Urea Synthesis Research Articles

Photocatalytic Co‐Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis

AbstractThe effective conversion of carbon dioxide (CO2) and nitrogen (N2) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2‐x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2‐500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C−N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC‐TEM) and Fourier transform infrared (FT‐IR) spectroscopy were used to research the atomic surface structure of CeO2‐500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C−N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

Photocatalytic Co-Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis.

The effective conversion of carbon dioxide (CO2 ) and nitrogen (N2 ) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H2 (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N2 and CO2 by introducing oxygen vacancies. Particularly, CeO2 -500 (CeO2 nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C-N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO2 -500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C-N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.

Selective electrochemical synthesis of urea from nitrate and CO2 via relay catalysis on hybrid catalysts

Selective electrochemical synthesis of urea from nitrate and CO2 via relay catalysis on hybrid catalysts

Identifying the facet-dependent active sites of Cu2O for selective C-N coupling toward electrocatalytic urea synthesis

Understanding the activity phases and reaction mechanisms at the atomic level is essential for the design of electrocatalysts. Herein we investigate the origin of the facet-dependent activity of model Cu2O catalyst for C-N coupling toward electrocatalytic urea synthesis. It was found that the activity of urea synthesis depends on the crystalline facets of Cu2O. The Cu2O (100) facet exhibits higher urea activity and selectivity than the (110) facet, with an average urea yield of 62.4 mmol·g−1·h−1 at –1.5 V (RHE). By using Raman, UV–vis and XPS techniques, it was observed that Cu+ serves as active sites at (100) face of Cu2O, which promotes C-N coupling through synergistic interaction with Cu0. Furthermore, the combined results of operando ATR-SEIRAS and DFT calculations demonstrate that the Cu-Cu2O (100) facet facilitates electrocatalytic C-N coupling between *CO and *NH intermediates due to the reduced energy barriers of hydrogenated *NO on the Cu-Cu2O (100) facet.

Hydrogen, Ammonia and Symbiotic/Smart Fertilizer Production Using Renewable Feedstock and CO2 Utilization through Catalytic Processes and Nonthermal Plasma with Novel Catalysts and In Situ Reactive Separation: A Roadmap for Sustainable and Innovation-Based Technology

This multi-disciplinary paper aims to provide a roadmap for the development of an integrated, process-intensified technology for the production of H2, NH3 and NH3-based symbiotic/smart fertilizers (referred to as target products) from renewable feedstock with CO2 sequestration and utilization while addressing environmental issues relating to the emerging Food, Energy and Water shortages as a result of global warming. The paper also discloses several novel processes, reactors and catalysts. In addition to the process intensification character of the processes used and reactors designed in this study, they also deliver novel or superior products so as to lower both capital and processing costs. The critical elements of the proposed technology in the sustainable production of the target products are examined under three-sections: (1) Materials: They include natural or synthetic porous water absorbents for NH3 sequestration and symbiotic and smart fertilizers (S-fertilizers), synthesis of plasma interactive supported catalysts including supported piezoelectric catalysts, supported high-entropy catalysts, plasma generating-chemical looping and natural catalysts and catalysts based on quantum effects in plasma. Their performance in NH3 synthesis and CO2 conversion to CO as well as the direct conversion of syngas to NH3 and NH3—fertilizers are evaluated, and their mechanisms investigated. The plasma-generating chemical-looping catalysts (Catalysts, 2020, 10, 152; and 2016, 6, 80) were further modified to obtain a highly active piezoelectric catalyst with high levels of chemical and morphological heterogeneity. In particular, the mechanism of structure formation in the catalysts BaTi1−rMrO3−x−y{#}xNz and M3O4−x−y{#}xNz/Si = X was studied. Here, z = 2y/3, {#} represents an oxygen vacancy and M is a transition metal catalyst. (2) Intensified processes: They include, multi-oxidant (air, oxygen, CO2 and water) fueled catalytic biomass/waste gasification for the generation of hydrogen-enriched syngas (H2, CO, CO2, CH4, N2); plasma enhanced syngas cleaning with ca. 99% tar removal; direct syngas-to-NH3 based fertilizer conversion using catalytic plasma with CO2 sequestration and microwave energized packed bed flow reactors with in situ reactive separation; CO2 conversion to CO with BaTiO3−x{#}x or biochar to achieve in situ O2 sequestration leading to higher CO2 conversion, biochar upgrading for agricultural applications; NH3 sequestration with CO2 and urea synthesis. (3) Reactors: Several patented process-intensified novel reactors were described and utilized. They are all based on the Multi-Reaction Zone Reactor (M-RZR) concept and include, a multi-oxidant gasifier, syngas cleaning reactor, NH3 and fertilizer production reactors with in situ NH3 sequestration with mineral acids or CO2. The approach adopted for the design of the critical reactors is to use the critical materials (including natural catalysts and soil additives) in order to enhance intensified H2 and NH3 production. Ultimately, they become an essential part of the S-fertilizer system, providing efficient fertilizer use and enhanced crop yield, especially under water and nutrient stress. These critical processes and reactors are based on a process intensification philosophy where critical materials are utilized in the acceleration of the reactions including NH3 production and carbon dioxide reduction. When compared with the current NH3 production technology (Haber–Bosch process), the proposed technology achieves higher ammonia conversion at much lower temperatures and atmospheric pressure while eliminating the costly NH3 separation process through in situ reactive separation, which results in the production of S-fertilizers or H2 or urea precursor (ammonium carbamate). As such, the cost of NH3-based S-fertilizers can become competitive with small-scale distributed production platforms compared with the Haber–Bosch fertilizers.

