Selective oxidation of methane and carbon deposition over Fe2O3/Ce1−x Zr x O2 oxides

Abstract

A series of Fe2O3/Al2O3, Fe2O3/CeO2, Ce0.7Zr0.3O2, and Fe2O3/Ce1−x Zr x O2 (x = 0.1–0.4) oxides was prepared and their physicochemical features were investigated by X-ray diffraction (XRD), transmission electron microscope (TEM), and H2-temperature-programmed reduction (H2-TPR) techniques. The gas–solid reactions between these oxides and methane for syngas generation as well as the catalytic performance for selective oxidation of carbon deposition in O2-enriched atmosphere were investigated in detail. The results show that the samples with the presence of Fe2O3 show much higher activity for methane oxidation compared with the Ce0.7Zr0.3O2 solid solution, while the CeO2-contained samples represent higher CO selectively in methane oxidation than the Fe2O3/Al2O3 sample. This suggests that the iron species should be the active sites for methane activation, and the cerium oxides provide the oxygen source for the selective oxidation of the activated methane to syngas during the reaction between methane and Fe2O3/Ce0.7Zr0.3O2. For the oxidation process of the carbon deposition, the CeO2-containing samples show much higher CO selectivity than the Fe2O3/Al2O3 sample, which indicates that the cerium species should play a very important role in catalyzing the carbon selective oxidation to CO. The presence of the Ce–Zr–O solid solution could induce the growth direction of the carbon filament, resulting in a loose contact between the carbon filament and the catalyst. This results in abundant exposed active sites for catalyzing carbon oxidation, strongly improving the oxidation rate of the carbon deposition over this sample. In addition, the Fe2O3/Ce0.7Zr0.3O2 also represents much higher selectivity (ca. 97 %) for the conversion of carbon to CO than the Fe2O3/CeO2 sample, which can be attributed to the higher concentration of reduced cerium sites on this sample. The increase of the Zr content in the Fe2O3/Ce1−x Zr x O2 samples could improve the reactivity of the materials for methane oxidation, but it also reduces the selectivity for CO formation.