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Showing papers on "Ammonia published in 2016"


Journal ArticleDOI
TL;DR: In this article, the authors report the development of new and cost-efficient catalysts, transition metal nitrides, which enable electrochemical reduction of molecular nitrogen to ammonia in aqueous media at ambient conditions with only a low applied bias.
Abstract: A rapid and facile reduction of nitrogen to achieve sustainable and energy-efficient production of ammonia is critical to its use as a hydrogen storage medium, chemical feedstock, and especially for manufacturing inorganic fertilizers. For a decentralization of catalytic ammonia production, small-scale N2 reduction devices are required that are equipped with the most stable, selective, and active catalysts that operate at low temperature and ambient pressure. Here, we report the development of new and cost-efficient catalysts, transition metal nitrides, which enable electrochemical reduction of molecular nitrogen to ammonia in aqueous media at ambient conditions with only a low applied bias. The most promising catalysts are VN, ZrN, NbN, and CrN, which are identified among a range of transition metal nitride surfaces through a comprehensive density functional theory based analysis. All four nitrides are found to be more active toward nitrogen reduction than toward the competing hydrogen evolution reaction...

300 citations


Journal ArticleDOI
TL;DR: It is demonstrated that deposition of reactive nitrogen in the United States has shifted from a nitrate-dominated to an ammonium-dominated condition, and future progress toward reducing US nitrogen deposition will be increasingly difficult without a reduction in ammonia emissions.
Abstract: Rapid development of agriculture and fossil fuel combustion greatly increased US reactive nitrogen emissions to the atmosphere in the second half of the 20th century, resulting in excess nitrogen deposition to natural ecosystems. Recent efforts to lower nitrogen oxides emissions have substantially decreased nitrate wet deposition. Levels of wet ammonium deposition, by contrast, have increased in many regions. Together these changes have altered the balance between oxidized and reduced nitrogen deposition. Across most of the United States, wet deposition has transitioned from being nitrate-dominated in the 1980s to ammonium-dominated in recent years. Ammonia has historically not been routinely measured because there are no specific regulatory requirements for its measurement. Recent expansion in ammonia observations, however, along with ongoing measurements of nitric acid and fine particle ammonium and nitrate, permit new insight into the balance of oxidized and reduced nitrogen in the total (wet + dry) US nitrogen deposition budget. Observations from 37 sites reveal that reduced nitrogen contributes, on average, ∼65% of the total inorganic nitrogen deposition budget. Dry deposition of ammonia plays an especially key role in nitrogen deposition, contributing from 19% to 65% in different regions. Future progress toward reducing US nitrogen deposition will be increasingly difficult without a reduction in ammonia emissions.

296 citations


Journal ArticleDOI
TL;DR: Co recovery via the ammoniacal leaching is believed to gain a competitive edge on convenitonal acid leaching both by reducing the sodium hydroxide expense for increasing the pH of leaching solution and by removing the separation steps of Mn and Al.

243 citations


Journal ArticleDOI
TL;DR: The selective conversion of dinitrogen into ammonia through plasmon-induced charge separation by using a strontium titanate (SrTiO3) photoelectrode loaded with gold nanoparticles (Au-NPs) and a zIRconium/zirconium oxide (Zr/ZrOx ) thin film is reported.
Abstract: The generation of ammonia from atmospheric nitrogen and water using sunlight is a preferable approach to obtaining ammonia as an energy carrier and potentially represents a new paradigm for achieving a low-carbon and sustainable-energy society. Herein, we report the selective conversion of dinitrogen into ammonia through plasmon-induced charge separation by using a strontium titanate (SrTiO3) photoelectrode loaded with gold nanoparticles (Au-NPs) and a zirconium/zirconium oxide (Zr/ZrOx ) thin film. We observed the simultaneous stoichiometric production of ammonia and oxygen from nitrogen and water under visible-light irradiation.

