Reduction Of NO Research Articles

Selective catalytic reduction of NO with NH3 over copper-manganese spinel oxides at low temperature: effects of calcination temperature and dispersant

Selective catalytic reduction of NO with NH3 over copper-manganese spinel oxides at low temperature: effects of calcination temperature and dispersant

Selective Formation of Cu Active Sites with Different Coordination States on Pseudospinel CuAl2O4 and Their NO Reduction Catalysis.

In the spinel framework, copper (Cu) in two distinct coordination states exhibits catalytic activity for NO reduction through different mechanisms. However, detailed exploration of their respective catalytic properties, such as the redox behavior of Cu and substrate molecule adsorption, has been challenging due to difficulties in their separate formation. In this study, we present the controlled formation of pseudospinel CuAl2O4, containing exclusively tetrahedrally or octahedrally coordinated Cu, achieved by manipulating aging temperature and O2 concentration. Through these materials, we observed that in the CO-NO reaction, the step primarily determining the rate differs: NO reduction dominates with octahedrally coordinated Cu, whereas carbon monoxide (CO) oxidation is prominent with tetrahedrally coordinated Cu. The lower coordination number of Cu significantly benefits NO reduction but negatively impacts the CO-NO reaction, albeit positively influencing NO reduction in three-way catalytic reactions.

RhNi Bimetallenes with Lattice-Compressed Rh Skin towards Ultrastable Acidic Nitrate Electroreduction.

Harvesting recyclable ammonia (NH3 ) from acidic nitrate (NO3 - )-containing wastewater requires the utilization of corrosion-resistant electrocatalytic materials with high activity and selectivity towards acidic electrochemical nitrate reduction (NO3 ER). Herein, ultrathin RhNi bimetallenes with Rh-skin-type structure (RhNi@Rh BMLs) are fabricated towards acidic NO3 ER. The Rh-skin atoms on the surface of RhNi@Rh BMLs experience the lattice compression-induced strain effect, resulting in shortened Rh-Rh bond and downshifted d-band center. Experimental and theoretical calculation results corroborate that Rh-skin atoms can inhibit NO2 */NH2 * adsorption-induced Rh dissolution, contributing to the exceptional electrocatalytic durability of RhNi@Rh BMLs (over 400 h) towards acidic NO3 ER. RhNi@Rh BMLs also reveal an excellent catalytic performance, boasting a 98.4% NH3 Faradaic efficiency and a 13.4mg h-1 mgcat -1 NH3 yield. Theoretical calculations reveal that compressive stress tunes the electronic structure of Rh skin atoms, which facilitates the reduction of NO* to NOH* in NO3 ER. The practicality of RhNi@Rh BMLs has also been confirmed in an alkaline-acidic hybrid zinc-nitrate battery with a 1.39V open circuit voltage and a 10.5mW cm-2 power density. This work offers valuable insights into the nature of electrocatalyst deactivation behavior and guides the development of high-efficiency corrosion-resistant electrocatalysts for applications in energy and environment.

Nickel Nanoparticles Confined in Core–Shell Derived from Covalent Organic Framework for the Efficient Electrocatalytic NO Reduction to NH3

Nickel Nanoparticles Confined in Core–Shell Derived from Covalent Organic Framework for the Efficient Electrocatalytic NO Reduction to NH₃

Al-rich Cu-SSZ-13 zeolite synthesized by interconversion from Y: Crystallization process resolution and application in the selective catalytic reduction of NO with NH3

