NH3 Conversion Research Articles

Enhanced photocatalytic ammonia oxidation over WO3@TiO2 heterostructures by constructing an interfacial electric field

WO3 nanorods and xWO3@TiO2 (WO3/TiO2 mass ratio (x) = 1−5) photocatalysts were synthesized using the hydrothermal and sol-gel methods, respectively. The photocatalytic activities of xWO3@TiO2 for NH3 oxidation first increased and then decreased with a rise in TiO2 content. Among them, the heterostructured 3WO3@TiO2 photocatalyst showed the highest NH3 conversion (58 %) under the simulated sunlight irradiation, which was about two times higher than those of WO3 and TiO2. Furthermore, the smallest amounts of by-products (i.e., NO and NO2) were produced over 3WO3@TiO2. The enhancement in photocatalytic performance (i.e., NH3 conversion and N2 selectivity) of 3WO3@TiO2 was mainly attributed to the formed interfacial electric field between WO3 and TiO2, which promoted efficient separation and transfer of photogenerated charge carriers. Based on the results of reactive species trapping and active radical detection, photocatalytic oxidation of NH3 over 3WO3@TiO2 was governed by the photogenerated holes and superoxide radicals. This work combines two strategies of morphological regulation and interfacial electric field construction to simultaneously improve light utilization and photogenerated charge separation efficiency, which promotes the development of full-spectrum photocatalysts for the removal of ammonia.

An experimental investigation into ammonia dissociation, oxidation and NO emission in a vertical flow reactor

Ammonia (NH3) dissociation, oxidation, and associated nitric oxide (NO) emission in a vertical cylindrical quartz reactor is investigated to establish the effect of temperature (1000 K–1400 K), initial NH3 concentration (2%, 4%, 6%, 8%, 10%) and flowrate (250 mL/min, 500 mL/min, 750 mL/min). Ammonia oxidation experiments also examine the effect of equivalence ratio (ɸ = 0.8, 0.9, 1.0, 1.1). The NH3 and O2 conversions, N2 yield, and NO emission are determined by analysing the reactor effluent compositions. Ammonia dissociation of <6% is observed for all conditions tested. Ammonia oxidation is initiated at ∼1100 K, with majority of NH3 conversion occurring at 1200 K–1300 K before completion at ∼1325 K. NO emission becomes significant at temperatures >1300 K for ɸ ≤ 1.0 and increases with decreasing equivalence ratio. Under fuel-lean conditions, increasing initial NH3 concentration increases NO emission. Fuel-rich conditions return negligible NO, attributed to the reductive effect of excessive NH3.

Role of cation in catalytic decomposition of ammonia over Ni supported zeolite Y catalysts

A series of nickel (Ni) catalysts were prepared using zeolites Y with different cation types (Na, Mg, Ca, Sr, Ba, Ce, and La) as supports and characterized by using XRD, BET, ICP-OES, XPS, and TEM, as well as NH3-TPD, CO2-TPD, and H2-TPR techniques. Their catalytic performances in decomposition of ammonia (NH3) to hydrogen (H2) were evaluated with a fixed-bed flow reactor system. The catalytic activities of the prepared catalysts for NH3 decomposition decreased in the order of Ni/SrY > Ni/BaY > Ni/LaY > Ni/CaY > Ni/NaY > Ni/MgY > Ni/CeY. The high activity of Ni/SrY catalyst may be attributed to its small Ni nanoparticle size, high basicity and strong interaction between highly dispersed Ni nanoparticles and SrY support. At 600 °C and GHSV of 9000 mLNH3·gcat−1·h−1, 98.0 % NH3 conversion with about 105.2 mmol min−1·gNi−1 H2 formation rate can be accomplished over Ni/SrY catalyst.