218 citations


Journal ArticleDOI
TL;DR: In this article, the response of AOA and AOB communities to organic and conventional nitrogen (N) fertilizers, and their relative contributions to the nitrification process were examined for an agricultural silage corn system using a randomized block design with 4-N treatments: control (no additional N), ammonium sulfate (AS) fertilizer at 100 and 200 kilograms N−1, and steer-waste compost (200 kilograms total N ha−1) over four seasons.
Abstract: In the majority of agricultural soils, ammonium (NH4+) is rapidly converted to nitrate (NO3−) in the biological ammonia and nitrite oxidation processes known as nitrification. The often rate-limiting step of ammonia oxidation to nitrite is mediated by ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The response of AOA and AOB communities to organic and conventional nitrogen (N) fertilizers, and their relative contributions to the nitrification process were examined for an agricultural silage corn system using a randomized block design with 4 N treatments: control (no additional N), ammonium sulfate (AS) fertilizer at 100 and 200 kg N ha−1, and steer-waste compost (200 kg total N ha−1) over four seasons. DNA was extracted from the soil, and real-time PCR and 454-pyrosequencing were used to evaluate the quantity and diversity of the amoA gene which encodes subunit A of ammonia monooxygenase. Soil pH, nitrate pools, and nitrification potentials were influenced by ammonium and organic fertilizers after the first fertilization, while changes in AOB abundance and community structure were not apparent until after the second fertilization or later. The abundance of AOA was always greater than AOB but was unaffected by N treatments. In contrast, AOB abundance and community structure were changed significantly by ammonium fertilizers. Specific inhibitors of nitrification were used to evaluate the relative contribution of AOA and AOB to nitrification. We found that AOB dominantly contributed to potential nitrification activity determined at 1 mM ammonium in soil slurries and nitrification potential activity was higher in soils treated with ammonium fertilizers relative to control soils. However, AOA dominated gross nitrification activity in moist soils. Our result suggests that AOB activity and community are more responsive to ammonium fertilizers than AOA, but that in situ nitrification rate is controlled by ammonium availability in this agricultural soil. Understanding this response of AOA and AOB to N fertilizers may contribute to improving strategies for the management of nitrate production in agricultural soils.

210 citations


Journal ArticleDOI
TL;DR: Ruthenium-loaded metal hydrides with hydrogen vacancies function as efficient catalysts for ammonia synthesis under low temperature and low pressure conditions.
Abstract: The efficient reduction of atmospheric nitrogen to ammonia under low pressure and temperature conditions has been a challenge in meeting the rapidly increasing demand for fertilizers and hydrogen storage. Here, we report that Ca2N:e−, a two-dimensional electride, combined with ruthenium nanoparticles (Ru/Ca2N:e−) exhibits efficient and stable catalytic activity down to 200 °C. This catalytic performance is due to [Ca2N]+·e1−x−Hx− formed by a reversible reaction of an anionic electron with hydrogen (Ca2N:e− + xH ↔ [Ca2N]+·e1−x−Hx−) during ammonia synthesis. The simplest hydride, CaH2, with Ru also exhibits catalytic performance comparable to Ru/Ca2N:e−. The resultant electrons in these hydrides have a low work function of 2.3 eV, which facilitates the cleavage of N2 molecules. The smooth reversible exchangeability between anionic electrons and H− ions in hydrides at low temperatures suppresses hydrogen poisoning of the Ru surfaces. The present work demonstrates the high potential of metal hydrides as efficient promoters for low-temperature ammonia synthesis.

171 citations


Journal ArticleDOI
TL;DR: In this article, the progress in urea based fuel cells and electrocatalysts for urea oxidation is reviewed, and the main limitation of urea fuel cells is the relative low power density due to the sluggish anode reaction.
Abstract: Urea is a new member of hydrogen-storage materials for low-temperature fuel cells. It avoids issues of toxicity and safety compared to ammonia and hydrazine. The main limitation of urea fuel cells is the relative low power density due to the sluggish anode reaction. Rapid advances in nano-catalysts for urea electrooxidation have been achieved in order to lower overpotential and improve activity. Urine, as a natural resource of urea, is also an environmental pollutant. Most technologies of treating urine with self-generation electricity are based on microbial fuel cells. However, microbes are only able to utilize the organic substrates rather than urea in urine. Chemical fuel cells in contrast directly oxidize urea to nitrogen gas and removed from urine. Thus urea fuel cells have been used as an alternative method to treat urine. In the paper, the progress in urea based fuel cells and electrocatalysts for urea oxidation is reviewed.

