Urea Production Research Articles

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.

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.

Electrocatalysis for Urea Evolution and Oxidation Through Confining Atomic Ni Into In2O3 Nanosheet Catalysts

AbstractUrea, a highly sought‐after fertilizer, is conventionally manufactured through the energy‐intensive Haber–Bosch process but is frequently encountered as a pollutant in wastewater. Thus, achieving sustainable urea production under ambient conditions and the potential to recycle urea from wastewater represent significant eco‐economic advancements. In this study, a novel Ni‐confined In2O3 (Ni‐In2O3) electrocatalyst demonstrating outstanding capabilities in both the urea evolution reaction (UER) from nitrate and carbon dioxide and the highly efficient urea oxidation reaction (UOR) for waste urea utilization is introduced. Computational data and in situ X‐ray absorption spectroscopy (XAS) analysis demonstrate that the unique Ni‐oxygen vacancy (Ni‐Vo) local structure effectively modulates the electronic configuration of neighboring In and Ni atoms. This structural refinement results in a significantly reduced energy barrier for the potential‐determining steps (PDS) in both UER (*COOHNH2 → *CONH2) and UOR (*CO(NH2)2 → *CONHNH2). Consequently, the optimized catalysts achieve a urea evolution faradic efficiency of 19.6%, accompanied by remarkable UOR performance, attaining a 100 mA cm−2 anodic current density at a potential of 1.35 V. This work not only offers a sustainable route to urea production but also highlights the potential for efficient urea oxidation, contributing to a greener and more economically viable future for the nitrogen cycle.

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.

Stabilization of Cuδ+ Sites Within MnO2 for Superior Urea Electro-Synthesis.

Electrocatalytic C-N coupling between NO3 - and CO2 has emerged as a sustainable route for urea production. However, identifying catalytic active sites and designing efficient electrocatalysts remain significant challenges. Herein, the synthesis of Cu-doped MnO2 nanotube (denoted as Cu-MnO2) with stable Cuδ+-oxygen vacancies (Ovs)-Mn3+ dual sites is reported. Compared with pure MnO2, Cuδ+ doping can effectively enhance urea production performance in the co-reduction of CO2 and NO3 -. Thus, Cu-MnO2 catalyst exhibits a maximum Faradaic efficiency (FE) of 54.7% and the highest yield rate of 116.7mmolh-1gcat. -1 in a flow cell. Remarkably, the urea yield rate remains over 78mmolh-1gcat. -1 across a wide potential range. Further experimental and theoretical results elucidate the unique role of Cu-MnO2 solid-solution for stabilizing Cuδ+ sites in Cuδ+-Ovs-Mn3+, endowing the catalyst with superior structural and electrochemical stabilities. This thermodynamically promotes urea formation and kinetically lowers the energy barrier of C-N coupling.

Simultaneous efficient production of hydrogen peroxide, urea and H2 by bifunctional Cu-doped TiO2 electrocatalyst from CO2, N2 and water

The production of three separated, high-value chemicals (H2O2, urea and H2) from CO2, N2, and H2O represents a significant challenge. It is a prospective and innovative way to simultaneously produce these chemicals in an anion exchange membrane (AEM) electrolyzer, which couples anodic 2e- water oxidation (2e-WOR) and cathodic CO2, N2 and water reduction reaction (CNWRR), but has not yet been realized. Here, we found that bifunctional CuxTi1-xO2-y catalysts can be employed in the electrochemical production of H2O2, urea and H2 from CO2, N2 and water, and the optimized Cu0.12Ti0.88O2-y catalyst exhibits an excellent productivity of 11.8 μmol cm−2 min−1, 0.3 mg cm-2h−1 and 0.82 mmol cm-2h−1 for H2O2, urea and H2 at 4.0 V (50 mA cm−2) in AEM electrolyzer, respectively. Theoretical calculations reveal that the superior performance of the 2e-WOR and CNWRR is attributed to the Cu doping effect, which not only promotes the coupling of *OH but also optimizes the adsorption energy barriers of COOH* and NNH*. It is worth noting that the AEM electrolyzer assembled by bifunctional Cu0.12Ti0.88O2-y reaches a current density of 50 mA cm−2 with a cell voltage of 4.0 V and exhibits excellent stability of 50-hour continuous operation.

