Selective Oxidation Of Ammonia Research Articles

Ammonia and toluene oxidation: Mutual activating effect of copper and cerium on catalytic efficiency

Copper and cerium containing hydrotalcite-like precursors Cux-Cey-Mg-Al were synthesized by mutual co-precipitation followed by calcination at 800 °C. The obtained mixed metal oxides were studied as catalysts for selective ammonia oxidation (NH3-SCO) and toluene combustion. Various techniques, such as temperature-programmed reduction with hydrogen, temperature-programmed desorption of toluene, scanning electron microscopy and reactive frontal chromatography were used to characterize the catalysts. Series 800-Cux-Ce2.5 showed the highest catalytic efficiency in both reactions, allowing complete NH3 and C7H8 conversion below 350 °C and 500 °C, respectively. CeO2 crystallites (12–18 nm), as well as dispersed CuO oxide forms were found in the most active samples. Both phases affect pollutants conversion, however, for ammonia oxidation the occurrence of Cu2+ is essential, while for toluene oxidation, the formation of Ce4+ is sufficient. Over the most active sample (800-Cu5-Ce2.5) the complete conversion in mutual oxidation of NH3 and toluene was achieved below 450 °C.

In-situ oxidation of ammonia nitrogen to N2 in low temperature groundwater through Cl• − mediated peroxymonosulfate – Fe3O4 / chlorine process

The conventional ammonia in-situ treatment technology fails to achieve complete NH4+-N degradation, while the high concentration of native iron in groundwater further complicates its removal process, potentially leading to adverse environmental consequences. This study investigates the introduction of peroxymonosulfate (PMS) into groundwater containing high concentrations Fe2+ (Fe3O4 as a ferrous source), which can act as persistent catalysts, and Cl-, causing the degradation of ammonia through chlorine free radical-based advanced oxidation processes (PMS- Fe3O4/Cl-), and evaluates the advantages and limitations of employing the PMS- Fe3O4/Cl- system for ammonia treatment. The rapid reaction between SO4•- and Cl- resulted in the formation of Cl• as primary products. Cl• initiates a cascade of subsequent reactions with pH-dependent secondary active products. Under optimal conditions, the ammonia removal efficiency reached 97.44 % using the PMS- Fe3O4/Cl- system within 120 min of operation, which can be attributed to the selective oxidation of ammonia by chlorine reactive species. And this finding was substantiated by observations from experiments involving free radical quenching and EPR spectra coupled with DMPO. The HCO3– and humic acid (HA) in water can significantly affect the removal of ammonia, owing to their capability of quenching SO4•- and Cl•. Meanwhile, the levels of generated toxic chlorates in our system remain within acceptable limits. The PMS- Fe3O4/Cl- system exhibited outstanding transport capacity and stability in simulated columns, demonstrating excellent ammonia oxidation efficiency in natural groundwater, thereby confirming its promising practical potential. All experiments were executed at a temperature of 12 ℃, thereby verifying the remarkable efficacy of the PMS- Fe3O4/Cl- system in removing ammonia even under microtherm conditions.

Surface States Governing the Activity and Selectivity of Pt-Based Ammonia Slip Catalysts for Selective Ammonia Oxidation

Surface States Governing the Activity and Selectivity of Pt-Based Ammonia Slip Catalysts for Selective Ammonia Oxidation

Zeolite-like ion-exchanged Cu-attapulgite catalysts for promoted selective oxidation of ammonia

Zeolite-like ion-exchanged Cu-attapulgite catalysts have been developed for selective catalytic oxidation of ammonia.