Cu-SSZ-13 zeolite is a promising catalyst in the selective catalytic reduction (SCR) of NOx with NH3 and the interzeolite conversion is considered as a convenient method with relatively low cost to get the Al-rich SSZ-13 zeolite with great hydrothermal stability. However, the crystallization process of interzeolite conversion and its relation to the catalytic performance of Cu-SSZ-13 in the NH3-SCR of NOx are still poorly understood. Herein, the interzeolite conversion process of Y to SSZ-13 was well resolved and the effect of major synthesis factors on the hydrothermal stability and catalytic performance of Cu-SSZ-13 in the NH3-SCR of NOx was investigated. The results indicate that highly crystalline SSZ-13 can be synthesized by the interzeolite conversion from Y, using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as the structure-directing agent (SDA) and with a SDA/Si molar ratio of 0.06–0.2. The Y zeolite of FAU framework is first degraded and decomposed into the oligomeric aluminosilicate fragments quickly in the alkaline circumstance; thereafter, the oligomeric fragments develop into the crystal nuclei that arouse the rapid crystallization of the SSZ-13 zeolite of CHA framework with the help of SDA and solid Al(OH)3, during which the Al(OH)3 source is dissolved and restructured to tetrahedral Al species and incorporated into the CHA framework. The synthesized Cu-SSZ-13 zeolite exhibits excellent catalytic performance in the NH3-SCR of NO, achieving an NO conversion of nearly 90% at a rather low temperature of 150 °C and a gaseous hourly space velocity (GHSV) of 100,000 h−1. Moreover, the Cu-SSZ-13 catalyst displays great hydrothermal stability and remains highly active even after aging at 800 °C. These results help to clarify the mechanism of interzeolite conversion and provide an effective method to synthesize highly crystalline Al-rich SSZ-13 zeolite with great potential for application in the NH3-SCR of NOx.

Promotional effect of aluminum doping on the sulfated Fe2O3 catalyst in selective catalytic reduction of NO with NH3

Promotional effect of aluminum doping on the sulfated Fe2O3 catalyst in selective catalytic reduction of NO with NH3

Mitigation of N2O emissions in water-saving paddy fields: Evaluating organic fertilizer substitution and microbial mechanisms

Water-saving irrigation strategies can successfully alleviate methane emissions from rice fields, but significantly stimulate nitrous oxide (N2O) emissions because of variations in soil oxygen level and redox potential. However, the relationship linking soil N2O emissions to nitrogen functional genes during various fertilization treatments in water-saving paddy fields has rarely been investigated. Furthermore, the mitigation potential of organic fertilizer substitution on N2O emissions and the microbial mechanism in rice fields must be further elucidated. Our study examined how soil N2O emissions were affected by related functional microorganisms (ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), nirS, nirK and nosZ) to various fertilization treatments in a rice field in southeast China over two years. In this study, three fertilization regimes were applied to rice cultivation: a no nitrogen (N) (Control), an inorganic N (Ni), and an inorganic N with partial N substitution with organic manure (Ni+No). Over two rice-growing seasons, cumulative N2O emissions averaged 0.47, 4.62 and 4.08 kg ha−1 for the Control, Ni and Ni+No treatments, respectively. In comparison to the Ni treatment, the Ni+No fertilization regime considerably reduced soil N2O emissions by 11.6% while maintaining rice yield, with a lower N2O emission factor (EF) from fertilizer N of 0.95%. Nitrogen fertilization considerably raised the AOB, nirS, nirK and nosZ gene abundances, in comparison to the Control treatment. Moreover, the substitution of organic manure for inorganic N fertilizer significantly decreased AOB and nirS gene abundances and increased nosZ gene abundance. The AOB responded to N fertilization more sensitively than the AOA. Total N2O emissions significantly correlated positively with AOB and nirS gene abundances while having a negative correlation with nosZ gene abundance and the nosZ/nirS ratio across N-fertilized plots. In summary, we conclude that organic manure substitution for inorganic N fertilizer decreased soil N2O emissions primarily by changing the soil NO3−-N, pH and DOC levels, thus inhibiting the activities of ammonia oxidation in nitrification and nitrite reduction in denitrification, and strengthening N2O reduction in denitrification from water-saving rice paddies.

Policy measures effectively reduce soil nitrous oxide emissions with minor trade‐offs in crop yield

