Urea Synthesis Research Articles

Recent Advances in Electrocatalytic C-N Coupling for Urea Synthesis.

Urea, one of the most widely used nitrogen-containing fertilizers globally, is essential for sustainable agriculture. Improving its production is crucial for meeting the increasing demand for fertilizers. Electrocatalytic co-reduction of CO₂ and nitrogenous compounds (NO₂-/NO₃-) has emerged as a promising strategy for green and energy-efficient urea synthesis. However, challenges such as slow reaction kinetics and complex multi-step electron transfers have hindered the development of efficient urea synthesis methods. This review explores recent advances in the electrocatalytic C-N coupling process, focusing on bimetallic catalysts, metal oxide/hydroxide catalysts, and carbon-based catalysts. The review also discusses the future prospects of designing effective catalysts for electrocatalytic C-N coupling to improve urea synthesis.

Electrocatalytic Urea Synthesis via C‐N Coupling over Fe‐Based Catalyst

Electrochemical urea synthesis under ambient conditions offers a promising alternative to traditional methods, yet suffers from inefficient production due to poor binding of reactants to the catalyst surface, leading to competitive pathways. Here, we report an electrochemical route for urea synthesis by dual reduction of CO2 and N2 gases using FePc catalyst. The FePc electrocatalyst showed a urea yield rate of 357 µmol h−1 gcat−1 with a Faradaic efficiency (FE) of 14.36% at −0.4 V vs RHE. This insight offers an awareness into the development of an electrochemical route for the efficient electrosynthesis of urea via C–N coupling.

Green Synthesis of Urea from Carbon Dioxide and Ammonia Catalyzed by Ultraporous Permanently Polarized Hydroxyapatite.

The sustainable synthesis of urea from ammonia (NH3) and carbon dioxide (CO2) using ultraporous permanently polarized hydroxyapatite (upp-HAp) as catalyst has been explored as an advantageous CO2-revalorization strategy. As the simultaneous activation of N2 and CO2 (single-step) demands an increase of the reaction conditions, we have re-visited the industrial two-step Bazarov reaction. upp-HAp has been designed as a stable multifunctional catalyst capable of promoting both CO2 and NH3 adsorption for their subsequent C-N bond formation. Herein we report the synthesis of 1 mmol/gcat of urea with a selectivity of 97% under strictly mild conditions (95-120 ºC and 1 bar of CO2; without applying any electrical currents or UV irradiation) which represents an efficiency of ~2% and ~30% with respect to the NH3 and CO2 content, respectively. The study of the NH3 content, products adsorbed in the catalyst, presence of intermediates and temperature of the reaction allows unveiling the great potential of upp-HAp as a green catalyst for sustainable Bazarov reactions. Results suggest that the double-step approach could be more advantageous for both synthesizing urea and as a CO2-revalorization strategy, which in turn promotes the development of specific technologies for the independent synthesis of green NH3.

Polyoxometalate Confined Synthesis of BiVO4 Nanocluster for Urea Production with Remarkable O2/N2 Tolerance.

Urea electrosynthesis from flue gas and NO3- under operating conditions represents a promising alternative technology to traditional energy-intensive industrial process. Herein, we explore a polyoxometalate confined synthesis strategy to prepare ultrafine BiVO4 nanocluster by pre-incorporating [V10O28]6- into NH2-MIL-101-Al (MIL) framework. The resulting BiVO4@MIL-n can efficiently drive co-reduction of NO3- and CO2 to urea. A record urea yield of 63.4 mmol h-1 gcat-1 was achieved under CO2/O2 mixed gases (33% O2) atmosphere, and comparable performance can be obtained by feeding flue gas, demonstrating remarkable O2/N2 tolerance and potential feasibility for urea production under operating conditions. Systematic investigations revealed that MIL carrier with -NH2 group can enrich CO2, and BiVO4 nanocluster can reduce both NO3- and CO2 to ensure efficient urea synthesis even in the presence of O2. This work demonstrates the key role of in situ growth of BiVO4 nanocluster within a NH2-framework in facilitating urea electrosynthesis with exceptional tolerance to O2/N2.

Synthesis and anion binding properties of (thio)urea functionalized Ni(II)-salen complexes.

