On the structure of γ-Al2O3

By R. Prins. 2020

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Abstract The structure of γ-Al2O3, the most important catalyst support, is still under discussion; especially the positions of the Al3+cations and vacancies are debated. One model proposes that γ-Al2O3 consists of irregularly stacked nanocrystals with all Al3+ cations occupying spinel positions, another that some Al3+ cations occupy non-spinel positions, while a third model proposes that γ-Al2O3 does not have a spinel structure. 17O and 27Al NMR measurements showed that 62.5-65% of the cations are at octahedral positions, in agreement with a spinel structure model, with DFT calculations, and with isostructural γ-Fe2O3, but in disagreement with the non-spinel model. A reconsideration of the non-spinel model is, therefore, strongly recommended. In agreement with DFT calculations, TEM measurements showed that strong reconstruction of the surface of γ-Al2O3 occurs. The (110) surface of γ-Al2O3 is not atomically flat but forms nanoscale (111) facets, indicating that (100) and (111) facets have the lowest energy.

Subfields: Ceramics and Composites, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/b93891ed85af47d108d56a708c9ac46f9a0befbb