Calcination products of gibbsite studied by X-ray diffraction, XPS and solid-state NMR

The changes caused by heat treatment of gibbsite powder at 300–1473 K were studied using the X-ray diffraction (XRD), X-ray photoemission (XPS) spectra and 27Al magic angle spinning nuclear magnetic resonance spectroscopy (27Al MAS NMR). XRD analysis indicates that the transformation sequence involves the formation of κ-Al2O3 as an intermediate phase between χ- and α-Al2O3. The crystallite size of χ-Al2O3 is as small as 10 nm. XPS analysis indicates that the ratio of aluminium atoms to oxygen atoms in χ-Al2O3 and κ-Al2O3 increases, whereas the expected ratio is observed in α-Al2O3. The percentage of AlO4 units in the transition aluminas follows the same behaviour as the ratio of Al/O. - Graphical abstract: The percentage of AlO4 units in transition aluminas follows the same behaviour as the ratio of Al/O. - Highlights: • Calcination products of gibbsite studied by XRD, XPS and solid-state NMR. • The crystallite size of χ-Al2O3 is as small as 10 nm. • The Al/O atomic ratio determined by XPS is larger than 2/3 in χ-Al2O3 and κ-Al2O3. • The percentage of AlO4 in the aluminas follows the same behaviour as the Al/O atomic ratio