Numerical analysis on ammonia decomposition for hydrogen production in a membrane reactor assisted by a parabolic trough solar collector

Ammonia (NH3) has emerged as a promising hydrogen storage carrier due to its considerable hydrogen storage density, storage and transportation convenience, and zero carbon emissions during endothermic decomposition. By utilizing a parabolic trough solar collector to provide heat and integrating NH3 decomposition with a membrane reactor, a clean and sustainable method of hydrogen production can be achieved. This paper establishes a comprehensive numerical model for NH3 decomposition within a parabolic trough solar receiver/membrane reactor (PTSMR). The model incorporates heat and mass transfer in porous catalyst beds, membrane permeation, and reaction dynamics to accurately capture the intricate phenomena under actual operating conditions. Special attention is paid to the influences of inlet temperature, flow rate, flow pattern, and reaction pressure on NH3 conversion and hydrogen recovery. The results demonstrate that the temperature distribution within the PTSMR exhibits non-uniformity, and the temperature at the bottom is always higher than that at the top, especially at the outlet, where the temperature difference is more than 100K. The NH3 conversion rate in counterflow is higher than that in parallel flow, while the hydrogen recovery rate in parallel flow is higher due to the reverse permeation of hydrogen in counterflow. For a 2-mm-thickness catalyst bed, the addition of membranes increases NH3 conversion rate by 9% at a reaction pressure of 5 bar, compared to a 3% increase for an 8-mm-thickness catalyst bed. The PTSMR with a 2-mm-thickness catalyst bed obtains the optimum hydrogen yield rate.

Metallic nickel exsolved from a two-dimensional MWW-type zeolitic nickel silicate: An effective catalyst for ammonia decomposition

Exsolution of active species from metal oxide materials is an effective strategy for preparing a highly active and stable catalyst. Here, we prepared two-dimensional nickel (Ni) silicate material with delaminated MWW layers (Ni-DMLs) by hydrothermal treatment of borosilicate MWW precursor (B-MWW(P)) with Ni nitrate solutions and applied on the catalytic decomposition of ammonia (NH3) via exsolution. The layered B-MWW(P) was transformed to a three-dimensional (3D) tectosilicate MWW, a two-dimensional (2D) Ni-DML, and a 2D phyllosilicate structures at temperature regions of 100–120 °C, 140–160 °C, and 170–180 °C, respectively. Meanwhile, the Ni contents on the samples increased from 3.6 to 37.6 wt.% as the hydrothermal temperature increased from 100 to 180 °C, owing to the substitution of framework B by Ni. The chemical state of Ni on each sample was characterized by various analytical tools and correlated with their catalytic properties of NH3 decomposition over the exsolved metallic Ni species. The NH3 decomposition over Ni-DMLs was evaluated in the temperature range of 300–600 °C, and the apparent activation energies were compared. The Ni-DML-160 exhibited the best catalytic activity, achieving an NH3 conversion of 70% at 500 °C and maintained 90% to initial conversion during 100 h on stream at 550 °C. The synergistic effect of the strong interaction between the exsolved metallic Ni and the zeolite support and the 2D nature of Ni-DMLs relieved the catalytic deactivation by sintering and coking, respectively.

The enhanced electro/photocatalytic activity for nitric oxide reduction to ammonia by B@g-C9N10 monolayer

Selective electro/photocatalytic reduction of nitride oxide (NO) to ammonia (NH3) provides a promising way to remove the pollutant under ambient conditions. The key to NO reduction reaction (NORR) is to develop more economical and efficient electrocatalysts compared to the industrialized Pt-based catalysts. In this work, the boron atom doping g-C9N10 monolayer (B@g-C9N10) is designed and the electro/photocatalytic NORR performance is systematically investigated by means of density functional theory (DFT). Among the N-end, O-end and side-on structures, the N-end NO adsorption is found to be the most stable one, which greatly favors the NO activation by the “σ-donation and π* back-donation” mechanism. Among the N-distal, N-alternating, O-distal, O-alternating, Mixed 1–3 hydrogenation pathways in the electrocatalytic process, the O-alternating and Mixed-2 pathways are the most efficient NORR routes, which have the same limiting potential (UL) of −0.386 V in the step of *NH2→*NH3. However, the NO molecule is more easily activated in *N–OH along O-alternating pathway than Mixed-2 pathway. The energy barrier can be further decreased by considering the implicit and explicit solvation model and the NH3 selectivity of B@g-C9N10 is higher than N2O, N2 and H2. The irradiating energy of 1.094 eV can decrease the reaction energy, resulting in the spontaneous NORR process along Mixed-2 pathway. Our findings uncover a promising approach to design a bifunctional NORR electro/photocatalyst with high NH3 selectivity and activity NO→NH3 conversion.

