Toxic NH3 Research Articles

Experimental investigations of plasma-assisted ammonia combustion using rod-electrode-type microwave plasma source

Ammonia have been attractive as one of the alternative fuels for reducing greenhouse gas (GHG) emissions. However, ammonia combustion has lower combustion performance than common hydrocarbon fuels. Furthermore, it may emit nitrous oxide (N2O), which is one of the GHGs. This paper presents the experimental investigations of plasma-assisted ammonia combustion (PAAC) using a rod-electrode-type microwave plasma source (MPS) at atmospheric pressure. The equivalence ratios of premixed ammonia/dry air (NH3/Air) gas are set below the stoichiometric combustion of NH3 to reduce toxic NH3 in the combustion gas. Under the condition of the equivalence ratios, the experiments are focused on reducing the unburned NH3 and produced N2O concentrations in the combustion gas. In the experiments, the unburned NH3, nitrogen oxide (NOx) (the sum of nitric oxide (NO) and nitrogen dioxide (NO2)), and N2O concentrations in the combustion gas are investigated in terms of the flow velocity of premixed NH3/Air gas inside the rod-electrode-type MPS and the transmission power to the rod-electrode-type MPS. In conclusion, the rod-electrode-type MPS is identified to be useful for PAAC. The NH3 and N2O concentrations in the combustion gas reach approximately 25 and 4 parts per million (ppm), respectively, under the conditions of the equivalence ratio of 1.0, flow velocity of approximately 0.167 m/s, and transmission power of about 84 W. At that time, the NOx concentration is approximately 4300 ppm, and the power transmission efficiency is approximately 68 %.

Optimization of Combustion Cycle Energy Efficiency and Exhaust Gas Emissions of Marine Dual-Fuel Engine by Intensifying Ammonia Injection

The capability of operational marine diesel engines to adapt to renewable and low-carbon fuels is considered one of the most influential methods for decarbonizing maritime transport. In the medium and long term, ammonia is positively valued among renewable and low-carbon fuels in the marine transport sector because its chemical elemental composition does not contain carbon atoms which lead to the formation of CO2 emissions during fuel combustion in the cylinder. However, there are number of problematic aspects to using ammonia in diesel engines (DE): in-tensive formation of GHG component N2O; formation of toxic NOx emissions; and unburnt toxic NH3 slip to the exhaust system. The aim of this research was to evaluate the changes in combustion cycle parameters and exhaust gas emissions of a medium-speed Wartsila 6L46 marine diesel engine operating with ammonia, while optimizing ammonia injection intensity within the limits of Pmax, Tmax, and minimal engine structural changes. The high-pressure dual-fuel (HPDF) injection strategy for the D5/A95 dual-fuel ratio (5% diesel and 95% ammonia by energy value) was investigated within the liquid ammonia injection pressure range of 500 to 2000 bar at the identified optimal injection phases (A −10° CAD and D −3° CAD TDC). Increasing ammonia injection pressure from 500 bar (corresponding to diesel injection pressure) in the range of 800–2000 bar determines the single-phase heat release characteristic (HRC). Combustion duration decreases from 90° crank angle degrees (CAD) at D100 to 20–30° CAD, while indicative thermal efficiency (ITE) increases by ~4.6%. The physical cyclic deNOx process of NOx reduction was identified, and its efficiency was evaluated in relation to ammonia injection pressure by relating the dynamics of NOx formation to local combustion temperature field structure. The optimal ammonia injection pressure was found to be 1000 bar, based on combustion cycle parameters (ITE, Pmax, and Tmax) and exhaust gas emissions (NOx, NH3, and GHG). GHG emissions in a CO2 equivalent were reduced by 24% when ammonia injection pressure was increased from 500 bar to 1000 bar. For comparison, GHG emissions were also reduced by 45%, compared to the diesel combustion cycle.

