Formation of (Rh-Fe)-FeO_x Complex Sites Enables Methanol Synthesis from CO₂

We addressed the challenges of designing catalysts for selective CO₂ hydrogenation by incorporating Fe oxide species onto Rh nanoparticles. Nanoscopic FeO_x domains created a “reverse catalyst” structure (i.e., a metal oxide supported on a metal) that increased the density of interfacial sites compared to traditional supported catalysts. The contact between the metal nanoparticle and the oxide overlayer induced the formation of a surface Rh-Fe alloy that stabilized methoxy groups while suppressing hydrogenolysis to methane. Sites at FeO_x-metal interfaces interact with CO₂ much stronger than sites on metal surfaces, show larger energy barriers to cleave the C-O bonds, and offer a barrierless pathway for the hydrogenation of methoxy species to methanol. Consequently, the multifunctional sites over FeO_x/Rh-Fe catalysts highlight and meet the requirements of a selective methanol catalyst: strong interaction with CO₂ to ensure a high density of transition states, metal sites to activate and make hydrogen available to surface intermediates, and high energy barriers for C-O bond cleavage to form carbides. These synthetic and catalytic chemistries, demonstrated for Rh-Fe-FeO_x interfaces, enable us to overcome the limitations to the design of methanol production catalysts.