Effect of transition metal on stability and activity of La-Ca-M-(Al)-O (M = Co, Cr, Fe and Mn) perovskite oxides during partial oxidation of methane

Abstract

Perovskite oxides of the type of LaxCa1-xMyAl1-yO3-δ (M = Co, Cr, Fe, Mn; x = 0.5; y = 0.7–1.0) were prepared using the polymerization methods and evaluated via N2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), energy dispersive X-ray (EDX) spectroscopy, temperature-programmed reduction by hydrogen (TPR-H2) and temperature-programmed oxidation by oxygen (TPO-O2). Catalytic behaviour of the perovskite oxides during methane oxidation was studied using a tubular fixed-bed reactor. In a partial oxidation, which proceeded in two steps, there was total oxidation in the first step and CO2 and H2O were formed; in the second step, the total oxidation products oxidized methane by (dry and wet) reforming reactions to yield CO and H2. Total oxidation and the two reforming reactions proceeded on two types of an active centre formed by transition metal ions, oxygen vacancies and oxide ions. The catalytic system La-Ca-Co-Al-O which contained aluminium, decomposed in partial oxidation of methane (POM) into a composite that contained firmly bonded cobalt nanoparticles in the surface of a substrate made up of La2O3, CaO and Al2O3 which catalysed POM with a high methane conversion and hydrogen selectivity.