167 citations


Journal ArticleDOI
TL;DR: In this article, a review of copper-based catalysts for the selective catalytic reduction of NO x with ammonia (NH 3 -SCR, DeNO x ) is presented.
Abstract: More restrictive standards of Euro VI concerning nitrogen oxide (NO x = NO, NO 2 ) emissions necessitate an enhanced urea injection, while generating a higher ammonia slip, which is also precisely limited. For this reason, ammonia slip catalysts (ASC) are an essential part of efficient aftertreatment systems. Currently, supported noble metal catalysts are applied but possess limited selectivity to nitrogen. Copper based catalysts present a promising alternative for the selective catalytic ammonia oxidation into nitrogen and water vapour (NH 3 -SCO). This review article focusses on NH 3 -SCO as appropriate solution to abate unreacted ammonia particularly after the selective catalytic reduction of NO x with ammonia (NH 3 -SCR, DeNO x ). A brief overview of potential catalyst systems is provided, followed by a comprehensive discussion of copper based catalysts. Potential material classes including oxides, exchanged zeolites, modified clays or mixed forms are described systematically. The review focusses on structure-performance correlations covering copper loading, redox properties of CuO species and available acid sites of the catalysts. Another emphasis concerns the influence of the feed composition on the catalytic performance including the content of oxygen and water vapour or sulphur oxide in the feed. Finally, the proposed i-SCR mechanism over copper based catalysts, including bimetallic systems, is described and critically reviewed followed by general conclusions together with a discussion of promising research directions.

162 citations


01 Dec 2016
TL;DR: Analysis of δ(15)N values of aerosol NH4(+) to be a promising new tool for partitioning atmospheric NH3 sources, providing policy makers with insights into NH3 emissions and secondary aerosols for regulation in urban environments is demonstrated.
Abstract: The reduction of ammonia (NH3) emissions is urgently needed due to its role in aerosol nucleation and growth causing haze formation during its conversion into ammonium (NH4(+)). However, the relative contributions of individual NH3 sources are unclear, and debate remains over whether agricultural emissions dominate atmospheric NH3 in urban areas. Based on the chemical and isotopic measurements of size-resolved aerosols in urban Beijing, China, we find that the natural abundance of (15)N (expressed using δ(15)N values) of NH4(+) in fine particles varies with the development of haze episodes, ranging from -37.1‰ to -21.7‰ during clean/dusty days (relative humidity: ∼ 40%), to -13.1‰ to +5.8‰ during hazy days (relative humidity: 70-90%). After accounting for the isotope exchange between NH3 gas and aerosol NH4(+), the δ(15)N value of the initial NH3 during hazy days is found to be -14.5‰ to -1.6‰, which indicates fossil fuel-based emissions. These emissions contribute 90% of the total NH3 during hazy days in urban Beijing. This work demonstrates the analysis of δ(15)N values of aerosol NH4(+) to be a promising new tool for partitioning atmospheric NH3 sources, providing policy makers with insights into NH3 emissions and secondary aerosols for regulation in urban environments.

143 citations


Journal ArticleDOI
TL;DR: Switching from CAN to stabilised urea formulations was found to be an effective strategy to reduce N2O emissions, particularly in wet, temperate grassland.

129 citations


Journal ArticleDOI
TL;DR: Analysis of two laboratory‐scale biogas reactors operating with thin stillage and subjected to an increase in free ammonia showed that ammonia concentration was detrimental for process performance, with the threshold for stability in both processes identified as being about 1 g NH3‐N L−1, irrespective of OLR.
Abstract: Biogas production from nitrogen-rich feedstock results in release of ammonia (NH3), causing inhibition of the microbial process. The reported threshold ammonia value for stable biogas production varies greatly between studies, probably because of differences in operating conditions. Moreover, it is often difficult to separate the effect of ammonia inhibition from that of organic loading rate (OLR), as these two factors are often interrelated. This study attempted to distinguish the effects of ammonia and OLR by analysis of two laboratory-scale biogas reactors operating with thin stillage and subjected to an increase in free ammonia (from 0.30 to 1.1 g L(-1)) either by addition of an external nitrogen source (urea) or by increasing the OLR (3.2-6.0 g volatile solids L(-1) d(-1)). The results showed that ammonia concentration was detrimental for process performance, with the threshold for stability in both processes identified as being about 1 g NH3-N L(-1), irrespective of OLR. Analysis of the methanogenic community showed limited differences between the two reactors on order level and a clear increase in the abundance of Methanomicrobiales, particularly Methanoculleus sp., in response to increasing ammonia concentration. Further comprehensive molecular analysis revealed that diverse Methanoculleus species dominated in the reactors at a given ammonia level at different OLR. The acetogenic community was clearly affected by both ammonia concentration and OLR, suggesting that the volatile fatty acid load in relation to the higher OLR was important for the dynamics of this community.

