Metal-exchanged carboxylato-alumoxanes and process of making metal-doped alumina

Abstract

A method has been developed for the solution-based metal exchange of carboxylato-alumoxanes [Al(O)x(OH)y(O2CR)z]n with a wide range of metal cations. Metal-exchanged carboxylato-alumoxanes are new, particularly those in which about 10% to about 50% or more of the Al ions are exchanged for other metal ions. Additionally, the carboxylic acid ligands can be stripped from the boehmite core of metal-exchanged carboxylato-alumoxanes at low temperature leading to the formation of metal-exchanged boebmite particles. These new material phases can be used as intermediates for preparation of mixed metal aluminum oxide materials. Thermolysis of the metal-exchanged carboxylato-alumoxanes or metal-exchanged boehmite particles results in doped aluminas (M/Al2O3), binary (MAlOx), ternary (MM′AlOx) and even more complex metal aluminum oxide compounds, where M and M′ are metal ions other than those of aluminum and are preferably those of Lanthanide metals or transition metals. The method allows preparation of pure phase materials as well as the preparation of metastable metal aluminum oxide phases. The carboxylato-alumoxanes are prepared by the reaction of boehmite (or pseudoboehmite) with carboxylic acids in a suitable solvent. Up to at least half of the aluminum cations in the boehmite lattice of the carboxylato-alumoxanes can be replaced by the reaction of metal acetylacetonates with the carboxylato-alumoxane in a suitable solvent. The metal exchange reaction can also be carried out by reaction with soluble metal salts. Reactions of boehmite with the metal acetylacetonates (or soluble metal salts) do not lead to the metal exchange reaction observed for the carboxylato-alumoxanes.

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