nitrogen-dioxide and ceric-oxide

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).

Topics: Cerium; Microscopy, Electron, Transmission; Nitrogen Dioxide; Silicon Dioxide; Temperature; Thermogravimetry; X-Ray Diffraction; Zirconium

First principles calculations using density functional theory with corrections for on-site Coulomb interactions (DFT + U) are presented in which we compute the energy for the conversion of CO to CO(2), NO(2) to NO and NO to N(2) over ceria surfaces. The surface sensitivity is discussed on the basis of the vacancy formation energies.

Topics: Carbon Monoxide; Catalysis; Cerium; Mathematical Computing; Models, Chemical; Nitric Oxide; Nitrogen Dioxide