Experimental and Modeling High-Pressure Study of Ammonia-Methane Oxidation in a Flow Reactor.

The present work deals with an experimental and modeling analysis of the oxidation of ammonia-methane mixtures at high pressure (up to 40 bar) in the 550-1250 K temperature range using a quartz tubular reactor and argon as a diluent. The impact of temperature, pressure, oxygen stoichiometry, and CH4/NH3 ratio has been analyzed on the concentrations of NH3, NO2, N2O, NO, N2, HCN, CH4, CO, and CO2 obtained as main products of the ammonia-methane mixture oxidation. The main results obtained indicate that increasing either the pressure, CH4/NH3 ratio, or stoichiometry results in a shift of NH3 and CH4 conversion to lower temperatures. The effect of pressure is particularly significant in the low range of pressures studied. The main products of ammonia oxidation are N2, NO, and N2O while NO2 concentrations are below the detection limit for all of the conditions considered. The N2O formation is favored by increasing the CH4/NH3 ratio and stoichiometry. The experimental results are simulated and interpreted in terms of an updated detailed chemical kinetic mechanism, which, in general, is able to describe well the conversion of both NH3 and CH4 under almost all of the studied conditions. Nevertheless, some discrepancies are found between the experimental results and model calculations.

Insight into hydroxyl groups in anchoring Ir single–atoms on vacancy–deficient rutile TiO2 supports for selective catalytic oxidation of ammonia

High–performance catalysts are extremely required for controlling NH3 emission via selective catalytic oxidation (SCO), and the anchoring structural feature of active sites is a key prerequisite for developing them. This study confirms the importance of hydroxyl groups on vacancy–deficient reducible oxides as active groups. On the one hand, spontaneous atomic dispersion of active metal Ir is promoted by the abundant terminal hydroxyl groups. On the other hand, Ir cations anchor on the TiO2 surface through exchange with H+ in Ti–OH groups, and thus occupy the Brönsted acid sites. The adsorption strength of NH3 is another key factor affecting the reaction rate–determining step, namely NH3 dehydrogenation, which occurs at a faster rate in the coordinated L–NH3 rather than the ionic B–NH4+. Meanwhile, the coordinated L–NH3 significantly avoids the competitive adsorption of water vapor in the NH3–SCO reaction by reducing the number of hydrogen bonding. The TOF of preferred 0.8Ir/TiO2 sample is significantly higher than 0.2Ir/TiO2 sample, although Ir is almost always atomic dispersed. Finally, NH3 conversion is 85% in a wet circumstance (5% H2O) at 240 °C (GHSV = 85 000 h–1), with a N2 selectivity of up to 65% on 0.8Ir/TiO2 sample.

Niobium Oxide Photocatalytically Oxidizes Ammonia in Water at Ambient Conditions

Ammonia contamination in water is a significant environmental issue since it is toxic and leads to eutrophication. Photocatalysis has been investigated as a strategy for ammonia degradation but can potentially form toxic nitrite (NO2 – ) and nitrate (NO3 – ) byproducts. This work reports on the ability of niobium oxide (Nb2O5) to photocatalytically oxidize aqueous-phase ammonia (NH3). Whereas as-synthesized Nb2O5 showed little catalytic activity (&lt; 1% NH3 conversion after 6 h of UV-C irradiation, at room temperature and atmospheric pressure, and under O2 headspace), Nb2O5 treated in basic solution (OH-Nb2O5) was able to photocatalytically degrade NH3 at ca. 9% conversion after six hours, with ca. 70% selectivity to the desired N2, with a first-order rate constant of ca. 12 times higher than the as synthesize catalyst (1.6 × 10–3 min–1 vs. 2.0 × 10–2 min–1). Raman spectroscopic analysis indicated the presence of terminal Nb=O species after base treatment of Nb2O5, implicating them as catalytically active sites. These results underscore how a simple structural modification can significantly affect photocatalytic activity for aqueous ammonia oxidation.

