ALUMINUM COMPLEXES IN PARTIALLY HYDROLYZED AQUEOUS ALCL3 SOLUTIONS USED TO PREPARE PILLARED CLAY CATALYSTS

Quantitative Al-27 nuclear magnetic resonance (NMR) spectroscopy was u sed to examine the partial hydrolysis with NaOH (OH/Al = 1.5, 2.0, 2.2 5, 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 ce ntre of the tridecamer [AlO4Al12(OH)24(OH2)12]7+, or Al13, was monitor ed to evidence the formation and decomposition of this cluster cation (a commonly used intercalant for interlayered clay minerals). The maxi mum amount of Al13 forms just after a turbid solution becomes clear (c a. 4 h at 353 K). After two days ageing, Al13 is largely transformed i nto Al24O72 (a 'defective' Al13 dimer). This preparation and ageing me thod is reproducible. An indirect method for verifying Td-Al substitut ion, knowing Al13 decomposition kinetics, is proposed.