Techno-economic feasibility of CO2 utilization for production of green urea by Indian cement industries

The cement industry contributes substantially to global carbon emissions, necessitating urgent adoption of mitigation pathways aligned with climate goals. This study investigates the technical and economic viability of capturing carbon dioxide (CO2) emissions from cement plants in India and using that captured CO2 to produce green urea. The research aims to determine the feasibility of the CCUS approach as a practical way to reduce CO2 emissions from cement production while also boosting India's self-sufficiency in producing urea, a crucial fertilizer. The research uses a multi-criteria analysis (MCA) framework to assess various factors, including the technological readiness of CCUS technologies, the capital and operating costs of setting up and running such a system, the market demand for green urea, and the potential reduction in CO2 emissions. The study focused on 32 major cement plants in India, using data from their annual reports to inform the MCA model with an assumption of a post-combustion Monoethanolamine (MEA) scrubbing capacity CO2 capture capacity of 0.5 million tonnes per year per plant and used existing data and modeling techniques to analyze the feasibility of converting the captured CO2 into urea. The key findings indicate that this approach is promising and projects a 12.4% reduction in CO2 emissions from the cement industry if these 32 plants implement the CCUS technology. Additionally, it highlights a favorable market for the green urea produced, with an estimated output of 21.82 million tonnes per year, enough to offset a significant portion of India's reliance on urea imports. Financially, the study projects a six-year payback period and a 16.7% return on investment. It concludes that implementing CCUS technology to create green urea in Indian cement plants is technically and economically feasible. The approach has the potential to significantly reduce CO2 emissions while also supporting India's goal of self-sufficiency in urea production. However, further investigation and pilot-scale projects are recommended to validate the model's findings and optimize various aspects, such as managing flue gas impurities and leveraging waste heat for energy efficiency.

Recent Advances in Urea Electrocatalysis: Applications, Materials and Mechanisms†

Comprehensive SummaryUrea plays a vital role in human society, which has various applications in organic synthesis, medicine, materials chemistry, and other fields. Conventional industrial urea production process is energy−intensive and environmentally damaging. Recently, electrosynthesis offers a greener alternative to efficient urea synthesis involving coupling CO2 and nitrogen sources at ambient conditions, which affords an achievable way for diminishing the energy consumption and CO2 emissions. Additionally, urea electrolysis, namely the electrocatalytic urea oxidation reaction (UOR), is another emerging approach very recently. When coupling with hydrogen evolution reaction, the UOR route potentially utilizes 93% less energy than water electrolysis. Although there have been many individual reviews discussing urea electrosynthesis and urea electrooxidation, there is a critical need for a comprehensive review on urea electrocatalysis. The review will serve as a valuable reference for the design of advanced electrocatalysts to enhance the electrochemical urea electrocatalysis performance. In the review, we present a thorough review on two aspects: the electrocatalytic urea synthesis and urea oxidation reaction. We summarize in turn the recently reported catalyst materials, multiple catalysis mechanisms and catalyst design principles for electrocatalytic urea synthesis and urea electrolysis. Finally, major challenges and opportunities are also proposed to inspire further development of urea electrocatalysis technology. Key ScientistsFor urea electrosynthesis, Furuya et al. firstly investigated the electrochemical coreduction of CO2 and NO3−/NO2− using gas‐diffusion electrodes in 1995. Then, Wang et al. effectively achieved C—N bond formation and urea synthesis on PdCu alloy nanoparticles in 2020. Shortly, Yan and Yu et al. proposed the formation of *CO2NO2 from *NO2 and *CO2 intermediates at early stage on In(OH)3 electrocatalyst in 2021, and employed defect engineering strategy to facilitate the *CO2NH2 protonation in 2022. Amal et al. Investigated the role that Cu‐N‐C coordination plays for both the CO2RR and NO3RR. After that, Zhang's group developed In‐based electrocatalysts with artificial frustrated Lewis pairs for urea, and they offered a systematic screening approach for catalyst design in urea electrosynthesis in 2023. And sargent et al. reported a strategy that increased selectivity to urea using a hybrid catalyst.For urea electrooxidation, Stevenson et al. investigated the effect of Sr substitution toward the urea oxidation reaction. Wang et al. provided insights into the urea electrooxidation process using a β‐Ni(OH)2 electrode and Qiao et al. elucidated a two‐stage reaction pathway for UOR in 2021.