Salen ligands (salen = N,N'-ethylenebis(salicylimine)) are well-known for their versatility and widespread utility in chelating metal complexes. However, installation of hydrogen-bonding units on the salen framework, particularly functional groups that require amine-based precursors such as (thio)ureas, is difficult to achieve without the use of protecting group strategies. In this report, we show that the phenylketone analog of salicyladehyde is a stable alternative that enables the facile installation of hydrogen bonding (thio)urea groups on the salen scaffold, thus imparting anion binding abilities to a metal salen complex. Synthesis of symmetric N-phenyl(thio)urea salen ligands functionalized at the 3,3'-position and an unsymmetric salen ligand with N-phenylurea at the 5-position was achieved. Subsequent metalation with nickel(II) acetate afforded the nickel(II) complexes that were investigated for their anion binding properties towards F-, Cl-, Br-, CH3COO-, and H2PO4-. Solid-state structures of the nickel(II) complexes as well as the Cl- bound dimer of the symmetric urea complex were obtained. The unusual acidity of the (thio)urea groups is reflected in the pKa-dependent anion binding behavior of the nickel(II) complexes, as elucidated by 1H and 19F Nuclear Magnetic Resonance (NMR) spectroscopy and Diffusion Ordered Spectroscopy (DOSY) experiments.

Unveiling the Mechanistic Landscape and Advantages of Two-Dimensional Phthalocyanine in Sustainable Urea Synthesis

Unveiling the Mechanistic Landscape and Advantages of Two-Dimensional Phthalocyanine in Sustainable Urea Synthesis

Green Pathway of Urea Synthesis Through Plasma–Ice Interaction: Optimization and Mechanistic Insights With N2 + CO2 and NH3 + CO2 Gas Mixtures

ABSTRACTThis study presents a green approach for urea synthesis using plasma–ice interaction with N₂ + CO₂ and NH₃ + CO₂ gas mixtures. Plasma characterization via electrical and optical emission spectroscopy revealed that urea formation involves complex reactions driven by high‐energy species, producing reactive nitrogen and carbon intermediates. Plasma‐treated ice exhibited increased pH, electrical conductivity (EC), and reduced oxidation–reduction potential (ORP). Optimization of parameters, especially treatment time, significantly influenced urea formation. The NH₃ + CO₂ plasma produced a higher urea concentration (7.7 mg L−1) compared to the N₂ + CO₂ plasma (0.55 mg L−1) due to ammonia's greater reactivity. This method offers a sustainable, energy‐efficient alternative to traditional urea synthesis processes.

The electrochemical synthesis of urea on triatomic cluster/Cu catalysts: A theoretical study

Urea (NH2CONH2), a crucial nitrogen fertilizer and industrial raw material, is typically synthesized under rigorous reaction conditions. Currently, the electrocatalytic transformation of N2 and CO2 into urea is a promising strategy. However, finding a high-selectivity and high-activity catalyst remains a significant challenge. Herein, the activity of a series of transition metal clusters (VIII and IB groups) on copper-based catalysts for electrochemical coupling of CO2 and N2 has been systematically studied to produce urea via density functional theory (DFT). Most catalysts exhibit good thermodynamic stability and accomplish co-adsorb CO2 and N2. Notably, Fe3 and Ni3/Cu100 catalysts achieve C-N coupling via *CO and *N2, whereas Ru3, Rh3, Os3, and Ir3/Cu100 catalysts accomplish C-N coupling via *CO and *NHNH. Among all catalysts, the Ni3/Cu100 catalyst features excellent catalytic activity with a rate-determining step as low as 0.480 eV, and its C-N coupling only needs to overcome a barrier of 0.844 eV. Additionally, the Ni3/Cu100 catalyst can effectively inhibit the hydrogen evolution reaction (HER), further protonation of *CO and ammonia formation, thereby ensuring high selectivity for urea. Electronic structures analysis further reveals an “acceptance-donation” mechanism for the activation of *CO2 and *N2, with the introduction of the Ni3 cluster showing a decisive role. Therefore, this study may establish the foundation for the electrochemical synthesis of urea.

A Strongly Coupled Metal/Hydroxide Heterostructure Cascades Carbon Dioxide and Nitrate Reduction Reactions toward Efficient Urea Electrosynthesis.

The direct coupling of nitrate ions and carbon dioxide for urea synthesis presents an appealing alternative to the Bosch-Meiser process in industry. The simultaneous activation of carbon dioxide and nitrate, however, as well as efficient C-N coupling on single active site, poses significant challenges. Here, we propose a novel metal/hydroxide heterostructure strategy based on synthesizing an Ag-CuNi(OH)2 composite to cascade carbon dioxide and nitrate reduction reactions for urea electrosynthesis. The strongly coupled metal/hydroxide heterostructure interface integrates two distinct sites for carbon dioxide and nitrate activation, and facilitates the coupling of *CO (on silver, where * denotes an active site) and *NH2 (on hydroxide) for urea formation. Moreover, the strongly coupled interface optimizes the water splitting process and facilitates the supply of active hydrogen atoms, thereby expediting the deoxyreduction processes essential for urea formation. Consequently, our Ag-CuNi(OH)2 composite delivers a high urea yield rate of 25.6 mmol gcat. -1 h-1 and high urea Faradaic efficiency of 46.1 %, as well as excellent cycling stability. This work provides new insights into the design of dual-site catalysts for C-N coupling, considering their role on the interface.