High-pressure study of the conversion of NH3/H2 mixtures in a flow reactor

Carbon free fuels such as hydrogen (H2) and ammonia (NH3) will probably play a fundamental role owing to their potential for clean combustion without CO2 emissions. To contribute to the knowledge and development of technologies based on carbon free combustion, the present work deals with an experimental and kinetic analysis of ammonia oxidation in its mixtures with hydrogen at high pressure (up to 40 bar), in the 250–1250 K temperature range using a quartz tubular reactor and argon as bath gas. The impact of temperature, pressure, stoichiometry and H2/NH3 ratio on the concentrations of NH3, NO, NO2, N2O, and N2 obtained as main products of oxidation has been analyzed. The main results indicate that either increasing pressure, H2/NH3 ratio or oxygen availability results in a shift of NH3 and H2 conversion to lower temperatures. The NH3 and H2 consumptions are promoted by the reactions that produce NH2, H, OH, O, HO2 and HNO species. The pressure effect is particularly significant in the low range of pressures studied. The main ammonia oxidation nitrogen products are N2 and N2O, while NO and NO2 concentrations are below the detection limit under all considered conditions. N2O formation is favored by increasing stoichiometry, pressure and H2/NH3 ratio. The experimental results are simulated and interpreted in terms of a literature detailed chemical kinetic mechanism, which, in general, is able to describe quite well both the H2 and NH3 conversion profiles under the studied conditions.

Effect of Equivalence Ratio on Pollutant Formation in CH4O/H2/NH3 Blend Combustion.

This paper investigates the effect of equivalence ratio on pollutant formation characteristics of CH4O/H2/NH3 ternary fuel combustion and analyzes the pollutant formation mechanisms of CO, CO2, and NOX at the molecular level. It was found that lowering the equivalence ratio accelerates the decomposition of CH4O, H2, and NH3 in general. The fastest rate of consumption of each fuel was found at φ = 0.33, while the rates of CH4O and NH3 decomposition were similar for the φ = 0.66 and φ = 0.4. CO shows an inverted U-shaped trend with time, and peaks at φ = 0.5. The rate and amount of CO2 formation are inversely proportional to the equivalence ratio. The effect of equivalence ratio on CO2 is obvious when φ > 0.5. NO2 is the main component of NOX. When φ < 0.66, NOX shows a continuous increasing trend, while when φ ≥ 0.66, NOX shows an increasing and then stabilizing trend. Reaction path analysis showed that intermediates such as CH3 and CH4 were added to the CH4O to CH2O conversion stage as the equivalence ratio decreased with φ ≥ 0.5. New pathways, CH4O→CH3→CH2O and CH4O→CH3→CH4→CH2O, were added. At φ ≤ 0.5, new intermediates CHO2 and CH2O2 were added to the CH2O to CO2 conversion stage, and new pathways are added: CH2O→CO→CHO2→CO2, CH2O→CO→CO2, CH2O→CHO→CO→CHO2→CO2, and CH2O→CH2O2→CO2. The reduction in the number of radical reactions required for the conversion of NH3 to NO from five to two directly contributes to the large amount of NOX formation. Equivalent ratios from 1 to 0.33 corresponded to 12%, 21.4%, 34%, 46.95%, and 48.86% of NO2 remaining, respectively. This is due to the fact that as the equivalence ratio decreases, more O2 collides to form OH and some of the O2 is directly involved in the reaction forming NO2.

