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

Abstract

Silicon (Si) has been proven to significantly enhance CO₂ 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-MnFe₂O₄ materials containing 0.0%–9.3%Si (2.3% increments, 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 CO₂ to carbon (C) performance of Nano-MnFe₂O₄ were systematically investigated. Results showed that introducing Si transformed Nano-MnFe₂O₄ into Nano-Mn_XFe_3–XO₄ (0.75 < X < 1.00) with degraded catalysis and Nano-Fe_YMn_ZSiO₄ with almost no activity, lowering CO₂ 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_XFe_3-XO₄, causing fewer oxygen vacancies and declined CO₂ 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_0.19Mn_1.70Fe_1.11O₄ reconstructed from Nano-MnFe₂O₄ with 2.3% Si exhibited 8.82 mmol/g CO₂ reduction and 100% carbon conversion at 350 °C. Mg²⁺ doping strengthened the conversion of Mn²⁺ to highly catalytically active Mn³⁺ and Mn⁴⁺ ions, increasing oxygen vacancies and electron transport for C=O rupture.