A homogeneously dispersed silica dopant for control of the textural and structural evolution of an alumina aerogel

• Published in: Catalysis today Vol. 43; no. 1; pp. 51 - 67
• Main Authors: Miller, James B., Ko, Edmond I.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 13.08.1998; Elsevier Science
• Subjects: Alumina aerogels; Chemistry; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Penta-coordinated aluminum; Silica-doped alumina; Silica-doped alumina; Alumina aerogels; Penta-coordinated aluminum; BET method; Aerogel; Doping; Differential thermal analysis; NMR spectrometry; Experimental study; X ray diffraction; Precursor; Silica; Pore size; Alkoxide; Alumina; Crystalline structure
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/S0920-5861(98)00134-5

We have prepared pure alumina and silica-doped alumina (9:1 Al:Si atom ratio) aerogels by supercritical drying of monolithic alcogels formed by slow, sub-stoichiometric (H 2O:Al=2.2) hydrolysis of solutions of alkoxide precursors (aluminum s-butoxide and tetraethyl orthosilicate) in s-butanol. Both aerogels were X-ray indifferent over a large temperature range, first ordering as the η transition form upon calcination at 1173 K. The silica dopant retarded sintering of the aerogel, thereby enhancing its surface area and delaying crystallization of α-alumina from 1373–1473 K. Silica did not, however, affect the surface-chemical properties of the X-ray amorphous alumina; both aerogels were inert to pyridine adsorption and butene isomerization probes at 523 K. Stabilization of structure and texture without alteration of surface-chemical properties is a result of the high dispersion of the silica dopant throughout the aerogel's bulk. Incorporation of silicon atoms into the growing pre-alumina network facilitates their insertion into vacancies in the transition alumina structure, thereby restricting lattice diffusion as a route for crystallization of the α phase.