Highly Selective Ammonia Oxidation on BiVO4 Photoanodes Co‐catalyzed by Trace Amounts of Copper Ions

AbstractHigh‐efficient photoelectrocatalytic direct ammonia oxidation reaction (AOR) conducted on semiconductor photoanodes remains a substantial challenge. Herein, we develop a strategy of simply introducing ppm levels of Cu ions (0.5–10 mg/L) into NH3 solutions to significantly improve the AOR photocurrent of bare BiVO4 photoanodes from 3.4 to 6.3 mA cm−2 at 1.23 VRHE, being close to the theoretical maximum photocurrent of BiVO4 (7.5 mA cm−2). The surface charge‐separation efficiency has reached 90 % under a low bias of 0.8 VRHE. This AOR exhibits a high Faradaic efficiency (FE) of 93.8 % with the water oxidation reaction (WOR) being greatly suppressed. N2 is the main AOR product with FEs of 71.1 % in aqueous solutions and FEs of 100 % in non‐aqueous solutions. Through mechanistic studies, we find that the formation of Cu−NH3 complexes possesses preferential adsorption on BiVO4 surfaces and efficiently competes with WOR. Meanwhile, the cooperation of BiVO4 surface effect and Cu‐induced coordination effect activates N−H bonds and accelerates the first rate‐limiting proton‐coupled electron transfer for AOR. This simple strategy is further extended to other photoanodes and electrocatalysts.

Highly Selective Ammonia Oxidation on BiVO4 Photoanodes Co-catalyzed by Trace Amounts of Copper Ions.

High-efficient photoelectrocatalytic direct ammonia oxidation reaction (AOR) conducted on semiconductor photoanodes remains a substantial challenge. Herein, we develop a strategy of simply introducing ppm levels of Cu ions (0.5-10 mg/L) into NH3 solutions to significantly improve the AOR photocurrent of bare BiVO4 photoanodes from 3.4 to 6.3 mA cm-2 at 1.23 VRHE , being close to the theoretical maximum photocurrent of BiVO4 (7.5 mA cm-2 ). The surface charge-separation efficiency has reached 90 % under a low bias of 0.8 VRHE . This AOR exhibits a high Faradaic efficiency (FE) of 93.8 % with the water oxidation reaction (WOR) being greatly suppressed. N2 is the main AOR product with FEs of 71.1 % in aqueous solutions and FEs of 100 % in non-aqueous solutions. Through mechanistic studies, we find that the formation of Cu-NH3 complexes possesses preferential adsorption on BiVO4 surfaces and efficiently competes with WOR. Meanwhile, the cooperation of BiVO4 surface effect and Cu-induced coordination effect activates N-H bonds and accelerates the first rate-limiting proton-coupled electron transfer for AOR. This simple strategy is further extended to other photoanodes and electrocatalysts.

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.

Isolated Pt Atoms Embedded in CuO Nanocatalysts for Selective Oxidation of Ammonia

Isolated Pt Atoms Embedded in CuO Nanocatalysts for Selective Oxidation of Ammonia

Low‐Valent Manganese Atoms Stabilized on Ceria for Nitrous Oxide Synthesis (Adv. Mater. 24/2023)

Oxidation Catalysts In article number 2211260, Javier Pérez-Ramírez and co-workers report the design of a novel atomically dispersed Mn catalyst on CeO2 for selective oxidation of ammonia to nitrous oxide. Effective stabilization of low-valence isolated manganese sites results in the formation of a unique catalytic ensemble, which enables facile oxygen activation and leads to unprecedented activity and stability.

Construction of the multi-layer TiO2-NTs/Sb-SnO2/PbO2 electrode for the highly efficient and selective oxidation of ammonia in aqueous solution: Characterization, performance and mechanism

