Insight into plasma-catalytic CO2 methanation mechanism at Ni-Ov-Ni and basic sites in NaF-modified Ni/La2O3 catalysts with excellent activity

Large-scale CO2 emissions have exacerbated the greenhouse effect, reinforcing the critical need for efficient CO2 mitigation methods. Plasma-catalytic technology enables CO2 conversion under mild conditions, especially for CO2 methanation (the Sabatier reaction), which has attracted significant attention due to its economic benefits and the potential for safe energy transportation via existing natural gas pipelines. The development of high-performance CO2 methanation catalysts remains an ongoing and long-term objective, and there is a lack of adequate in-situ characterization techniques to investigate the mechanisms. This study focuses on the Ni/La2O3 (LN) catalyst and introduces two CO2 activation strategies through F and Na modifications: the Ni-Ov-Ni site activation with electron transfer from Ni0 under low-power conditions and basic site activation under high-power conditions. The LN-NaF catalysts enhance CO2 methanation activity across the entire power range compared to LN, achieving a CO2 conversion of 86.3 % and CH4 selectivity of 99.4 %. Additionally, LN-F(h) reaches a CH4 yield 4.15 times higher than that of LN at low power. Furthermore, in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy with a self-made reactor are performed under plasma-catalytic conditions to reveal the CO2 adsorption and conversion mechanisms, indicating that different dopants (F, Na, and NaF) exhibit promoting effects on different intermediates, resulting in variations in CO2 methanation activity. This study provides valuable insights for improving catalyst performance and a thorough comprehension of mechanisms in CO2 methanation.