SYNTHESIS AND CHARACTERIZATION OF NIOBIA-CONTAINING AEROGELS

Niobium ethoxide was used as a precursor either by itself to impregnate a silica aerogel or in conjunction with tetraethyl orthosilicate to produce a mixed oxide aerogel. In contrast with bulk niobia, niobia in these samples did not crystallize into the high-temperature form even after calcination at 1273 K. Niobia-silica interactions, which apparently stabilized niobia from crystallization, also introduced acidity as shown by n-butylamine titration and infrared study of pyridine adsorption. Furthermore, niobia on silica was found to have stronger Bronsted acid sites than niobia in silica, in agreement with previous observations on samples prepared with more conventional methods. All these samples were also active in the isomerization of 1-butene.