STRUCTURAL AND ACIDIC CHARACTERIZATION OF NIOBIA AEROGELS

A niobia (Nb2O5) gel was prepared by the hydrolysis and condensation of niobium pentaethoxide and subsequently dried by supercritical extraction with carbon dioxide to produce an aerogel. The structural and acidic properties of this aerogel heat-treated at different temperatures were characterized by surface area measurements, X-ray diffraction, Raman spectroscopy, n-butylamine titration, pyridine adsorption, and 1-butene isomerization. These results were then compared to those of a niobia xerogel, a precipitated niobia, and a commercial niobic acid. The synthetic route to produce the aerogel was found to stabilize a porous network consisting of NbO6 octahedra with NbO bonds which gave rise to strong Lewis acid sites. Steady-state activity and selectivity data of 1-butene isomerization suggested that all niobia samples possessed comparable Brønsted acidity. © 1992.