Abstract
27Al MAS n.m.r. spectroscopy, 13C MAS n.m.r. spectroscopy, in situ infrared spectroscopy, and thermogravimetric analysis were employed to study acetylacetone adsorbed on HZSM-5 samples of varying acid-site concentration and extralattice aluminum content. Three types of adsorbed acetylacetone were observed: (1) physisorbed acetylacetone, (2) acetylacetone interacting strongly via the carbonyl groups with acid sites within the zeolite structure, and (3) acetylacetone weakly adsorbed on extralattice aluminum and giving rise to a sharp octahedral aluminum signal observed in the 27Al MAS n.m.r. spectra. The extralattice aluminum acetylacetone species decomposes slowly under ambient laboratory conditions. The implications of these observations to the use of acetylacetone as a means of visualizing “n.m.r. invisible” aluminum are discussed.
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