Synergetic effect of non-thermal plasma and supported cobalt catalyst in plasma-enhanced CO₂ hydrogenation

Non-thermal plasma can provide an alternative to CO₂ utilization under mild conditions. Understanding the effect of plasma on catalysis is highly desired. Herein, a comparative study was performed on CO₂ hydrogenation under thermal-catalytic and plasma-catalytic conditions using an alumina-supported cobalt catalyst. Significant plasma-catalyst synergy was attained at the low-temperature range between 423 K and 498 K where the CO₂ conversion increased up to approximately 3.6 times of the sum of that using plasma or catalyst individually. The plasma-catalytic reaction showed a significantly lower activation energy (∼40 kJ/mol), which is only half of that in the thermal catalytic reaction (∼80 kJ/mol). Kinetic analysis and DRIFTS results indicate that CO₂ activation is promoted by plasma with the assistance of active H species from gas phase. Furthermore, the total H₂ adsorption capacity and the coverage of irreversible adsorbed H species on the metal surface were decreased under plasma. The promotion effect is very likely due to a new reaction pathway introduced by plasma on the 15Co/Al₂O₃ catalyst under the conditions studied. No obvious difference in the structure and morphology changes was observed between the spent catalysts after thermal and plasma reactions.