Effect of extra-framework gallium on the structure of iron species in Fe/ZSM-5

A series of Fe/Ga-ZSM-5 catalysts with different Ga contents were prepared by solid-state ion exchange method. Ultraviolet and visible Raman spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, H2-temperature-programmed reduction, and N2O decomposition at 523 K were used to investigate the effect of extra-framework Ga on the nature of the Fe species in Fe/Ga-ZSM-5 catalysts. Introducing extra-framework Ga and high-temperature treatment can significantly affect the distribution even the nature of the Fe species in Fe/Ga-ZSM-5. For the high-temperature treated catalysts, the presence of extra-framework Ga remarkably increases the amount of the Fe(II) sites and the activity of direct N2O decomposition, suggesting that extra-framework Ga can promote the formation of the active sites for N2O decomposition. The possible interpretation of the beneficial role of extra-framework Ga is that extra-framework Ga facilitates the reduction of bi- and oligo-nuclear Fe(III) sites to form the Fe(II) sites and interacts with the Fe sites with low nuclearity to form a mixed Fe–Ga–O phase for the high-temperature treated catalysts.