Abstract
Vanadia has been grafted on high surface area titania–silica, titania and silica aerogels prepared using the sol–gel method and ensuing drying by extraction with supercritical CO 2. The aerogels exhibited favourable textural properties (high surface area combined with dominant mesoporosity) and the capability to stabilise vanadia in a well-dispersed form up to high loadings. Titania aerogel with a BET-surface area of 165 m 2 g −1 proved to be the most suitable support for vanadia affording excellent activity for the selective catalytic reduction (SCR) of NO by NH 3 at low temperature (400 K). With titania–silica aerogels, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicated a preferential deposition of vanadia on Ti sites at low vanadia loading. SCR activities were found to depend mainly on the vanadia loading and the support material. High loadings of dispersed vanadia (6–10 μmol m −2) were favourable on all aerogel supports. Vanadia grafted on titania aerogel was superior in activity compared to vanadia deposited on the other aerogels. V 2O 5–SiO 2 as well as V 2O 5–TiO 2–SiO 2 catalysts showed significant deactivation at temperatures ca. >500 K. Deactivation of vanadia deposited on TiO 2–SiO 2 could be avoided at loadings ca. >6 μmol m −2. Deactivated catalysts showed a decrease in both Brönsted as well as Lewis sites, as revealed by desorption studies after exposure to SCR conditions.
Published Version
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