Highly sensitive and selective sensing-performance of 2D Co-decorated phthalocyanine toward NH3, SO2, H2S and CO molecules

Developing excellent sensing-materials for detecting and monitoring toxic gases in the air is significant for environmental monitoring and industrial emission evaluation. Herein, the first-principles calculations were employed to systematically investigate the adsorption characteristics of twelve different gas molecules (NH3, NO, NO2, SO2, H2S, CO, CO2, CH4, H2O, H2, O2, N2) on the two-dimensional phthalocyanine (Pc) and Co decorated phthalocyanine (CoPc), the electronic properties of various adsorption systems and their sensing-mechanism were also elucidated. The results show that the toxic NH3, NO, NO2, SO2, H2S are chemically adsorbed on the pristine Pc surface, whereas the poor sensitivity of Pc monolayer makes it not suitable to be a sensing-material. By contrast, the CoPc monolayer exhibits the appropriate adsorption strength toward the six poisonous gases (NH3, NO, NO2, SO2, H2S, CO), which is detailedly explained by the analysis of charge transfer, charge density difference and density of states. Moreover, the CoPc monolayer possesses high selectivity to those six gases even if it is in a humid environment. The CoPc monolayer also has excellent sensitivity for those toxic gases due to the obvious variations of bandgap, magnetic moment or work function. Additionally, the recovery time of NH3, SO2, H2S and CO is estimated to be about 3.91 min, 0.02 s, 24.19 ns and 226.38 ns at room temperature, respectively. Consequently, the CoPc monolayer based gas sensor has a great potential application for the NH3, SO2, H2S and CO detection.

Characterization of WO3 thin films deposited by spray pyrolysis technique and its role in gas sensing

The work investigated in this paper focused on the fabrication of WO3 films by the spray pyrolysis technique, and different analyses were made to find optimized samples for studying properties suitable for the application of gas sensing. The substrate temperature is the most important parameter among other spray parameters for the synthesis of thin films hence WO3 thin films were deposited on glass substrates by maintaining the substrate temperature at 350 ºC, 450 ºC, 550 ºC, and 650 °C using compressed air as a carrier gas. The influence of the substrate temperature on the structural, morphological, compositional, and optical properties of the WO3 thin films has been justified using XRD data. Good and enhanced crystallinity is observed for the film deposited at a substrate temperature of 550 ºC. The nonconventional properties were studied by different investigations and confirmed by past research work. The manipulation of surface morphology with the different deposition temperatures is monitored. Only the characteristic peaks of W and O are present in the fabricated WO3 thin films. The optical activity of about 70 to 80 % of the selected sample in the visible region (300 to 1200 nm) is found. The selective absorption activity of light in the ultraviolet region and visible region is checked. The obtained IR bands confirmed the inter bridge stretching and bending modes of W-O and O-W-O. A high response towards ammonia compared to other test gases is exhibited. The repeatability of WO3 towards NH3 over three periodic sensing cycles, response, and recovery time has also been discussed. From all the characteristic studies, it has been suggested that the fabricated WO3 thin films have been used in the health care field to detect the toxic NH3 gas

Contamination and Toxicity of Surface Waters Along Rural and Urban Regions of the Capibaribe River in Tropical Northeastern Brazil.

