The reaction mechanism for the Selective Catalytic Reduction (SCR) of NO
by NH3 on V2O5 surface was simulated by means of density functional theory
(DFT) calculations performed at B3LYP/6-31G** level.
As the initiation reaction, ammonia activation on V2O5 was investigated.
Coordinate driving calculations showed that ammonia is adsorbed on Brø / nsted
acidic V-OH site as NH4
+ species by a nonactivated process with a relative energy
of -23.6kcal/mol. Vibration frequencies were calculated as 1421, 1650, 2857 and
2900cm-1 for the optimized geometry, in agreement with the experimental
literature. Transition state with a relative energy of -17.1kcal/mol was also
obtained. At the end of the Lewis acidic ammonia interaction calculations, it was
observed that ammonia is hardly adsorbed on the surface. Therefore, it is
concluded that the SCR reaction is initiated more favorably by the Brø / nsted
acidic ammonia adsorption.
As the second step of the SCR reaction, NO interaction with the
preadsorbed NH4
+ species was investigated. Accordingly, NO interaction results
in the formation of gas phase NH2NO molecule with a relative energy difference
of 6.4kcal/mol.
For the rest of the reaction sequence, gas phase decomposition of NH2NO
was considered. Firstly, one of the hydrogen atoms of NH2NO migrates to
oxygen. It then isomerizes in the second step. After that, the reaction proceeds
with the isomerization of the other hydrogen. Finally, a second hydrogen atom
migration to the oxygen leads to the formation of N2 and H2O. Total relative
energy for this reaction series was obtained as -60.12kcal/mol, in agreement
with the literature.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/4/1090430/index.pdf |
| Date | 01 January 2003 |
| Creators | Uzun, Alper |
| Contributors | Onal, Isik |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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