Application of Copper-Based Catalysts and Strontium Ferrite as Bed Materials for Plasma-Driven CO₂ Splitting

Activation of the stable CO2 molecule presents the key barrier to the synthesis of value-added chemicals via heterogeneous catalysis. Catalyst-based processes have been widely studied for CO2 valorization, although their coupling with nonthermal plasma (NTP) has received comparatively little attention. The work presented herein utilizes NTP from mixtures of CO2 with N2 or Ar over Al2O, SrFeO3−δ, and Cu-based catalysts to investigate: (1) the cleavage of CO2 to CO; (2) the plasma discharge characteristics and electrical power requirement. NTP was generated in a packed bed reactor through dielectric barrier discharge (DBD), with all bed materials increasing the number of microdischarges compared to DBD operated in the empty reactor. Gas analysis confirmed the evolution of CO and O2 in a ∼2:1 ratio, as expected for CO2 → CO + 1/2 O2, with diminishing power requirements for gas mixtures 100 vol % CO2 > 50 vol % CO2/N2 > 50 vol % CO2/Ar. With plasma initiated at 20 °C, appreciable warming of the reactor was measured owing to dissipated power, reaching a steady temperature between 150 and 350 °C depending upon the bed material. The highest conversion of CO2 to CO was 2.5–3% over the Cu–CeO2 and SrFeO3−δ. The two materials withhold vacancies in the crystal structure, potentially interacting with the evolved oxygen to prevent recombination with CO. In contrast, both the Cu–ZnO and Cu–ZrO2 catalyzed the recombination of CO and oxygen, giving an overall CO2 conversion of just 1% or less. Relatively high CO2 splitting conversion of 2 to 2.5% was found over Al2O3 and at the lowest power input for all materials examined─a result of salience given the application of Al2O3 as a support for copper catalysts. This work demonstrates that catalysts modulate plasma to support gas-phase CO2 dissociation and participate in catalytic reactions with species generated in NTP.