期刊
JOURNAL OF SOLID STATE CHEMISTRY
卷 217, 期 -, 页码 1-8出版社
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jssc.2014.05.004
关键词
Gamma alumina; Porous materials; Crystal structure; PDF analysis
资金
- Swedish Research Council within the Ro ntgen-Angstrom Cluster program [2011-6512]
- Center for Bio-Inspired Solar Fuel Production, an Energy Frontier Research Center - U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001016]
- Swedish Research Council [2010-4943]
- Knut and Alice Wallenberg Foundation
- Faculty of Sciences at Stockholm University
Two highly porous gamma-aluminas, a commercial catalyst obtained from the calcination of boehmite and a highly mesoporous product obtained from amorphous aluminum (oxy)hydroxide via a sol-gel-based process were investigated by Al-27 nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and atomic pair distribution function (PDF) analysis of synchrotron powder diffraction data. NMR data showed for both materials a distribution of tetrahedrally and octahedrally coordinated Al at a 0.30:0.70 ratio, which is typical for gamma-aluminas. TEM studies revealed that rod-shaped particles with about 5 nm in thickness are the building blocks of the porous structure in both materials. These particles often extend to a length of 50 nm in the commercial catalyst and are considerably shorter in the sol-gel-based material, which has a higher surface area. Refinement of PDFs revealed the presence of a similar to 1 nm scale local structure and the validity of a tetragonal average structure for both materials. This tetragonal average structure contains a substantial fraction of non-spinel octahedral Al atoms. It is argued that the presence of local structure is a general feature of gamma-alumina, independent of precursor and synthesis conditions. The concentration of non-spinel Al atoms seems to correlate with surface properties, and increases with increasing pore size/surface area. This should have implications to the catalytic properties of porous gamma-alumina. (C) 2014 The Authors. Published by Elsevier Inc.
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