Low-Temperature CO2 Methanation: Synergistic Effects in Plasma-Ni Hybrid Catalytic System

Abstract

Thermodynamic and kinetic limitations can restrict the feasibility and scalability of conventional catalytic processes for CO2 methanation at the industrial level. Due to its nonequilibrium nature, nonthermal plasma (NTP) promises to reduce reaction barriers and make this gas conversion approach viable even at low temperatures. However, the current understanding of the fundamental chemical and physical behaviors in the hybrid plasma catalytic interactions is insufficient. This study demonstrates plasma-driven CO2 conversions approaching the reaction equilibrium with high methane yields even at low temperature (150 °C). It was observed that the addition of plasma to the catalytic bed enhanced the CO2 conversion around 20 times relative to thermal activity, whereas the CH4 selectivity increased around 5 times by introducing the nickel catalyst into plasma discharge compared to plasma only (at 150 °C). Moreover, the findings provide new insights into the gas phase activation of reactants (CO2 and H2) and the reaction over Ni0 to decouple the plasma and catalyst synergy. The catalyst did not undergo significant structural changes under plasma discharge, apart from a slight decrease in Ni crystallite size, while an enhanced metal dispersion was evident (24% to 42%, from CO pulse chemisorption). The optimized system achieved a CO2 conversion of 60% with a CH4 selectivity of over 97% at 150 °C, which required much higher temperatures (320-330 °C) to achieve equivalent conversion in thermal catalysis. This study is a step toward an understanding and effective control of the plasma enhanced catalytic CO2 transformation via low energy reaction pathways that utilize the NTP for low-temperature CO2 methanation with high conversion, selectivity, stability, and controllability.