Interactions of NO2 at ambient temperature with cerium-zirconium mixed oxides supported on SBA-15.

New silica-based composites were obtained using a slow precipitation of mixed oxide Ce(1-x)Zr(x)O(2) on the surface of mesoporous silica, SBA-15. The samples were tested as NO(2) adsorbents in dynamic conditions at room temperature. The surface of the initial and exhausted materials was characterized using N(2) sorption, XRD, TEM, potentiometric titration, and thermal analysis before and after exposure to NO(2). In comparison with unsupported Ce(1-x)Zr(x)O(2) mixed oxides, a significant increase in the NO(2) adsorption capacity was observed. This is due to the high dispersion of active oxide phase on the surface of SBA-15. A linear trend was found between the NO(2) adsorption capacity and the amount of Zr(OH)(4) added to the structure. Introduction of Zr(4+) cations to ceria contributes to an increase in the amount of Ce(3+), which is the active center for the NO(2) adsorption, and to an increase in the density of -OH groups. These groups are found to be involved in the retention of both NO(2) and NO on the surface. After exposure to NO(2), an acidification of the surface caused by the oxidation of the cerium as well as the formation of nitrite and nitrates took place. The structure of the composites appears not to be affected by reactive adsorption of NO(2).