Selective catalytic oxidation of ammonia to nitrogen on mixed and dual-layer monolithic catalysts

In this paper, the effects of mixed and dual-layer monolithic catalysts on NH3 conversion efficiency and by-product formation performance were studied under different conditions, in order to find a coating structure with both high activity and high N2 selectivity. The results show that in the absence of NO, the dual-layer structure of Cu-SSZ-13 as the top layer and Ag/Al2O3 as the bottom layer reduces the NH3 conversion efficiency, and the NH3 conversion efficiency further decreases with the increase of the catalyst loading on the top layer, and this trend is further strengthened at higher space velocity. However, the dual-layer catalyst significantly reduces the formation of NOx byproducts. At 600 ℃, NO decreases from 305 ppm in single-layer to 51, 40 and 35 ppm respectively, NO2 and N2O are hardly produced on the dual-layer structure catalyst. In the presence of NO, the dual-layer catalyst is conducive to improving the conversion efficiency of NH3 and NO, and the conversion efficiency of NH3 and NO will be further improved with the increase of Cu-SSZ-13 catalyst loading. In addition, the results of catalytic oxidation performance of mixed structure and dual-layer catalyst under different air conditions show that the mixed structure catalyst has a higher NH3 conversion efficiency than the dual-layer catalyst in the absence of NO, but the by-product generation amount of the mixed structure catalyst is slightly higher than that of the dual-layer catalyst. In the presence of NO, the dual-layer catalyst showed a higher NO conversion efficiency than the mixed catalyst.

Wide pH photocatalytic nitrate reduction at adaptive microenvironment-dominated liquid–liquid-solid trilayer reaction interfaces

Developing highly efficient photocatalysts with a wide pH application range is the key to achieving widespread practical application of photocatalytic denitrification. However, the current study neglects the limitations of diffusion and mass transfer efficiency in the reaction interfacial microenvironment on high activity and selectivity, resulting in the inability to achieve the ideal results. Herein, the photocatalytic NO3– reduction system with a microenvironment-dominated trilayer reaction interface of liquid (external liquid)-liquid (adaptive interfacial microenvironment)-solid (Br-Bi2WO6-x photocatalysts with different charge transfer mechanisms under acid/base conditions and hydrophilic surfaces) (LEL-LIM-S) was successfully constructed. The interfacial microenvironment in the system can self-adapt and adjust its ion composition according to the changes in the pH environment, which facilitates timely supplementation of NO3–/HCOO– required for the reaction from external liquid, thus maintaining the relative stability of the microenvironment and achieving an excellent NO3– removal rate of over 90 % in a wide pH range from 3 to 9. Meanwhile, the trilayer reaction interface of LEL-LIM-S collectively constitutes a unique carrier shuttle and molecular reaction channel from the catalyst interior to the surface contaminants. Highly selective NO3– to NH3 conversion (NH3 selectivity of 91.7 %, NH3 yield of 750 μmol g-1h−1) could be accomplished utilizing this channel.

Present State and Future Outlook of Ammonia Production through Photocatalytic Nitrate Reduction

Ammonia (NH3) production has gained increasing attention owing to its versatility in both industrial and agricultural applications, as well as its potential as a next‐generation energy carrier with a high hydrogen density. Given the energy‐intensive and environmentally impactful nature of the Haber–Bosch process, there is a pressing need for a sustainable NH3 synthesis method under ambient conditions. Nitrate (NO3−) emerges as a compelling nitrogen source due to its numerous advantages over inert nitrogen (N2) gas, such as its relatively low dissociation energy and high aqueous solubility. Moreover, NO3− is a common contaminant found in wastewater, posing a threat to aquatic ecosystems. The photocatalytic NO3− reduction to NH3, which utilizes sunlight to convert contaminants into value‐added chemicals, aligns perfectly with the need for sustainable solutions. This perspective reviews the latest advancements in the field of photocatalytic NO3− to NH3 conversion. The mechanism behind the conversion of NO3− to NH3 is briefly explained, and photocatalysts exhibiting high selectivity and activity in NH3 production, along with other influential factors, are summarized. Additionally, current challenges and future prospects within this field are discussed.This perspective will provide a valuable guidance for future research in the realm of photocatalytic NH3 production via NO3− reduction.