AbstractNitrous oxide (N2O) emissions are closely linked to agricultural fertilisation. European and national policy incentives have been set to reduce greenhouse gas (GHG) emissions; however, only a few evaluations have been conducted. Avoiding such emissions is an important climate change mitigation measure, but it is still uncertain which management measures over a long‐term, best out‐balance crop yield and GHG balances in agricultural systems. We here used the process‐based LandscapeDNDC model to simulate N2O emissions and trade‐offs in yield and soil nitrogen budget for four alternative arable cropping systems in three Austrian agricultural production zones belonging to different climatic regions. We evaluated statistical data on crop rotations and management practices, predominant soil types, and 10‐year daily weather conditions for four cropping systems: (1) conventional farming receiving the maximum allowed nitrogen fertilisation rate (Nmax), (2) conventional farming receiving 15% less fertiliser, (3) conventional farming receiving 25% less fertiliser, and (4) organic farming. Our results showed that soil N2O emissions could be best reduced in wet, high‐yield regions. Reducing nitrogen fertilisation by 15% and 25% mitigated N2O emissions by, on average, 22% and 39%, respectively, while the yield was reduced by 5% and 9%, respectively. In comparison, the same crops grown in the organic cropping system released 60% less N2O, but yield declined on average by 23%. Corn, winter barley, and vegetables showed the highest N2O reduction potential under reduced fertiliser input in conventional farming. In addition to N2O emissions, reduced fertilisation substantially decreased other nitrogen losses into the water and atmosphere. Generally, the soils under all cropping systems maintained a positive mean nitrogen budget. Our results suggest a significant emission reduction potential in certain production zones which, however, were accompanied by yield reductions. Knowledge of the emission patterns from cropping systems under different environmental conditions is essential to set the appropriate measures. In addition, region‐specific measures to reduce soil N2O emissions have to be in line with farmers' interests in order to facilitate the successful implementation of targeted nitrogen management.

Enhanced performance of oxygen vacancy-rich In-TiO2 materials for electrocatalytic urea synthesis via a relay catalysis strategy

As an essential source of nitrogen fertilizer for agricultural production and an important raw material in the chemical industry, urea is of great importance to the sustainable development of our economy and society. Oxygen vacancy-rich In3+-doped TiO2, denoted as Vo-In-TiO2, exhibits high catalytic activity for the co-activated reduction of NO3− and CO2 to synthesize urea, with respectively Faraday efficiency (FE) and urea yield (Rurea) of 9.06 % and 759.8 μg mg−1h−1 at an applied potential of −0.65 V versus reversible hydrogen electrode (vs. RHE), which can be attributed to the respective efficacy of oxygen vacancies (Vo) and In3+ and their synergistic effect through relay catalysis. Both experimental and theoretical investigations show that the doped In3+ endows the catalyst with a strong ability to capture CO2, while the Vo acts directly as active site to effectively facilitate the adsorption of *NO3 and further conversion of *NO2, and shows high activity for the NO3− reduction reaction (NO3−RR). That is, Vo reduces NO3− to *NH2, and In3+ plays a role in inducing the direct combination of *NH2 and *CO2 adsorbed on the surface of the catalyst to form the key intermediate *CO2NH2 and thus urea. This strategy of relay catalysis can make full use of the advantages of different parts of the catalyst to achieve a synergistic effect, providing a new approach to the design of highly efficient catalysts.

On the oxy-combustion of blends of coal and agro-waste biomass under dry and wet conditions

Integrating bioenergy into carbon capture and storage systems (Bio-CCS) is a novel concept aiming at reducing CO2 emissions, pointing to a short-term need to increase the use of non-conventional biomasses. The main objective of this experimental research is to characterize the behavior of two agro-waste biomasses under oxy-co-firing conditions, as concerns fuel conversion and NO formation, compared to the use of typical raw pine wood. The effect of replacing CO2 with H2O in the firing atmosphere is also sought. Two different biomass shares in the blends, 20 % and 50 %, are selected. The experiments are conducted in a lab-scale entrained flow reactor for two O2 concentrations (21 % and 35 %) and four H2O concentrations (0 %, 10 %, 25 %, 40 %). Some operating conditions are kept the same to enable the comparisons: mean residence time (3 s), initial reactor temperature (1000 °C) and oxygen excess (1.25). New results have been obtained from the experiments, optimizing burnout degrees and reducing NO levels. Minimum differences in conversions are detected for the 35 % O2 cases when the agro-biomasses replace the pine wood: less than 0.7 and 1.1 percentage points. Burnout degrees are maximized when 25 % CO2 is replaced with H2O in most cases, with maximum values in the range 97.3–97.7 %. The higher the agro-biomasses share in the blend, the higher the N-fuel to NO conversion, consistent with their larger nitrogen contents. Significant decreases of NO are detected when CO2 is replaced with H2O, with maximum reductions of 17.6 %. The extent of these NO reductions shows a clear dependence on the volatiles-to-char ratios for the fired blends: the higher the ratio, the lower the decrease. For the largest steam additions (40 %), the NO depleting effect caused by H2O is partially compensated with the enhancement of the N-volatiles oxidation, limiting the NO reductions to 1.7–7.3 % compared to the dry atmospheres.

