Structural analysis of highly porous gamma-Al2O3
Number of Authors: 7
2014 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 217, 1-8 p.Article in journal (Refereed) Published
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.
Place, publisher, year, edition, pages
2014. Vol. 217, 1-8 p.
Gamma alumina, Porous materials, Crystal structure, PDF analysis
IdentifiersURN: urn:nbn:se:su:diva-106737DOI: 10.1016/j.jssc.2014.05.004ISI: 000339148800001OAI: oai:DiVA.org:su-106737DiVA: diva2:739151