Ce-Driven Ce-MnOx/Na2WO4/SiO2 Composite Catalysts for Low-Temperature Oxidative Coupling of Methane

Mn/Na2WO4/SiO2 catalyst is widely used in the oxidative coupling of methane (OCM) reactions because of its high catalytic performance and stability. Nevertheless, the complex elemental composition makes the role of each active component in these catalysts still controversial. Herein, we conducted separate studies on Mn/Na2WO4/SiO2 catalyst by separating it into MnOx and Na2WO4/SiO2 (NaWSi). This provided a persuasive strategy to turn manganese oxide from a combustion catalyst into a selective catalyst for the OCM at low temperatures through a synergistic effect between the Ce-MnOx catalyst and Na2WO4/SiO2 catalyst. The introduction of Ce is a key factor in improving the low-temperature OCM activity of the catalyst. The temperature-programmed desorption of oxygen (O2-TPD) and 18O isotope labeling experiments confirm that surface lattice oxygen is the main active oxygen species in the OCM reaction for the Ce-driven catalyst. The presence of Ce strengthens the surface lattice oxygen cycle process on the catalyst, resulting in higher oxygen exchange ability and improved migration of active lattice oxygen. Furthermore, in situ Raman spectroscopy shows that both 3Ce-MnOx and NaWSi catalysts can enhance resistance to carbon deposition in the catalysts. Hence, the 3Ce-MnOx/NaWSi composite catalyst achieved 38.4% conversion of CH4 and a 15.6% yield of C2 at 700 °C and the catalytic activity remained stable for at least 25 h.