Anomalous increase in global atmospheric ammonia during COVID-19 lockdown: Need policies to curb agricultural emissions

The restrictions imposed on human activities during the COVID-19 lockdown (LD) period provided a new scenario to identify potential sources of atmospheric pollution. There are several studies that deal with changes in air quality around the world during LD, but very few on atmospheric ammonia (NH3). Therefore, we examine the changes in global NH3 during LD (April–May 2020) in comparison to the pre-lockdown (PreLD, April–May 2017–2019) and post-lockdown (PostLD, April–May 2021) periods, and assess the factors responsible for these changes. We observe an increase in NH3 during LD across the latitudes, with very high values in the western Europe, Eastern China (EC), the Indian subcontinent and the eastern United States of America (USA). However, a decline in NH3 is observed in some regions of South America (SA) and North America (NA). Similar changes in NH3 during LD are also observed in smaller spatial scales, as found in 3000 cities across the globe. The reduction of sulphur dioxide (SO2), nitrogen dioxide (NO2), nitric acid (HNO3), humidity and cloud cover as a result of restrictions on human activities, particularly in the western Europe and the USA, may have impeded the conversion of NH3 to particulates, which led to a higher NH3 there. Nevertheless, agricultural activities and livestock are the most prominent sources of atmospheric NH3, and were not under restriction during LD, show an enhancement in terms of the use of nitrogen fertilizer, crop production and area harvested, which also cause a rise in NH3 in these regions. Therefore, it is evident that the changes in meteorology and atmospheric composition, together with increased agricultural activities, led to the global increase in atmospheric NH3 during LD. That is, most pollutants show a decline during LD, but NH3 exhibits a rise due to its sources such as agricultural activities. Henceforth, environmental regulations, policies and advanced technologies are required in the agricultural sector, such as fertilizer deep placement using urea briquettes and restricted application of nitrogen fertilizers, to curb NH3 emissions.

(Invited) Ammonia Electrolysis from Fundamentals to Scale up

Dr. Botte’s research group has been studying the ammonia electrolysis process, for the production of nitrogen and hydrogen from ammonia and ammonia waste streams, from fundamentals in materials for electrocatalysis including computational work, mathematical modeling, optimization studies and microkinetic models combined with hydrodynamic analysis, simulation on parallel plates flow cells to system integration and scale-up in a skid with a stack of 6000 cm2 electrolysis cell, the biggest reported in the literature. In this presentation, we will discuss how the integration of the components have been critical for the evolution of the technology. In addition, results from the most recent prototype of this technology, installed in a wastewater treatment plant in line with a clinocliptolite ion exchange system that capture the ammonia from wastewater and concentrated it prior to the inlet of the electrolyzer, will be discussed. The electrochemical process operates in a polarity pulse mode that allows NH3 conversions above 80% with specific energy consumption of 5.7 kWh kg−1 of NH3-N without considering the energy that can be obtained from the H2.

A novel bifunctional Pt/Ce/WZrOx catalyst for efficient selective oxidation of high-concentration NH3

A novel bifunctional catalyst with excellent NH3-SCO and NH3-SCR functions is effective to achieve excellent low-temperature activity and high N2 selectivity simultaneously, especially for removing high-concentration NH3 slipped from NH3-fuel engine exhaust gas. Herein, a small amount of noble metal Pt (0.1 wt%) was introduced in Ce/WZrOx to synthesize a novel bifunctional NH3-SCO catalyst. The experimental results showed that deposition order of Pt and Ce active species supported on WZrOx had a significant influence on NH3-SCO performance. Pt/Ce/WZrOx catalyst prepared through impregnation-precipitation method exhibited a much superior comprehensive NH3 removal performance compared to Pt/Al2O3 catalyst (Pt 0.1 wt%). It achieved an NH3 conversion of 96.4 % and a N2 selectivity of 94.2 % at 310 °C. A series of characterization tests were adopted to compare the physicochemical properties of Pt/Ce/WZrOx and Ce/WZrOx catalysts to reveal the possible functions of Pt and Ce active species in NH3-SCO reactions. The results of H2-TPR implied that there was a strong interaction between the Pt and Ce active species, which greatly enhanced the low-temperature redox property of Pt/Ce/WZrOx catalyst. Besides, electron transfer between Pt0/Ptn+ and Ce3+/Ce4+ cycles facilitated the generation of oxygen vacancies on the Pt/Ce/WZrOx catalyst surface, which played a key role in the reaction for removing high-concentration NH3. In-situ DRIFTS results suggested that NH3-SCO reactions over Pt/Ce/WZrOx catalyst might follow both imide (–NH) and hydrazine (-N2H4) mechanisms.

