New insights into the effect of sodium on Fe3O4-based nanocatalysts for CO2 hydrogenation to light olefins

A series of Fe3O4-based nanocatalysts with different residual sodium contents were prepared by a simple one-pot synthesis method. The effects of residual sodium on the physico-chemical properties and catalytic performance for CO2 hydrogenation of the catalysts were investigated. The residual sodium has significant influences on the textural properties of the iron-based catalysts, and slightly hinders the reduction of the catalysts. However, it obviously promotes the surface basicity of the catalysts, which is favored for olefin production. Furthermore, increasing sodium content can greatly improve the carbonization of the iron catalysts. Compared with the sodium-free Fe3O4 catalysts, the sodium-containing Fe3O4 catalysts exhibited higher activity and produced more C-2-C-4 olefins and C5+ hydrocarbons. The optimized FeNa(1.18) (Na/Fe weight ratio of 1.18/100) catalyst showed excellent catalytic activity with a high olefin/paraffin ratio (6.2) and selectivity to C-2-C-4 olefins (46.6%) and C5+ (30.1%), as well as low CO and CH4 production at a CO2 conversion of 40.5%.