Formation Of NH Research Articles

Lean NOx trap catalyst formulation for selective ammonia synthesis from captured NOx

In the Lean NOx Trap (LNT) technology, ammonia (NH3) occurs as reaction intermediate in conversion of trapped nitrogen oxides (NOx) to nitrogen gas (N2) using hydrogen gas (H2) reductant. The use of an LNT for synthesizing NH3 from NOx is potentially an attractive option for small-scale green NH3 production by converting locally produced NOx pollutant to an important chemical. In this work, it is investigated to what extent the product selectivity towards NH3 on the standard model catalyst Pt/BaO/Al2O3 can be maximized depending on reaction conditions for trapping and reducing NOx with H2 in the temperature range of 75–200 °C. The LNT catalyst preparation was varied by using Pt, Pd and bimetallic combinations, as well as different support materials, namely Al2O3, TiO2, ZrO2 and MgO. NOx adsorption and selectivity of captured NOx reduction to ammonia is discussed in terms of texture and the chemical nature of the support. The NH3 selectivity is influenced by the water vapor content in the gas feed. Storage of NOx in absence of water followed by reduction with hydrogen gas in presence of water vapor was found to be the most favorable operation mode of the LNT for NH3 formation. The NH3 selectivity reached 82% at 150 °C. Explanations for the role of water and in this catalytic chemistry are offered and its consequences for catalyst preparation are discussed. The optimum water content of the reacting gases is predicted to be strongly dependent on catalyst preparation.

Fixation of air nitrogen to ammonia and nitrate using cathodic plasma and anodic plasma in the air plasma electrolysis method

AbstractThe fixation of nitrogen (N2) from the air into ammonia (NH3) and nitrate (NO3−) is usually conducted using the Haber–Bosch process, which requires the raw material of hydrocarbons for hydrogen (H2), which has a large amount of energy but produces high CO2 emissions. An environmentally friendly and energy‐saving alternative is the air plasma electrolysis method, which can be used to synthesize NH3 and NO3− under ambient conditions. In this study, this method was used to inject air into the plasma zone in a K2SO4 electrolyte solution to produce N2 fixation compounds. The results showed that the use of cathodic plasma promoted the formation of NH3 but suppressed NO3− production. The optimal air injection rate was achieved at 0.6 L.min−1 and an electrical power of 452 W, with a total fixed N2 of 51.66 mmol. The highest formation of NO3− in cathodic plasma was obtained in 35 min, with a value of 29.92 mmol, and 2.57 mmol NH3 was achieved at 60 min. The high concentration of H2 gas, which is a by‐product of this process, can contribute to increasing the use of Haber–Bosch green technology in the production of NH3.

Availability and reactivity of N2(v) for NH3 synthesis by plasma catalysis

Production of vibrationally excited N2 (N2(v)) in atmospheric pressure nonthermal plasma and loss of N2(v) by gas-phase reactions and reactions on catalytic surfaces are analyzed to examine the role of N2(v) in NH3 formation by plasma catalysis. Vibrational state-to-state kinetic models complemented with molecular beam mass spectrometry (MBMS) measurements demonstrate that N2(v> 0) is produced with densities 100× greater than the density of N radicals by a radiofrequency atmospheric pressure plasma jet. The experimentally measured loss of N2(v) corresponds with a state-to-state kinetic model that describes loss of N2(v) by surface-mediated vibrational relaxation without consideration of reactions that convert N2(v) to NH3 over the catalyst surface. Rate constants for vibrational relaxation of N2(v) on catalyst surfaces exceed upper bounds on proposed rate constants for NH3 formation reactions from N2(v) over Fe when v < 9, Ni when v < 18, and Ag when v < 39, which indicates that only higher vibrational levels can possibly contribute to catalytic NH3 formation faster than they undergo vibrational relaxation on the surface. Densities of N2(v> 8), vibrational levels that can possibly react over Fe to form NH3 faster than they undergo vibrational relaxation, are less than or similar to N densities at the inlet of the catalyst bed and measured NH3 formation for the investigated conditions in this work, while densities of N2(v> 17) and N2(v> 38) are orders of magnitude below the N density at the inlet of the catalyst bed and the measured NH3 formation. The loss of N2(v) by vibrational relaxation on the surface limits the ability of N2(v) to contribute to catalytic NH3 formation and explains why N2(v) does not produce NH3 in quantities that are comparable to NH3 formation from N even though N2(v > 0) is more abundantly produced by the plasma.

