Pore structure stabilization during the preparation of single phase ordered macroporous α-alumina

Abstract

Ordered porous materials are highly relevant for applications in fields such as catalysis, adsorption and chromatography. Strategies such as soft and hard templating are now routinely applied to prepare for instance ordered mesoporous silica. In other cases, most notably when several polymorphic phase transformations are involved, achieving high quality ordered oxides is challenging. We present a strategy for the preparation of ordered macroporous α-alumina with a high degree of pore order. The preparation is based on impregnation of ordered polymeric spheres with an alumina precursor. Most notably it involves a first heating step in inert atmosphere, leading to conversion of the polymeric template into carbon effectively delaying the phase transitions and stabilizing the pore structure up to high temperatures. A subsequent heat treatment in oxidative atmosphere then removes the carbon and ordered marcoporous α-alumina is obtained with circa 220 nm cages interconnected by windows of circa 105 nm, and a specific surface area of circa 25 m2 g−1. Our method led to a strong preservation of the long-range order of the pore structure, as not only evidenced by electron microscopy, but also quantified by spectroscopy. High surface area α-alumina is of particular interest as a catalyst support, but the preparation method might also be extended to other ordered macroporous oxides that are difficult to prepare due to phase transitions such as TiO2.