Chemistry of NO{sub 2} on CeO{sub 2} and MgO: Experimental and theoretical studies on the formation of NO{sub 3}
- Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973 (United States)
- National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973 (United States)
- Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
- Molecular Simulations Inc., 9685 Scranton Road, San Diego, California 92121 (United States)
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 CeO{sub 2} and MgO. The only product of the reaction of NO{sub 2} with pure CeO{sub 2} at 300 K is adsorbed nitrate. The NO{sub 3} is a thermally stable species which mostly decomposes at temperatures between 450 and 600 K. For the adsorption of NO{sub 2} on partially reduced ceria (CeO{sub 2-x}), there is full decomposition of the adsorbate and a mixture of N, NO, and NO{sub 3} coexists on the surface of the oxide at room temperature. Ce{sup 3+} cations can assist in the transformation of NO and NO{sub 2} in DeNOx operations. Adsorbed NO{sub 3} (main product) and NO{sub 2} are detected after exposing MgO to NO{sub 2} gas. A partial NO{sub 2,ads}{yields}NO{sub 3,ads} transformation is observed on MgO(100) from 150 to 300 K. DFT-GGA calculations show strong bonding interactions for NO{sub 2} on Mg sites of this surface, and dicoordination via O, O is more favorable energetically than monocoordination via N. The NO{sub 2,ads} species disappears from magnesium oxide at temperatures below 600 K, whereas part of the NO{sub 3,ads} is stable up to temperatures near 800 K. MgO can be very useful as a sorbent for trapping NO{sub 2}. A general trend is found after comparing the chemical behavior of NO{sub 2} on different types of oxides (CeO{sub 2}, MgO, TiO{sub 2}, Fe{sub 2}O{sub 3}, CuO, ZnO). On all these systems, the main product after adsorbing NO{sub 2} at 300 K is nitrate with minor amounts of chemisorbed NO{sub 2} and no signs of full decomposition of the adsorbate. This trend and the results of DFT-GGA calculations indicate that NO{sub 2} is very efficient for the nitration (i.e., formation of NO{sub 3} as a ligand) of metal centers that are missing O neighbors in oxide surfaces. (c) 2000 American Institute of Physics.
- OSTI ID:
- 20216530
- Journal Information:
- Journal of Chemical Physics, Vol. 112, Issue 22; Other Information: PBD: 8 Jun 2000; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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