Synergistic effects of rare-earth and lanthanoid elements on P123-modified Ni-HiMO catalysts for enhanced CO2 methanation under thermal and DBD-assisted conditions

Abstract

Optimizing catalysts for CO₂ conversion targeting CH₄ is a difficult task. In this work, NiMgAl-hydrotalcite-induced mixed-oxide (Ni-HiMO) catalysts were modified by polymer P123, promoted with Sc, Y, La, and Gd (SYLaG) in one step, and tested for thermal and DBD plasma conditions for the first time. The Ni(SYLaG)-HiMO@P123 catalysts were then evaluated from physicochemical to electrical aspects. It was observed that incorporating such elements altered the distribution of basicity, leading to increased CO₂ adsorption and activation. Additionally, nickel–support interactions were altered by introducing d and f blocks. We found that this series of catalysts showed highly catalytic activities at low temperatures. Exceptionally, thermal tests on Y- and Gd-supported catalysts showed ca. 79.4–83.3% CO₂ conversion at only 250 °C, which is much better than current data reported in the literature, and all studied catalysts showed 88–90% CO₂ conversion, with CH₄ selectivity being 99.8% at 300 °C (GHSV = 12 000 h⁻¹). This catalyst series showed a huge potential for low-temperature CO₂ methanation. Furthermore, the La-promoted catalyst was the best under plasma-assisted conditions, converting 82.8% at 28 W owing to its smallest Ni⁰ and lowest dielectric constant (ε = 9.43). These observations indicated that our catalyst synthesis method is very well developed both for thermal (mild conditions) and DBD plasma CO₂ methanation. The catalytic performance robustly increased when the specific energy input threshold exceeded 3.4 eV per molecule for all catalysts. Lastly, charge transfer per half-cycle increased with increasing applied voltage but not as a linear function, reaching a maximum at 281.97 nC with La incorporation. Our research is one of the few investigations that have reported perspectives on both the physicochemical and electrical properties of hydrotalcite-based catalysts, simultaneously comparing thermal and plasma CO₂ methanation activity.