Electrochemical oxidation is a promising technology to convert ammonia nitrogen to environmental-friendly gaseous nitrogen, but the high cost of the precious metal as an electrode limits its application. Herein, the multi-layer TiO2-NTs/Sb-SnO2/PbO2 electrode, a cheap and efficient dimensionally stable anode (DSA), was constructed for selective electrocatalytic oxidation of ammonia. The surface morphology, crystalline structure, and composition of the TiO2-NTs/Sb-SnO2/PbO2 electrode were investigated by the field emission scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The synergistic effect of the multi-layer structures of the electrode contributed to a stable structure and efficient electrocatalytic activity. Accelerated lifetime measurements and electrode recycling tests proved that the electrode possessed outstanding stability and long life with continuously used for 935 h. Compared with the commercial Ti/RuO2-IrO2, the TiO2-NTs/Sb-SnO2/PbO2 electrode displayed a more excellent performance of chlorine evolution and higher removal efficiency of ammonia. Under the optimal conditions, 30 mg/L of ammonia nitrogen could be completely removed with 92.3% selective conversion to gaseous nitrogen after 60 min. Moreover, the difference between oxygen evolution potential and chlorine evolution potential exceeded 0.45 V on the TiO2-NTs/Sb-SnO2/PbO2 electrode, which enhanced the anodic chlorine evolution reaction. Hypochlorite radical (ClO•) was supposed as the dominant oxidant to transform ammonia in water, which could promote ammonia removal and the selectivity of gaseous nitrogen with minimizing by-products formation such as nitrite and nitrate, etc. Therefore, this study suggests that the constructed multi-layer TiO2-NTs/Sb-SnO2/PbO2 electrode might be a promising anode for the electrochemical oxidation of ammonia nitrogen to N2 in an aqueous solution.

Selective oxidation of ammonia to dinitrogen gas by facile Co2+/PMS/chloridion process through reactive chlorine radicals

The selective oxidation of ammonia to dinitrogen gas in some special wastewater is of paramount significance, but still a challenge. In this study, chlorine radical (Cl•)-mediated oxidation process was developed to realize the selective oxidation of NH4+-N to N2, in which Cl• was generated in Co2+/peroxymonosulfate (PMS)/chloridion (Cl−) system. The effect of various operational parameters on the efficiency and selectivity of ammonia oxidation to N2 was investigated, such as PMS concentration, Co2+ concentration, Cl− concentration and pH value. The experiment results showed that Cl•-mediated NH4+-N oxidation reaction exhibited high NH4+-N removal efficiency and considerable selectivity to N2 in the range of pH from 2.0 to 6.5. The removal efficiency of NH4+-N was 90.39%, and the selectivity of NH4+-N to N2 achieved up to 97.16%. The possible mechanism for high efficient and selective oxidation of NH4+-N to N2 was tentatively proposed. The process developed in this study could provide a novel technology for the treatment and selective oxidation of ammonium in some special types of ammonium-containing wastewater.

Oxygen vacancies enhancing performance of Mg-Co-Ce oxide composite for the selective catalytic ozonation of ammonia in water

Catalytic ozonation based on heterogeneous metal oxides is a promising approach to removing ammonia as gaseous nitrogen from water. Herein, MgO/Co3O4/CeO2 was prepared for catalytic ozonation of ammonia in an aqueous solution. The influence of various reaction conditions was systematically investigated and optimized, in which the reaction kinetics was also analyzed. After doping Ce, the catalyst with Mg-Co-Ce molar ratio of 4:1:1 and calcined at 700 °C for 3 h, has abundant surface oxygen vacancies and exhibited excellent performance for the selective catalytic oxidation of ammonia to gaseous nitrogen by ozone. It was found that the catalytic activity of catalysts was positively related to oxygen vacancies concentration on the composites surface, which might play a vital role in selective catalytic ozonation. Under the optimal conditions, the ammonia removal rate in MgO/Co3O4/CeO2 catalytic system was 0.03328 min−1 (R2 = 0.99942), about 2.1 times greater than that of MgO/Co3O4 (0.01597 min−1, R2 = 0.99813), and the selectivity was further enhanced from 73.57% to 86.94%. Moreover, the evolution of nitrogen and chlorine species was determined to discuss the mechanism of selective oxidation of ammonia in the low chlorine-containing solution. This study might promote the understanding of catalytic ozonation of ammonia to gaseous nitrogen selectively.

