The role of aluminum in atomically dispersed M(Fe, Co, Ni, Cu)/ZSM-5 catalysts for methane selective oxidation

Abstract

Transition metal-containing ZSM-5 has proven effective as a catalyst for the selective oxidation of methane under mild conditions. However, the diversity of catalytic sites hinders the efficient and highly selective conversion of methane. This study investigates the role of Al sites in ZSM-5 in influencing the formation and stability of active species at the atomic level. Using Fe-based zeolites as the main object of study, detailed spectroscopic analysis combined with density functional theory (DFT) calculations showed that framework Al can reduce the dispersion resistance of exogenous Fe_xO_y particles, prevent the agglomeration of Fe species during annealing, and maximize atomically dispersed Fe as the active sites. Furthermore, the ligand structure, which interacts strongly with the active metal, provides suitable acid sites to promote surface *OOH generation, leading to higher HCOOH productivity. The optimized catalyst achieved a yield of 44.2 mmol•g_cat⁻¹•h⁻¹ and 91.5 % selectivity of liquid oxygenate products, which was 4.5 times higher than that of the catalyst without Al sites. The formation of isolated Co, Ni, and Cu active sites is equally facilitated by the presence of Al.