Scalable production of tissue-like vascularized liver organoids from human PSCs.

The lack of physiological parity between 2D cell culture and in vivo culture has led to the development of more organotypic models, such as organoids. Organoid models have been developed for a number of tissues, including the liver. Current organoid protocols are characterized by a reliance on extracellular matrices (ECMs), patterning in 2D culture, costly growth factors and a lack of cellular diversity, structure, and organization. Current hepatic organoid models are generally simplistic and composed of hepatocytes or cholangiocytes, rendering them less physiologically relevant compared to native tissue. We have developed an approach that does not require 2D patterning, is ECM independent, and employs small molecules to mimic embryonic liver development that produces large quantities of liver-like organoids. Using single-cell RNA sequencing and immunofluorescence, we demonstrate a liver-like cellular repertoire, a higher order cellular complexity, presenting with vascular luminal structures, and a population of resident macrophages: Kupffer cells. The organoids exhibit key liver functions, including drug metabolism, serum protein production, urea synthesis and coagulation factor production, with preserved post-translational modifications such as N-glycosylation and functionality. The organoids can be transplanted and maintained long term in mice producing human albumin. The organoids exhibit a complex cellular repertoire reflective of the organ and have de novo vascularization and liver-like function. These characteristics are a prerequisite for many applications from cellular therapy, tissue engineering, drug toxicity assessment, and disease modeling to basic developmental biology.

Amination of Isonitriles in Water: Urea Synthesis under Biocompatible Conditions

AbstractBioorthogonal reactions have been widely used to track biomolecules in living systems. Due to stringent requirements of physiological conditions, enriching the toolkit of bioorthogonal reactions remains the most important and challenging issue. Herein, the biocompatible ligation of isonitriles and amines to ureas in neutral aqueous medium was developed for the first time. The ligation showed benign nature of biocompatibility, broad substrate scope, and specific chemoselectivity. Meanwhile, urea as a natural linkage, its derivatives played an important role in medicinal chemistry. The second‐order reaction rate constant (k2) was determined, which was higher or comparable to that of Staudinger ligation and strain‐promoted azide‐alkyne cycloaddition (SPAAC). Direct labeling of Ac4GlcN has been achieved in Hep G2 cells.

(Invited) Electrocatalytic Synthesis of Ammonia and Urea

Many industrial chemical processes involve a high-energy demand (often still derived from fossil fuels), toxic reactants, and the production of high amounts of waste. A good example is the production of ammonia and urea via the Haber-Bosh and Bosch-Meiser processes, respectively. These two nitrogen-containing compounds are mostly used in the fertilizer industry and with the increase in the world population, their production is expected to increase. Additionally, NH3 itself is responsible for 2% of the annual world energy consumption and has a carbon footprint of 1.5 tons of CO2 per ton of NH3 [1]. Therefore, the development of more efficient, less hazardous technologies that are based on renewable energies to produce valuable N- containing compounds, has become one of the most challenging topics for chemical synthesis. By using electrochemical methods for the synthesis of ammonia and urea, toxic and dangerous chemicals can be replaced with clean electrons. Furthermore, the efficiency and selectivity of the reactions can be tuned by the applied potential, and more importantly, the energy used can come from renewable sources like wind or solar [2].In this talk, I will show the recent advances from our group in the development of catalysts for the electrocatalytic synthesis of ammonia and urea (as for example Cu2O and CuRh) and the reaction mechanism when using nitrate as a substrate [3].