Journal ArticleDOI
TL;DR: In this article, the influence of ammonia (NH3) emissions on PM2.5 concentrations in central Europe has been investigated, and it was found that a reduction of ammonia emissions by 50% lead to a 24% reduction of the total PM2.

Journal ArticleDOI
TL;DR: Pilot tests demonstrated that high-purity ammonium sulfate crystals could be produced by controlling sulfuric acid content and maintaining acid solution saturated with ammonium sulphate, and no volatile organic compounds were found in the recovered crystals.

Journal ArticleDOI
Peng Peng1, Yun Li1, Yanling Cheng1, Shaobo Deng1, Paul Chen1, Roger Ruan1 
TL;DR: In this article, the effects of operational parameters including applied voltage, frequency, gas component and flow rate on catalytic ammonia synthesis under NTP conditions are studied and different selected catalysts and absorbents were investigated under different conditions of NTP treatment.
Abstract: This paper described a novel and green approach on catalytic ammonia synthesis using non-thermal plasma (NTP). The process studied in this paper involves the synthesis and absorption of ammonia under atmospheric pressure and low temperature. The effects of operational parameters including applied voltage, frequency, gas component and flow rate on ammonia synthesis under NTP conditions are studied in this paper. In addition, different selected catalysts and absorbents were investigated under different conditions of NTP treatment and the ammonia efficiency was reported and analyzed. Ru catalyst with carbon nanotube support, along with Cs promoter and micro porous absorbents including Molecular Sieve 13X and Amberlyst 15 yield the highest ammonia efficiency in this process. Results further indicated that frequency and applied voltage of 10,000 Hz and 6000 V, with N2:H2 feed ratio of 3:1 provided the optimized efficiency of ammonia synthesis of 2.3 gNH3/kWh.

Journal ArticleDOI
TL;DR: Ammonia strongly inhibited methanogenesis but minimally affected hydrolysis and acidification, and the metabolism of hydrogenotrophic methanogens Methanobacterium and Methanospirillum were inhibited when the ammonium concentration further increased.
Abstract: The effects of ammonia on semicontinuous anaerobic digestion (AD) of food waste were studied. Inhibition effects were observed when the total ammonium concentration in the AD reactor exceeded 2g/L. Ammonia strongly inhibited methanogenesis but minimally affected hydrolysis and acidification. Inhibition of AD by ammonia enhanced the accumulation of acetate and propionate and consequently decreased the pH, which worsened the inhibition effects. With increasing ammonium concentration, methane production from acetate shifted from acetoclastic methanogenesis (mostly by Methanosaeta) to syntrophic acetate oxidation coupled with hydrogenotrophic methanogenesis (mostly by Methanosarcina). The metabolism of hydrogenotrophic methanogens Methanobacterium and Methanospirillum were inhibited when the ammonium concentration further increased to about 6 g/L. Microorganisms irrelevant in the methane fermentation process were enriched with the increase of ammonium concentration.

Journal ArticleDOI
TL;DR: In this study, the tolerance of the biogas process under supply of hydrogen, to ammonia toxicity was studied under mesophilic and thermophilic conditions and it was found that hydrogentrophic methanogens were more tolerant to the ammonia toxicity than acetoclastic methanogen in the hydrogen enriched biogAs production and upgrading processes.

Journal ArticleDOI
TL;DR: This reaction suggests a new mechanism for the formation of ammonium sulfate in the atmosphere, especially when the concentration of NH3 is high (e.g., ∼10 μg m(-3)) in the air, as well as on the surface of a water droplets with adsorbed NH3 and SO3 molecules.
Abstract: In the atmosphere, a well-known and conventional pathway toward the formation of ammonium sulfate is through the neutralization of sulfuric acid with ammonia (NH3) in water droplets. Here, we present direct ab initio molecular dynamics simulation evidence of the formation of ammonium bisulfate (NH4HSO4) from the hydrated NH3 and SO3 molecules in a water trimer as well as on the surface of a water droplet. This reaction suggests a new mechanism for the formation of ammonium sulfate in the atmosphere, especially when the concentration of NH3 is high (e.g., ∼10 μg m–3) in the air. Contrary to the water monomer and dimer, the water trimer enables near-barrierless proton transfer via the formation of a unique loop structure around the reaction center. The formation of the loop structure promotes the splitting of a water molecule in the proton-transfer center, resulting in the generation a NH4+/HSO4– ion pair. The loop-structure promoted proton-transfer mechanism is expected to be ubiquitous on the surface of c...