Supplanted by electron-deficient B to form RuN2B-CoN4 moiety as superior catalytic site to further promote urea production

The potential significance of electrocatalytic urea synthesis as a promising alternative to traditional manufacture is widely recognized. However, the critical hindrance is lack of its highly efficient and robust electrocatalysts until now. Alongside the exploration of novel urea catalysts, it is equally crucial to explore feasible strategies to boost the performance of the identified active sites. In this work, we proposed and demonstrated a modulatory scheme to further promote urea production in Ru-Co dual-metal sites through the substitution of electron-deficient B atom in RuN3 subunit to form RuN2B-CoN4 moiety in graphene. The B-coordinated Ru active site can effectively decrease charge transfer amount from the Ru atom to the substrate. The enhanced single-atomic similarity to free Ru atom results in more negative adsorption energy for N2 molecule and superior catalytic activity/selectivity for urea generation. More significantly, this study provides a new perspective to promote the catalytic performance of the carbon-based diatomic active sites for urea production.

Enhanced Electrocatalytic Urea Synthesis over Iron-Doped InOOH Nanosheets under Ambient Conditions.

Ambient urea synthesis via C-N coupling from CO2 and nitrate reduction offers an attractive alternative to the Bosch-Meiser route, but it is hindered by the lack of efficient catalysts. Herein, we report that Fe-doped InOOH nanosheets effectively catalyze the coreduction of CO2 and nitrate, giving a high Faradaic Efficiency of 26.9%, a yield rate of 980.6 μg h-1 mgcat.-1, and a good durability. Theoretical calculations further elucidate that iron dopants can tailor the reactivity of the In site, facilitating the hydrogenation of the key *CO2NH2 intermediate and suppressing the hydrogen production with a higher energy barrier.

Efficient electrocatalytic urea synthesis from CO2 and nitrate over the scale-up produced FeNi alloy-decorated nanoporous carbon

Electrocatalytic urea synthesis provides a favorable strategy for conventional energy-consuming urea synthesis, but achieving large-scale catalyst synthesis with high catalytic efficiency remains challenging. Herein, we developed a simple method for the preparation of a series of FeNi-alloy-based catalysts, named FeNi@nC-T (n represents the content of nanoporous carbon as 1, 3, 5, 7 or 9 g and T = 900, 950, 1000 or 1100 °C), for highly performed urea synthesis via NO3− and CO2 co-reduction. The FeNi@7C-1000 achieved a high urea yield of 1041.33 mmol h−1 gFeNi−1 with a Faradaic efficiency of 15.56% at –1.2 V vs. RHE. Moreover, the scale-up synthesized FeNi@7C-950-S (over 140 g per batch) was achieved with its high catalytic performance and high stability maintained. Mechanism investigation illuminated that the Ni and Fe sites catalyze and stabilize the key *CO and *N intermediates and minimize the C–N coupling reaction barriers for highly efficient urea synthesis.

Electrocatalysts for Urea Synthesis from CO2 and Nitrogenous Species: From CO2 and N2/NOx Reduction to urea synthesis.

The traditional industrial synthesis of urea relies on the energy-intensive and polluting process, namely the Haber-Bosch method for ammonia production, followed by the Bosch-Meiser process for urea synthesis. In contrast, electrocatalytic C-N coupling from carbon dioxide (CO2) and nitrogenous species presents a promising alternative for direct urea synthesis under ambient conditions, bypassing the need for ammonia production. This review provides an overview of recent progress in the electrocatalytic coupling of CO2 and nitrogen sources for urea synthesis. It focuses on the role of intermediate species and active site structures in promoting urea synthesis, drawing from insights into reactants' adsorption behavior and interactions with catalysts tailored for CO2 reduction, nitrogen reduction, and nitrate reduction. Advanced electrocatalyst design strategies for urea synthesis from CO2 and nitrogenous species under ambient conditions are explored, providing insights for efficient catalyst design. Key challenges and prospective directions are presented in the conclusion. Mechanistic studies elucidating the C-N coupling reaction and future development directions are discussed. The review aims to inspire further research and development in electrocatalysts for electrochemical urea synthesis.

