A combination of quantum chemistry, molecular dynamics and computer graphics methods was applied in the investigation of the adsorption and activation mechanism of methane and NOx molecules on Ga-exchanged ZSM-5 catalyst. For CH4 we found that the initial step is a weak physical adsorption on the Ga site at the distance between gallium and carbon atoms of 2.9 Å and the adsorption energy was -4.9 kcal/mol. In the next step the dissociative adsorption of methane was studied. The dissociated complex with CH3 attached to Ga at 2.0 Å and H bonded to the extraframework oxygen appeared to be very favorable and led to energetic stabilization of -63.0 kcal/mol. Another dissociated adsorption state was found when a hydrogen atom was attached to Ga and CH3 bonded to the extraframework oxygen. In this case stabilization energy was estimated to be -31.4 kcal/mol. Moreover, we described the transition state of methane dissociation. The activation barrier on the Ga site was 31.3 kcal/mol, which means kinetically favorable reaction. For the NOx molecules there is no energy barrier before chemisorption. The adsorption energy for NO and for NO2 were -18.4 and -10.3 kcal/mol, respectively. It is found that NO is slightly, while NO2 is significantly activated. The spin distribution analysis also shows an activated NO2 part after adsorption. It is also observed that the Ga atom becomes stable, tetrahedrally coordinated after each of the adsorption processes.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry