The La₂O₃ catalyst exhibits good performance in OCM reactions for its promising C₂ selectivity and yield. Previous studies have affirmed that the formation of carbonates in La₂O₃ impedes the catalyst’s activity as a result of poisoning from CO₂ exposure. In this study, a series of Na₂WO₄-impregnated La₂O₃ catalysts were synthesized to investigate the poisoning-resistant effect. The bulk phase and kinetics of the catalysts were analyzed in reactors employed with in situ XRD-MS and online MS, focusing on the CO₂ adsorption on La₂O₃ and the phase transition process to La₂O₂CO₃ in temperature zone correlated to OCM light-off. In situ XRD analysis revealed that, with Na₂WO₄ doped, CO₂ exposure at elevated temperatures formed La₂O₂CO₃ in tetragonal crystal phases, exhibiting distinctive differences from the hexagonal phase carbonates in undoped commercial La₂O₃. The ability to develop tetragonal or monoclinic La₂O₂CO₃ was suggested as a descriptor to assess the sensitivity of La₂O₃ catalysts to CO₂ adsorption, a tunable characteristic found in this study through varying Na₂WO₄ doping levels. Coupled XRD-MS analysis of CO₂ adsorption uptake and phase change further confirmed a positive dependence between the resistivity of La₂O₃ catalyst to CO₂ adsorption and its low-temperature C₂ selectivity. The results extended the previous CO₂ poisoning effect from multiple perspectives, offering a novel modification approach for enhancing the low-temperature performance of La₂O₃ catalysts in OCM.

The characterization of the electronic structure and chemical states at heterogeneous interfaces (e.g., gas–solid or liquid–solid) can be effectively achieved using ambient pressure x-ray photoelectron spectroscopy (AP-XPS). However, acquiring these properties under plasma conditions remains a significant challenge. In this study, we introduce an AP-XPS system equipped with a custom-built spatially confined plasma source. This configuration confines the plasma to a controlled region, with the plasma intensity precisely regulated by adjusting either the working distance or the applied voltage. This system enables the direct detection of plasma electrons and the real-time characterization of surface states during plasma–surface interactions. To validate its efficacy and versatility, we conducted two proof-of-concept experiments: argon (Ar) plasma etching of graphene and oxygen (O2) plasma oxidation of platinum (Pt). The results demonstrate that the Ar plasma effectively etches graphene, as evidenced by distinct changes in the XPS spectra. Similarly, the exposure of a Pt surface to the oxygen plasma induces pronounced surface oxidation. This system significantly extends the operando capabilities of AP-XPS for in situ studies of plasma-enhanced reactions. Its application holds considerable promise for advancing fundamental and applied research in materials science and chemical engineering, particularly in the areas of surface modification and catalytic processes.

The oxidative coupling of methane (OCM) is a promising process for converting methane directly into more valuable ethane and ethylene. In this work, high time resolution online mass spectrometry was employed to track the OCM reaction over a commercial La₂O₃ catalyst, focusing on the effects of methane to oxygen ratio, gas hourly space velocity (GHSV), and the presence of H₂O and CO in the feed gas on methane conversion and C₂ yield. The results demonstrated that an optimized GHSV (44,640 to 93,000 mL·g⁻¹·h⁻¹) and methane to oxygen ratio (CH₄/O₂ = 3) would achieve the highest methane conversion and C₂ yield at 740 °C. Furthermore, at a GHSV of 44,640 mL·g⁻¹·h⁻¹, the introduction of 1% H₂O into the reaction mixture resulted in a twofold increase in C₂ yield at 650 °C, while the addition of 1% CO led to a threefold increase in C₂ yield at 550 °C. A model in which only the front-end catalyst is active was also developed to show excellent agreement with the experimental data. The relationship between catalytic performance and the effective catalyst position in the catalyst bed provides important insights into optimizing reactor design and operating conditions to maximize C₂ yield and selectivity in the OCM reaction.

The Oxidative Coupling of Methane (OCM) is a promising process for converting methane directly into more valuable ethane and ethylene. In this work, high-time-resolution online mass spectrometry was employed to track the OCM reaction over a commercial La2O3 catalyst, focusing on the effects of methane to oxygen ratio, Gas Hourly Space Velocity (GHSV), and the presence of H2O and CO in the feed gas on methane conversion and C2 yield. The results demonstrated that an optimized GHSV (44640 to 93000 mL·g−1·h−1) and methane to oxygen ratio (CH4/O2= 3) would achieve the highest methane conversion and C2 yield at 740 °C. Furthermore, the introduction of 1% H2O into the reaction mixture resulted in a twofold increase in C2 yield at 650 °C, while the addition of 1% CO led to a threefold increase in C2 yield at 550 °C. A model in which only the front-end catalyst is active was also developed to show excellent agreement with the experimental data. The relationship between catalytic performance and the effective catalyst position in the catalyst bed provides important insights into optimizing reactor design and operating conditions to maximize C2 yield and selectivity in the OCM reaction.