High-Rate and Sustainable Production of Urea and Ammonia via Electrochemical Reduction of CO2 and Nitrates

Over the past century, nitrogen fertilization has fed approximately 27% of the world’s population.1 Urea and ammonia are two of the most important nitrogen fertilizers used world-widely. The current industrial production of urea is mainly realized by an energy-intensive reaction of carbon dioxide and ammonia under harsh conditions (150-200 °C, 150-250 bar) with large energy consumption, for which nearly 80% of synthesized ammonia is used.2 Furthermore, ammonia is also produced under extreme condition (350-550 °C, 150-350 bar) by an energy-consuming Haber-Bosch method.3 Therefore, it is of great significance to synthesize urea and ammonia under mild conditions to meet the demands of ever-increasing population in the world. The electrocatalytic co-reduction of CO2 and NO3 - emerges as a promising approach to realize the direct synthesis of urea via C-N coupling, with ammonia produced as a side product. However, the state-of-the-art yield rates of urea and ammonia through this electrosynthesis are typically below 1 mg h-1 mgcat -1 and 3 mg h-1 mgcat -1.4, 5 In this study, we realize high-rate production of urea on an economic Cu-based organic molecule catalyst through electrochemically coupling CO2 with NO3 -, with ammonia as another useful byproduct. The rationally design of the catalysts guarantees the accurate adsorption and activation of NO3 - and CO2, which further promotes the desired electrochemical C-N coupling in urea synthesis. Efficient urea synthesis was achieved with yield rates ranging from 2.7 to 3.6 mg h-1 mgcat -1 in a potential window of -0.49~-0.67V vs. RHE, together with ammonia with high yield rates ranging from 0.15 to 9.7 mg h-1 mgcat -1. This work proposes an appealing route of sustainable production of artificial nitrogen fertilizers with high efficiencies. Widespread adoption of this approach is promising to re-use the greenhouse gas CO2 and NO3 - from waste toward a full circulate of economy and sustainable energy consumption. The demonstrated production of nitrogen fertilizer in conjunction with renewable electricity is of great potential to meet the rising demand for global food security. Acknowledgements Research Grants Council (26206115, 16304821 and 16309418) and Innovation and Technology Commission (grant no. ITC-CNERC14EG03) of the Hong Kong Special Administrative Region. The work described in this paper was substantially supported by a fellowship award from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKUST PDFS2021-4S12). References J. W. Erisman, M. A. Sutton, J. Galloway, Z. Klimont and W. Winiwarter, Nat. Geosci., 2008, 1, 636-639.M. Yuan, J. Chen, Y. Xu, R. Liu, T. Zhao, J. Zhang, Z. Ren, Z. Liu, C. Streb, H. He, C. Yang, S. Zhang and G. Zhang, Energy Environ. Sci., 2021, 14, 6605-6615.A. J. Martín, T. Shinagawa and J. Pérez-Ramírez, Chem, 2019, 5, 263-283.C. Lv, L. Zhong, H. Liu, Z. Fang, C. Yan, M. Chen, Y. Kong, C. Lee, D. Liu, S. Li, J. Liu, L. Song, G. Chen, Q. Yan and G. Yu, Nat. Sustain., 2021, 4, 868-876.X. Wei, X. Wen, Y. Liu, C. Chen, C. Xie, D. Wang, M. Qiu, N. He, P. Zhou, W. Chen, J. Cheng, H. Lin, J. Jia, X.-Z. Fu and S. Wang, J. Am. Chem. Soc., 2022, 144, 11530-11535.

Early onset of urea synthesis and ammonia detoxification pathways in three terrestrially developing frogs.

