Obtaining aluminas from the thermal decomposition of their different precursors: An 27Al MAS NMR and X-ray powder diffraction studies

• We synthesized three precursors of alumina from different methods.
• The calcination of the precursors generated several alumina polymorphs.
• XRD and NMR were used for structural investigation of the polymorphs.
• The synthesis route determines the structural and textural properties of the solids.

A commercial sample of Boehmite was used as precursor of alumina polymorphs. For comparison, three other precursors were synthesized from different methods. Particularly, the use of excess of urea promoted a very crystalline form of basic aluminum carbonate. The characteristics of the four precursors were investigated by thermal, vibrational and X-ray powder diffraction (XRD) analysis. Additionally, the nuclear magnetic resonance, with magic angle spinning (27Al MAS NMR), was used to verify the coordination of aluminum cations. Each precursor was calcined at various temperatures generating alumina polymorphs, which were structurally analyzed by XRD and 27Al MAS NMR. Due to interest in catalysis supports, special attention was given to the γ-Al2O3 phase, which in addition to structural investigation was subjected to textural analysis. The results showed that, from different synthesis procedures and common route of calcination, one can obtain materials with the same composition but with different structural and textural properties, which in turn can significantly influence the performance of a supported catalyst.

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