From mesoporous alumina to Pt/Al 2O 3 catalyst: A comparative study of the aluminas synthesis in aqueous medium, physicochemical properties and stability

Abstract

In the present paper are compared the physicochemical properties and stability of mesoporous aluminas synthesized following five routes in which water is the solvent. TEM shows that high pHs lead to heterogeneous materials because of the initial formation of bayerite, which is converted to η-alumina upon calcination and may reappear upon contacting the calcined oxide with water. The most promising procedures use neutral organic additives at moderate pH; materials are homogeneous, with specific surface areas of 350 ± 20 m 2 g −1. The similarity of results obtained for the different routes, whatever the organic additive, suggests that the formation of the precipitated phase occurs not around micelles, but through the formation and sticking of boehmite nanoparticles, mediated by the organic agent present in a molecular form or as aggregates. The different ways to overcome the limits imposed by this mechanism are discussed. The alumina prepared with the addition of glucose is checked to be suitable as support for a Pt/Al 2O 3 catalyst prepared by impregnation with a basic solution.