Formation Of NH Research Articles

Electrochemical nitrogen reduction reaction over gallium - a computational and experimental study.

Ga was identified earlier as one of the "overlooked" metals for catalyzing the electrochemical nitrogen reduction reaction (ENRR). We investigate here the electrocatalytic activity of Ga towards the nitrogen reduction reaction. We used a combination of molecular modelling and simulations using periodic density functional theory calculations (DFT), and experimental ENRR measurements. The ENRR was found to proceed via an associative mechanism where the first PCET to dinitrogen forming the surface adsorbed N2H* species is the overpotential limiting step. The bare Ga cathode has a high overpotential (>2 V (SHE)) for the ENRR. We also investigated the effect of a water-in-salt electrolyte (WISE) on the rate of ammonia formation. The addition of an Li salt lowers the overpotential to 1.88 V (SHE). DFT calculations revealed that the H-adatom was more favorably bound than the N-adatom, and the hydrogen evolution reaction (HER) is expected to dominate at high cathodic potentials. Experimental ENRR tests corroborate our results wherein no significant NH3 formation was detected. The low electrochemical activity of Ga is attributed to poor binding and activation of N2 which originates from an electropositive surface charge distribution.

W/Mo-heteropoly blue-modified defective W18O49 as Z-Scheme heterostructure photocatalysts for efficient N2 fixation

Photocatalytic N2 fixation can convert the abundant but inert N2 into NH3 under atmospheric conditions. However, the dissatisfactory yield rate of NH3 greatly hinders its development. The rational design of a highly efficient N2 fixation photocatalyst enables large-scale ammonia production but is challenging due to the thermodynamic obstacles of N2 activation. Herein, the W/Mo-heteropoly blue modified defective W18O49 heterojunction composite catalysts (r-HPW/W18O49 and r-HPMo/W18O49) are prepared for N2 photofixaiton without sacrificial agents and cocatalysts under ambient conditions for the first time. The heteropoly blue nanoparticles are loaded on the surface of W18O49 by electro-reduction and subsequent solvothermal methods. The as-fabricated r-HPW/W18O49 show unusual activity with NH3 formation rates of 184.54 µmol g−1 h−1, about 2.6 times higher than that of initial W18O49. The excellent photocatalysis property is attributed to the synergistic effect between W18O49 and heteropoly blues. The defective W18O49 provides rich active sites for the effective adsorption of N2 molecules and acts as a robust support to inhibit the aggregation of heteropoly blues. The photo-generated electrons in W18O49 quickly transfer to the heteropoly blues, retarding charge pair recombination and enabling the constructed “Z-Scheme” heterostructure to stronger redox capacity. This work offers a new perspective for preparing advanced heteropoly blues-based N2 photofixation nanomaterials.

Syngas production and gas-N evolution over heterogeneously doped La-Fe-O perovskite-type oxygen carriers in chemical looping gasification of microalgae

Chemical looping gasification (CLG) is a promising technology for syngas production with low pollutant emission. In this study, doped La-Fe-O perovskites including LaFeO3 (LF), LaFe0.5Ni0.5O3 (LN5F5) and La0.3Ba0.7FeO3 (L3B7F) were developed for microalgae CLG. The as-prepared perovskites exhibited an outstanding performance in syngas production with accumulative syngas yield > 33 mol/kg. For gas-N evolution, perovskites were beneficial to the formation of NH3 and HCN, while the iron ore may convert precursors to NO. Below 400 °C, NOx can be stored on the perovskite surface in the form of nitrite/nitrate species. When the temperature was above 700 °C, NOx can be selectively reduced by reducing components in tar or syngas under the catalysis of L3B7F, resulting in the final reduction of NOx emission. Thus, CLG over L3B7F may be a promising way for efficient utilization of microalgae to overcome the intractable nitrogen-related obstacles in the commercial application of biomass gasification technologies.

