Oxidation of benzene to phenol by nitrous oxide: Activity of iron in zeolite matrices of various composition Original Research Article

Catalytic properties of Fe introduced in the pentasil type zeolite matrices of various composition (B-ZSM-5, Al-ZSM-5, Ga-ZSM-5, Ti-ZSM-5) have been studied. All the matrices were shown to be inert in the title reaction. However, upon iron introduction they may serve as a basis for the development of very active and selective catalysts. The amount of iron needed for this purpose depends dramatically on the matrix composition: Al-ZSM-5 and Ga-ZSM-5 zeolites exhibit high activity even in the presence of 0.01–0.03 wt.% Fe, while B-ZSM-5 and Ti-ZSM-5 zeolites need a 10–100 times more Fe.The distinctions in zeolite activity relate to the fact that the formation of Fe-containing α-sites, catalyzing the reaction, strongly depends on the Brönsted acidity and proceeds with different efficiency in various matrices. But being formed, α-sites in their catalytic performance have only slight dependence on the matrix composition. Activity of B-ZSM-5, Al-ZSM-5, and Ti-ZSM-5 zeolites is described by a common dependence on the concentration of α-sites, revealing their identity in these matrices. In Ga-ZSM-5 matrix, α-sites exhibit a two to three times higher activity. The role of Fe admixtures in the literature disagreement on the origin of zeolite activity is discussed.