Photoelectrochemical and photocatalytic studies by applying an organic p-n bilayer for the selective oxidation of ammonia to dinitrogen

• Platinum-loaded MWCNT was newly fabricated as a co-catalyst for NH 3 oxidation. • The selective oxidation of NH 3 to N 2 occurred at the cocatalyst-loaded organo-photoanode. • The overall decomposition of NH 3 was photoelectrochemically and photocatalytically accomplished. • Even when Pt was subjected to a high potential, its stable catalysis for the NH 3 oxidation was verified. • By embedding the co-catalyst in a Nafion membrane, the disorder of Pt was avoided at the high applied potential. Ammonia (NH 3 ) is a pollutant that needs to be treated properly. Its oxidative degradation to dinitrogen (N 2 ) involves the transfer of six electrons, and thus, an active catalyst must be applied to accomplish the selective formation of N 2 from NH 3 . In this work, polycrystalline Pt was newly prepared on a multi-walled carbon nanotube (MWCNT) supporter, which was used as a co-catalyst by embedding it in a Nafion® membrane (i.e., Nf[Pt/MWCNT]). The 10 nm-sized Pt particles were well characterized by means of transmission electron microscopy and electrochemistry. We have found that an organic p-n bilayer, comprising fullerene ( n -type) and phthalocyanine (p-type), works as a photoanode capable of oxidation at the phthalocyanine surface. When applying Nf[Pt/MWCNT] as the co-catalyst at the organo-bilayer, the selective NH 3 oxidation was confirmed to occur stably in terms of photoelectrochemistry and photocatalysis, particularly under visible light irradiation.

Selective catalytic oxidation of ammonia to nitric oxide via chemical looping

Selective oxidation of ammonia to nitric oxide over platinum-group metal alloy gauzes is the crucial step for nitric acid production, a century-old yet greenhouse gas and capital intensive process. Therefore, developing alternative ammonia oxidation technologies with low environmental impacts and reduced catalyst cost are of significant importance. Herein, we propose and demonstrate a chemical looping ammonia oxidation catalyst and process to replace the costly noble metal catalysts and to reduce greenhouse gas emission. The proposed process exhibit near complete NH3 conversion and exceptional NO selectivity with negligible N2O production, using nonprecious V2O5 redox catalyst at 650 oC. Operando spectroscopy techniques and density functional theory calculations point towards a modified, temporally separated Mars-van Krevelen mechanism featuring a reversible V5+/V4+ redox cycle. The V = O sites are suggested to be the catalytically active center leading to the formation of the oxidation products. Meanwhile, both V = O and doubly coordinated oxygen participate in the hydrogen transfer process. The outstanding performance originates from the low activation energies for the successive hydrogen abstraction, facile NO formation as well as the easy regeneration of V = O species. Our results highlight a transformational process in extending the chemical looping strategy to producing base chemicals in a sustainable and cost-effective manner.

Применение продуктов процесса риформинга аммиака для питания двигателя внутреннего сгорания, работающего по циклу Дизеля

This article discusses the use of ammonia reforming to generate hydrogen to be used as an additive to the main type of fuel in the internal combustion engine operating on the Diesel cycle. The feed of the hydrogen additive with the reforming products is implemented through the intake manifold to the engine cylinders. There was carried out a comparative analysis of ammonia with other types of fuel in terms of gross calorific value and hydrogen content. Autothermal reforming of ammonia (NH3 - ATR), combining selective oxidation of ammonia (to nitrogen (N) and water (H2O)) and thermal decomposition of ammonia on a ruthenium catalyst with using air as a source of oxygen is considered. The article provides an assessment of the application of reforming and the effect of the product on the combustion of fuel and exhaust gases. The addition of a fairly small amount of non-carbon reformate, approximately 5 % of the diesel fuel, is quite effective in reducing engine carbon emissions, including CO2, CO and total hydrocarbons (CHx).

Rational ensemble design of alloy catalysts for selective ammonia oxidation based on machine learning

High-throughput computation and machine learning studies are conducted for the rational design of ensembles of alloy catalysts for selective catalytic oxidation of NH3 (NH3-SCO).

Theoretical design principles of metal catalysts for selective ammonia oxidation from high throughput computation

High throughput calculation is performed to reveal the ruling laws of catalytic performance and further screen potential alloy catalysts with high activity and selectivity for selective catalytic oxidation of ammonia (NH3-SCO).