Low temperature NH3 selective catalytic reduction of NOx over CeOx-biochar catalyst prepared by air oxidation

A highly efficient CeOx-BC0.6 (BC: biochar. 0.6: mass ratio of Ce/(BC + Ce)) catalyst was prepared by air oxidation for low temperature NH3 selective catalytic reduction of NOx. The catalytic performance, characterization and reaction mechanism of the CeOx-BC0.6 were investigated. The results showed that NOx conversion and N2 selectivity of CeOx-BC0.6 catalyst obtained by calcining in air were above 90 % at 150–300 °C and 100,000 h−1. The surface oxygen groups, acid sites and oxygen vacancies were generated by air oxidation treatment, which promoted the adsorption and activation of reactants. NH3 and NOx were adsorbed on the catalyst surface in the form of NH4+, NH3+, nitrite and nitrate adspecies. The redox cycles of ketonic carbonyl/phenol (CO/C–OH) pairs and Ce4+/Ce3+ pairs were responsible for the activation of NH3 and NOx. NH2NO and NH4NO2 were the main active intermediates. The reaction of NH3 selective catalytic reduction of NOx over CeOx-BC0.6 mainly followed Eley-Rideal mechanism. These results will promote the understanding of mechanism of NH3 selective catalytic reduction of NOx for biochar-based catalyst prepared by air oxidation.

MgAl layered double hydroxide (LDH) for promoting ammonia synthesis in non-thermal plasma: Role of surface oxygen vacancy

Here, the MgAl layered double hydroxide (LDH) supports and relevant metal on LDH catalysts (i.e., Ni, Co, and Ru) were prepared and investigated under non thermal plasma (NTP) conditions to probe the role of surface oxygen vacancy (OV) in NTP-assisted ammonia (NH3) synthesis. The findings show that OV on the LDH carrier is highly beneficial to NH3 formation under NTP conditions, and concentration of OV on the LDH can be regulated by the post-synthesis calcination and hydrogen plasma etching. Additionally, loading of active metal species on the LDH could promote the NH3 synthesis further due to presence of multiple reaction pathways and the synergy between the surface OV and metal sites in such NTP-catalytic systems. As the result, the catalysts developed by this work showed high ammonia synthesis rates of 4.42−4.52 mmol g−1 h−1 and energy efficiencies of 1.67−1.71 gNH3 kWh−1, respectively. The findings of the work pave the way for the rational design and optimization of highly efficient catalysts with dual active sites for intensifying the NTP-catalytic ammonia synthesis.

Efficiency of nitrogen, gibberellic acid and potassium on canola production under sub-tropical regions of Pakistan

The global demand for crop production is rapidly growing due to the continued rise in world population. Crop productivity varies generally with soil nutrient profile and climate. The optimal use of fertilizers might help to attain higher crop yield in canola. To circumvent nutrient imbalance issues in soil, two separate field trials were conducted to determine (a) the best source of nitrogen (N) between ammonium sulfate (NH4)2SO4) and ammonium nitrate (NH4NO3), (b) significance of gibberellic acid (GA3) and potassium (K), in an attempt to enhance canola yield and yield attributes. Both experiments were carried out in randomized complete block design (RCBD) with three replicates. The nitrogen source in the form of NH4)2SO4 (0, 10, 20 and 30 kg/ha) and NH4NO3 (0, 50, 75 and 100 kg/ha) was applied in the rhizosphere after 3 and 7 weeks of sowing, referred to as experiment 1 (E1). In another separate experiment (E2), the canola crop was sprayed with four level of GA3 (0, 10, 15, 30 g/ha) and K (0, 2.5, 3.5, 6 g/ha) individually or in combination by using hydraulic spryer, 30 days after sowing (DAS). The data was collected at different growth stages of canola and analyzed statistically. The E1 trail showed that N fortification in the form of NH4NO3 (100 kg/ha) and (NH4)2SO4 (30 kg/ha) had a positive effect on the plant height, number of branches, fruiting zone, seed yield per plant, seed yield per hectare of canola except oil percentage. Moreover, canola plants (E2) also displayed a significant improvement on all studied features with high doses of GA3 (30 g/ha) and K (6 g/ha) individualy and in combined form. The correlation coefficient analysis of (NH4)2SO4 and NH4NO3 was highly significant to plant height, number of branches, fruiting zone, seed yield per plant, seed yield per hectare of canola In a nutshell, compared to both source of N, NH4NO3 was more efficient and readily available source of N. GA3 being a growth elicitor and potassium as a micronutrient serve as potential source to improve yield and to manage nutrient profile of canola.