Frogs evolved terrestrial development multiple times, necessitating mechanisms to avoid ammonia toxicity at early stages. Urea synthesis from ammonia is a key adaptation that reduces water dependence after metamorphosis. We tested for early expression and plasticity of enzymatic mechanisms of ammonia detoxification in three terrestrial-breeding frogs: foam-nest-dwelling larvae of Leptodactylus fragilis (Lf) and arboreal embryos of Hyalinobatrachium fleischmanni (Hf) and Agalychnis callidryas (Ac). Activity of two ornithine-urea cycle (OUC) enzymes, arginase and CPSase, and levels of their products urea and CP in tissues were high in Lf regardless of nest hydration, but reduced in experimental low- vs. high-ammonia environments. High OUC activity in wet and dry nests, comparable to that under experimental high ammonia, suggests terrestrial Lf larvae maintain high capacity for urea excretion regardless of their immediate risk of ammonia toxicity. This may aid survival through unpredictably long waiting periods before rain enables their transition to water. Moderate levels of urea and CP were present in Hf and Ac tissues and enzymatic activities were lower than in Lf. In both species, embryos in drying clutches can hatch and enter the water early, behaviorally avoiding ammonia toxicity. Moreover, glutamine synthetase was active in early stages of all three species, condensing ammonia and glutamate to glutamine as another mechanism of detoxification. Enzyme activity appeared highest in Lf, although substrate and product levels were higher in Ac and Lf. Our results reveal that multiple biochemical mechanisms of ammonia detoxification occur in early life stages of anuran lineages that evolved terrestrial development.

The effects of acutely elevated ammonia concentrations on haemolymph parameters in the Mediterranean mussel, Mytilus galloprovincialis

In aquaculture systems, ammonia nitrogen is a major component of waste products arising from the metabolism of cultured organisms and can significantly affect the quality of the rearing environment. The purpose of the current study was to determine modulation of the haemocyte population and selected haemolymph biochemical parameters of the Mediterranean mussel Mytilus galloprovincialis (Lamarck, 1919) exposed to acutely elevated ammonia concentrations.In order to investigate the extent and dynamics of an expected reduction of physiological fitness and survival rate of cultured mussels the stress-on-stress test was conducted combining ammonia and air exposure. The latter test illustrated the extent of reduced mussel physiological fitness and survival rate upon 72 h exposure to 10 and 30 mM NH4Cl in experimental tanks followed by additional exposure to air. Mussels cultured for up to 48 h in experimental tanks comprising 5, 10 and 30 mM NH4Cl, revealed dose and time dependent increase in haemolymph enzyme lactate dehydrogenase levels, urea, and uric acid metabolite levels, as well as the corresponding redistribution in haemocyte population profiles, indicating an inherent response of this organism to ammonia. Finally, a significant negative linear correlation between the mussel hyalinocytes subpopulation and the mean urea levels was observed. The obtained result suggests a possible function of basophilic and acidophilic granulocyte subpopulations in ammonia metabolism leading to urea synthesis by means of surplus ammonium ions are sequestered and extracted from the body. Therefore, defined modulation of the mussel haemocyte population structure may serve as an accurate bioindicator of mussels exposure to acutely elevated ammonia concentrations in environmental and aquaculture biomonitoring studies.

Understanding urea electro synthesis using layered perovskite NdBa0.25Sr0.75Co2O5+ δ cathode material

Urea production through an electro-synthetic approach emerges as a sustainable alternative compared to its conventional energy-intensive and polluting technologies. However, the advancement of the aforementioned technique is primarily impeded by existing inefficient electrocatalysts. Therefore, the rational design of the indispensable catalyst along with the unveiling of the reaction pathway through intermediate identification, would enable the utmost deployment of the proposed strategy. Herein, we prepared a non-noble layered perovskite NdBa0.25Sr0.75Co2O5+ δ using the citric acid-metal nitrate combustion method and utilized it as an electrocatalyst alongside CO2 and nitrite contaminants used as input sources for urea synthesis. The synthesized electrocatalyst proffered remarkable electrochemical performance for the above-stated urea electrosynthesis reaction with a yield rate of 6.66 µmol g−1 h−1 and Faradaic efficiency (F.E) of 9.5%, respectively, at − 1.04 V vs RHE optimized conditions. High-performance liquid chromatography analysis was performed for end-product quantification. The favourable urea formation could be attributable to the unique distribution of prevailing oxygen vacancies in the perovskite cathode material. The insights provided in the article unravel a novel paradigm for the use of layered perovskite materials in urea electrosynthesis.

Indium-activated bismuth-based catalysts for efficient electrocatalytic synthesis of urea

Urea is of great importance for the survival and development of mankind because of its advantages in effectively increasing crop yields. A novel carbon-supported indium-doped bismuth nanoparticles (Bi: 10 %In/C NPs) was prepared for the synthesis of urea via the co-activated reduction of nitrate and CO2 with an average Faraday efficiency (FE) of 20.31 % and urea yield (Rurea) of 606.38 μg mg−1 h−1. Interestingly, the In doped here not only serves as the active site, but also acts as an activator to stimulate the activity of Bi through electronic interaction, thus making Bi also the active site for the electrocatalytic C-N coupling reaction. Simultaneously, the key intermediates of the reaction are revealed to be *NH2 and *CO. This work provides further insight into the role of indium in the electrocatalytic C-N coupling for the synthesis of urea, which gives a direction for thinking about the design and construction of subsequent highly efficient electrocatalysts.

