Evaluation of MgO as a promoter for the hydrogenation of CO2 to long-chain hydrocarbons over Fe-based catalysts

Thermocatalytic conversion of CO2 into liquid fuels and chemicals is a promising approach to mitigate global warming. Although, the CO2 conversion and long-chain hydrocarbon selectivity are highly dependent on the choice of metal-oxide promoter, but role of the promoter remains unclear. Herein, the role of MgO as a promoter for an Fe-based catalyst was investigated. Bimetallic Na-FeMgOx catalyst exhibited a high C5+ yield of 25.1% with a CO2 conversion of 49.1% at the early stage of the reaction. The presence of MgO facilitates the reduction of Fe oxides and formation of oxygen vacancies by transferring electrons to Fe-based phases. In addition, at the early stage of reaction, the decoration of the Mg oxide surface with nanosized χ-Fe5C2 enhances the C5+ yield. However, the progressive transformation of MgO to MgCO3 during CO2 conversion deactivates the Na-FeMgOx catalyst. A detailed deactivation mechanism is also discussed. [Display omitted] •MgO-promoted Fe3O4 produced a C5+ yield of 25.1% at a CO2 conversion of 49.1%.•MgO performed its role as an electronic promoter on Fe3O4 and Fe5C2.•The formation of MgCO3 suppressed the promotional effect of MgO.•Re-oxidation of Fe5C2 to Fe3O4 during CO2 conversion was main deactivation mechanism.