Photobiocatalytic conversion of solar energy to NH3 from N2 and H2O under ambient condition

NH3 is an important chemical fertilizer and expecting as H2 carrier. Several methods have been investigated for eco-friendly NH3 production under mild conditions instead of Haber-Bosch process using 400 °C, 20 MPa. Here, cyanobacterial Anabaena variabilis was utilized as a nitrogenase-producing biocatalyst that converts N2/H2O to NH3 under ambient conditions. Biocatalytic reactions revealed that MV•+ can penetrate cell membrane and transfer electrons generated in inorganic photocatalyst. We first reported photobiocatalytic NH3 production of cyanobacteria and TiO2. Comparing with natural system, NH3 formation rate of the hybrid system increased 81.3 times with an initial rate of 2031.7 nmol·h−1 and turnover number of 216.8.

Conversion of methylamine in a flow reactor and its interaction with NO

The conversion of methylamine (CH3NH2, 1000 ppm) has been studied in an atmospheric-pressure flow reactor from both experimental and modeling points of view. Several values of the oxygen excess ratio (λ), from pyrolysis to fuel-lean conditions, have been tested, and a large number of different species have been quantified experimentally by three different diagnostic techniques: gas chromatography, Fourier Transform Infra-red spectroscopy (FTIR) and an infra-red NO analyzer. For the first time, the influence of NO addition (500 and 1000 ppm) on the stoichiometric oxidation of methylamine has also been experimentally evaluated, and the main products of such interaction have been identified. Results indicate that, unlike the little influence of oxygen availability on methylamine conversion, the presence of different concentrations of NO promotes methylamine oxidation at lower temperatures. A literature mechanism has been validated against the present experimental data since previous experimental works under these conditions are scarce. The largest discrepancies have been found for the formation of NH3 and NO as oxidation products, which are under and overestimated by the model, respectively, and under pyrolysis conditions, where modification of the kinetic parameters for the reaction CH2NH2 ⇌ CH2NH + H from the original mechanism notably improves the agreement between experimental and simulated results.

Nitrogen Reduction to Ammonia on a Fe16 Nanocluster: A Computational Study of Catalysis.

The sequence of elementary steps leading to reductive ammonia formation from N2 and H2 catalyzed by a Fe16 cluster is studied using generalized gradient approximation density functional theory and an all-electron basis set of triple-ζ quality. The computational methods are validated by comparison to experimental data such as binding energies where possible. First, the associative and dissociative attachment of N2 to Fe16 is considered, followed by exploration of the pathways leading to distal (Fe16-N-NH2) and enzymatic (NFe16-NH2) formation of an amino group. Next, the pathways leading to NH3 formation in both distal and enzymatic cases are examined. Two mechanisms for NH3 detachment have been discovered. An interesting peculiarity of the pathways is that they often proceed with total spin fluctuations, which are related to the rupture and formation of bonds on the surface of the catalyst over the course of the reactions. The reaction Fe16 + N2 + 2H2 → Fe16NH + NH3 is found to be exothermic by 1.02 eV (93.8 kJ/mol).

How Can the PtPd‐Based High‐Entropy Alloy Triumphs Conventional Twc Catalyst During the NO Reduction? A Density Functional Theory Study

AbstractDensity functional theory is used to compare the catalytic performance of PtPdRhFeCo(100) high entropy alloy (HEA) three‐way catalyst (TWC) to the conventional Pt(100) in the NO reduction step during NH3 production that supplies to passive NH3‐SCR. Stronger adsorption of NO on the HEA(100) surface is beneficial to capture NO. During adsorption, the catalyst surface acts as an electron donor while the adsorbate is the acceptor on both HEA(100) and Pt(100) systems. Herein, the reaction mechanism of NO reduction can be classified into two steps: 1) NO activation and 2) product formation. During NO activation, direct NO dissociation is the preferable pathway on both HEA(100) and Pt(100) surfaces with the same Ea, whereas HNO and NOH pathways on HEA(100) are suppressed. For NH3, N2, and N2O production on HEA(100) is found to be more difficult than on Pt(100). However, the thermodynamic driving force of all reactions on HEA(100) is more spontaneous than on Pt(100). Also, the rate‐determining step on HEA(100) is found to be NH3 formation different from the Pt(100), while difficult H diffusion on HEA(100) is the key factor that reduces NH3 production.

