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

Abstract

New silica-based composites were obtained using a slow precipitation of mixed oxide Ce1−xZrxO2 on the surface of mesoporous silica, SBA-15. The samples were tested as NO2 adsorbents in dynamic conditions at room temperature. The surface of the initial and exhausted materials was characterized using N2 sorption, XRD, TEM, potentiometric titration, and thermal analysis before and after exposure to NO2. In comparison with unsupported Ce1−xZrxO2 mixed oxides, a significant increase in the NO2 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 NO2 adsorption capacity and the amount of Zr(OH)4 added to the structure. Introduction of Zr4+ cations to ceria contributes to an increase in the amount of Ce3+, which is the active center for the NO2 adsorption, and to an increase in the density of –OH groups. These groups are found to be involved in the retention of both NO2 and NO on the surface. After exposure to NO2, 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 NO2.