The impact of surface-impregnated versus support-dispersed Fe in Fe–Ni/γ-Al₂O₃ catalysts for partial oxidation of methane: Insights into the effect of Fe incorporation method on coking and on the reaction mechanism

Two sets of Fe-modified Ni/γ-Al₂O₃ catalysts were prepared and tested in partial oxidation of methane. In one set, Fe was co-impregnated on the surface (NiFe) and in the other set Fe was incorporated in the support bulk (Ni/Fe). The two types showed significantly different coking resistance and performance. While Fe well dispersed in the support bulk significantly enhanced coking resistance, Fe co-impregnated with Ni on the surface enhanced the rate of coke deposition on the catalysts’ surfaces. The impact of Fe in the Ni/Fe catalysts is referred to its partially reduced ions (Fe²⁺) in redox reactions, and to the Ni-support strong interaction retarding the coke formation pathways. On the contrary, carbon formation on the NiFe catalysts is referred to the formation of Ni–Fe alloy particles which may block Ni active sites and can promote cracking of methane as well as CO molecules resulting in higher rates of coking.