Emerging Electrocatalysts in Urea Production.

Urea synthesis from abundant CO2 and N-feedstocks via renewable electricity has attracted increasing interests, offering a promising alternative to the industrial-applied Haber-Meiser process. However, the studies toward electrochemical urea production remain scarce and appeal for more research. Herein, in this perspective, an up-to-date overview on the urea electrosynthesis is highlighted and summarized. Firstly, the reaction pathways of urea formation through various feedstocks are comprehensively discussed. Then, we focus on the strategies of materials design to improve C-N coupling efficiency by identifying the descriptor and understanding the reaction mechanism. Finally, the current challenges and disadvantages in this field are reviewed and some future development directions of electrocatalytic urea synthesis are also prospected. This Minireview aims to promote future investigations of the electrochemical urea synthesis.

Neural Network Weight Comparison for Industrial Causality Discovering and Its Soft Sensing Application

Due to the complex reaction mechanisms of industrial process units, causality and correlations exist between industrial process variables. Causal discovery algorithms have been utilized to discover the knowledge on variable relationships and guide process modeling and control optimization. However, most of them are limited by strict assumptions, such as linear relationships, additive noise, steady-state process, etc. Therefore, these methods cannot gain good performance for most practical industrial processes. To solve these problems, a novel weight comparison causal mining (WCCM) algorithm is proposed in this paper for industrial causal graph discovery. It first trains a group of hidden layer neural networks with process data, then mines an undirected skeleton of the process variables according to the comparison of the network weights, and further determines the causal directions of the undirected edges in the skeleton to get a directed causal graph. The effectiveness of WCCM is verified on a benchmark and a practical industrial case from the Urea Synthesis process. The undirected and direct edges mined by WCCM show high consistency with the ground truths. Moreover, the causal discovery results of WCCM is utilized to guide the feature selection of soft sensor modeling, resulting in improved prediction accuracy and enhanced model interpretability.

Efficient urea electrosynthesis from carbon dioxide and nitrate via alternating Cu–W bimetallic C–N coupling sites

Electrocatalytic urea synthesis is an emerging alternative technology to the traditional energy-intensive industrial urea synthesis protocol. Novel strategies are urgently needed to promote the electrocatalytic C–N coupling process and inhibit the side reactions. Here, we report a CuWO4 catalyst with native bimetallic sites that achieves a high urea production rate (98.5 ± 3.2 μg h−1 mg−1cat) for the co-reduction of CO2 and NO3− with a high Faradaic efficiency (70.1 ± 2.4%) at −0.2 V versus the reversible hydrogen electrode. Mechanistic studies demonstrated that the combination of stable intermediates of *NO2 and *CO increases the probability of C–N coupling and reduces the potential barrier, resulting in high Faradaic efficiency and low overpotential. This study provides a new perspective on achieving efficient urea electrosynthesis by stabilizing the key reaction intermediates, which may guide the design of other electrochemical systems for high-value C–N bond-containing chemicals.

Difficulties in diagnostics of urea synthesis cycle disturbance

Introduction. Hereditary metabolic diseases include a large group of diseases caused by genetic mutations with a high potential risk of transmitting this disorder to future offspring. Manifesting at any age and accompanied by recurrent and progressive clinical symptoms, some of these mutations become incompatible with life, while most lead to gross violations of the normal physiological process of child development. The paper presents a clinical case of hereditary urea synthesis disorder caused by deficiency of ornithine transcarbamylase of mitochondrial matrix in liver (hyperammonemia type 2) as a result of mutation of the OTC gene (MIM 300461). The disease recessive, linked with the X-chromosome and is associated with a high risk of mortality due to accumulation of toxic concentrations of ammonia. Materials and methods. The boy E., born in 2015. Introduction of protein-based complimentary foods and increase in its portion volume is associated with decrease in appetite, regurgitation, nausea, vomiting, flatulence, dyspepsia appear, and sharp weakness progresses. There is a significant increase in the blood concentration of intracellular liver enzymes. Physical development is slowed due to poor weight gain, and neuropsychiatric development lags significantly. Repeatedly examined in the hospital at the place of residence. Results obtained. A total of 47 genes with mutations causing hereditary diseases with predominant liver damage were studied by mass parallel sequencing. Substitution of c.523G>A (p.Asn175Asp) in the OTC gene in hemizygous state was detected. Clinical diagnosis was established: urea cycle metabolism disorder, hyperammonemia, ornithine transcarbamylase deficiency, E 72.2. Dietary recommendations were given. Carbaglu, Recordati, France at the rate of 100 mg/kg/24 h was prescribed on vital signs. Against the background of the therapy and dietary recommendations the condition of the child had a pronounced positive trend. Conclusions. Since the true incidence of this pathology in Russia has not been established (many cases of metabolic disorders of the urea cycle remain undiagnosed), the presented clinical case will allow clinicians, using modern possibilities of structural and functional analysis of the human genome, to make a timely diagnosis and prescribe adequate therapy, thereby not only prolonging the life of a young patient but also significantly improving its quality.

