakes of Al 2O 3 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 sol-gel 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 γ-modification. The γ-Al 2O 3 aerogels were much more stable than they should be, and even after extended (80 h) high-temperature (1200 °C) treatment only an insignificant part has converted to the thermodynamically stable α-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 Al 2O 3 materials with the same surface area demonstrates that the γ-Al 2O 3 are superior in activity and selectivity regarding the formation of the desired product 1-hexene.
AB - 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 (Al 2O 3) was selected for the current study as it exists not only in the stable α-form but also as the metastable γ-polymorph. Kinetic control was realized by combining an aerosol-based synthesis approach and a highly reactive, volatile precursor (AlMe 3). Monolithic flakes of Al 2O 3 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 sol-gel 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 γ-modification. The γ-Al 2O 3 aerogels were much more stable than they should be, and even after extended (80 h) high-temperature (1200 °C) treatment only an insignificant part has converted to the thermodynamically stable α-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 Al 2O 3 materials with the same surface area demonstrates that the γ-Al 2O 3 are superior in activity and selectivity regarding the formation of the desired product 1-hexene.
KW - aerosol synthesis
KW - heterogeneous catalysis
KW - metal oxides
KW - metastable polymorphs
KW - porous materials
UR - http://www.scopus.com/inward/record.url?scp=85016940567&partnerID=8YFLogxK
U2 - 10.1021/acsami.6b16721
DO - 10.1021/acsami.6b16721
M3 - Article
VL - 9
SP - 11599
EP - 11608
JO - ACS Applied Materials & Interfaces
JF - ACS Applied Materials & Interfaces
SN - 1944-8244
IS - 13
ER -