Density functional study on the transition state of methane activation over ion-exchanged ZSM-5

In order to investigate the methane dissociation over Ga-ZSM-5. the transition state of the reaction pathway was determined by density functional calculations (DFT). We revealed that the activation energy is 25.8 kcal/mol and that the chemisorption state in which CH₃ is attached to the Ga³⁺ ion and H forms a hydroxyl group with the extraframework oxygen is the main product. We also investigated the influence of the cluster size on the transition state of methane dissociation. It was shown that [Al(OH)₄]^- can express the trend and is adequate for use to model the zeolytic structure. The transition states of the methane dissociation reaction over Al-ZSM-5 and In-ZSM-5 were also investigated.