Understanding the role of catalyst in hybrid nonthermal plasma-catalytic methanation of CO2

Abstract

Thermodynamic and kinetic limitations can restrict the feasibility and scalability of conventional thermal catalytic CO2 methanation. Due to non-equilibrium nature, nonthermal plasma (NTP) has potential to overcome reaction barriers and attain the substantial conversion even at low temperatures. However, the current understanding of the fundamental chemical and physical behaviours in the hybrid plasma-catalytic interactions are insufficient. This work focused on gaining insights into catalyst behaviour under plasma-driven CO2 methanation. The mutual interactions were systematically investigated through activity tests, characterization and in situ plasma diagnostics. To understand the role of Ni in plasma-driven methanation of CO2, a custom-designed plasma system was employed which exhibited the effective dissociation of CO2 into CO. Incorporation of Ni shifted the selectivity towards CH4 that can be attributed to plasma-catalyst synergy, where the formation of formate led the possible pathway for low temperature conversion. The optimum metal loading (10% Ni) demonstrated the conversion (60%) and selectivity (97%) at 150 oC. Moreover, the reciprocating effects of plasma influenced physical properties of catalysts; however, the catalysts exhibited high stability during the reaction. A comparative study for Ni supported catalysts was conducted with four different supports (Al2O3, CeO2, BaTiO3 and SrTiO3) to examine the influence of material properties on catalytic behaviour under plasma. This study elucidated the enhancement in the catalytic performance of the CeO2 and SrTiO3; where the basicity, metal support interaction, metal dispersion and the surface oxygen vacancies played a vital role in catalysts performance. Bimetallic nickel-iron catalysts were evaluated for plasma-catalytic CO2 methanation, which exhibited improved catalytic performance compared to their monometallic counterparts. The introduction of iron into nickel catalysts attributed to structural modification, modified redox properties, improved dispersion, and increased active sites. Overall, this study revealed the activation of reactant gases in plasma discharge, terminated in the dissociation of CO2 into CO. Ni based catalysts were studied and found viable for selective CO2 methanation. This work contributed to establishing the fundamental aspects of hybrid plasma-catalytic CO2 methanation whilst providing the new insights into plasma-catalyst interaction and methanation route under plasma.