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Structure and energetics of nitrous oxide and methane adsorption on the FE-ZSM-5 zeolite: Oniom and density functional studies
Author(s)
Pabchanda, S.
Pantu, P.
Tantanak, D.
Limtrakul, J.
Date Issued
January 1, 2004
Type
Conference Paper
Abstract
The quantum cluster and ONIOM methods have been used to investigate interactions between adsorbed nitrous oxide and methane on the active iron center in Fe-ZSM-5, prior to its catalytic oxidation to methanol. A model of mononuclear iron complex as an active site of the highly dispersed state of Fe-ZSM-5 was adopted in cluster models of 5T quantum cluster and 46T ONIOM2. The extended crystal framework included in the ONIOM model significantly enhances the interactions of both adsorbates with the active site. The adsorption energy of N2O on Fe-ZSM-5 calculated by the 5T quantum cluster is only -41.2 kJ/mol, whereas, the 46T ONIOM model gives the adsorption energy of -57.3 kJ/mol, which is comparable to the experimental estimate of -67 kJ/mol. After correction with single point calculation at MP2/6-31G**:UFF//B3LYP/ 6-31G**:UFF, the adsorption energy is calculated to be 66.9 kJ/mol, which is apparently identical to the experimental estimate. The ONIOM2 model also predicts the adsorption energy of -30.5 kJ/mol for the [CH4]/Fe-ZSM-5 complexes. These results demonstrate that the adsorption properties of Fe-ZSM-5 depend significantly on the specific environment of the zeolite crystal lattice.
Citation
Studies in Surface Science and Catalysis, 154 B, 1844-1848, 2004