title: Phase progression of γ-Al2O3 nanoparticles synthesized in a solvent-deficient environment.
abstract: Our simple and uniquely cost-effective solvent-deficient synthetic method produces 3-5 nm Al2O3 nanoparticles which show promise as improved industrial catalyst-supports. While catalytic applications are sensitive to the details of the atomic structure, a diffraction analysis of alumina nanoparticles is challenging because of extreme size/microstrain-related peak broadening and the similarity of the diffraction patterns of various transitional Al2O3 phases. Here, we employ a combination of X-ray pair-distribution function (PDF) and Rietveld methods, together with solid-state NMR and thermogravimetry/differential thermal analysis-mass spectrometry (TG/DTA-MS), to characterize the alumina phase-progression in our nanoparticles as a function of calcination temperature between 300 and 1200 °C. In the solvent-deficient synthetic environment, a boehmite precursor phase forms which transitions to γ-Al2O3 at an extraordinarily low temperature (below 300 °C), but this γ-Al2O3 is initially riddled with boehmite-like stacking-fault defects that steadily disappear during calcination in the range from 300 to 950 °C. The healing of these defects accounts for many of the most interesting and widely reported properties of the γ-phase.
authors.affiliation: Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, United States.
authors.forename: Stacey J
authors.initials: SJ
authors.lastname: Smith
authors.forename: Samrat
authors.initials: S
authors.lastname: Amin
authors.forename: Brian F
authors.initials: BF
authors.lastname: Woodfield
authors.forename: Juliana
authors.initials: J
authors.lastname: Boerio-Goates
authors.forename: Branton J
authors.initials: BJ
authors.lastname: Campbell