Exploring the feasibility of liquid fuel synthesis from CO2 under cold plasma discharge: role of plasma discharge in binary metal oxide surface modification

Abstract

The conversion of CO₂ to CH₃OH over binary mixed metal oxides of NiO–Fe₂O₃ is investigated in the study. A series of catalysts, i.e., NiO, Fe₂O₃, 5% NiO–Fe₂O₃ (5NF), 10% NiO–Fe₂O₃ (10NF), and 15% NiO–Fe₂O₃ (15NF), was tested for CO₂ conversion and CH₃OH selectivity performance. The results show that binary mixed metal oxides are more active in comparison to pure metal oxides. Moreover, increasing NiO mixing leads to the agglomeration of NiO particles. At 200 °C, around 1.5%, 2%, and 3.2% CO₂ conversion is achieved for 5NF, 10NF, and 15NF, respectively. Interestingly, when cold plasma was ignited at 200 °C, around 5.4%, 6.2%, and 10.2% CO₂ conversion was achieved for the 5NF, 10NF, and 15NF catalysts, respectively. 15NF exhibited the highest CO₂ conversion, but produced only CH₄. Plasma coupling with the catalyst led to an increase in the CH₃OH yield, and around an 5.8-fold enhancement was achieved with 10NF at 200 °C compared to thermal catalysis. We showed that the combination of plasma and thermal heating brings about significant changes to the catalyst morphology, which significantly improved the catalytic activity. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterization revealed that plasma treatment leads to the formation of a mixture of spinel compounds (NiO–Fe₂O₃, NiFe₂O₄, and Fe₃O₄).