Journal ArticleDOI
TL;DR: In this article, the effect of ammonium sulfate and Cu sulfate species on low-temperature NOx reduction activity was investigated using Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).
Abstract: SO2 poisoning of NH3-SCR over Cu-SAPO-34 was studied, specifically to evaluate the forms/states of stored S and the effect of such species on low-temperature NOx reduction activity. Two primary sulfur species types were observed and were found to be interchangeable depending on whether NH3 was available or not. In one case both ammonium sulfate and Cu sulfate species could be present and in the other only Cu sulfate species. Cu sulfate, in the absence of ammonia, was found in three different states/forms, identified by three desorption features during temperature-programmed desorption (TPD) experiments. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NO adsorption was used to investigate the nature and accessibility of the Cu species before and after sulfate formation, without the interference of ammonium sulfate; these data revealed that the Cu2+ inside the six-membered rings was completely blocked by sulfur and that the nature of the [CuOH]+ close to the eight-membered ring chang...

Journal ArticleDOI
15 May 2016-Fuel
TL;DR: In this article, a rice husk char was pyrolyzed and then impregnated with ammonium halides to develop an efficient sorbent for gaseous mercury removal from flue gas.

Journal ArticleDOI
TL;DR: Adding sucrose to sludge compost could promote ammonia assimilation and reduce ammonia emission, and the activities of glutamate dehydrogenase, glutamate synthase and glutamine synthetase were enhanced by the addition of sucrose.

Journal ArticleDOI
TL;DR: The relationship between ammonia oxidation and primary production does not simply indicate that ammonia oxidation increased with ammonium supply through decomposition of organic matter produced by primary production but that ammonia oxidizers might also be controlled by micronutrient availability as with primary production.
Abstract: We examined nitrification in the euphotic zone, its impact on the nitrogen cycles, and the controlling factors along a 7500 km transect from the equatorial Pacific Ocean to the Arctic Ocean. Ammonia oxidation occurred in the euphotic zone at most of the stations. The gene and transcript abundances for ammonia oxidation indicated that the shallow clade archaea were the major ammonia oxidizers throughout the study regions. Ammonia oxidation accounted for up to 87.4% (average 55.6%) of the rate of nitrate assimilation in the subtropical oligotrophic region. However, in the shallow Bering and Chukchi sea shelves (bottom ⩽67 m), the percentage was small (0–4.74%) because ammonia oxidation and the abundance of ammonia oxidizers were low, the light environment being one possible explanation for the low activity. With the exception of the shallow bottom stations, depth-integrated ammonia oxidation was positively correlated with depth-integrated primary production. Ammonia oxidation was low in the high-nutrient low-chlorophyll subarctic region and high in the Bering Sea Green Belt, and primary production in both was influenced by micronutrient supply. An ammonium kinetics experiment demonstrated that ammonia oxidation did not increase significantly with the addition of 31–1560 nm ammonium at most stations except in the Bering Sea Green Belt. Thus, the relationship between ammonia oxidation and primary production does not simply indicate that ammonia oxidation increased with ammonium supply through decomposition of organic matter produced by primary production but that ammonia oxidation might also be controlled by micronutrient availability as with primary production.