Synthesis of spinel type 2D Co3O4 nanodiscs using gallic acid for electrochemical NH3 formation by N2 reduction

The production of ammonia through electrochemical nitrogen reduction reaction (ENRR) has garnered significant interest as a potential method of artificial nitrogen fixation in ambient conditions. This study reports an environmentally friendly synthesis of pristine Co3O4 nanodiscs (NDs) as a catalyst to effectuate electrochemical nitrogen reduction to ammonia. The absorption spectra of Co3O4 NDs revealed two peaks at 435 and 735 nm, indicative of O2− to Co2+/Co3+ charge transfer. The particles exhibited a distinct propensity for the growth along the (311) direction with induced oxygen vacancies which resulted from the release of NOx from the decomposition of precursor in the calcination step. The diameter and thickness of Co3O4 NDs were determined to be 240 and 35.5 nm, respectively. Faradaic efficiency of NH3 production of 2.6% was achieved with a yield rate of 8.8 µg h−1 mgcat.−1 at −1.25 V (vs. Ag/AgCl). Co3O4 NDs/TCP electrode showed six times higher Faradaic efficiency (FE) for ENRR compared to the bare TCP electrode. However, prolong electrolysis could result a reduction in FE due to sacrifice of active Co(III) sites due to the formation of Co(OH)2. Co2+ in tetrahedral sites easily bond with the N≡N, whereas Co3+ in octahedral sites facilitate the electron transfer for ENRR.

Theoretical Study on the Formation Mechanism of NOx Precursors During the Pyrolysis of 2,4-Imidazolinediketone

ABSTRACT The incineration technology of food waste is one of the effective technologies for achieving waste resource utilization and harmless utilization. As the most fundamental and important stage in the incineration process, it is necessary to conduct detailed research on the pyrolysis mechanism. Therefore, this article selects 2,4-imidazolidinedione as the representative chemical compound for food waste. Study the pyrolysis mechanism of 2,4-imidazolidinedione and the reaction pathway of NOx precursor generation by using density functional theory (DFT) calculation.The possible paths of NH3, HCN and HNCO formation from C-N/C-C bond fracture and C-N bond direct fracture caused by H-transfer are proposed. The formation path of NH3 has low energy barrier and high reaction rate constant at low temperature. At the same time, it explained that the release of HCN increases with the increase of temperature. In addition, this study has also theoretically demonstrated that the reaction path of NH3 is more prone to occur compared to HCN, which finely interprets the yield trend of NH3 and HCN in the experiment.

Amine functionalized Fe doped g-C3N4 for rapidly and thoroughly selective degradation of anionic organic pollutants

The Fenton reaction was widely used for the elimination of organic contaminants for treating wastewater. It is still a challenge to realize the selective degradation of target pollutants. Amine functionalized Fe-doped carbon nitride (Fe-CNNH2) was first prepared to catalyze the Fenton reaction. The Brönsted alkaline of the catalyst was enhanced for the -NH2 formation. The positive zeta potential was strengthened by the formation of -NH3+ at the catalyst's surface through the combination of -NH2 and H+. The catalyst exhibited rapid and thoroughly selective degradation for anionic organic pollutants. Simultaneously, the catalytic activity of Fe-CNNH2 was higher than those reported for tetracycline (TC) removal, and total organic carbon (TOC) removal reached 84%. The catalyst showed a strong detoxification ability for the pollutants. This study provides a new design strategy to prepare highly efficient catalysts for the selective degradation of organic contaminants.

