Theoretical Study on the Synthesis of Urea by Electrochemical Nitrate and Carbon Dioxide over COF Series Catalysts

Abstract

Catalytic synthesis of urea is a bright substitutable to Haber–Bosch progression and industrial urea synthesis. Electrochemical C–N coupling of carbon dioxide and nitrogen oxides under environmental conditions is a newly developed method, which also provides a novel opinion for solving nitrate contamination. Conjugated organic frameworks (COFs) have been used as prospective electrocatalysts for nitrogen reduction reactions and carbon dioxide reduction reactions (CO₂RR) as a result of their regulate structure and multihole properties, resulting in efficient electron transfer. This paper reports the efficient synthesis of urea from carbon dioxide and nitrate over MoM₁S-Pc-M₂PPs COF (M as a transition metal) electrocatalyst. According to the calculation of DFT, it was found that it was difficult for carbon dioxide and nitrogen oxide to coadsorb on MoM₁S-Pc to synthesize urea, so we chose to synthesize CO on the metal porphyrin (M₂PPs) structural unit, and then overflow on the bimetallic phthalocyanine and nitrogen oxide to synthesize urea. The possibility of nitrate adsorption on different catalysts was verified by calculation. We screened the stability, nitrate adsorption strength, and catalytic activity of MoM₁S-Pc candidates, and the results showed that the most promising candidate catalyst was MoFeS-Pc. At the same time, the CO₂RR M₂PPs substrate was also screened, and the VPPs structure was selected as the best. In the study of coupling between different nitrogen-containing intermediates and *CO, the C–N coupling mechanism shows that *NOH and *CO are two possible C–N coupling nitrogen intermediates, which are shown to be thermodynamically spontaneous and have an inferior activation barrier. This study not only provisions novel perceptions into urea synthesis by coupling nitrogen oxides with carbon dioxide under environmental conditions, but also paves the way for boosting the sustainable production of carbon and nitrogen-coupled products.