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Title: Structural analysis of highly porous γ-Al{sub 2}O{sub 3}

Two highly porous γ-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 {sup 27}Al 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 γ-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 ∼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 γ-alumina, independent of precursor and synthesis conditions. The concentration of “non-spinel” Al atoms seems to correlate with surface properties, and increases with increasingmore » pore size/surface area. This should have implications to the catalytic properties of porous γ-alumina. - Graphical abstract: Boehmite-derived and sol–gel synthesized porous γ-Al{sub 2}O{sub 3} possess identical structural properties, featuring a nm scale local structure and a tetragonal average structure. - Highlights: • Porous γ-Al{sub 2}O{sub 3} generally possesses a nm-scale local structure. • The tetragonal average structure contains a substantial fraction of “non-spinel” Al atoms. • The concentration of “non-spinel” Al atoms correlates with surface properties.« less
Authors:
 [1] ; ;  [2] ; ;  [3] ;  [4] ;  [1]
  1. Department of Materials and Environmental Chemistry, Stockholm University, S-10691 Stockholm (Sweden)
  2. Department of Materials and Environmental Chemistry, Physical Chemistry Division, Stockholm University, S-10691 Stockholm (Sweden)
  3. Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604 (United States)
  4. ICTS Centro Nacional de Microscopía Electrónica, Facultad CC. Químicas, Universidad Complutense de Madrid, Madrid E-28040 (Spain)
Publication Date:
OSTI Identifier:
22443378
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 217; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ALUMINIUM; ALUMINIUM 27; ALUMINIUM OXIDES; CALCINATION; CATALYSTS; CRYSTAL STRUCTURE; DIFFRACTION; HYDROXIDES; NANOSTRUCTURES; PARTICLES; POROUS MATERIALS; POWDERS; SOLS; SPINELS; SURFACE AREA; SYNTHESIS; THICKNESS; TRANSMISSION ELECTRON MICROSCOPY