Photocatalytic nitrogen fixation under an ambient atmosphere using a porous coordination polymer with bridging dinitrogen anions

The design of highly electron-active and stable heterogeneous catalysts for the ambient nitrogen reduction reaction is challenging due to the inertness of the N2 molecule. Here, we report the synthesis of a zinc-based coordination polymer that features bridging dinitrogen anionic ligands, {[Zn(L)(N2)0.5(TCNQ-TCNQ)0.5]·(TCNQ)0.5}n (L is tetra(isoquinolin-6-yl)tetrathiafulvalene and TCNQ is tetracyanoquinodimethane), and show that it is an efficient photocatalyst for nitrogen fixation under an ambient atmosphere. It exhibits an ammonia conversion rate of 140 μmol g-1 h-1 and functions well also with unpurified air as the feeding gas. Experimental and theoretical studies show that the active [Zn2+-(N≡N)--Zn2+] sites can promote the formation of NH3 and the detachment of the NH3 formed creates unsaturated [Zn2+···Zn+] intermediates, which in turn can be refilled by external N2 sequestration and fast intermolecular electron migration. The [Zn2+···Zn+] intermediates stabilized by the sandwiched cage-like donor-acceptor-donor framework can sustain continuous catalytic cycles. This work presents an example of a molecular active site embedded within a coordination polymer for nitrogen fixation under mild conditions.

Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN 3 P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Postmodification

Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN ³ P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Postmodification

First Principles Study of Double Boron Atoms Supported on Graphitic Carbon Nitride (g-C3N4) for Nitrogen Electroreduction

Electrocatalytic reduction of N2 provides a clean, sustainable way for NH3 production. Efficient catalysts thus play a key role but remain a long-term challenge. In this study, the catalytic activity of double boron supported on graphitic carbon nitride (g-C3N4) for a N2 reduction reaction (NRR) is explored by density functional theory (DFT) calculations. Our results show that double boron atoms embedded in g-C3N4 with coordination of four N atoms and two boron atoms exhibits an excellent NRR performance with negligible energy consumption for adding hydrogen to *N2, while a moderate ΔG of 0.58 eV for the formation of the second NH3 suggests this catalyst is a potential candidate for N2 fixation.

The First Interferometric Measurements of NH2D/NH3 Ratio in Hot Corinos

The chemical evolution of nitrogen during star and planet formation is still not fully understood. Ammonia (NH3) is a key specie in the understanding of the molecular evolution in star-forming clouds and nitrogen isotope fractionation. In this paper, we present high-spatial-resolution observations of multiple emission lines of NH3 toward the protobinary system NGC1333 IRAS4A with the Karl G. Jansky Very Large Array. We spatially resolved the binary (hereafter, 4A1 and 4A2) and detected compact emission of NH3 transitions with high excitation energies (≳100 K) from the vicinity of the protostars, indicating the NH3 ice has sublimated at the inner hot region. The NH3 column density is estimated to be ∼1017–1018 cm−2. We also detected two NH2D transitions, allowing us to constrain the deuterium fractionation of ammonia. The NH2D/NH3 ratios are as high as ∼0.3–1 in both 4A1 and 4A2. From comparisons with the astrochemical models in the literature, the high NH2D/NH3 ratios suggest that the formation of NH3 ices mainly started in the prestellar phase after the formation of bulk water ice finished, and that the primary nitrogen reservoir in the star-forming cloud could be atomic nitrogen (or N atoms) rather than nitrogen-bearing species such as N2 and NH3. The implications on the physical properties of IRAS4A’s cores are discussed as well.

The HD Reaction of Nitrogenase: a Detailed Mechanism.

Nitrogenase is the enzyme that converts N2 to NH3 under ambient conditions. The chemical mechanism of this catalysis at the active site FeMo-co [Fe7 S9 CMo(homocitrate)] is unknown. An obligatory co-product is H2 , while exogenous H2 is a competitive inhibitor. Isotopic substitution using exogenous D2 revealed the N2 -dependent reaction D2 +2H+ +2e- →2HD (the 'HD reaction'), together with a collection of additional experimental characteristics and requirements. This paper describes a detailed mechanism for the HD reaction, developed and elaborated using density functional simulations with a 486-atom model of the active site and surrounding protein. First D2 binds at one Fe atom (endo-Fe6 coordination position), where it is flanked by H-Fe6 (exo position) and H-Fe2 (endo position). Then there is synchronous transfer of these two H atoms to bound D2 , forming one HD bound to Fe2 and a second HD bound to Fe6. These two HD dissociate sequentially. The final phase is recovery of the two flanking H atoms. These H atoms are generated, sequentially, by translocation of a proton from the protein surface to S3B of FeMo-co and combination with introduced electrons. The first H atom migrates from S3B to exo-Fe6 and the second from S3B to endo-Fe2. Reaction energies and kinetic barriers are reported for all steps. This mechanism accounts for the experimental data: (a) stoichiometry; (b) the N2 -dependence results from promotional N2 bound at exo-Fe2; (c) different N2 binding Km for the HD reaction and the NH3 formation reaction results from involvement of two different sites; (d) inhibition by CO; (e) the non-occurrence of 2HD→H2 +D2 results from the synchronicity of the two transfers of H to D2 ; (f) inhibition of HD production at high pN2 is by competitive binding of N2 at endo-Fe6; (g) the non-leakage of D to solvent follows from the hydrophobic environment and irreversibility of proton introduction.

