Why is calcium an effective promoter for plasma CO2 methanation over polymer P123-modified NiMgAlOx-mixed oxide catalysts?

This work demonstrated the impact of Ca and Ba on the properties and activity of Polymer P123-modified NiMgAlOx-mixed oxide catalysts over thermal and plasma CO2 methanation. Both elements influenced the basicity and redox properties of the 3 P-NMA catalyst. Although the high CO2 affinity of the promoted-Ca catalyst limited its low-temperature performance, the plasma tests revealed efficient conversion of carbonates to methane, attributed to the presence of highly energetic electrons. Ni15Ba1 demonstrated notable effectiveness in conventional tests (XCO2= 80.5%, SCH4= 99.7%, at 250ºC), meanwhile, Ni15Ca1 displayed a significant enhancement in plasma (XCO2= 86.8%, SCH4 ≈ 100%, at 24.8 W discharge power), with 73.5% of energy efficiency, the highest reported. Both catalysts showed increased conversion to 88–89% at 300ºC. Operando FTIR measurements uncovered the different intermediates under thermal and plasma conditions. The Ca concentration was optimized at 1 wt% for plasma performance, likely due to the strong adsorption capacity of Ca and the catalyst dielectric constant.