Facile Synthesis for Ordered Mesoporous γ-Aluminas with High Thermal Stability

Abstract

The facile synthesis of highly ordered mesoporous aluminas with high thermal stability and tunable pore sizes is systematically investigated. The general synthesis strategy is based on a sol-gel process associated with nonionic block copolymer as templates in ethanol solvent. Small-angle XRD, TEM, and nitrogen adsorption and desorption results show that these mesoporous aluminas possess a highly ordered 2D hexagonal mesostructure, which is resistant to high temperature up to 1000 degrees C. Ordered mesoporous structures with tunable pore sizes are obtained with various precursors, different acids as pH adjustors, and different block copolymers as templates. These mesoporous aluminas have large surface areas (ca. 400 m2/g), pore volumes (ca. 0.70 cm3/g), and narrow pore-size distributions. The influence of the complexation ability of anions and hydro-carboxylic acid, acid volatility, and other important synthesis conditions are discussed in detail. Utilizing this simple strategy, we also obtained partly ordered mesoporous alumina with hydrous aluminum nitrate as the precursor. FTIR pyridine adsorption measurements indicate that a large amount of Lewis acid sites exist in these mesoporous aluminas. These materials are expected to be good candidates in catalysis due to the uniform pore structures, large surface areas, tunable pore sizes, and large amounts of surface Lewis acid sites. Loaded with ruthenium, the representative mesoporous alumina exhibits reactant size selectivity in hydrogenation of acetone, D-glucose, and D-(+)-cellobiose as a test reaction, indicating the potential applications in shape-selective catalysis.

Synthesis, characterization, and catalytic application of highly ordered mesoporous alumina-carbon nanocomposites

“…Previously, we found that hydroxycarboxylic acids (HCA) can complex Al cations and even induce the arrangement of AlOOH particles, just like a structure-directing agent [30]. Following our work, Yan et al used citric acid as an inhibitor for the hydrolysis-condensation process of aluminium species [31]. Via evaporation-induced co-assembly of triblock copolymer and Al-citrate complex, they produced highly ordered mesoporous γ-alumina.…”

“…This result indicates that although the walls of the OMCA nanocomposite are composed of continuous carbon and alumina, aggregation of the highly dispersed alumina particles and their subsequent crystallization will inevitably destroy the mesostructure. According to Yan et al [31], ordered mesoporous γ-Al 2 O 3 with crystalline walls can be prepared by heat treatment at 800-1000 °C , whilst calcination at 1100 °C promotes the transformation of γ-Al 2 O 3 into α-Al 2 O 3 . However, in our case, pyrolysis at 1100 °C still yielded a γ-Al 2 O 3 phase.…”

“…Since the hydrolysis and condensation of aluminum is very complex and difficult to control [30,31], the synthesis of carbonalumina nanocomposites with an ordered mesoporous structure presents a challenge. Previously, Górka and Jaroniec [16] reported a facile method for incorporation of alumina nanoparticles into mesoporous carbon by using an alumina colloid as the aluminum source.…”

“…Herein, we report the synthesis of a new nanocomposite material composed of carbon and alumina, by means of multi-component co-assembly of an alumina sol, resol, and triblock copolymer Pluronic F127. In this work, we used citric acid as a good coordination agent to regulate the hydrolysis-condensation of aluminum species [30,31]. The resulting carbon-alumina nanocomposites possess highly ordered mesoporous structures, and the alumina content in the nanocomposite can be continuously tuned from 10 to 53 wt.%.…”

A comparative study of different fluorine-containing compounds in the preparation of novel alumina binders with rich Brönsted acid sites

“…After calcination at 550°C, both phases were converted to cAl 2 O 3 phase, which is consistent with our previous reported results. [15] Further increasing the calcination temperature to 750°C, the XRD pattern obtained did not show much difference with that obtained at 550°C, which is attributed to the high thermal stability of c-Al 2 O 3 [16]. N 2 adsorption results in Fig.…”