In situ membrane separation drives nitrous oxide enrichment from nitrate denitrification for energy recovery

Efficiently enriching nitrous oxide (N2O) can provide a foundation for energy recovery during wastewater treatment. In this study, gas-liquid separation membranes were placed in a sequencing batch reactor fed with acidic nitrate-containing wastewater to determine the feasibility of enriching N2O by in situ separation of dissolved gases. Gas separation across the membrane (GSM) had no obvious effect on chemical oxygen demand and nitrate removal, but N2O production efficiency (NPE) increased from 11.0 % to 82.6 %. Denitrifying bacteria with low N2O yield such as Thauera, Diaphorobacter, and Flavobacterium were eliminated, and Propioniclava (46.79 %) and Candidatus_Competibacter (22.53 %) became dominant. Metagenomic sequencing showed that the abundance of the nosZ gene encoding N2O reductase decreased from 17.3 % to 6.1 %. In conclusion, GSM prevented the further reduction of N2O, eliminating denitrifying bacteria carrying the nosZ gene, which the enriched Propioniclava likely lacked. This demonstrates that GSM is an alternative strategy for N2O enrichment through nitrate denitrification.

Efficient and Selective Electrochemical Nitrate Reduction to N2 Using a Flow-Through Zero-Gap Electrochemical Reactor with a Reconstructed Cu(OH)2 Cathode: Insights into the Importance of Inter-Electrode Distance.

Electrochemically converting nitrate, a widely distributed nitrogen contaminant, into harmless N2 is a feasible and environmentally friendly route to close the anthropogenic nitrogen-based cycle. However, it is currently hindered by sluggish kinetics and low N2 selectivity, as well as scarce attention to reactor configuration. Here, we report a flow-through zero-gap electrochemical reactor that shows a high performance of nitrate reduction with 100% conversion and 80.36% selectivity of desired N2 in the chlorine-free system at 100 mg-N·L-1 NO3- while maintaining a rapid reduction kinetics of 0.07676 min-1. More importantly, the mass transport and current utilization efficiency are significantly improved by shortening the inter-electrode distance, especially in the zero-gap electrocatalytic system where the current efficiency reached 50.15% at 5 mA·cm-2. Detailed characterizations demonstrated that during the electroreduction process, partial Cu(OH)2 on the cathode surface was reconstructed into stable Cu/Cu2O as the active phase for efficient nitrate reduction. In situ characterizations revealed that the highly selective *NO to *N conversion and the N-N coupling step played crucial roles during the selective reduction of NO3- to N2 in the zero-gap electrochemical system. In addition, theoretical calculations demonstrated that improving the key intermediate *N coverage could effectively facilitate the N-N coupling step, thereby promoting N2 selectivity. Moreover, the environmental and economic benefits and long-term stability shown by the treatment of real nitrate-containing wastewater make our proposed electrocatalytic system more attractive for practical applications.

The reduction of copper in LaFeO3, La2CuO4 and CuO three-phase system improves the efficiency of NO removal: Experimental and density functional theory calculation

Hollow spherical LaCu0.5Fe0.5O3 (LCF) and La0.8Ce0.1Cu0.5Fe0.5O3 (LCCF) catalysts are synthesized by solvothermal method, and CuO is reduced in two samples, so that the two corresponding multiphase catalysts (R-LCF and R-LCCF) were prepared and used for the selective catalytic reduction of NO with CO (CO-SCR). The results show that the balance of Ce3++Cu2+↔Cu++Ce4+ between Ce and Cu ions promotes the reduction of CuO in the Ce-doped LCCF catalyst more obviously. In addition, the reduction of Ce and Cu in R-LCCF generates more oxygen vacancies, which leads to more surface adsorbed oxygen species, thus facilitating the conversion of more NO to NOx species. Besides, the presence of reduced Cu is highly active and can inhibit the production of carbonates occupying the active site. The ability to activate both CO and NO after the evolution of Cu0 to the key species Cu+ leads to a rapid reaction between Cu+-CO and NOx species. These are the key factors for the significant increase in catalytic activity at low temperatures. It is worth noting that the CO-SCR reaction on the R-LCCF catalyst corresponds to the Langmuir-Hinshlwood (L-H) and Eley-Rideal (E-R) mechanisms at different temperature windows, respectively.

