Reaction Mechanisms of H2 Reduction and N2O Decomposition on Fe/ZSM-5 Zeolite: A Density Functional Theoretical Study

The Fe/ZSM-5 catalysts are usually prepared with H-2 pretreatment. In this work, the reaction mechanisms of H-2 reduction and N2O decomposition on Fe/ZSM-5 zeolite were studied with B3LYP density functional calculations, Before reduction, the vertical H-2 adsorption mode oil the high-spin Fe(III)/ZSM-5 zeolite must transform into the parallel mode, which is almost barrierless. Both high- and low-spin Fe(III)/ZSM-5 zeolites play an important role during the H-2 reduction processes; in addition, Fe(III)/ZSM-5 zeolite is readily reduced by H-2 pretreatment at moderate temperatures, because the ZPE-corrected energy barriers of the high- and low-spin states equal 46.22 and 18.61 kJ mol(-1), respectively. Albeit with large H-2 adsorption energies, Fe(III)/ZSM-5 zeolite may not be Suitable for H-2 Storage due to the difficulty of releasing the H-2 molecules. On the H-2-reduced Fe(II)/ZSM-5 zeolite, the energy barrier of N2O decomposition was calculated at 117.77 kJ mol(-1), which is less than those of the high- and low-spin Fe(III)/ZSM-5 zeolites. In Fe(III)/ZSM-5 zeolite, the high-spin state predominates the N2O decomposition process due to the higher structural stabilities, where the ZPE-corrected energy barrier is equal to 148.14 kJ mol(-1) and in good agreement with the previous data. Accordingly, the N2O decomposition reactions are facilitated by H-2 pretreatment. In addition, the "alpha-oxygen" species produced by N2O decomposition over the reduced Fe(II)/ZSM-5 zeolite should be responsible for the reaction activities of the monoiron species.