Selective oxidation of methane and carbon deposition over Fe 2 O 3 /Ce 1− x Zr x O 2 oxides

Abstract

Abstract A series of Fe 2 O 3 /Al 2 O 3 , Fe 2 O 3 /CeO 2 , Ce 0.7 Zr 0.3 O 2 , and Fe 2 O 3 /Ce 1− x Zr x O 2 ( x = 0.1–0.4) oxides was prepared and their physicochemical features were investigated by X‐ray diffraction (XRD), transmission electron microscope (TEM), and H 2 ‐temperature‐programmed reduction (H 2 ‐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 O 2 ‐enriched atmosphere were investigated in detail. The results show that the samples with the presence of Fe 2 O 3 show much higher activity for methane oxidation compared with the Ce 0.7 Zr 0.3 O 2 solid solution, while the CeO 2 ‐contained samples represent higher CO selectively in methane oxidation than the Fe 2 O 3 /Al 2 O 3 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 Fe 2 O 3 /Ce 0.7 Zr 0.3 O 2 . For the oxidation process of the carbon deposition, the CeO 2 ‐containing samples show much higher CO selectivity than the Fe 2 O 3 /Al 2 O 3 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 Fe 2 O 3 /Ce 0.7 Zr 0.3 O 2 also represents much higher selectivity (ca. 97 %) for the conversion of carbon to CO than the Fe 2 O 3 /CeO 2 sample, which can be attributed to the higher concentration of reduced cerium sites on this sample. The increase of the Zr content in the Fe 2 O 3 /Ce 1− x Zr x O 2 samples could improve the reactivity of the materials for methane oxidation, but it also reduces the selectivity for CO formation.