The Capibaribe River provides water to a population of 1.7 million people in the Brazilian northeast, while receiving agricultural runoff and industrial and domestic effluents along its 280 km. The present study evaluated the ecotoxicity of surface waters along ten sites in rural and urban areas using zebrafish (Danio rerio) early-life stages and related it to water quality indices and chemical abiotic variables. Lethality rates, delays in embryo-larval development quantified by the general morphology score (GMS), and frequencies of developmental abnormalities were analyzed. A correlation was detected between zebrafish GMS and water quality index (WQI), sensitivity to domestic sewage contamination, and trophic state index, focused on eutrophication. These indices agreed in identifying a spatial pattern of smaller impact in terms of ecotoxicity, domestic sewage contamination, and eutrophication risk at three sites in rural areas (mean GMS 16.9), an intermediate impact at four sites with urban and agricultural influence (mean GMS 16.4), and greatest impacts at three more urbanized sites (mean GMS 14.9). Most frequent developmental abnormalities included noninflation of the swim bladder, delayed hatching, nonprotrusion of the mouth, blood stasis, and nondevelopment of pectoral fins. Toxic NH3 concentrations varied spatially, with higher concentrations in urban sites; and blood stasis correlated positively with NH3 , suggesting a causal relationship. Polycyclic aromatic hydrocarbons were detected in both rural and urbanized sites, contributing to detected toxicity. The present study demonstrates the potential of zebrafish early-life stages as an ecotoxicological model that may contribute to a better understanding of surface water quality and ecotoxicity in tropical river systems. Environ Toxicol Chem 2021;40:3063-3077. © 2021 SETAC.

Environmentally Benign Synthesis and Color Tuning of Strontium-Tantalum Perovskite Oxynitride and Its Solid Solutions.

A facile method was successfully developed to prepare strontium-tantalum perovskite oxynitride, SrTaO2N, and its solid solutions. Urea was employed as a solid nitriding agent to eliminate the use of toxic NH3 gas. In addition, utilization of sol-gel-derived Ta2O5 gel as a Ta precursor allowed for completion of nitridation within a shorter period and at a lower calcination temperature compared with the conventional ammonolysis process. Optimization of the reaction conditions, such as the urea content, allowed for the production of solid solutions of SrTaO2N and Sr1.4Ta0.6O2.9. The products exhibited optical absorption and chromatic colors because of the narrower band gaps of oxynitrides compared with those of oxides. The O/N ratios of the solid solutions were easily adjusted by varying the amount of urea in the mixture of precursors. As a result, the colors of the products ranged from yellow to brown. The nitridation process and products developed in this study are interesting environmentally benign alternatives to conventional inorganic pigments.

Silver-loaded carbon nanofibers for ammonia sensing

Abstract Carbon nanofibers (CNFs) were prepared by electrospinning, and silver (Ag) ions were grown on the surface of the CNFs by in situ solution synthesis. The structure and morphology of obtained Ag-doped CNFs (Ag-CNFs) were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The gas sensibility of the composite fiber was investigated by ammonia (NH3) obtained by natural volatilization from 1 to 4 mL of NH3 solution at room temperature. It was found that the fibers exhibited a sensitive current corresponding to different NH3 concentrations and a greater response at high concentrations. The sensing mechanism was discussed, and the good absorptivity was demonstrated. The results show that Ag-CNF is a promising material for the detection of toxic NH3.

Conductive elastic sponge-based triboelectric nanogenerator (TENG) for effective random mechanical energy harvesting and ammonia sensing

Abstract Triboelectric nanogenerator (TENG) based on elastic materials is increasing interests for irregular and random mechanical energies harvesting. However, the conductive design of the elastic materials in TENGs often limits its applications. Herein, a new conductive and elastic sponge-based triboelectric nanogenerator (ES-TENG) is developed for random mechanical energy harvesting, which integrates the elastic material and the conductive material on a flexible sponge to realize the collection of mechanical energies, particularly for irregular and random motions. The conductive elastic sponge is prepared by a simple dilute chemical polymerization of aniline to grow conductive polyaniline nanowires (PANI NWs) on the surface of elastic sponge. Due to the flexible deformation of sponge, it can harvest the kinetic energy of disordered motion with different amplitudes and from variable directions. As the triboelectric layer of ES-TENG, the porous sponge and polyaniline nanowires on its surface can provide a large contact area and improve the triboelectric efficiency. At the same time, the conductive polyaniline coating on the surface of sponge can also be used as the electrode of ES-TENG to conduct electrons and generate an output of 540 V and 6 μA respectively, which can be used on various flexible object surfaces to collect irregular and random mechanical energy ubiquitous in daily life. In addition, based on the NH3-sensing performance and the three-dimensional reticular structure of the polyaniline nanowires on the elastic sponge, the ES-TENG can make it work as self-powered sensor for detecting toxic NH3 with the detection limit up to 1 ppm and the response time less than 3 s. In view of the microporous and nanowire structures, elasticity, conductivity and easy fabrication of the conductive elastic sponge, the ES-TENG has promising applications in various irregular and random mechanical energy harvesting and self-powered NH3 sensors.

