Application\nof Copper-Based Catalysts and Strontium\nFerrite as Bed Materials for Plasma-Driven CO<sub>2</sub> Splitting

Activation of the stable CO<sub>2</sub> molecule presents\nthe key\nbarrier to the synthesis of value-added chemicals via heterogeneous\ncatalysis. Catalyst-based processes have been widely studied for CO<sub>2</sub> valorization, although their coupling with nonthermal plasma\n(NTP) has received comparatively little attention. The work presented\nherein utilizes NTP from mixtures of CO<sub>2</sub> with N<sub>2</sub> or Ar over Al<sub>2</sub>O, SrFeO<sub>3−δ</sub>, and\nCu-based catalysts to investigate: (1) the cleavage of CO<sub>2</sub> to CO; (2) the plasma discharge characteristics and electrical power\nrequirement. NTP was generated in a packed bed reactor through dielectric\nbarrier discharge (DBD), with all bed materials increasing the number\nof microdischarges compared to DBD operated in the empty reactor.\nGas analysis confirmed the evolution of CO and O<sub>2</sub> in a\n∼2:1 ratio, as expected for CO<sub>2</sub> → CO + 1/2\nO<sub>2</sub>, with diminishing power requirements for gas mixtures\n100 vol % CO<sub>2</sub> > 50 vol % CO<sub>2</sub>/N<sub>2</sub> >\n50 vol % CO<sub>2</sub>/Ar. With plasma initiated at 20 °C, appreciable\nwarming of the reactor was measured owing to dissipated power, reaching\na steady temperature between 150 and 350 °C depending upon the\nbed material. The highest conversion of CO<sub>2</sub> to CO was 2.5–3%\nover the Cu–CeO<sub>2</sub> and SrFeO<sub>3−δ</sub>. The two materials withhold vacancies in the crystal structure,\npotentially interacting with the evolved oxygen to prevent recombination\nwith CO. In contrast, both the Cu–ZnO and Cu–ZrO<sub>2</sub> catalyzed the recombination of CO and oxygen, giving an overall\nCO<sub>2</sub> conversion of just 1% or less. Relatively high CO<sub>2</sub> splitting conversion of 2 to 2.5% was found over Al<sub>2</sub>O<sub>3</sub> and at the lowest power input for all materials examineda\nresult of salience given the application of Al<sub>2</sub>O<sub>3</sub> as a support for copper catalysts. This work demonstrates that catalysts\nmodulate plasma to support gas-phase CO<sub>2</sub> dissociation and\nparticipate in catalytic reactions with species generated in NTP.