Electrical-Driven Directed-Evolution of Copper Nanowires Catalysts for Efficient Nitrate Reduction to Ammonia.

The electrocatalytic conversion of nitrate (NO3 -) to NH3 (NO3RR) at ambient conditions offers a promising alternative to the Haber-Bosch process. The pivotal factors in optimizing the proficient conversion of NO3 - into NH3 include enhancing the adsorption capabilities of the intermediates on the catalyst surface and expediting the hydrogenation steps. Herein, the Cu/Cu2O/Pi NWs catalyst is designed based on the directed-evolution strategy to achieve an efficient reduction of NO3‾. Benefiting from the synergistic effect of the OV-enriched Cu2O phase developed during the directed-evolution process and the pristine Cu phase, the catalyst exhibits improved adsorption performance for diverse NO3RR intermediates. Additionally, the phosphate group anchored on the catalyst's surface during the directed-evolution process facilitates water electrolysis, thereby generating Hads on the catalyst surface and promoting the hydrogenation step of NO3RR. As a result, the Cu/Cu2O/Pi NWs catalyst shows an excellent FE for NH3 (96.6%) and super-high NH3 yield rate of 1.2molh-1gcat. -1 in 1m KOH and 0.1m KNO3 solution at -0.5V versus RHE. Moreover, the catalyst's stability is enhanced by the stabilizing influence of the phosphate group on the Cu2O phase. This work highlights the promise of a directed-evolution approach in designing catalysts for NO3RR.

Complete genome sequence of Afipia carboxidovorans strain SH125, a non-denitrifying nitrous oxide-reducing bacterium isolated from anammox biomass.

Here, we report a genome sequence of Afipia carboxidovorans strain SH125 isolated from an anammox reactor. This facultative anaerobic strain possesses the clade I-type nitrous oxide (N2O) reductase gene, devoid of nitrite- and nitric oxide reductase genes. Deciphering the genome will help explore N2O reducers instrumental in N2O mitigation.

Insight into the Alkali Resistance Mechanism of FeMoTiOx Catalysts for NH3 Selective Catalytic Reduction of NO: Self-Defense Effects of MoOx for Alkali Capture.

The deactivation of selective catalytic reduction (SCR) catalysts caused by alkali metal poisoning remains an insurmountable challenge. In this study, we examined the impact of Na poisoning on the performance of Fe and Mo co-doped TiO2 (FeaMobTiOx) catalysts in the SCR reaction and revealed the related alkali resistance mechanism. On the obtained Fe1Mo2.6TiOx catalyst, the synergistic catalytic effect of uniformly dispersed FeOx and MoOx species leads to remarkable catalytic activity, with over 90% NO conversion achieved in a wide temperature range of 210-410 °C. During the Na poisoning process, Na ions predominantly adsorb on the MoOx species, which exhibit stronger alkali resistance, effectively safeguarding the FeOx species. This preferential adsorption minimizes the negative effect of Na poisoning on Fe1Mo2.6TiOx. Moreover, Na poisoning has little influence on the Eley-Rideal reaction pathway involving adsorbed NHx reacting with gaseous NOx. After Na poisoning, the Lewis acid sites were deteriorated, while the abundant Brønsted acid sites ensured sufficient NHx adsorption. As a benefit from the self-defense effects of active MoOx species for alkali capture, FeaMobTiOx exhibits exceptional alkali resistance in the SCR reaction. This research provides valuable insights for the design of highly efficient and alkali-resistant SCR catalysts.

