Oxidative coupling of methane by Mn-Na2WO4/γ-Al2O3 catalyst: effect of Mn/W ratio

In this study, Mn-Na 2 WO 4 / γ -Al 2 O 3 catalysts with varying ratios of Mn/W were prepared using the dry impregnation method. These catalysts were then tested for their suitability in the oxidative coupling of methane reaction. The X-ray photoelectron results revealed the presence of the tetrahedral WO 4 2− phase in all prepared catalysts. It is believed that the presence of this phase is associated with high catalyst activity, indicating the potential of the catalysts for the desired reaction. The activity results show that the catalyst with a high Mn/W ratio exhibited higher activity at 800 °C, whereas the catalyst with a low Mn/W ratio showed greater activity at 850 °C. This suggests that the Mn/W ratio influences the reaction temperature at which the catalyst is most active. Furthermore, the X-ray diffraction results of the treated catalysts revealed that the catalyst with a high Mn/W ratio exhibited more MnAl 2 O 4 at 800 °C, whereas the catalyst with a low Mn/W ratio contained more MnWO 4 at 850 °C. The results suggest that the presence of MnAl 2 O 4 sites may promote a more facile Mn 2+ ↔ Mn 3+ cycle at lower temperatures than the MnWO 4 site, potentially contributing to the enhanced catalyst activity in the oxidative coupling of methane reaction at 800 °C.