Single and dual-atom catalysts towards electrosynthesis of ammonia and urea: a review.

Ammonia and urea represent two important chemicals that have contributed to the rapid development of humanity. However, their industrial production requires harsh conditions, consuming excessive energy and resulting in significant greenhouse gas emission. Therefore, there is growing interest in the electrocatalytic synthesis of ammonia and urea as it can be carried out under ambient conditions. Recently, atomic catalysts (ACs) have gained increased attention for their superior catalytic properties, being able to outperform their micro and nano counterparts. This review examines the advantages and disadvantages of ACs and summarises the advancement of ACs in the electrocatalytic synthesis of ammonia and urea. The focus is on two types of AC - single-atom catalysts (SACs) and diatom catalysts (DACs). SACs offer various advantages, including the 100% atom utilization that allows for low material mass loading, suppression of competitive reactions such as hydrogen evolution reaction (HER), and alternative reaction pathways allowing for efficient synthesis of ammonia and urea. DACs inherit these advantages, possessing further benefits of synergistic effects between the two catalytic centers at close proximity, particularly matching the NN bond for N2 reduction and boosting C-N coupling for urea synthesis. DACs also possess the ability to break the linear scaling relation of adsorption energy of reactants and intermediates, allowing for tuning of intermediate adsorption energies. Finally, possible future research directions using ACs are proposed.

Multifunctional Strategies of Advanced Electrocatalysts for Efficient Urea Synthesis.

The electrochemical reduction of nitrogenous species (such as N2, NO, NO2 -, and NO3 -) for urea synthesis under ambient conditions has been extensively studied due to their potential to realize carbon/nitrogen neutrality and mitigate environmental pollution, as well as provide a means to store renewable electricity generated from intermittent sources such as wind and solar power. However, the sluggish reaction kinetics and the scarcity of active sites on electrocatalysts have significantly hindered the advancement of their practical applications. Multifunctional engineering of electrocatalysts has been rationally designed and investigated to adjust their electronic structures, increase the density of active sites, and optimize the binding energies to enhance electrocatalytic performance. Here, surface engineering, defect engineering, doping engineering, and heterostructure engineering strategies for efficient nitrogen electro-reduction are comprehensively summarized. The role of each element in engineered electrocatalysts is elucidated at the atomic level, revealing the intrinsic active site, and understanding the relationship between atomic structure and catalytic performance. This review highlights the state-of-the-art progress of electrocatalytic reactions of waste nitrogenous species into urea. Moreover, this review outlines the challenges and opportunities for urea synthesis and aims to facilitate further research into the development of advanced electrocatalysts for a sustainable future.

Ligand engineering towards electrocatalytic urea synthesis on a molecular catalyst

Electrocatalytic C-N coupling from carbon dioxide and nitrate provides a sustainable alternative to the conventional energy-intensive urea synthetic protocol, enabling wastes upgrading and value-added products synthesis. The design of efficient and stable electrocatalysts is vital to promote the development of electrocatalytic urea synthesis. In this work, copper phthalocyanine (CuPc) is adopted as a modeling catalyst toward urea synthesis owing to its accurate and adjustable active configurations. Combining experimental and theoretical studies, it can be observed that the intramolecular Cu-N coordination can be strengthened with optimization in electronic structure by amino substitution (CuPc-Amino) and the electrochemically induced demetallation is efficiently suppressed, serving as the origination of its excellent activity and stability. Compared to that of CuPc (the maximum urea yield rate of 39.9 ± 1.9 mmol h−1 g−1 with 67.4% of decay in 10 test cycles), a high rate of 103.1 ± 5.3 mmol h−1 g−1 and remarkable catalytic durability have been achieved on CuPc-Amino. Isotope-labelling operando electrochemical spectroscopy measurements are performed to disclose reaction mechanisms and validate the C-N coupling processes. This work proposes a unique scheme for the rational design of molecular electrocatalysts for urea synthesis.

Trace Cu-Induced Low C─N Coupling Barrier on Amorphous Co Metallene Boride for Boosting Electrochemical Urea Production.