Aerobic Denitrification Microbial Community and Function in Zero-Discharge Recirculating Aquaculture System Using a Single Biofloc-Based Suspended Growth Reactor: Influence of the Carbon-to-Nitrogen Ratio.

In this study, the effect of aerobic denitrification on nitrogen removal was investigated using two zero-discharge biofloc-based recirculating aquaculture systems with representative carbon-to-nitrogen (C/N) ratios of 15 (CN15) and 20 (CN20). Aquaculture wastewater, residual feed, and fish feces were treated in an aerated suspended growth reactor (SGR, dissolved oxygen > 5.0 mg L–1). Low toxic NH3 (<0.1 mg L–1) and NO2–-N (<0.5 mg L–1) concentrations and high NO3–-N (83.3%) and NO2–-N (100%) removal efficiencies were achieved in the fish tank and SGR of CN20, respectively. The nitrogen mass balances indicated that the gaseous nitrogen loss accounted for 72–75% of the nitrogen input. Illumina sequencing and quantitative polymerase chain reaction revealed that increasing the C/N ratio significantly increased the amount of aerobic denitrifying bacteria (Dechloromonas, Rhodobacter, Flavobacterium, and Zoogloea) and aerobic denitrifying functional genes (napA, nirK, and nosZ). Autotrophic Nitrosomonas was the dominant nitrifying bacteria in the CN15 system, and autotrophic (Nitrosomonas) and heterotrophic nitrifiers coexisted in the CN20 system. Moreover, the functional prediction analysis showed that the carbohydrate, energy, and amino acid metabolisms in the SGR of the latter increased. In conclusion, aerobic denitrification should widely exist in biofloc systems.

Facile synthesis of ultrafine rGO/WO3 nanowire nanocomposites for highly sensitive toxic NH3 gas sensors

We introduce a facile and scalable synthesis of rGO/WO3 nanocomposites by hydrothermal method for gas sensing applications. The characterization of rGO/WO3 nanocomposites by some advanced techniques such as scanning electron microscopy, high resolution transmission electron microscopy and Raman spectroscopy revealed that high quality rGO/WO3 nanocomposites included single crystal WO3 nanowires (average diameter of 10 nm) entangled by thin rGO layers. Sensing measurements demonstrated that the rGO/WO3 nanocomposite-based sensor can detect highly toxic NH3 gas at low concentrations ranging from 20 ppm to 500 ppm and fulfills practical applications. The developed gas sensors based on rGO/WO3 nanocomposites have significant application prospects in environment pollution monitoring at detection limit of about 138 ppb. We also discussed the gas sensing mechanism of the rGO/WO3 nanocomposites based on the p-n junction.

Density functional theory-based investigation of HCN and NH3 formation mechanisms during phenylalanine pyrolysis.

As sludge pyrolysis produces large amounts of toxic NH3 and HCN, many works have studied nitrogen transfer during this process, commonly employing amino acids as models of sludge protein. Herein, density functional theory is used to probe the production of HCN and NH3 during the pyrolysis of phenylalanine as a model, revealing the existence of two formation paths for each gas. In the first (lower-energy-barrier) NH3 formation path, the hydrogen bonding-assisted transfer of carboxyl group hydrogen to the amino group is followed by direct NH3 generation via decarboxylation, and the second (higher-energy-barrier) path features decarboxylation followed by the transfer of carboxyl group hydrogen to the adjacent carbon atom to form phenethylamine, the deamination of which affords NH3 and styrene. For HCN, the first (lower-energy-barrier) path features C2–C3 bond cleavage to afford dehydroglycine, which further decomposes to produce HCN, while in the second path, the decomposition of phenylalanine into phenethylamine, CO, and H2O is followed by internal hydrogen transfer in phenethylamine to generate HCN. The overall energy barrier of the two HCN formation paths exceeds that of NH3 formation paths, i.e., phenylalanine is more prone to afford NH3 than HCN upon pyrolysis.