Theoretical insights into transition metal clusters supported on graphyne as electrocatalysts for N2–to–NH3 conversion

NH3 is not only an important energy intermediates and carbon-free energy carrier, but also essential for various production and life processes. Under ambient conditions, electrocatalytic nitrogen reduction reaction (NRR) is considered to be a very attractive approach, the process converts clean electrical energy into chemical energy, and realizes the efficient use and conversion of renewable energy, which is of great significance in energy and environmental protection. In this study, density functional theory was applied to transition metal clusters supported on graphyne as electrocatalysts (TM3@GY) to realize the NRR process. The effects of cluster types and doping atoms on catalytic performance were systematically studied. Finally, Fe3@BGY was selected as a potential NRR catalytic system with an initial potential of −0.560 V. The reason of the high catalytic activity was revealed through the calculation of electronic properties, which provides a theoretical basis for designing new high-performance cluster catalysts.

Lattice-Stabilized Chromium Atoms on Ceria for N2O Synthesis.

The development of selective catalysts for direct conversion of ammonia into nitrous oxide, N2O, will circumvent the conventional five-step manufacturing process and enable its wider utilization in oxidation catalysis. Deviating from commonly accepted catalyst design principles for this reaction, reliant on manganese oxide, we herein report an efficient system comprised of isolated chromium atoms (1 wt %) stabilized in the ceria lattice by coprecipitation. The latter, in contrast to a simple impregnation approach, ensures firm metal anchoring and results in stable and selective N2O production over 100 h on stream up to 79% N2O selectivity at full NH3 conversion. Raman, electron paramagnetic resonance, and in situ UV-vis spectroscopies reveal that chromium incorporation enhances the density of oxygen vacancies and the rate of their generation and healing. Accordingly, temporal analysis of products, kinetic studies, and atomistic simulations show lattice oxygen of ceria to directly participate in the reaction, establishing the cocatalytic role of the carrier. Coupled with the dynamic restructuring of chromium sites to stabilize intermediates of N2O formation, these factors enable catalytic performance on par with or exceeding benchmark systems. These findings demonstrate how nanoscale engineering can elevate a previously overlooked metal into a highly competitive catalyst for selective ammonia oxidation to N2O, paving the way toward industrial implementation.

Ethanolammonium chloride-glycerol deep eutectic solvents for efficient and reversible absorption of NH3 through multiple hydrogen-bond interaction

Efficiently separating NH3 from the exit gas of NH3 synthesis tower has significant economic and environmental benefits, such as improving the NH3 conversion rate and reducing pollution emission. In this study, a series of EtOHACl + Gly deep eutectic solvents (DESs) with numerous hydrogen-bond sites were synthesized. The findings suggest that the use of EtOHACl + Gly DESs can result in both exceptional NH3 absorption capacities and superior selectivities. EtOHACl + Gly (1:2) has the NH3 capacities of up to 12.39 mol/kg at 298.2 K and 105.5 kPa, while its N2 and H2 capacities are negligible. Additionally, the absorbed NH3 can be easily released by heating and reducing pressure, and the NH3 capacities remain stable after undergoing six cycles. The study also examined the interaction mechanism of EtOHACl + Gly DESs for the NH3 separation, utilizing spectral characterizations, quantum chemistry calculations and molecular dynamics simulations.