Study on the Synergistic Effect of SiO and HO on Oxidative Coupling of Methane over Mn-NaWO/SiO Catalyst.

Mn-NaWO-based catalysts with different supports were prepared using the incipient wetness impregnation method and evaluated for their oxidative coupling of methane (OCM) reaction performance. The results demonstrated that the SiO- supported catalyst exhibited the best catalytic performance, and the introduction of HO further enhanced its activity. Under the conditions of a feed gas mixture of CH/O/HO = 6:1:24 at 800 °C and atmospheric pressure, the CH conversion and C selectivity over the Mn-NaWO/SiO catalyst increased from 28.4% and 77.4% (without HO) to 33.2% and 84.9%, respectively. In contrast, the catalytic activity using TiO and MgO supports drastically declined. Characterizations using X-ray diffraction (XRD), infrared spectroscopy ( IR), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H-TPR), and oxygen temperature-programmed desorption (O-TPD) revealed that the introduction of steam not only served as a diluent to decrease the partial pressures of the reactants CH and O, thereby reducing deep oxidation reactions in the gas phase, but also interacted with surface oxygen species (O ) and silica to form adjacent surface-bonded disilanol free radicals Si-OH. This interaction facilitated the dehydrogenation and coupling of two methane molecules on the catalyst surface, resulting in the generation of C products, significantly enhancing the catalytic activity and selectivity of OCM.