Mechanistic insight into the effects of alkali metal ions on the formation of NOx precursors during the pyrolysis of 2,5-diketopiperazine

The inherent metal ions in food wastes have significant influences on the production of NOx precursors to affect the release of NOx during the incineration process. However, the detailed catalytic mechanism of metal ions remains unclear. Herein, 2,5-diketopiperazine (DKP) was employed as the N-containing model to study the effects of Na+ and K+ on the production of NOx precursors in the pyrolysis process. Based on density functional theory calculations and wave function analyses, all the energy barriers of the initial reactions decrease with the catalysis of Na+, whereas K+ can only promote part of the reactions and with weaker effects than Na+. Because of the varied influence on distinct reactions, Na+/K+ can change the rate-determining steps of the production pathways of NOx precursors. As for the same pathway, Na+ usually results in a relatively lower energy barrier than K+. Elevated temperatures lead to higher rate constants of K+ than Na+ for the favorable production pathways of NOx precursors. With the catalysis of Na+ and K+, the formation of NH3 is always more competitive than HCN and HNCO based on the comparison of overall energy barriers and the rate constants. Particularly, the competitiveness for NH3 production is enhanced by the catalysis of Na+ and K+ according to the increased rate constant advantage over other pathways.

Nitrogen Availability in Upland Soil Treated with Swallow Dropping

One of the problems in upland soils is poor in nutrient N. One effort to increase the availability of N in the soil is by providing swallow’s droppings which has a high N content. Thus, the purpose of this research was to determine the availability of N on upland soil was by applying swallow manure. This research employed Completely Randomized Design (CRD) with single factors (several levels of swallow’s manure: 0.0; 2.5; 5.0; 7.5; and 10.0 t ha–1). The availability of N in the soil was observed through the experimental column leaching, where 20 g of Ultisols was mixed with 20 g of quartz sand and swallow’s manure on a leaching column of 1-inch diameter and 20 cm height. Mineralized amounts of NH4+ and NO3– from the soil were determined by the percolation method (leaching) in every five days for 25 days. The results showed that the application of swallow’s manure increased the availability of total-N in the soil in the form of NH4+ and NO3–, and produced the release pattern of NH4+ and NO3– which was still relatively high until the end of the testing period. The results of this study demonstrate that application of swallow’s manure may be used as a slow-release fertilizer.

Dynamic Structural Evolution of [Rh(NO)2]+ Complex/Rh Metal Cluster in Zeolite during de-NOx via in Situ Formed NH3 under Lean/Rich Periodic Conditions

The dynamic structural evolution of Rh species in mordenite (MOR) zeolite was investigated using in situ spectroscopic techniques and density functional theory (DFT) calculations. In situ X-ray absorption spectroscopy and operando infrared (IR) revealed that metallic Rh species were oxidized to afford isolated [Rh(NO)2]+ species under NO flow at 200 °C, whereas small Rh metal clusters are formed under the subsequent H2 flow. Ab initio thermodynamics analysis shows that the plausible structures under NO and H2 at 200 °C are [Rh(NO)2]+ and Rh clusters in MOR, which is consistent with the experimental observations. A comparative study of Rh-loaded Al2O3 suggests that Al sites in MOR increase the thermodynamic stability of isolated Rh+ species and thus prevent their overoxidation to Rh2O3 under NO. NO capture in the form of [Rh(NO)2]+ and its selective reduction toward NH3 under H2 flow were observed by in situ IR measurements. The RhMOR catalyst exhibited ∼60% of NOx conversion above 200 °C under periodic lean/rich conditions. Transition-state calculations showed that the activation barrier for NO reduction to NH3 on [Rh(NO)2]+ (178 kJ/mol) is higher than that for Rh13 (156 kJ/mol), suggesting that Rh metal clusters are preferable NH3 formation sites, where the Rh13-catalyzed NO reduction into N2 and N2O was less preferable than NH3 formation, which is consistent with the experimental results. Combined with operando IR experiments under lean (NO + O2) and rich (NO + H2) conditions, we show that the reversible dynamic structural evolution of Rh species ([Rh(NO)2]+ ↔ Rh metal clusters under lean and rich conditions) is a key mechanistic feature for unsteady-state de-NOx via the capture of NO, its selective reduction to NH3, and the selective reduction of NO with NH3 formed in situ.

