Nanocrystalline Mesoporous γ-Alumina Powders “UPMC1 Material” Gathers Thermal and Chemical Stability with High Surface Area

Abstract

The designed elaboration of alumina sub-micrometric spherical powder that combines 3D ordered mesoporosity of high accessibility, nanocrystalline structure, and thermal stability up to 900 °C is reported. The strategy used to elaborate such new materials labeled “UPMC1” involves specific block-copolymer templating, aluminum sol−gel chemistry, tuned aerosol generation (spray drying), and sequential thermal treatments that allow designing of a whole set of mesoporous catalytic supports by adjusting ceramization conditions between 700 and 900 °C. When calcination temperature reaches 700 °C, the network remains amorphous and displays structural features of highly porous materials (i.e., porosity, 0.56 cm3·g-1; surface area, 403 m2·g-1; well-calibrated pore diameter, 13 nm). After 30 min at 900 °C, crystallization into γ-Al2O3 particles of around 6 nm has occurred, which has modified the network characteristics (i.e., porosity, 0.34 cm3·g-1; surface area, 134 m2·g-1; well-calibrated pore diameter, 12.5 nm) without destroying the mesostructure. Both amorphous and crystalline final materials present the remarkable properties of mesoporous materials with the unique amphoteric properties of the γ-alumina surface (40% of tetragonal acid sites) that have great potential application in catalysis, in environment, and as an adsorbent. The present work points out that ordered mesoporosity has the ability to stabilize materials with amorphous or metastable crystalline structure at higher temperatures than what is observed for nonordered mesoporous analogous systems. Such a phenomenon is discussed on the basis of extensive materials characterization mainly based on TEM, XRD, and 29Al high-resolution solid-state NMR.

Filter and buffer-pot confinement effect of hollow sphere catalyst for promoted activity and enhanced selectivity

“…23 This is a typical H-2 shaped hysteresis loop, suggesting clear pore connectivity with uniform ink-bottle like pores. This type of pores further conrmed the presence of huge cavities which could only be accessed through entrances smaller than several nanometers, 24 well consistent with SEM and TEM surface rendering.…”

Aerosol Route to Functional Nanostructured Inorganic and Hybrid Porous Materials

“…[ 157 ] By contrast, the successful preparation of large mesopores γ -alumina mesostructured powder was reported in 2006 by using a [E(B) 75 ]-[EO] 86 block copolymer called KLE which hydrophobic block is stable up to 300 ° C. [ 60 ] In this latter case, the use of thermally stable structuring agents allowed limiting the massive contraction of inorganic matrix observed during the dehydration of AlOOH in Al 2 O 3 . [ 158 ] As a consequence, after calcinations at 700 ° C, the produced Al 2 O 3 materials (cf.…”

“…Following the one-pot procedure, four main types of organic or hybrid components were introduced in mesostructured microparticles: (i) fl uorescent dyes (rhodamine B, [ 41 ] phenanthroline Eu 3 + /Tb 3 + complexes, [ 63 ] photoacid generator and the pH-sensitive dye dimethyl yellow, [ 63 ] photochromic dyes Figure 11 . TEM pictures of a) Al 2 O 3 [ 60 ] and b) ZrO 2 [ 154 ] mesostructured powders calcined at 700 ° C and 500 ° C respectively. [ 60 ] Copyright 2006, American Chemical Society.…”

Mesoporous transition alumina with uniform pore structure synthesized by alumisol spray pyrolysis

“…In contrast to morphology, the porosity of alumina prepared by spray methods has received little attention. Boissière et al [29] applied the spray drying method to prepare alumina mesoporous spheres using AlCl 3 ·6H 2 O as the Al precursor and [E(B)] 75 -[EO] 86 block copolymer as the templating agent. Additionally, Kim et al [30] prepared mesoporous alumina particles via spray pyrolysis using Al(NO) 3 ·9H 2 O and cetyltrimethylammonium bromide (CTAB) as the Al precursor and pore directing agent, respectively.…”