Boosting Electroreduction of Nitrate and CO2 to Urea on a Tandem Fe1/MoS2 Catalyst.

Urea electrosynthesis by coelectrolysis of NO3- and CO2 (UENC) holds enormous promise for sustainable urea production, while the efficient UENC process relies on the rational design of high-performance catalysts to facilitate the electrocatalytic C-N coupling efficiency and the hydrogenation reaction process. Herein, Fe single atoms supported on MoS2 (Fe1/MoS2) are developed as a highly effective and robust catalyst for UENC. Theoretical calculations and operando spectroscopic measurements reveal a tandem catalysis mechanism of the Fe1-S3 motif and MoS2-edge to jointly promote the UENC process, where the Fe1-S3 motif drives the early C-N coupling and subsequent *CO2NO2-to-*CO2NH2 step. The generated *CO2NH2 is then migrated from the Fe1-S3 motif to the nearby MoS2-edge, which facilitates the *CO2NH2 → *COOHNH2 step for urea formation. Noticeably, Fe1/MoS2 assembled in a flow cell reaches a maximum urea Faraday efficiency of 54.98% with a corresponding urea yield rate of 18.98 mmol h-1 g-1, performing at the top level among all of the UENC catalysts reported to date.

Rational Linker Design for Enhanced Performance of MOF-Derived Catalysts in Electrochemical Urea Synthesis.

2D metal-organic frameworks (2D MOFs) offer promising electrocatalytic potential for urea synthesis, yet the underlying reaction mechanisms and structure-activity relationships remain unclear. Using Cu-BDC as a model, density functional theory (DFT) calculations to elucidate these aspects are conducted. The results reveal a novel coupling mechanism involving *NO─CO and *NO─*ONCO, emphasizing the impact of linker modifications on Cu spin states and charge distribution. Notably, Cu-BDC-NH2 and Cu─BDC─OH emerge as promising catalysts. Additionally, structure-activity relationships through descriptors like d-band center, IE ratio, and L(Cu─O), providing insights for rational catalyst design is established. These findings pave the way for optimized catalysts and sustainable urea production, opening avenues for future research and technological advancements.

Rate expression model from thermodynamics application and optimal kinetic parameters determination for urea synthesis and production process

