DFT Study of Direct Methanol Oxidation to Formaldehyde by N2O on the [Fe]2+-ZSM-5 Zeolite Cluster

The mechanistic pathways of direct oxidation of methanol to formaldehyde by N2O were theoretically investigated by means of density functional theory (DFT) over an extra framework species in ZSM-5 zeolite represented by a [Si6Al2O9H14](2-)[Fe](2+) cluster model. The catalytic reactivity of these species is compared with that of mononuclear Fe1+ and (FeO)(1+) sites in ZSM-5 investigated in our earlier work at the same level of theory (J. Catal. 2011, 282, 191). The formation of the grafted species including methoxy on the [Fe](2+) site was calculated to be thermodynamically more stable than on the [FeO](1+) site and less stable than on the [Fe](1+) site. The order of activation barrier values of a critical step, proton transfer from grafted methoxy to form formaldehyde and water, on these sites is as follows: [Fe](1+) > [Fe](2+) >> [FeO](1+). The calculated vibrational frequencies for grafted species on the iron site on the surface are in good agreement with the experimental values.