Aluminum complexes in partially hydrolyzed aqueous A1C13 solutions used to prepare pillared clay catalysts Original Research Article

Quantitative 27Al nuclear magnetic resonance (NMR) spectroscopy was used to examine the partial hydrolysis with NaOH (OH/A1= 1.5, 2.0, 2.25, 2.5), and subsequent ageing at 353 K, of aqueous AlCl3 (0.25 mol dm−3). The sharp resonance of the tetrahedral aluminum (Td-Al) at the centre of the tridecamer [AlO4Al12(OH)24(OH2)12]7+, or Al13, was monitored to evidence the formation and decomposition of this cluster cation (a commonly used intercalant for interlayered clay minerals). The maximum amount of Al13 forms just after a turbid solution becomes clear (ca. 4 h at 353 K). After two days ageing, Al13 is largely transformed into A124O72 (a ‘defective’ Al13 dimer). This preparation and ageing method is reproducible. An indirect method for verifying Td-Al substitution, knowing Al13 decomposition kinetics, is proposed.