Urea, an essential organic fertilizer, enhances soil fertility by providing 0.466 nitrogen for maximum crop yield. In this study, urea is synthesized from NH3 and CO2 in an equilibrium reaction process adhering to Le Chatelier's principle, maintained under process conditions: flow rate of 63.5 kg/s, temperature of 184 °C, and pressure of 160 kg/cm2. A new rate expression model, formulated in terms of extent of reaction and mole fraction, was developed based on mass action relations and thermodynamic models. Two industrial reactors were considered: a plug flow reactor (PFR) at Notore and a continuous stirred tank reactor (CSTR) at Indorama plants. Transient reactor models, based on material and energy balance conservation principles, were numerically resolved using MATLAB version 2020 with specified input conditions. A non-linear regression statistical optimization model was employed to refine kinetic parameter values, ensuring optimal and high-quality urea yield. Model validations were conducted using literature data, revealing higher urea yields of 0.726 and 0.7032 for the CSTR and PFR, respectively. Deviations (0.134, 0.10 to 1.135 and 0.635, 0.326 to 0.850) and root mean square errors (RMSE) (0.043, 0.033 to 0.193 and 0.137, 0.087 to 0.162) were observed when validated against plant and literature values for the CSTR and PFR respectively. The refined kinetic parameters (activation energies, Arrhenius constants, and rate constants) exhibited negligible deviations (0.0004–0.0466 and 0.0004 to 0.0491) and RMSE (0.0228, 0.0055, and 0.0256 and 0.0241, 0.0096, and 0.0269) when validated against plant data, significantly enhancing urea yield in CSTR and PFR reactors respectively.

Promoting Electrocatalytic Reduction of CO2 and Nitrate to Urea on N-Doped Porous Hollow Carbon Spheres.

The electrocatalytic coreduction of CO2 and nitrate is a green method for urea synthesis, mitigating CO2 emission and nitrate contamination. However, its slow kinetics and high energy barrier result in a poor urea production performance. Herein, we reported N-doped porous hollow carbon spheres (N-PHCS) for promoting CO2 and nitrate conversion to urea via nanoconfinement and N-doping from both reaction kinetics and thermodynamics. A high urea yield of 12.0 mmol h-1 gcat-1 with Faradaic efficiency of 19.1% was achieved on N-PHCS at -1.0 V (vs Ag/AgCl), which was comparable to or even higher than those of metal-based electrocatalysts reported. The experimental and theoretical calculation results revealed that carbon spheres with an appropriate interior void and pore size were favorable for confining reactants and intermediates to accelerate urea production, while N-doping can reduce the energy barrier for urea synthesis. By regulating the microstructure and N doping of N-PHCS, it showed a superior performance for urea electrosynthesis. The energy favorable pathway for urea synthesis was through the C-N coupling reaction of *NO and *CO, and pyridinic N can reduce the reaction energy barrier.

Mechanistic studies on defective hBN-supported metal-nonmetal synergistic catalysis for urea electrosynthesis

This study explores electrocatalytic urea synthesis promoted by a newly-designed bimetallic-tricenter catalyst consisting of defective hexagonal boron nitride (hBN) and embedded dimerized 3d metal, by means of density functional theory calculations. Among all candidates, Mn was proved to be the most feasible catalytic center originating from its unique electronic structure and metal-support interactions. The metal-nonmetal synergistic effects of the Mn2N center effectively drive site-selective co-adsorption of CO and NO, spontaneous C-N coupling, low-energy-demand NO hydrogenation, and adequate protection of the carbonyl group, achieving highly active and selective urea production. The calculated limiting potential of urea formation is as low as −0.19 V, making it more favorable energetically compared to other competing reactions such as hydrogen evolution and NO reduction reactions.

Effect of cannabidiol and hemp extract on viability and function of hepatocytes derived from human induced pluripotent stem cells

Since the passage of the 2018 Agriculture Improvement Act (2018 Farm Bill), the number of products containing cannabis-derived compounds available to consumers have rapidly increased. Potential effects on liver function as a result from consumption of products containing cannabidiol (CBD), including hemp extracts, have been observed but the mechanisms for the effects are not fully understood. In this study, hepatocytes derived from human induced pluripotent stem cells (iPSCs) were used to evaluate potential hepatic effects of CBD and hemp extract at exposure concentrations ranging from 0.1 to 30 μM. Despite that a significant reduction in cell viability occurred only in the 30 μM group for both CBD and hemp extract, significant changes to cytochrome P450 activity, mitochondrial membrane potential, and lipid accumulation occurred within the concentration range of 0.1–3 μM for both CBD and hemp extract. Albumin and urea production, caspase 3/7 activity, and intracellular glutathione were significantly affected within the concentration range of 3–30 μM by CBD or hemp extract. These findings indicate that CBD and hemp extract can alter hepatic function and metabolism. The current study contributes data to help inform the evaluation of potential hepatotoxic effects of products containing cannabis-derived compounds.

