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

Abstract

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 γ-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.

A Novel Synthesis Route of Mesoporous γ-Alumina from Polyoxohydroxide Aluminum

“…This alumina is used as well as a catalyst scaffold allowing the dispersion of several active phases as metals and metallic oxides for important organic reactions and several advanced technological applications [22][23][24][25]7,10,12 . The main precursor for the synthesis of γ-alumina commonly used is the aluminum oxyhydroxide (Boehmite), γ-AlOOH.…”

The impact of nanocrystallite size and shape on phase transformation: Application to the boehmite/alumina transformation

“…Alumina is among the most widely used oxide materials. The c-alumina is of particular interest due to its importance in the preparation of controlled porosity catalysts with enhanced textural, surface and mechanical properties [1,7,8]. This oxide is typically obtained by calcinating aluminum oxyhydroxides (Al 2 O 3 ÁxH 2 O), among which boehmite (c-AlOOH) is the most important precursor material.…”

“…This oxide is typically obtained by calcinating aluminum oxyhydroxides (Al 2 O 3 ÁxH 2 O), among which boehmite (c-AlOOH) is the most important precursor material. Boehmite is easily obtained via aqueous precipitation or the sol-gel route [8,9]. To improve the catalyst support properties, the boehmite crystallite size, shape, sample porosity, and surface area are optimized through the preparation conditions.…”

Ammonium aluminium carbonate hydroxide NH4Al(OH)2CO3 as an alternative route for alumina preparation: Comparison with the classical boehmite precursor

“…Once more, high temperature, high particles concentration and pH value close the boehmite PZC favor strong aggregation. Formation of such fibrous particles has already been observed in literature by TEM [25,26] and can be explained by crystallites oriented aggregation, a common phenomenon for boehmite [24]. It has been recently proposed that sulfate anions absorbed on boehmite play a key role for this oriented aggregation [27].…”