Chemistry of NO2 on CeO2 and MgO: Experimental and Theorectical Studies on the Formation of NO3

Published

June 1, 2000

Author(s)

J A. Rodriguez, T Jirsak, S Sambasivan, Daniel A. Fischer, A Maiti

Abstract

In environmental catalysis the destruction or removal of nitrogen oxides (DeNOx process) is receiving a lot of attention. Synchrotron-based x-ray absorption near-edge spectroscopy, high-resolution photoemission, and first-principles density-functional calculations (DFT-GGA) were used to study the interaction of nitrogen dioxide with CeO₂ and MgO. The only product of the reaction of NO₂ with pure CeO₂ at 300 K is adsorbed nitrate. The NO₃ is a thermally stable species which mostly decomposes at temperatures between 450 and 600 K. For the adsorption of NO₂ on partially reduced ceria (CeO_2-x), there is a full decomposition of the adsorbate and a mixture of N, NO and NO₃ coexists on the surface of the oxide at room temperature Ce³⁺ cations can assist in the transformation of NO and NO₂ in DeNOx operations. Adsorbed NO₂ and NO₃ (main product) are observed after exposing MgO to NO₂. A partial NO_2,ads -> NO_3,ads transformation is observed on MgO(100) from 150 to 300 K. DFT-GGA calculations show strong bonding interactions for NO₂ on Mg sites of this surface, and discoordination via O,O is more favarable energetically than monocoordination via N. The NO_2,ads species disappears from magnesium oxide at temperatures below 600 K, whereas part of the NO_3,ads is stable up to temperatures near 800 K. MgO can be very useful as a sorbent for trapping NO₂. A general trend is found after comparing the chemical behavior of NO₂ on different types of oxides (CeO₂, MgO, TiO₂, Fe₂O₃, CuO, ZnO). On all these systems, the main product after adsorbing NO₂ at 300 K is nitrate with minor amounts of chemisorbed NO₂ and no signs of full decomposition of the adsorbate. This trend and the results of DFT-GGA calculations indicate that NO2 is very efficient for the nitration (i.e. formation of NO₃ as a ligand) of metal centers that are missing O neighbors in oxide surfaces.

Citation

Journal of Chemical Times

Volume

112

Issue

No. 22

Pub Type

Journals

Keywords

cerium oxide, intermediates, magnesium oxide, nitorgen oxides, photoemission, soft x-ray, surface science

Citation

Rodriguez, J. , Jirsak, T. , Sambasivan, S. , Fischer, D. and Maiti, A. (2000), Chemistry of NO₂ on CeO₂ and MgO: Experimental and Theorectical Studies on the Formation of NO₃, Journal of Chemical Times (Accessed April 20, 2024)