Potassium Promoted Ferrocene/Graphene for Ammonia Synthesis

Abstract

Innovation of catalysts for mild condition ammonia synthesis promotes the carbon neutrality. Herein we report that ferrocene supported on reduced graphene oxide (rGO) and promoted by alkali metal K is active catalyzing NH₃ synthesis from N₂/H₂ mixture. It exhibits a NH₃ formation rate of $0.1\,\,{\rm{\mu mo}}{{\rm{l}}_{{\rm{N}}{{\rm{H}}_3}}} \cdot g_c^{ - 1} \cdot {{\rm{h}}^{ - 1}}$ at 190 °C and increases by one order of magnitude to $2.1\,\,{\rm{\mu mo}}{{\rm{l}}_{{\rm{N}}{{\rm{H}}_3}}} \cdot g_c^{ - 1} \cdot {{\rm{h}}^{ - 1}}$ at 230 °C and under 0.1 MPa. By contrast, both rGO promoted by K and ferrocene supported on rGO without K promotion are almost inactive under the same conditions. Density functional theory calculations validate the essential role of K promoter for facilitating the adsorption of N₂ at the coordination unsaturated iron sites in the cyclopentadienylidene form. This finding could guide further development of metal complex catalysts for mild condition ammonia synthesis.