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

Abstract

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-O_v-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.