AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP34
DeNOx Reactions on MgO(100): Photoemission and Density Functional Studies

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: T. Jirsak, Brookhaven National Laboratory
Authors: T. Jirsak, Brookhaven National Laboratory
J.Z. Larese, Brookhaven National Laboratory
A. Maiti, Molecular Simulations Inc.
J.A. Rodriguez, Brookhaven National Laboratory
Correspondent: Click to Email
In environmental catalysis the destruction or removal of nitrogen oxides (DeNOx process) is receiving a lot of attention. Nitrogen oxides (NO and NO@sub 2@) are formed in automotive engines and industrial combustion systems. Metal oxides can be useful in the control of environmental pollution. It has been found that MgO has the ability of trapping the NO@sub 2@ formed in automotive engines during the burning of fuels under oxygen-rich conditions. Synchrotron-based photoemission and first-principles density-functional calculations (DF-GGA) have been used to study the chemistry of NO and NO@sub 2@ on MgO(100). NO is weakly adsorbed on the oxide surface. On flat MgO(100), DF results predict an NO adsorption energy of 6 kcal/mol, which is close to the value of 5 kcal/mol observed experimentally. At steps of the surface, NO interacts with tetra- and penta-coordinated Mg atoms and the adsorption energy can increase to 9 kcal/mol. On MgO@sub 1-x@, O vacancies and defect sites enhance the bonding energy of NO, and lead to the production of N@sub 2@O at 100 K plus the deposition of N above 200 K. NO@sub 2@ is very reactive on terraces and steps of MgO(100). Adsorbed NO@sub 3@ and NO@sub 2@ are detected after exposing the oxide to NO@sub 2@ at 150 K. Strong bonding interactions between Mg sites and NO@sub 3@ favor disproportionation of adsorbed NO@sub 2@. The large differences in the reactivity of NO and NO@sub 2@ reflect the fact that nitrogen dioxide is a much better electron acceptor. The role of metal promoters (K,Cs,Cr,Ni) on DeNOx operations on MgO will be discussed.