Molecular-level insight into photocatalytic reduction of N2 over Ruthenium single atom modified TiO2 by electronic Metal-support interaction

The sustainable production of NH3 by fixing N2 under mild conditions via photocatalysis is fascinating compared to current industrial processes operated at critical conditions. However, the inert N2 is extremely difficult to adsorb and activate. And the transfer of photogenerated electrons to the NN bond is energetically challengeable. Herein, we presented a photocatalyst designed based on electronic metal-support interactions (EMSI), which proved to be a reliable strategy for improving the photocatalytic N2 fixation performance. The introduction of Ru single atoms into TiO2 by a molten salt method can stabilize the oxygen vacancies, thus achieving an ammonia yield rate of 18.9 μmol·g−1·h−1 under mild conditions without any sacrificial agent due to the significant enhancement of EMSI. The combination of experimental results with first-principles simulations confirmed that the EMSI can tune the local atomic structure and accelerate the transfer of photogenerated carriers between Ru single atoms and TiO2 carriers, thus effectively enhancing photocatalytic N2 reduction activity. Additionally, the alternating pathway is more favored route for NH3 formation on the optimized single atom Ru/TiO2. Our atomic-level design and mechanistic studies provided a new reference for efficiently photocatalytic nitrogen fixation.

Local Proton Source Enhanced Nitrogen Reduction on a Combined Cobalt‐Molybdenum Catalyst for Electrochemical Ammonia Synthesis

AbstractElectrochemical nitrogen reduction reaction (NRR) under ambient conditions has attracted considerable scientific and engineering interest as a green alternative route for NH3 production. Molybdenum is a promising candidate as an electrocatalyst for NRR as it has a suitable binding strength with N species. However, the design of an efficient Mo‐based catalyst remains elusive. To enhance the selectivity of NRR toward NH3, we have developed a carbon nanofiber catalyst embedded with molybdenum and cobalt (Co−Mo−CNF). Co with a strong ability to dissociate water enhances local proton source near Mo, where the hydrogenation step of the NRR occurs. A NH3 formation rate of 72.72 μg h−1 mg−1 and a Faradaic efficiency of 34.5 % were obtained at −0.5 V vs. RHE. We also attempted to provide a mechanistic understanding of the NRR via in situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) and isotopic labeling experiments using 15N2 and D2O.

Local Proton Source Enhanced Nitrogen Reduction on a Combined Cobalt-Molybdenum Catalyst for Electrochemical Ammonia Synthesis.

Electrochemical nitrogen reduction reaction (NRR) under ambient conditions has attracted considerable scientific and engineering interest as a green alternative route for NH3 production. Molybdenum is a promising candidate as an electrocatalyst for NRR as it has a suitable binding strength with N species. However, the design of an efficient Mo-based catalyst remains elusive. To enhance the selectivity of NRR toward NH3 , we have developed a carbon nanofiber catalyst embedded with molybdenum and cobalt (Co-Mo-CNF). Co with a strong ability to dissociate water enhances local proton source near Mo, where the hydrogenation step of the NRR occurs. A NH3 formation rate of 72.72 μg h-1 mg-1 and a Faradaic efficiency of 34.5 % were obtained at -0.5 V vs. RHE. We also attempted to provide a mechanistic understanding of the NRR via in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotopic labeling experiments using 15 N2 and D2 O.

How do moisture content, friability, and crust development of litter influence ammonia concentrations in broiler production?

Litter is the main source of ammonia (NH3) in broiler houses. The quality thereof affects the amount of NH3 volatilized and emitted from the broiler house as well as the welfare of the birds. A trial was conducted to determine how the addition of water to broiler litter (by spraying the surface) and raking of the litter or leaving the litter undisturbed will influence NH3 concentrations at litter level, litter composition, bird welfare, and performance under experimental conditions. A total of 2160 Ross 308 male broilers were divided into the following 6 treatments, each with 6 replicates of 60 animals: NR(0) = no raking of the litter, no water added; R(0) = raking of the litter, no water added; NR(1.5) = no raking of the litter, 1.5 L of water added; R(1.5) = raking of the litter, 1.5 L of water added; NR(3.0) = no raking of the litter, 3.0 L of water added; R(3.0) = raking of the litter, 3.0 L of water added. The addition of water and raking of the litter was introduced at 10 d of age, with a frequency of 2 to 3 times per week. At 38 d of age, NH3 concentrations were higher for the raked litter treatments than the treatments which were not raked (P < 0.001). The higher NH3 concentrations of the raked litter treatments coincided with a higher litter pH (P < 0.001) and temperature (P R × W < 0.001) as well as a lower uric acid and total nitrogen (N) concentration in the litter at 37 d of age. The addition of water to the litter resulted in lower litter quality scores at 29 and 37 d of age (P < 0.001) and a higher incidence of foot lesions at 29 (P W = 0.006) and 37 (P R × W = 0.025). Regardless of raking or not raking the litter, addition of moisture to the litter lead to litter of lower quality and subsequent higher incidence of foot lesions in broilers. This study demonstrates that the development of a crust on top of the litter layer reduces the formation and concentration of NH3 volatilized from the litter. Compacted litter resulted in lower NH3 concentrations while friable litter led to more NH3 being volatilized from the litter.