Self-powered ammonia nanosensor based on the integration of the gas sensor and triboelectric nanogenerator

A new self-powered ammonia (NH3) nanosensor with flexibility, portability, good selectivity and sensitivity has been developed from conducting polyaniline nanofibers (PANI NFs) based triboelectric nanogenerator (TENG). The power supply and gas sensor have been successfully integrated into one device. The PANI NFs with NH3 sensing property work both as a frictional layer and an electrode in the TENG. The TENG shows high output performance with the maximum short current circuit of 45.70 μA and output voltage of 1186 V in air, while its output voltage is obviously reduced in varying degrees after being exposed to NH3 with different concentrations, resulting from the change of electroconductivity of PANI, which is the design principle of the NH3 sensor. Meanwhile, this NH3 nanosensor exhibits good selectivity and sensitivity with the limit detection of 500 ppm at room temperature. This work proposes a new thought to design the self-powered NH3 nanosensor, which has the widespread application prospect to harvest ambient energy for detecting toxic NH3 without any external power sources.

Synthesis and characterization of highly selective and sensitive Sn/SnO2/N-doped carbon nanocomposite (Sn/SnO2@NGC) for sensing toxic NH3 gas

In the present study, a facial synthesis of Sn/SnO2 nanoparticles embedded in nitrogen doped carbon based nanocomposites has been disclosed which was used as a fast and high-performance NH3 gas sensor. The prepared nanocomposite was characterized by various analytical technique including FTIR, TGA/DTA, Raman, XRD, FESEM, TEM/HRTEM and XPS. The presence of both Sn and SnO2 nanoparticles in carbon matrix are supported by FTIR, Raman and XRD. The XRD analysis showed the tetragonal crystal phase of SnO2 nanoparticles, and the BET results revealed 148.9 m2 g−1 surface area of the nanocomposite. Furthermore, SEM image showed that Sn and SnO2 nanoparticles were well dispersed in the nitrogen doped carbon matrix. The fabricated sensor was characterized against various concentration of NH3 and the results indicated that the prepared sensor showed excellent responses at 65 °C working temperature, with 300 ppm concentration of NH3 and the sensitivity was observed 172.70. Additionally, the fabricated sensor also showed quick response and the recovery time of 60 s and 55 s, respectively. The fabricated sensor with its quick response and recovery time, good repeatability, excellent selectivity, and slight humidity effects has the potential and could be used as NH3 sensor on industrial scale.

The influence of temperature and SRT on high-solid digestion of municipal sewage sludge

The influence of temperature and solids retention time (SRT) on high-solid digestion of municipal sewage sludge was investigated in laboratory-scale reactors. Digestion with high-solid concentration reduces the required digestion volume and is advantageous for urban areas. The experimental conditions comprised total suspended solids (TSS) in digested sludge between 4.0 and 4.6%, temperatures in a range of 33 to 41 °C and the SRT between 10 and 25 d. High-solid digestion operates with increased NH4-N concentrations released from organic compounds. The anaerobic process can be limited by high NH4-N concentration and toxic NH3. In this study a stable digestion was observed up to 2,000 mg L(-1) NH4-N and 75 mg L(-1) NH3. Volatile suspended solids (VSS) and chemical oxygen demand removal was 53% and 57% respectively. However, digestion with 10 d SRT led to a declined VSS removal of 49%. The removal at 41 and 37 °C showed minor differences, while reduced NH4-N release and reduced methane production were observed at 33 °C. For economic reasons, high-solid digestion at 41 °C is not recommended, but will not impair VSS removal. The outcomes of this study confirm that digestion with up to 7.8% TSS in the feed is feasible for the tested temperatures and SRT down to 15 d.

