Influence of lanthanum carbonate phases of Ni/La0.98Sr0.02O x catalyst over the oxidative transformation of methane

This work combines the advantages of ~2 mol.% Sr/La₂O₃ (i.e. La_0.98Sr_0.02O _x ) for OCM (oxidative coupling of methane) with well-dispersed nickel over metal oxides for POM (partial oxidation of methane) to efficiently transform methane to desirable products. The catalysts were prepared by sequential impregnation and characterized by X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, temperature-programmed reduction, temperature-programmed decomposition of carbonates and BET surface area measurements. The aim of this work is to find out not only the effect of the catalyst compositions over the formation and growth of carbonate phases, but also their influence over the transformation oxidative of methane. The La_0.98Sr_0.02O _x – supported Ni catalyst precursors show a strong nickel oxide–lanthana interaction, involving anionic vacancies or structural defects that induce the formation of island-like structure of La_2-x Sr _x NiO₄-type mixed oxide for 2 mol.% Ni/La_0.98Sr_0.02O _x . Higher nickel composition facilitates the formation of LaNiO₃. Surface lanthanum hydroxycarbonate formation is probably associated with a conjugated effect between lanthanum oxide and oxidized nickel phases. For high-nickel amount containing catalysts, carbonate-enriched La₂(OH)_6-2x (CO₃) _x as intermediate phase in methane reforming reaction is proposed. For low nickel composition (i.e. 2%), partial oxidation of methane could follow predominantly the pyrolysis mechanism. In which, carbon monoxide is the direct product and carbon dioxide is subsequently formed from carbon monoxide oxidation.