Journal ArticleDOI
TL;DR: In this article, the authors evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3) and show that better constraints on the vertical distribution of ammonia and on the sources and sinks of nitric acid (e.g., heterogeneous reaction on dust) are needed to improve estimates of future nitrate optical depth.
Abstract: . We update and evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3). Accounting for the radiative effects of nitrate aerosols generally improves the simulated aerosol optical depth, although nitrate concentrations at the surface are biased high. This bias can be reduced by increasing the deposition of nitrate to account for the near-surface volatilization of ammonium nitrate or by neglecting the heterogeneous production of nitric acid to account for the inhibition of N2O5 reactive uptake at high nitrate concentrations. Globally, uncertainties in these processes can impact the simulated nitrate optical depth by up to 25 %, much more than the impact of uncertainties in the seasonality of ammonia emissions (6 %) or in the uptake of nitric acid on dust (13 %). Our best estimate for fine nitrate optical depth at 550 nm in 2010 is 0.006 (0.005–0.008). In wintertime, nitrate aerosols are simulated to account for over 30 % of the aerosol optical depth over western Europe and North America. Simulated nitrate optical depth increases by less than 30 % (0.0061–0.010) in response to projected changes in anthropogenic emissions from 2010 to 2050 (e.g., −40 % for SO2 and +38 % for ammonia). This increase is primarily driven by greater concentrations of nitrate in the free troposphere, while surface nitrate concentrations decrease in the midlatitudes following lower concentrations of nitric acid. With the projected increase of ammonia emissions, we show that better constraints on the vertical distribution of ammonia (e.g., convective transport and biomass burning injection) and on the sources and sinks of nitric acid (e.g., heterogeneous reaction on dust) are needed to improve estimates of future nitrate optical depth.

Journal ArticleDOI
TL;DR: In this paper, the synthesis of ammonia in a non-equilibrium atmospheric-pressure plasma using functionalized-nanodiamond and diamond-like-carbon coatings on α-Al2O3 spheres as catalysts was investigated.
Abstract: We investigate the synthesis of ammonia in a non-equilibrium atmospheric-pressure plasma using functionalized-nanodiamond and diamond-like-carbon coatings on α-Al2O3 spheres as catalysts. Oxygenated nanodiamonds were found to increase the production yield of ammonia, while hydrogenated nanodiamonds decreased the yield. Neither type of nanodiamond affected the plasma properties significantly. Using diffuse-reflectance FT-IR and XPS, the role of different functional groups on the catalyst surface was investigated. Evidence is presented that the carbonyl group is associated with an efficient surface adsorption and desorption of hydrogen in ammonia synthesis on the surface of the nanodiamonds, and an increased production of ammonia. Conformal diamond-like-carbon coatings, deposited by plasma-enhanced chemical vapour deposition, led to a plasma with a higher electron density, and increased the production of ammonia.

Journal ArticleDOI
TL;DR: In this article, Ni catalysts supported on various rare-earth oxides were prepared by the impregnation method and employed for ammonia decomposition, and the Ni/Y2O3 catalyst exhibited the best performance among the samples investigated.
Abstract: Ammonia decomposition has attracted the interest of many researchers as a promising process for the on-site generation of H2. In this study, Ni catalysts supported on various rare-earth oxides were prepared by the impregnation method and employed for ammonia decomposition. The Ni/Y2O3 catalyst exhibited the best performance among the samples investigated. The reaction kinetics study indicated that most of rare-earth oxide supports were effective for the alleviation of the hydrogen inhibition phenomenon in the decomposition reaction. The desorption behavior of hydrogen has revealed that the amount of hydrogen atoms adsorbed strongly on the Ni surface up to high temperatures was relatively small in the case of Ni/Y2O3. Furthermore, for Ni/Y2O3 the optimal Ni loading was 40 wt % in terms of the catalytic activity because of the appropriate Ni dispersion.

Journal ArticleDOI
TL;DR: The pyrolysis characteristics of rice husk impregnated with different kinds of ammonia source (ammonium acetate, urea, ammonium sulfate and ammonium dihydrogen phosphate) in a fixed bed reactor are presented.

Journal ArticleDOI
TL;DR: The grant numbers were RSF 13S430, RSF 11S138 and RSF 14S430 as mentioned in this paper for the Irish Department of Agriculture Food and Marine (DFAF).
Abstract: Irish Department of Agriculture Food and Marine. Grant Numbers: RSF 13S430, 11S138.Teagasc Walsh Fellowship Programme

Journal ArticleDOI
TL;DR: In this paper, high surface area bulk molybdenum nitride catalysts were synthesized via temperature-programmed ammonolysis of an ammonium heptamolybdate and citric acid (CA) composite.

