Examination of Spinel and Nonspinel Structural Models for γ-Al₂O₃by DFT and Rietveld Refinement Simulations

Abstract

Despite the widespread use of gamma-Al2O3, there is still considerable disagreement over the nature of its structure due to both its poor crystallinity and differing preparation techniques during experimentation. Using density-functional theory (DFT) calculations and Rietveld simulations and refinement, the structure of three spinel-related models and a recently proposed nonspinel model were studied in reference to synchrotron X-ray powder diffraction (SXPD) patterns. The spinel-based structural models represent the structural features of gamma-Al2O3 better than the nonspinel model. The major failure of the nonspinel model is that the model cannot reproduce the SXPD reflection originating from tetrahedral aluminum. The Rietveld-refined spinel model can accurately reproduce the lattice parameters and other structural features of gamma-Al2O3, and it can generate a consistent diffraction peak at 2theta which lies between the splitting peaks of the experimental pattern that are originated from the disordered tetrahedral aluminum cations.

Towards advanced structural analysis of iron oxide clusters on the surface of γ-Al2O3 using EXAFS

“…These structures are dependent upon the conditions in which they are synthesised and the role of this disordered structure of spinel-like forms of alumina in catalysis is still a matter of discussion [41][42][43][44] [49]. These models will be referred to as surface-based models.…”

Mechanism of CO methanation on the Ni4/γ-Al2O3 and Ni3Fe/γ-Al2O3 catalysts: A density functional theory study

“…The defective spinel model [30,31] and nonspinel model [32] have been proposed for research on g-Al 2 O 3 . In this study, we employed the nonspinel model because its (100) surface exposes the penta-Al sites, as experimentally observed in previous works [33,34].…”

Energy-level alignment in the adsorption of phosphonyl reagents on γ-Al2O3

“…The bulk-(and thus the surface-) structure of c-Al 2 O 3 is a subject of controversy [18][19][20][21][22][23][24][25][26][27][28][29], the essential aspects of which are summarized elsewhere [30][31][32]. Realistic models of high-surface-area c-Al 2 O 3 powders, even in the absence of hydroxylation, may involve a wide variety of different Al and O surface sites as discussed in, for example, Ref.…”