Evaluating the potential of green hydrogen, ammonia and urea in Lao PDR energy transitions.

Abstract We report the results of a systematic evaluation of the redeployment of surplus hydropower electricity to produce green hydrogen (H2), ammonia (NH3) and urea (CH4N2O) in Lao PDR. Participatory system mapping (PSM) workshops convened across multiple Lao PDR ministries revealed both direct and indirect opportunities and risks as probable consequences of green H2, NH3 and urea production. Participants debated and prioritized green urea fertilizer to replace “grey” imports; coal co-firing; and fuel cells as the products that contribute to the opportunities and manage the risks identified by the PSM process. Techno-economic modelling indicates the levelized cost of urea (US$467/tonne) is competitive with Thai imports, associated with opportunities for trading carbon offsets. Carbon credits were not sufficient to offset the additional co-firing costs of coal generation, and fuel cells are a likely future enterprise. A targeted capacity building and training program was a central pillar of a systems-based dissemination strategy to develop necessary technical and planning skills and community and awareness raising. The collated research results represent an integrated foundation to draft the Lao PDR National green H2 and NH3 road map and action plan, and a cross-sectoral revision of energy transition development plans.

Chemical Dermal Exposure Risk Assessment in the Water Treatment Plant of Fertilizer Industry

Introduction:In water treatment plants (WTP), chemicals play a crucial role. However, some of these chemicals are hazardous. This study aims to conduct a dermal risk assessment in the WTP of an ammonia and urea production facility. Methods: The study was performed in August 2023 and assessed dermal exposure risk for four hazardous chemicals: NaOCl (30%), HCl (60%), H2SO4 (98%), and NaOH (48%), utilizing the Tier 2 RISKOFDERM model. Intrinsic toxicity was evaluated using risk phrases and toxicity information. Potential dermal exposure rates (PERBODY and PERHANDS) were determined based on task group and exposure modifier, while actual dermal exposure rates (AERBODY and AERHANDS) were determined based on clothing type and activity time. Health risk was assessed using actual exposure scores and intrinsic toxicity levels, which were categorized into 10 different levels ranging from 1 to 10. Results: The risk phrases indicated that four chemicals possessed a high level of intrinsic toxicity in terms of local effect but no systemic effect. PERBODY and PERHANDS were high (NaOCl, HCl) and low (H2SO4, NaOH). The actual exposure scores were determined to be 1 (high) for NaOCl and HCI, 0.01 (low) for H2SO4, and 0.03 (medium) for NaOH. Health risk values were 8 for NaOCl and HCI, 5 for H2SO4, and 6 for NaOH. Conclusion: Health risks in NaOCl and HCl were assigned action priority (AP) 1, followed by NaOH at AP-2, and H2SO4 at AP-3. The study recommends the implementation of control measures encompassing engineering solutions, administration, and personal protective equipment.

Atomically Dispersed Cu on In2O3 for Relay Electrocatalytic Conversion of Nitrate and CO2 to Urea.

Urea electrosynthesis from coelectrolysis of NO3- and CO2 (UENC) holds a significant prospect to achieve efficient and sustainable urea production. Herein, atomically dispersed Cu on In2O3 (Cu1/In2O3) is designed as an effective and robust catalyst for the UENC. Combined theoretical calculations and in situ spectroscopic analysis reveal the synergistic effect of the Cu1-O2-In site and the In site to boost the UENC energetics via a relay catalysis pathway, where the Cu1-O2-In site drives *NO3 → *NH2 and the In site catalyzes *CO2 → *CO. The generated *CO is then migrated from the In site to the Cu1-O2-In site, followed by C-N coupling with *NH2 on the Cu1-O2-In site to generate urea. Consequently, Cu1/In2O3 assembled within a flow cell exhibits an impressive urea yield rate of 28.97 mmol h-1 g-1 with a urea-Faradaic efficiency (FEurea) of 50.88%.