The electrochemical C─N coupling of carbon dioxide (CO2)and nitrate(NO3 -)is an alternative strategy to the traditional high-energy industrial pathway for urea synthesis, which urgently requires the design of efficient catalysts to achieve high yield and Faraday efficiency (FE). Here, amorphous low-content copper-doped cobalt metallene boride (a-Cu0.1CoBx metallene) is designed for urea synthesis via electrochemical C─N coupling. The a-Cu0.1CoBx metallene can drive electrocatalytic C─N coupling of CO2 and NO3 - for urea synthesis in CO2-saturated 0.1m KNO3 electrolyte, with 27.7% of FE and 312µgh-1mg-1 cat. of yield at -0.5V, as well as superior cycling stability. The in situ Fourier transform infrared and theoretical calculations reveal that electronic effect between Cu, Co, and B causes Cu and Co as dual active sites to promote the adsorption of reactants. Furthermore, the introduced trace Cu reduces the reaction energy barrier of the C─N coupling to facilitate urea synthesis. This work provides a promising route for the optimization of Co-based metallene for the electrosynthesis of urea through C─N coupling.

Principles of designing electrocatalysts to boost C–N coupling reactions for urea synthesis

AbstractThe electrocatalytic C–N coupling reaction can achieve green and sustainable urea synthesis as well as CO2 conversion and nitrogen fixation. However, the electrocatalytic C–N coupling reaction still faces challenges such as difficult adsorption and activation of reactive species, a large number of reactive intermediates, high reaction energy barriers, and inert reactive kinetics, resulting in the low urea yielding rate and Faradic efficiency. The development of efficient catalysts is key to improve the urea yielding rate and Faradic efficiency. This review covers the development history and basic principles of electrocatalytic C–N coupling for urea production, analyzes the nanostructure–catalytic activity relationship as well as the electronic structure–catalytic activity relationship, and discusses the main reaction mechanism of electrocatalytic C–N coupling for urea production. Based on these analyses, the concept of designing efficient C–N coupling catalysts is derived. Finally, the research status of electrocatalytic C–N coupling for urea synthesis is summarized, and the prospect for developing efficient electrocatalysts and C–N coupling mechanism are proposed.

Dynamic Control of Asymmetric Charge Distribution for Electrocatalytic Urea Synthesis.

Constructing dual catalytic sites with charge density differences is an efficient way to promote urea electrosynthesis from parallel and CO2 reduction yet still challenging in static system. Herein, a dynamic system is constructed by precisely controlling the asymmetric charge density distribution in an Au-doped coplanar Cu7 clusters-based 3D frameworkcatalyst (Au@cpCu7CF). In Au@cpCu7CF, the redistributed charge between Au and Cu atoms changed periodically with the application of pulse potentials switching between -0.2 and -0.6 V and greatly facilitated the electrosynthesis of urea. Compared with the static condition of pristine cpCu7CF (FEurea = 5.10%), the FEurea of Au@cpCu7CF under pulsed potentials is up to 55.53%. Theoretical calculations demonstrated that the high potential of -0.6V improved the adsorption of *HNO2 and *NH2 on Au atoms and inhibited the reaction pathways of by-products. While at the low potential of -0.2V, the charge distribution between Au and Cu atomic sites facilitated the thermodynamic C-N coupling step. This work demonstrated the important role of asymmetric charge distribution under dynamic regulation for urea electrosynthesis, providing a new inspiration for precise control of electrocatalysis.

Pregnancy alters fatty acid metabolism, glucose regulation, and detoxification of the liver in synchrony with biomechanical property changes

Pregnancy places a metabolic burden on the body including the liver, which is responsible for ensuring adequate nutrition for the maternal and fetal systems. To gain a better understanding of liver adaptation, this study investigates metabolic shifts occurring in livers of pregnant rats. Metabolic capacities of the livers of pregnant and non-pregnant female Wistar rats were assessed using comprehensive metabolic models. Kinetic metabolic models were generated for each animal based on protein abundance data from proteomics analysis allowing for a subject-specific assessment of hepatic metabolic functions. Data are available via ProteomeXchange with identifier PXD050758. Additionally, tissue stiffness, viscosity, and water diffusion obtained from magnetic resonance imaging and elastography were correlated with metabolic capabilities to study the relationship between metabolic function and biophysical properties. Proteome profiling revealed differences in protein expression in the livers of pregnant and non-pregnant animals. Functional analysis showed significant variations in metabolic capacities. Livers of pregnant rats had reduced capacities in carbohydrate and fatty acid metabolism, along with altered urea synthesis. Additionally, there were associations between metabolic functions and biophysical properties highlighting potential links between changes in liver structure and metabolic capacities during pregnancy. In summary, our work reveals extensive hepatic metabolic changes in pregnant rats. The liver adapts its metabolic capacities to ensure whole-body metabolic homeostasis but may struggle to counteract nutritional challenges, such as hypoglycemia. The study, employing a personalized approach combining proteomics, kinetic modeling, and advanced imaging, sheds light on the intricate interplay between hepatic adaptations and medical imaging markers, providing a foundation for further investigations into the implications for maternal and fetal health.