Efficient carbon dioxide conversion by nickel ferrite-based catalysts derived from metallurgical electroplating sludge collaborating with low-temperature plasma

Abstract

An innovative, environment-friendly, and efficient method was proposed for the synergistic low-temperature plasma conversion of CO₂ by using nickel ferrite (NiFe₂O₄) catalyst. NiFe₂O₄, characterised by a mesoporous spinel structure, was successfully synthesised from electroplating sludge by a single-step heat treatment. The catalyst was uniformly distributed with SiO₂ glass beads throughout the plasma discharge area, enabling an efficient transition from single filament to filament-surface coupled discharge. The outcomes were a 39.02 % increase in discharge charge and a 15 % increase in output power compared with plasma-only situation. CO₂-conversion optimisation tests showed the formation of a ‘microreaction zone’ enhanced the development of gas vortices and turbulence, promoting the CO₂-conversion ratio, CO generation ratio, and energy efficiency to 20.64 %, 15.74 %, and 1.864 %, respectively, under the NiFe₂O₄ catalyst-facilitated low-temperature plasma conditions. The conversion route involved generating excited-state CO, O₂, and electrons through plasma ionisation of CO₂, alongside the creation of oxygen vacancies (V_o). These vacancies regenerated by consuming lattice oxygen (O²⁻), facilitating CO₂ convert to CO and O₂ by electrons. Furthermore, the catalysts offered sites for adsorbing reaction intermediates, which further facilitated CO₂ dissociation and product formation. The Fe and Ni ions in the NiFe₂O₄ catalyst reacted by redox to produce O²⁻ and V_o and maintain charge equilibrium. This study demonstrated that the NiFe₂O₄ catalyst and synergistic plasma effectively converted CO₂ whilst reducing the reaction’s energy barrier, thereby providing theoretical support for improved CO₂ utilisation as a resource.