The nitrogen transformation and controlling mechanism of NH3 and HCN conversion during the catalytic pyrolysis of amino acid

Pyrolysis can convert biomass into sustainable chemicals and fuels, but the nitrogen compounds in its non-lignocellulosic components may produce hazardous NOx and its precursors. In this paper, catalytic pyrolysis of glutamic acid (Glu), used as a representing compound for biomass nitrogen source, was investigated at bench scale to study the transformation of the nitrogen element and the mechanism of Ammonia (NH3) and Hydrogen Cyanide (HCN) formation. The yields of the liquid, gaseous and solid products and the distribution of nitrogen compounds were systematically analysed. The experimental results showed that catalytic pyrolysis with H-ZSM-5 could increase the nitrogen compounds in the gas product from 38.54 % to 53.95 %, while it can reduce the nitrogen in the tar and char by 69.22 % and 58.07 %, respectively. The result of Density Functional Theory (DFT) study showed that the deamination to ternary cyclic ethers was the optimum pathway for NH3 formation. The formation of HCN has been dominated by the removal of side chain groups (reaction path 8). The energy barrier of the reaction path 9 was reduced to a level comparable to the energy barrier of path 8 during the catalytic pyrolysis, which may compete with each other. The 8T cluster model of the H-ZSM-5 catalyst revealed that the hydrogen bond formed between the acid sites and the reactants played an significant role in decreasing the reaction energy barrier. The experimental and computational results demonstrated the controlling mechanism of acid sites on the production of NH3 and HCN compounds and provided fundamental understanding to nitrogen transformation during the biomass pyrolysis.

Urea Production on Metal-Free Dual Silicon Doped C9 N4 Nanosheet Under Ambient Conditions by Electrocatalysis: A First Principles Study.

The development of cheap, eco-friendly electrocatalysts for urea synthesis which avoids the traditional nitrogen reduction to form ammonia, is very important to meet our growing demand for urea. Herein, based on density functional theory, we propose a novel electrocatalyst (dual Si doped C9 N4 nanosheet) composed of totally environmentally benign non-metal earth abundant elements, which is able to adsorb N2 and CO2 together. Reduction of CO2 to CO happens, which is then inserted into activated N-N bond, and it produces *N(CO)N intermediate, which is the crucial step for urea formation. Eventually following several proton coupled electron transfer processes, urea is formed under ambient conditions. The limiting potential value for urea formation is found to be lower than that of NH3 formation and HER (hydrogen evolution reaction). Moreover, the faradaic efficiency of our proposed catalyst system is 100 % for urea formation, which suggests greater selectivity of urea formation over other competitive reactions.

Significant Reduction of the Formation of N2O and NH3 on an Efficient Three-Way PtRh Catalyst Modified by LaFeCu Perovskite

This work designed a series of three-way catalysts (TWCs) with and without the modification by La0.67Fe0.83Cu0.17O3 (LaFeCu) perovskite to reduce the formation of N2O and NH3 emissions from natural gas vehicles (NGVs). The modified PtRh catalyst was found to have an efficient TWC performance and to reduce the formation of N2O and NH3 significantly. The X-ray diffraction and CO-Fourier transform infrared results demonstrated the formation of Rhx species, which would reduce the formation of NCO*, the main precursor of NH3. In situ diffuse reflectance infrared Fourier transform spectroscopy was used to confirm that no NCO* groups were found on the modified catalyst. The X-ray photoelectron spectroscopy results revealed the increase in the Pt2+ content on the modified catalyst, promoting the decomposition of N2O. Also note that the modified catalyst produced far fewer N2O than the catalyst without modification in the model reaction of CO + NO. Our work would provide a solution to develop an advanced TWC for NGVs.

