Triple-atom catalysts for one-step N–C–N coupling toward urea synthesis: A DFT study

Abstract

Electrocatalytic synthesis of urea from carbon dioxide (CO2) and nitrous oxides (NOx) provides promising approaches to alleviate the greenhouse effect. However, this approach still lacks efficient electrocatalysts, which is a key challenge. Here we design a group of electrocatalysts that are triple-single-atom supported on C9N4 monolayer for urea production. Our extensive density functional theory calculations, including reaction barrier obtained through transition state theory, suggest that the as-designed triple-atom catalyst (TAC) Ni2Zn/C9N4 enables efficient electrocatalytic production of chemicals that require multiple coupling, such as urea. Ni2Zn/C9N4 can catalyse the conversion of CO2 and NOx to coupling precursors, and also facilitate the coupling between precursors to urea via a concurrent N–C–N coupling mechanism. Within such a mechanism, * CO inserts into * NOdimerization derived H2N* –* NH2 and binds concurrently with two N atoms. The mechanism promotes the direct and selective synthesis of urea from CO2 and NO, whilst competing CO and NH3 formations are inhibited due to unfavorable thermodynamics and sluggish kinetics. Our findings show that TAC is promising in the electrosynthesis of urea through onestep N–C–N bond synthesis, with the potential to expand to the sustainable synthesis of other organonitrogens that needs synergistic catalysis.