Nitrogen Runoff from Tunnel Blasted Rocks— a Large-Scale Test

Eight tunnel blasted rock samples were washed five times in 10 m3 containers to calculate the runoff potential of nitrogen from unexploded remains of the ammonium nitrate slurry explosive in rock piles. During the first wash, 65% of total nitrogen was washed off. The average concentrations of NH4+ and NO3- in the first wash water were 46 mg N/L and 58 mg N/L, respectively, being reduced to 2.5 and 1.2 mg N/L after the last wash. The average runoff of total nitrogen from the blasted rocks was 24.2 g N/ton, being 14.7% of nitrogen in the loaded explosives. pH was high (range 8.1 to 11.8) resulting from shotcrete spill, pushing the NH4+/NH3 equilibrium toward the toxic NH3. The consequences of runoff from blasted rock piles may be damaging for water quality and biology in small recipients, and abatement measures should be assessed.

Influence of cyanobacteria blooms on sediment biogeochemistry and nutrient fluxes

To explore the influence of cyanobacteria blooms on internal nutrient loading and sediment biogeochemistry, we conducted a 3 yr (2008–2010) field investigation in the upper Sassafras River, a shallow tidal freshwater tributary of Chesapeake Bay, Maryland. During 2010 a dense diazotrophic cyanobacteria bloom was accompanied by abnormally high pH (9.0–10.5) and supersaturated oxygen throughout the summer. With the persistence of high pH in the water column and organic matter inputs from sedimented phytoplankton detritus, flux rates of NH+4 and soluble reactive phosphate were significantly higher during the summer of the bloom year than the same period in nonbloom years. Although low summer N2‐N flux rates generally coincided with reduced water‐column NO−3 concentrations, the efficiency of nitrification was constrained by elevated pH that converted NH+4 to more toxic NH3. Denitrification was subsequently limited by nitrate supply, elevated pH, and the deepening of the oxic layer in the sediment. During blooms, we observed increases in bioavailable nutrient release from the sediment, coupled with decreases in inorganic N : P flux ratios and inhibition of N2 loss from the ecosystem. These changes in sediment nutrient recycling created positive feedbacks that may have fueled the prolonged blooms and selectively fostered growth of diazotrophic cyanobacteria.

Intercontinental transfer of adultAcipenser oxyrinchus- impact assessment of aviation transport conditions on blood parameters

Summary In order to facilitate intercontinental air transport of live sturgeon broodstock, a simulation test for an 8-h flight was performed in a pressure chamber (pressure profiles resembling conditions during trans-Atlantic cargo flights). Atlantic sturgeon (Acipenser oxyrinchus) were maintained in sealed polyethylene bags with water and an oxygen-enriched atmosphere at a ratio of 1 : 5 : 10 (fish:water:oxygen by volume) over a 10 h period at 15� C water temperature. Minimum pressure during the simulated flight was regulated at an elevation of 2600 m equalling 850 hPa. Decompression and compression phases to simulate takeoff and landing were set at 30 min each. Respiration frequency was recorded during flight simulation. Blood pH, blood pO2 and pCO2 as well as Ca 2+ ,N a + ,K + , Cl ) , glucose and cortisol, cholesterol and trigycerids were also monitored prior to and after transport (at 12, 24, 36, 280 and 366 h). During exposure in the bags, blood pH decreased from a mean of 7.35 to 7.11 and blood pCO2 increased from 2.48 to 8.53 hPa. Both parameters revealed the most significant deviations from control levels immediately following the trial, returning to normal levels after 36 h. In contrast, the Na 2+ , Ca 2+ and Cl ) ion as well as glucose concentration required 72 h following the simulated transport until baseline levels were reached. During the subsequent transatlantic transport trials from Canada to Germany, blood parameters were utilized to assess fish recovery following transport. Additionally, testing of the transport water revealed that NH4–N reached critical levels of 6 mg l )1 within 16–18 h when the fish were kept in the sealed bags at 10� C. Following transport, adaptation of pH in the water of the rearing facility to levels of pH 6.9–7.0 for 20–28 h minimized toxic NH3 concentrations and ensured recovery. Recovery times varied to a large extent, influenced by the condition factor of the fish. Fish survival was 100% for 2 months post-transport, indicating that the critical parameters were met during transport.

