CO₂ hydrogenation to hydrocarbons over iron-based catalyst: Effects of physicochemical properties of Al₂O₃ supports

The effects of surface hydroxyl groups and SiO₂ content of alumina supports for FeK/Al₂O₃ catalysts on their activity and product selectivity for CO₂ hydrogenation to hydrocarbons reaction were investigated. A series of iron-based catalysts supported on six commercial Al₂O₃ supports were prepared and tested for hydrocarbons production in a fixed-bed reactor. Surface acidic-basic hydroxyls distribution of the supports were evaluated by Fourier transform infrared (FT-IR) and point of zero charge (PZC) measurement. It was found that the PZC of Al₂O₃ supports strongly affects the dispersion as well as particle size of the Fe-based catalysts. Increasing PZC value of Al₂O₃, the iron dispersion increased and particle size decreased. The highest CO₂ conversion (54.4%) and C₅+ hydrocarbons selectivity (31.1%) were achieved when the PZC was 8.0. CO₂ conversion and the long-chain products selectivity decreased when PZC declined. Moreover, SiO₂-doping of alumina strongly affected the surface acidic-basic hydroxyls distribution of the supports, while a desired SiO₂ content improved the catalyst activity by adjusting CO adsorption and the reduction behavior of the iron-based catalysts.