Efficient C-N coupling in the direct synthesis of urea from CO2 and N2 by amorphous SbxBi1-xOy clusters.

ABSTRACT

Although direct generation of high-value complex molecules and feedstock by coupling of ubiquitous small molecules such as CO2 and N2 holds great appeal as a potential alternative to current fossil-fuel technologies, suitable scalable and efficient catalysts to this end are not currently available as yet to be designed and developed. To this end, here we prepare and characterize SbxBi1-xOy clusters for direct urea synthesis from CO2 and N2 via C-N coupling. The introduction of Sb in the amorphous BiOx clusters changes the adsorption geometry of CO2 on the catalyst from O-connected to C-connected, creating the possibility for the formation of complex products such as urea. The modulated Bi(II) sites can effectively inject electrons into N2, promoting C-N coupling by advantageous modification of the symmetry for the frontier orbitals of CO2 and N2 involved in the rate-determining catalytic step. Compared with BiOx, SbxBi1-xOy clusters result in a lower reaction potential of only -0.3 V vs. RHE, an increased production yield of 307.97 µg h-1 mg-1cat, and a higher Faraday efficiency (10.9%), pointing to the present system as one of the best catalysts for urea synthesis in aqueous systems among those reported so far. Beyond the urea synthesis, the present results introduce and demonstrate unique strategies to modulate the electronic states of main group p-metals toward their use as effective catalysts for multistep electroreduction reactions requiring C-N coupling.