First-principle studies on the exceptionally active triplet oxygen species in microporous zeolite materials: Reservation and catalysis

Density functional theory calculations were used to explore the reservation and catalytic properties of the exceptionally active triplet oxygen species in microporous ZSM-5 zeolite. It was found that the triplet oxygen species in H-form ZSM-5 zeolite can be reserved in the form of the more stable singlet oxygen species commonly found in solid-state materials, and moreover the single oxygen species is facile to be photolyzed into the triplet oxygen species without destructions to zeolite frameworks. It thus provides a route to store the triplet oxygen species ready for catalytic uses. On the contrary, the metal-exchanged ZSM-5 zeolites are proven to be unsuitable reservoirs to the triplet oxygen species due to the comparable instability of the singlet species. The activation barrier of methane hydroxylation catalyzed by the triplet oxygen species in H-form ZSM-5 zeolite was calculated to be 7.12 kcal mol−1, which is much lower than that in Fe-exchanged ZSM-5 zeolite and will proceed at room temperature. Combined with the previous results, it was shown that the triplet oxygen species anchored by the isolated Brönsted acidic sites in H-form ZSM-5 zeolite are potentially excellent oxidants for varieties of important processes.