PNNL

Abstract

We addressed the challenges of designing catalysts for selective CO2 hydrogenation by incorporating oxide Fe species onto Rh nanoparticles. Nanoscopic FeOx 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 stabilize methoxy groups while suppressing hydrogenolysis to methane. Sites at FeOx-metal interfaces interact with CO2 sevenfold stronger than sites on metal surfaces, show larger energy barriers to cleave the C-O bonds, and offer a barrierless pathway for hydrogenation of methoxy species to methanol. Consequently, the multifunctional sites over FeOx/Rh-Fe catalysts highlight and meet the requirements of a selective methanol catalyst: strong interaction with CO2 to ensure 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 synthesis and catalytic chemistries, demonstrated for Rh-Fe-FeOx interfaces, enable us to overcome the limitations to the design of methanol production catalysts.