Comparative analysis of eight urea-electricity-heat-cooling multi-generation systems: Energy, exergy, economic, and environmental perspectives

The Haber-Bosch process for urea production is known for its significant carbon emissions. While the chemical looping ammonia generation method presents a potential alternative, its technical and economic feasibility still requires further investigation. This paper conducts a comparative analysis of eight renewable energy-driven urea-electricity-heat-cooling multi-generation systems by developing their energy, exergy, economic, and environmental evaluation models. Considering the fluctuation in renewable energy resources, an annual evaluation of the different systems is conducted based on a monthly time scale. The results indicate that systems based on the Haber-Bosch process have higher average energy and exergy efficiencies of 60–80 % and 40–50 %, respectively. For the chemical looping ammonia generation process, the respective efficiencies are 50–70 % and 30–40 %. Additionally, the system integrating the Haber-Bosch reaction, reduction reactor, and solid oxide fuel cell yields the highest energy and exergy efficiencies among the eight systems, at 68.2 % and 45.78 %, respectively. However, it is inferior to the multi-generation system integrating the chemical looping ammonia generation process in terms of economic and environmental performance. In addition, the system integrating the chemical looping ammonia generation process and solid oxide fuel cell has the shortest discounted payback period of 8 years, with annual revenue and net present value of 32.63 and 11.66 MUSD, respectively. While the operating expenditures of the Haber-Bosch (12.6–15.7 MUSD) are lower than those of the chemical looping ammonia generation process (14.0–17.5 MUSD), its capital expenditures (382.0–410.8 MUSD) are significantly higher than those of the chemical looping ammonia generation process (302.4–307.3 MUSD). Furthermore, the conducted environmental evaluation shows that the multi-generation system integrating the chemical looping ammonia generation process and reduction reactor exhibits lower overall carbon emissions (0.013 t CO2/t urea) compared to the state-of-the-art method of oxy-fuel coal-fired power plant for urea synthesis.

Enhanced solar urea synthesis from CO2 and nitrate waste via oxygen vacancy mediated-TiOx support lead-free perovskite

The nitrogen fertilizer industry, particularly urea production, notably contributes to greenhouse gas emissions and energy consumption. Urea synthesis via solar energy encounters several challenges. Specifically, solar urea synthesis methods often exhibit low efficiency and yield, primarily stemming from inefficient energy conversion processes and intricate reaction pathways. Moreover, the kinetics of the urea synthesis reaction may be sluggish, thereby impacting the overall production rate. Therefore, in this study, we introduce a novel electron-reserve-enhanced Cs2CuBr4/TiOx-Ar (CCBT-Ar) structure for the photocatalytic synthesis of urea from CO2 and nitrate waste. Theoretical calculations and spectroscopic analysis underscore the critical role of oxygen vacancies (Ov) within the amorphous TiOx shell, enhancing reactant adsorption and catalyzing the rate-determining step (*OCONH2→*HOCONH2). However, the presence of Ov also results in significant carrier recombination, acting as trapping centers and reducing urea production activity. Importantly, we demonstrate that in-situ-grown carbon nanosheets, in conjunction with TiOx, function as efficient electron reservoirs, markedly mitigating trapping-induced recombination and facilitating electron redistribution. These reserved electrons can then actively participate in the urea synthesis process. As a result, the electron-reserve-enhanced structure exhibits robust solar urea yield and selectivity, even in challenging wastewater conditions. This work provides a rational and innovative approach to catalyst development in complex solar synthesis, offering promising avenues for the sustainable production of value-added chemicals while concurrently reducing carbon emissions.