Light‐off Performance of Three‐Way Catalysts Before and After Accelerated Aging Test with an Engine‐Dynamometer

AbstractThis study demonstrates the reaction behavior during the purification of model automotive exhaust gases over Pd catalysts before and after thermal degradation. In particular, to investigate the relationship between the Pd state and the reaction behavior of Pd/Al2O3 and Pd/CeO2−ZrO2 (CZ), operando X‐ray absorption spectroscopy measurements were performed during purifying exhaust gases over real and model catalysts mimicking the degradation of Pd particles and CZ supports after accelerated aging tests. The NO reduction activity of the aggregated Pd metal species was as high as that of the highly dispersed Pd species, but hydrocarbon (HC) poisoning was significantly enhanced by the aggregation of Pd metal particles caused by thermal aging. The existence of a three‐phase boundary (TPB) between the CZ, the Pd particles, and the gas phase strongly affected the catalytic activity at low temperatures, and the presence of a sufficient TPB facilitated the combustion of unburned HCs owing to the oxygen storage performance of CZ. Thus, the TPB reduced the poisoning of the precious metal surface by HC species at low temperatures. Therefore, the findings of this study will facilitate the development of next‐generation gas purification catalysts with high activity and durability.

Enhanced Activity and Water Resistance on CuO/SiO2-TiO2 Catalyst for CO Oxidation and NO Reduction by CO: The Promotion Effect of SiO2

Enhanced Activity and Water Resistance on CuO/SiO2-TiO2 Catalyst for CO Oxidation and NO Reduction by CO: The Promotion Effect of SiO2

‘Climate Healing Stones’: Common Minerals Offer Substantial Climate Change Mitigation Potential

This review proposes that mineral-based greenhouse gas (GHG) mitigation could be developed into a substantial climate change abatement tool. This proposal was evaluated via three objectives: (1) synthesise literature studies documenting the effectiveness of geological minerals at mitigating GHG emissions; (2) quantify, via meta-analysis, GHG magnitudes that could be abated by minerals factoring-in the carbon footprint of the approach; and (3) estimate the global availability of relevant minerals. Several minerals have been effectively harnessed across multiple sectors—including agriculture, waste management and coal mining—to mitigate carbon dioxide/CO2 (e.g., olivine), methane/CH4 (e.g., allophane, gypsum) and nitrous oxide/N2O (e.g., vermiculite) emissions. High surface area minerals offer substantial promise to protect soil carbon, albeit their potential impact here is difficult to quantify. Although mineral-based N2O reduction strategies can achieve gross emission reduction, their application generates a net carbon emission due to prohibitively large mineral quantities needed. By contrast, mineral-based technologies could abate ~9% and 11% of global CO2 and CH4 anthropogenic emissions, respectively. These estimates conservatively only consider options which offer additional benefits to climate change mitigation (e.g., nutrient supply to agricultural landscapes, and safety controls in landfill operations). This multi-benefit aspect is important due to the reluctance to invest in stand-alone GHG mitigation technologies. Minerals that exhibit high GHG mitigation potential are globally abundant. However, their application towards a dedicated global GHG mitigation initiative would entail significant escalation of their current production rates. A detailed cost-benefit analysis and environmental and social footprint assessment is needed to ascertain the strategy’s scale-up potential.

An Alternative Calibration Method for Measuring N2O5 with an Iodide-Chemical Ionization Mass Spectrometer and Influencing Factors.

In this work, we developed an alternative calibration method for measuring N2O5 with an iodide adduct mass spectrometer (I-CIMS). In this calibration method, N2O5 is heated and then quantified based on the decrease in the amount of NO due to its reaction with the pyrolysis product (NO3). This alternative calibration method was compared with the commonly used method utilizing NOx analyzers equipped with a photolytic converter, which gauge NO2 reduction as a result of its reaction with O3 to quantify N2O5. It is notable that the two methodologies demonstrate favorable consistency in terms of calibrating N2O5, with a variance of less than 10 %. The alternative calibration method is a more reliable way to quantify N2O5 with CIMS, considering the instability of the NO2 conversion efficiency of photolytic converters in NOx analyzers and the loss of N2O5 in the sampling line. The effects of O3 and relative humidity (RH) on the sensitivity toward N2O5 were further examined. There was minimal perturbation of N2O5 quantification upon exposure to O3 even at high concentrations. The N2O5 sensitivity exhibited a nonlinear dependence on RH as it initially rose and then fell. Besides I(N2O5)-, the collisional interaction between I(H2O)- and N2O5 also forms I(HNO3)-, which may interfere with the accurate quantification of HNO3. As a consequence of the pronounced dependence on humidity, it is advisable to implement humidity correction procedures when conducting measurements of N2O5.