Coupling N2 and CO2 in H2O to synthesize urea under ambient conditions

Abstract

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. The use of nitrogen fertilizers has been estimated to have supported 27% of the world's population over the past century. Urea (CO(NH2)2) is conventionally synthesized through two consecutive industrial processes, N2 + H2 → NH3 followed by NH3 + CO2 → urea. Both reactions operate under harsh conditions and consume more than 2% of the world's energy. Urea synthesis consumes approximately 80% of the NH3 produced globally. Here we directly coupled N2 and CO2 in H2O to produce urea under ambient conditions. The process was carried out using an electrocatalyst consisting of PdCu alloy nanoparticles on TiO2 nanosheets. This coupling reaction occurs through the formation of C-N bonds via the thermodynamically spontaneous reaction between *N=N* and CO. Products were identified and quantified using isotope labelling and the mechanism investigated using isotope-labelled operando synchrotron-radiation Fourier transform infrared spectroscopy. A high rate of urea formation of 3.36 mmol g-1 h-1 and corresponding Faradic efficiency of 8.92% were measured at-0.4 V versus reversible hydrogen electrode.

Unveiling the Electrooxidation of Urea: Intramolecular Coupling of the N−N Bond

“…3172 cm −1 represent the stretching vibrations of NH 2 (Figure 4 a,b). [5b, 23] After 1.45 V, the vibration intensities of NH and NH 2 reduced, whereas the vibration intensity of C‐N only reduced after 1.55 V. However, for the vibration intensities of the C=O bond in urea and the O−H bond in the electrolyte, there was no noticeable attenuation, which indicated that the dehydrogenation of the amino group occurs prior to C−N bond rupture during the UOR (Figure 4 a–c). A difficulty then remains in how to analyze paths of rearrangement and N−N bond coupling during the UOR.…”

“…100 % N 2 selectivity [13] . Operando synchrotron‐radiation Fourier‐transform infrared spectroscopy (SR‐FTIR) and in situ DEMS were carried out to trace bond rupture and formation during the UOR [5b, 22] . Before 1.40 V, and without reaction, urea and electrolyte adsorbed on electrode were identified by operando SR‐FTIR over the β‐Ni(OH) 2 electrode during UOR.…”

Defect Chemistry on Electrode Materials for Electrochemical Energy Storage and Conversion

“…F) TEM image of Pd 1 Cu 1 /TiO 2 ‐400. Reproduced with permission [54] . Copyright 2020, Springer Nature.…”

“…Moreover, because of its optimized electronic structure and the strong interaction between metal and support, the catalytic activity of urea synthesis can be greatly improved. The experimental results showed that the TiO 2 support with oxygen‐rich vacancy defects was of great significance for promoting the synthesis of urea and improving the benign co‐chemical adsorption of N 2 and CO 2 on the surface of Pd 1 Cu 1 /TiO 2 ‐400 catalyst, which provided a prerequisite for the coupling reaction [54] . Therefore, this work provides a new idea for the fixation of nitrogen and carbon dioxide molecules and is of great significance for the development of green and efficient urea synthesis.…”

Electrochemical activation of C–H by electron-deficient W2C nanocrystals for simultaneous alkoxylation and hydrogen evolution

“…Principally, the preparation of cost-effective and active electrode materials is at least as important as the development of a new methodology for selective C−H bonds activation [19][20][21][22][23][24][25][26] , and only non-targeted, commercial rst generation electrodes (such as carbon rod, platinum and reticulated vitreous carbon) are applied as the current collectors in electrochemical organic synthesis at the moment. The signi cant progress reported using well-designed reaction-speci ed electrodes in improving the catalytic activity for water splitting, nitrogen reduction reactions and even carbon dioxide reduction reactions [27][28][29][30] further manifests the huge gap between the design of novel electrode materials and the requirements of sustainable electrochemical organic synthesis.…”