Enhancing catalytic CO2 reduction to carbon performance of nano-MnFe2O4 prepared from high-silica manganese ores via MgO phase reconstruction strategy

Silicon (Si) has been proven to significantly enhance CO 2 reduction efficiency of numerous catalysts. However, the lack of research on Si's effect on manganese ferrite catalytic performance presents a challenge in using high-silica manganese ore to prepare cost-effective, efficient manganese-based ferrite decarbonization catalysts. This work prepared Nano-MnFe 2 O 4 materials containing 0.0%–9.3%Si (2.3% increments, in mass fraction) by solid-phase synthesis (1300 °C, air) and nano-grinding. The effect, mechanism, and enhancement strategy of Si on the low-temperature catalytic reduction of CO 2 to carbon (C) performance of Nano-MnFe 2 O 4 were systematically investigated. Results showed that introducing Si transformed Nano-MnFe 2 O 4 into Nano-Mn X Fe 3– X O 4 (0.75 < X < 1.00) with degraded catalysis and Nano-Fe Y Mn Z SiO 4 with almost no activity, lowering CO 2 reduction to C from 5.55 mmol/g to 2.81 mmol/g. Increasing Si concentration simultaneously decreased the content and X -value of Nano-Mn X Fe 3- X O 4 , causing fewer oxygen vacancies and declined CO 2 reduction. A phase reconstruction strategy to eliminate Si impact and enhance catalysis was proposed, i.e. , adding MgO, increasing Mn/Fe ratio, and nano-grinding followed by magnetic separation. Nano-Mg 0.19 Mn 1.70 Fe 1.11 O 4 reconstructed from Nano-MnFe 2 O 4 with 2.3% Si exhibited 8.82 mmol/g CO 2 reduction and 100% carbon conversion at 350 °C. Mg 2+ doping strengthened the conversion of Mn 2+ to highly catalytically active Mn 3+ and Mn 4+ ions, increasing oxygen vacancies and electron transport for C=O rupture. • Deteriorating effect and mechanism of Si on CO 2 reduction to C of Nano-MnFe 2 O 4 were revealed. • A phase reconstruction strategy to eliminate Si impact and greatly enhance catalysis was proposed. • CO 2 reduction to C of Nano-MnFe 2 O 4 with 2.3% (in mass) Si was improved from 4.65 mmol/g to 8.82 mmol/g. • Crucial role of Mn 4+ /Mn 3+ redox of Nano-Mn X Mg Y Fe 3- X-Y O 4 on CO 2 reduction to solid C was clarified.