Synthesis of Ultra-Fine Conducting Polyaniline Micro/Nanotubes Using Fiber Template and Their NH3 Gas Sensitivity

We have recently fabricated ultra-fine conducting polyaniline (PANI) tubes with high gas sensitivity. This route includes two steps. Firstly, aniline polymerizes on the surface of a suitable fiber template prepared by electrospun nitrocellulose (NC). Then, the NC fiber template is dissolved and the ultra-fine PANI tubes are obtained. The structure of the conducting PANI tubes is characterized by IR spectrum and wide-angle X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results indicate that the PANI shows the shape of ultra-fine tubes with average inner diameter of 250-350 nm. The wall thickness of the ultra-fine PANI tubes increases with increasing the content of oxidant. The conductivity of the doped PANI tubes is about 6.9 x 10(-2) S. The results of gas sensitivity of the ultra-fine PANI tubes indicate that the PANI tubes can act as "electronic nose" to detect toxic NH3 gas below 20 ppm.

Industrial H2-SCR of NO on a novel Pt/MgO–CeO2 catalyst

We describe here the performance of a novel MgO–CeO2-supported Pt (0.1wt%) catalyst towards the selective conversion of NO into N2 (SN2>80%) by using H2 (H2-SCR) under process conditions similar to those encountered in the NH3-SCR in the low-temperature range of 150–200°C. At 200°C, 100% conversion of NO and 85% N2-selectivity were obtained with a feed stream containing 1000ppm NO, 5% O2, 5% H2O, 10% CO2, 0–0.5% CO, and using 1.5% H2 in the feed as reducing agent (GHSV=40,000h−1). Thus, a N2-yield of 85% similar to that obtained in most NH3-SCR applications could make H2-SCR as the most environmentally friendly NOx control catalytic technology with great potential to replace the existing NH3-SCR technology. The latter is currently used industrially mainly in power and nitric acid plants, gas turbines, furnaces, boilers, and waste incinerators for the elimination of NOx. However, this technology faces several problems such as catalyst deterioration, emissions of non-reacted toxic NH3 (ammonia slip), ash odor, air-heaters fouling, and a high running cost.

Field investigations of ammonia exchange between barley plants and the atmosphere. II. Nitrogen realiocation, free ammonium content and activities of ammonium‐assimilating enzymes in different leaves

ABSTRACTThe activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) in different leaves of field‐grown spring barley were measured during the reproductive growth phase in 2 consecutive years. Concurrently, the contents of soluble ammonium ions and free amides in the leaves were determined. The studies were carried out to investigate the relationship between variations in these parameters and emission of NH3 from the plant foliage. GS and GOGAT activities declined very rapidly with leafage. The decline in enzyme activities was followed by an increase in soluble ammonium ions and amides in the leaf tissues. During the same period, about 75% of leaf and stem nitrogen was reallocated to the developing ear. The amount of NH3 volatilized from the foliage during the reproductive growth phase amounted to about 1% of the reallocated nitrogen. The experimental years were characterized by very favourable conditions for grain dry matter formation and for re‐utilization of nitrogen mobilized from leaves and stems. Ammonia volatilization occurring under conditions with declining GS and GOGAT activities and increasing tissue concentrations of NH4+ may be useful in protecting the plant from accumulation of toxic NH3 and NH4+ concentrations in the tissues.