Progress on Noble Metal-Based Catalysts Dedicated to the Selective Catalytic Ammonia Oxidation into Nitrogen and Water Vapor (NH3-SCO).

A recent development for selective ammonia oxidation into nitrogen and water vapor (NH3-SCO) over noble metal-based catalysts is covered in the mini-review. As ammonia (NH3) can harm human health and the environment, it led to stringent regulations by environmental agencies around the world. With the enforcement of the Euro VI emission standards, in which a limitation for NH3 emissions is proposed, NH3 emissions are becoming more and more of a concern. Noble metal-based catalysts (i.e., in the metallic form, noble metals supported on metal oxides or ion-exchanged zeolites, etc.) were rapidly found to possess high catalytic activity for NH3 oxidation at low temperatures. Thus, a comprehensive discussion of property-activity correlations of the noble-based catalysts, including Pt-, Pd-, Ag- and Au-, Ru-based catalysts is given. Furthermore, due to the relatively narrow operating temperature window of full NH3 conversion, high selectivity to N2O and NOx as well as high costs of noble metal-based catalysts, recent developments are aimed at combining the advantages of noble metals and transition metals. Thus, also a brief overview is provided about the design of the bifunctional catalysts (i.e., as dual-layer catalysts, mixed form (mechanical mixture), hybrid catalysts having dual-layer and mixed catalysts, core-shell structure, etc.). Finally, the general conclusions together with a discussion of promising research directions are provided.

Enhanced Ammonia Oxidation Catalysis by a Low-Spin Iron Complex Featuring Cis Coordination Sites

The goal of using ammonia as a solar fuel motivates the development of selective ammonia oxidation (AO) catalysts for fuel cell applications. Herein, we describe Fe-mediated AO electrocatalysis with [(bpyPy2Me)Fe(MeCN)2]2+, exhibiting the highest turnover number (TON) reported to date for a molecular system. To improve on our recent report of a related iron AO electrocatalyst, [(TPA)Fe(MeCN)2]2+ (TON of 16), the present [(bpyPy2Me)Fe(MeCN)2]2+ system (TON of 149) features a stronger-field, more rigid auxiliary ligand that maintains cis-labile sites and a dominant low-spin population at the Fe(II) state. The latter is posited to mitigate demetalation and hence catalyst degradation by the presence of a large excess of ammonia under the catalytic conditions. Additionally, the [(bpyPy2Me)Fe(MeCN)2]2+ system exhibits a substantially faster AO rate (ca. 50×) at significantly lower (∼250 mV) applied bias compared to [(TPA)Fe(MeCN)2]2+. Electrochemical data are consistent with an initial E1 net H-atom abstraction step that furnishes the cis amide/ammine complex [(bpyPy2Me)Fe(NH2)(NH3)]2+, followed by the onset of catalysis at E2. Theoretical calculations suggest the possibility of N-N bond formation via multiple thermodynamically plausible pathways, including both reductive elimination and ammonia nucleophilic attack. In sum, this study underscores that Fe, an earth-abundant metal, is a promising metal for further development in metal-mediated AO catalysis by molecular systems.

Highly Selective Ammonia Oxidation to Nitric Oxide over Pty/TixCe(1-x)O2 Catalysts

The resulting supported catalytic materials were probed for a series of Pty/TixCe(1-x)O2 (y = 0.005, 0.05, 0.5, 1, 5; x = 0.98, 0.9, 0.7, 0.5, 0.3, 0.02) supports primed by the sol-gel method. By using modern Analysis techniques such as Raman, XRD, SEM, H2-TPR, XPS N2-isotherm. Catalysts are organized by impregnation are categorized in detail and also tested in the bed reactor of ammonia oxidation. The NO selectivity attained over Pty/TixCe(1-x)O2 in the middle of 873 and 1073 K was about 97.7% and surpassed that of Pt gauzes, because of adsorbed and lattice oxygen species contribute to ammonia oxidation. The catalytic performance of Pty/TixCe(1-x)O2 did not increase with the content of platinum. Depending entirely on the investigational results, a reasonable reaction mechanism where thermodynamics and kinetic are tortuous.