The impact of Si/Al ratio on properties of aluminosilicate aerogels

• Published in: Microporous and mesoporous materials 2017-10, Vol.251, p.105-113
• Main Authors: Shalygin, Anton S., Kozhevnikov, Ivan V., Gerasimov, Evgeny Yu, Andreev, Andrey S., Lapina, Olga B., Martyanov, Oleg N.
• Format: Article
• Language: English
• Subjects: Aerogels; Aluminosilicate; Si/Al ratio; Sol-gel method; Supercritical drying
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2017.05.053

The Si/Al ratio is a key parameter of acid-base, structural, textural and, consequently, catalytic properties of amorphous crystalline (micro- and mesoporous) aluminosilicates. The changes of structural and textural characteristics of Al-Si aerogels with gradual increase of aluminum content are investigated. Aerogels were prepared via sol-gel method using prehydrolysed tetraethoxysilane and aluminium isopropoxide stabilized by acetylacetone. The gelation of the obtained sols took place in the presence of ammonia with the following drying in supercritical isopropanol. It was shown all aluminum reacts with prehydrolyzed tetraethoxysilane forming spherical particles in case the content of Al in the samples is less than 20 mol %. Aluminum drives the increase of interparticle coupling leading to the particle agglomeration, which is associated with the increase of the particle size and decrease of specific surface area and pore volume. For the samples with the aluminum content of >50 mol % the formation of pseudoboehmite plate-like particles is observed. The pseudoboehmite particles prevent the sintering of SiO2 particles that leads to the increase of the aerogel specific surface area and pore volume. In case the high aluminum content (>80 mol %) the silica particles serve as a connector between boehmite plates. The ratio between Brønsted and Lewis acid sites decreases gradually with the increase of aluminum content of the aluminosilicate aerogels. [Display omitted] •Al-Si aerogels has been prepared by two-stage sol-gel method using ammonia for sol gelation.•The first shows the changes in the morphology and texture of A-Si aerogels on the mole ratio of Si/Al from 49 to 0,11.•The aerogel particle vary from amorphous spheres to boehmite plates.•The pseudoboehmite layers (or plates) play the role of antiblocking agent for amorphous spherical particles.