Mn–Na2WO4/SiO2 synthesized by Urea-assisted hydrothermal-Impregnation route has more and stronger surface basic sites, and more surface lattice oxygen, leading to higher methane conversion with higher selectivity toward ethane and ethylene in oxidative
coupling of methane reaction, compared to Mn–Na2WO4/SiO2 produced by Co-precipitation-Impregnation (CPI) and Sequential Impregnation (SI) methods.
Yilin Zhao,Fangwei Liu,Jingbo Hu,Yang Yang,Jianzhou Wu,Shihui Zou,Jie Fan
The Mn–Na2WO4/SiO2 catalyst for oxidative coupling of methane (OCM) is highly appealing and promising but its high light-off temperature (>800 °C) hinders its industrial application. Engineering catalysts for efficient catalytic performance is attractive yet challenging. In this study, we demonstrate that the incorporation of small amounts of silver into the Mn–Na2WO4/SiO2 catalyst significantly improves its performance, achieving a C2 yield of up to 20% at 750 °C. Characterization results indicate that silver facilitates O2 activation and promotes C–H bond activation, thereby further enhancing CH4 conversion. The findings offer valuable insights into advancing the design concept of high-performance OCM catalysts.
Mn–Na2WO4-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 SiO2- supported catalyst exhibited the best catalytic performance, and the introduction of H2O further enhanced its activity. Under the conditions of a feed gas mixture of CH4/O2/H2O = 6:1:24 at 800 °C and atmospheric pressure, the CH4 conversion and C2+ selectivity over the Mn–Na2WO4/SiO2 catalyst increased from 28.4% and 77.4% (without H2O) to 33.2% and 84.9%, respectively. In contrast, the catalytic activity using TiO2 and MgO supports drastically declined. Characterizations using X-ray diffraction (XRD), in situ infrared spectroscopy (In-situ IR), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), and oxygen temperature-programmed desorption (O2-TPD) revealed that the introduction of steam not only served as a diluent to decrease the partial pressures of the reactants CH4 and O2, thereby reducing deep oxidation reactions in the gas phase, but also interacted with surface oxygen species (O22–) and silica to form adjacent surface-bonded disilanol free radicals Si–OIH. This interaction facilitated the dehydrogenation and coupling of two methane molecules on the catalyst surface, resulting in the generation of C2+ products, significantly enhancing the catalytic activity and selectivity of OCM.
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