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

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 (Vo). 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 Vo 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.