Efficient C–N coupling in the direct synthesis of urea from CO 2 and N 2 by amorphous Sb x Bi 1-x O y clusters

Abstract

Although direct generation of high-value complex molecules and feedstock by coupling of ubiquitous small molecules such as CO 2 and N 2 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 Sb x Bi 1-x O y clusters for direct urea synthesis from CO 2 and N 2 via C–N coupling. The introduction of Sb in the amorphous BiO x clusters changes the adsorption geometry of CO 2 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 N 2 , promoting C–N coupling by advantageous modification of the symmetry for the frontier orbitals of CO 2 and N 2 involved in the rate-determining catalytic step. Compared with BiO x , Sb x Bi 1-x O y 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 −1 cat , 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.