(Invited) Electroreduction of Nitrogen to Ammonia at Iron Catalytic Sites Generated at Interfaces Utilizing Iron Phosphides and Heme-Type Complexes

The feasibility of performing nitrogen electroreduction reaction, or nitrogen fixation, particularly in aqueous solutions, constitutes an attractive prospect to produce ammonia under ambient, or near ambient, conditions. Development of durable, specific and reasonably efficient low-cost catalysts remains a great challenge for electrochemical science and technology. Currently, most of electrochemical approaches to N2-fixation suffers from slow kinetics due to the difficulty of achieving the appropriate adsorption and activation of dinitrogen leading to cleavage of the strong, triple N≡N bond. This symposium will feature presentations on research dealing with the fundamental and applied aspects of nitrogen reduction reactions of relevance various aspects of science and existing technologies.Transition metal phosphides are promising non-noble earth-abundant catalysts with broad electrocatalytic properties, in particular when it comes to electroreduction of such inert reactants as carbon dioxide. Herein, we report the successful electrocatalytic reduction of nitrogen (N2) using different phases of iron phosphide activated at 450 °C. For example, the FeP and Fe2P phases have been found to act as efficient catalysts for the formation of NH3 in alkaline and semineutral media. Detection of in-situ formed product has been achieved by probing the electrooxidation of NH3 to nitrogen (N2) using the additional working electrode modified with Pt nanoparticles. On mechanistic grounds, the iron (Fe0) sites seem to be electrocatalytic active during the reduction of nitrogenThe iron sites can also be generated within the porphyrin rings and related coordination structures. Their high electrocatalytic activity was historically demonstrated for the CO2-reduction. The results obtained here indicate the feasibility of horseradish peroxidase (HRP) to act as the biocatalyst, when deposited on the glassy carbon (an inert electrode substrate), capable of inducing electroduction of not only CO2 but also N2. HRP is a metalloenzyme, in which a large alpha-helical protein which binds heme as a redox cofactor. The actual electrocatalytic properties shall be attributed to the existence of heme groups, i.e. complexes of iron ions coordinated to porphyrin units. On mechanistic grounds, the nitrogen molecules seems to be chemisorbed or attracted to the heme centers during the activation step. Indeed, only “adsorbates” of N2 are catalytically reduced. In other words, the HRP-surface-attached N2 molecules, rather than the bulk reactant, are reduced at the electrocatalytic interface. The reduction reaction of nitrogen is a multielectron and multiproton transfer process suffering from high over-potentials and limited selectivity The N2 molecule with triple bond requires special means of activation through strong adsorption at the electrocatalytic interface. Obviously most of electrocatalysts will be more active toward hydrogen evolution than ammonia production. Consequently, ammonia is produced at trace levels, and the reaction efficiency is very low. On the whole, the presence of the α-helix HRP secondary structure (composed of backbone N−H groups that hydrogen-bonded to the backbone C=O groups of the amino acid network) is likely to contribute to the system’s good stability and selectivity (e.g., with respect to the competing hydrogen evolution reaction).

Oxidation of municipal sewage sludge, chicken and swine manure in the water-oxygen fluid flow under uniform heating

The paper presents the research results of the oxidation of municipal sewage sludge (MSS), chicken (CM) and swine (SM) manure when pumping water-oxygen fluid through their bed at a uniform temperature increase (1.5 K/min) to 733 K. Temperature dependences were obtained for the yield of volatile and liquid products, as well as data on the content of mineral components in the ash residue and water, collected at the reactor outlet. From the time-dependent temperature of the reactor wall, the power of resistive heaters, and the degree of total organic carbon removal, it follows that most of the organic matter of biowastes is oxidized at T < 643 K. It is shown that the rate of organic carbon removal increases in the sequence: CM < MSS < SM, and is determined by the consumption of oxygen supplied to the reactor. According to IR spectroscopy and ultimate analysis data, an increase in the oxidation duration and temperature leads to a decrease in the content of functional groups, and to an increase in the proportion of aromatic compounds in liquid products. Liquid products, formed during the oxidation of CM are characterized by the highest N/C atomic ratio. It was revealed that during the oxidation of biowastes, from 50% to 75% of nitrogen passes into the aqueous phase in the form of NH4+ ions, while the main elements (Si, Ca, Mg, P, K, and Al) are concentrated in the ash residue. The results of XRD analysis show that CaCO3 and SiO2 predominate in the composition of ash residues of CM and SM, respectively.