Electrocatalytic Urea Synthesis with 63.5 % Faradaic Efficiency and 100 % N-Selectivity via One-step C-N coupling.

Electrocatalytic urea synthesis via coupling N2 and CO2 provides an effective route to mitigate energy crisis and close carbon footprint. However, the difficulty on breaking N≡N is the main reason that caused low efficiencies for both electrocatalytic NH3 and urea synthesis, which is the bottleneck restricting their industrial applications. Herein, a new mechanism to overcome the inert of the nitrogen molecule was proposed by elongating N≡N instead of breaking N≡N to realize one-step C-N coupling in the process for urea production. We constructed a Zn-Mn diatomic catalyst with axial chloride coordination, Zn-Mn sites display high tolerance to CO poisoning and the Faradaic efficiency can even be increased to 63.5 %, which is the highest value that has ever been reported. More importantly, negligible N≡N bond breakage effectively avoids the generation of ammonia as intermediates, therefore, the N-selectivity in the co-electrocatalytic system reaches100 % for urea synthesis. The previous cognition that electrocatalysts for urea synthesis must possess ammonia synthesis activity has been broken. Isotope-labelled measurements and Operando synchrotron-radiation Fourier transform infrared spectroscopy validate that activation of N-N triple bond and nitrogen fixation activity arise from the one-step C-N coupling process of CO species with adsorbed N2 molecules.

Electrocatalytic Urea Synthesis with 63.5 % Faradaic Efficiency and 100 % N‐Selectivity via One‐step C−N coupling

AbstractElectrocatalytic urea synthesis via coupling N2 and CO2 provides an effective route to mitigate energy crisis and close carbon footprint. However, the difficulty on breaking N≡N is the main reason that caused low efficiencies for both electrocatalytic NH3 and urea synthesis, which is the bottleneck restricting their industrial applications. Herein, a new mechanism to overcome the inert of the nitrogen molecule was proposed by elongating N≡N instead of breaking N≡N to realize one‐step C−N coupling in the process for urea production. We constructed a Zn−Mn diatomic catalyst with axial chloride coordination, Zn−Mn sites display high tolerance to CO poisoning and the Faradaic efficiency can even be increased to 63.5 %, which is the highest value that has ever been reported. More importantly, negligible N≡N bond breakage effectively avoids the generation of ammonia as intermediates, therefore, the N‐selectivity in the co‐electrocatalytic system reaches100 % for urea synthesis. The previous cognition that electrocatalysts for urea synthesis must possess ammonia synthesis activity has been broken. Isotope‐labelled measurements and Operando synchrotron‐radiation Fourier transform infrared spectroscopy validate that activation of N−N triple bond and nitrogen fixation activity arise from the one‐step C−N coupling process of CO species with adsorbed N2 molecules.

Sustainable and High-Rate Electrosynthesis of Nitrogen Fertilizer.

The conventional industrial production of nitrogen-containing fertilizers, such as urea and ammonia, relies heavily on energy-intensive processes, accounting for approximately 3 % of global annual CO2 emissions. Herein, we report a sustainable electrocatalytic approach that realizes direct and selective synthesis of urea and ammonia from co-reduction of CO2 and nitrates under ambient conditions. With the assistance of a copper (Cu)-based salphen organic catalyst, outstanding urea (3.64 mg h-1 mgcat -1 ) and ammonia (9.73 mg h-1 mgcat -1 ) yield rates are achieved, in addition to a remarkable Faradaic efficiency of 57.9±3 % for the former. This work proposes an appealing sustainable route to converting greenhouse gas and waste nitrates by renewable energies into value-added fertilizers.