Journal ArticleDOI
Daegi Kim, Kyung Jin Min1, Kwanyong Lee, Min Sung Yu1, Ki Young Park1 
TL;DR: In this article, the effects of pH, molar ratios and pre-treatment of effluent of anaerobically digested swine wastewater were investigated to improve struvite crystallization.
Abstract: Struvite precipitation has been proven to be an effective method in removing and recovering ammonia nitrogen (N) and phosphate phosphorus (P) from wastewater. In this study, effects of pH, molar ratios and pre-treatment of effluent of anaerobically digested swine wastewater were investigated to improve struvite crystallization. The magnesium : ammonium : phosphate ratio of 1.2 : 1.0 : 1.0 was found to be optimal, yet the molar ratio in the wastewater was 1 : 74.9 : 1.8. From the analysis, the optimum pH was between 8.0 and 9.0 for maximal phosphate P release and from 8.0 to 10.0 for maximal ammonia N and phosphate P removal from real wastewater. Analysis from Visual MINTEQ predicted the pH range of 7-11 for ammonia N and phosphate P removal and recovery as struvite. For pre-treatment, microwave pre-treatment was ineffective for phosphate P release but ultrasound pre-treatment showed up to 77.4% phosphate P release at 1,000 kJ/L of energy dose. Precipitates analysis showed that phosphorus and magnesium in the collected precipitate had almost same values as theoretical values, but the ammonia content was less than the theoretical value.

Journal ArticleDOI
TL;DR: In this article, the effect of temperature and pressure on the rates of reaction was systematically studied, and the potential and limits of low-pressure ammonia synthesis were elucidated, and qualitatively investigated the absorptive separation of ammonia using calcium chloride in a reaction-separation process.
Abstract: Ammonia is normally made at high temperature and pressure using a promoted iron catalyst. High temperatures are needed to get fast kinetics; the high pressure is used to ensure high conversion. Alternatively, ammonia can be made at high temperature but lower pressure if the product ammonia is rapidly separated. Here, we have systematically studied the effect of temperature and pressure on the rates of reaction. We then have qualitatively investigated the absorptive separation of ammonia using calcium chloride in a reaction–separation process. Rapid separation reduces the constraint of reversible reaction and enables us to obtain appropriate reaction rates at relatively lower pressure. The effect of different operating conditions—reaction temperature, pressure, absorption temperature, and gas transport—on production rates is carefully measured, and this elucidates the potential and the limits of this type of low-pressure ammonia synthesis.

Journal ArticleDOI
TL;DR: In this article, a multi-site kinetic model was developed to describe the sulfur poisoning and gradual sulfur removal over Cu/SSZ-13 used for NH3-SCR, and the effect of sulfur poisoning was examined on NH3 TPD and ammonia oxidation experiments.
Abstract: In this study, we have developed a multi-site kinetic model that describes the sulfur poisoning and gradual sulfur removal over Cu/SSZ-13 used for NH3-SCR. Sulfur poisoning was conducted under SCR conditions and thereafter, repeated SCR experiments were conducted to examine the effect of such poisoning and the subsequent gradual removal of sulfur. In addition, the effect of sulfur poisoning was examined on NH3 TPD and ammonia oxidation experiments. The following sites were used in the kinetic model: copper in the six-membered rings as described by S1Cu, copper in the larger cages with S2 and S3 as a site where physisorbed ammonia can attach. Further, ammonia was also adsorbed on the Bronsted sites, represented by S1Bron in the model, but in order not to further complicate the model, small amounts of ammonia storage on Bronsted sites were also lumped into S2. In the model, SO2 was adsorbed on the sites containing copper, which are S1Cu and S2. It should be noted that S1Cu and S2 represents hydrated copper sites. Interestingly, we observed experimentally that ammonia storage was larger after sulfur poisoning compared to before, which is why we added ammonia storage and desorption to the S1Cu-SO2 and S2-SO2 sites. However, ammonia was already adsorbing on the copper site; thus, these steps did not result in increased storage. Consequently, reaction steps were added where additional ammonia was adsorbed to form S1Cu-SO2-(NH3)2 and S2-SO2-(NH3)2 species, which could be interpreted as precursors to ammonium sulfates. Another aspect that must be addressed in the model is the observation in the literature that SO2 is more easily desorbed in SO2+NH3+O2 TPD than SO2+O2 TPD. Reversible reaction steps were therefore added whereby the S1Cu-SO2-NH3 and S2-SO2-NH3 species were decomposed to form SO2. A final reaction step was incorporated into the model to describe the SCR reaction with ammonia attached to the sulfur sites. The developed model could well describe the sulfur poisoning and gradual regeneration during repeated SCR experiments. In addition, the model well described the NH3 TPD and NH3 oxidation before and after sulfur poisoning.