Control of the textural properties of nanocrystalline boehmite (γ-AlOOH) regarding its peptization ability

Kneading-extrusion is a key shaping process, especially used to prepare extrudates for catalytic applications. It usually involves several successive steps, mainly used to control textural properties such as pore diameter and pore volume of gamma-alumina catalyst supports. The ability to successfully tune these properties is highly dependent on the boehmite precursor features. This work aims at understanding the influence of the peptization and neutralization steps on the textural properties of boehmite exhibiting similar crystallite size and shape but different peptization abilities. Three kinds of boehmite (low, medium and high peptization ability) obtained either by precipitation or by alkoxide hydrolysis were subjected to a peptization and neutralization steps in order to simulate the full shaping process of kneading extrusion. After peptization and neutralization, no significant changes were found in crystallite shape and size, but only in their spatial arrangement. For the boehmite exhibiting the lowest peptization ability, the particle packing seems to be frozen and no modifications result from peptization or neutralization. However for boehmite with the medium peptization ability, obtained by precipitation from the same precursors as the low peptizable sample, the particles were initially poorly organised and their spatial packing was very affected by the peptization and neutralization phases, giving a narrower pore size distribution than the synthesized powder. Though the third boehmite, obtained by alkoxide hydrolysis, was fully peptizable, this does not allow tailoring the textural properties, whatever the phase of the shaping process. Finally the partially peptizable boehmite seems to be the most versatile starting material for the control of the textural properties. (C) 2013 Elsevier B.V. All rights reserved.