CO2 plasma gasification of bakelite-based electrical switch waste feedstock

Poor degradability of e-waste causes severe soil and water contamination. In recent times, plasma gasification has been an attractive way of solid waste management towards energy recovery considering the environmental benefits. To reduce the short end-of-life electrical products and net CO2 emissions, the low-grade feed of electrical switch waste (ESW) comprising of bakelite (BAK) is chosen for generating clean syngas through the plasma method using CO2. The influence of the feed rate of solid waste, feed CO2 gas and plasma torch power on the product yield and syngas composition is evaluated. Energy and exergy (2-E) analyses are performed to assess the feasibility of the process. The experiment results indicate a maximum syngas yield of ∼85% at the highest torch power of 1.6 kW, with high concentrations of H2 (24.36 vol%) and CO (43.61 vol%). At low torch power of 0.5 kW, the residual solid yield reaches 24.58%. Considering all the cases, syngas with a medium calorific value of up to 10.20 MJ/m3 is attained. For the optimum feed rate of 40 g/10 min, CO2 flow rate of 0.6 lpm and plasma power of 0.75 kW, the process achieved the highest cold gas and exergy efficiency of 42.33% and 35.99%, respectively. The obtained oil (viscosity = 6.43 cP, density = 0.975 g/ml, pH = 8.01 and LHV = 31.47 MJ/kg) is suitable for applications in combustion, transportation and chemical production after quality upgradation. The solid residue (volatile matter = 11 wt%, fixed carbon = 65.67 wt%, ash = 23.33 wt% and LHV = 15.51 MJ/kg) obtained containing Ba (70.42 wt%), Zn (3.87 wt%), Ti (3.25 wt%), etc. in the ash, can be used for making corrosion coating agents, alloys and paints after recovery. The oil analysis showed the formation of NH3 during the reaction at a high torch power of 1.6 kW. Lastly, the reaction mechanism of plasma gasification for the conversion of ESW into syngas is proposed.

Electrocatalytic Reduction of Dinitrogen to Ammonia with Water as Proton and Electron Donor Catalyzed by a Combination of a Tri-ironoxotungstate and an Alkali Metal Cation.

The electrification of ammonia synthesis is a key target for its decentralization and lowering impact on atmospheric CO2 concentrations. The lithium metal electrochemical reduction of nitrogen to ammonia using alcohols as proton/electron donors is an important advance, but requires rather negative potentials, and anhydrous conditions. Organometallic electrocatalysts using redox mediators have also been reported. Water as a proton and electron donor has not been demonstrated in these reactions. Here a N2 to NH3 electrocatalytic reduction using an inorganic molecular catalyst, a tri-iron substituted polyoxotungstate, {SiFe3W9}, is presented. The catalyst requires the presence of Li+ or Na+ cations as promoters through their binding to {SiFe3W9}. Experimental NMR, CV and UV-vis measurements, and MD simulations and DFT calculations show that the alkali metal cation enables the decrease of the redox potential of {SiFe3W9} allowing the activation of N2. Controlled potential electrolysis with highly purified 14N2 and 15N2 ruled out formation of NH3 from contaminants. Importantly, using Na+ cations and polyethylene glycol as solvent, the anodic oxidation of water can be used as a proton and electron donor for the formation of NH3. In an undivided cell electrolyzer under 1 bar N2, rates of NH3 formation of 1.15 nmol sec-1 cm-2, faradaic efficiencies of ∼25%, 5.1 equiv of NH3 per equivalent of {SiFe3W9} in 10 h, and a TOF of 64 s-1 were obtained. The future development of suitable high surface area cathodes and well solubilized N2 and the use of H2O as the reducing agent are important keys to the future deployment of an electrocatalytic ammonia synthesis.

Improving the Nitrogen Reduction Reaction Activity of Ti2n Nitride Mxene through pH and Electrolyte Selection

Electrochemical nitrogen reduction reaction (NRR) is used to convert atmospheric nitrogen (N2) to ammonia (NH3) at ambient temperature and pressure. In general, acidic electrolytes are used to provide protons (H+) for the reduction process. However, this leads to a low NH3 selectivity because of H2 by-product formation via the hydrogen evolution reaction (HER). Recently, we showed that a Ti2N MXene is active and selective for NRR. We demonstrated that this catalyst works through a Mars-van Krevelen (MvK) mechanism rather than the conventional associative/dissociative mechanisms. However, the effect of pH and electrolyte on its catalytic activity and selectivity was not well understood. Here, we investigate these effects by performing experiments in varying electrolytic conditions and develop relations between pH, electrolyte choice, and performance. The Ti2N nitride MXene was synthesized via an oxygen-assisted molten salt fluoride etching technique and characterized through XRD and Raman and FTIR spectroscopies. Our findings showed that changing pH does not affect the NRR onset potential. We found that as pH increases, selectivity towards NH3 also increases presumably due to a lack of free H+ available to participate in HER. We also found that smaller cations with smaller solvation shells suppress HER activity, while smaller anions prevent catalyst poisoning during the NRR process, as evidenced by cyclic voltammetry before and after experimental conditions. We confirm production rates and the method of NH3 formation via NMR analytical techniques, including isotopic exchange. We plan to expand these findings to other materials and systems, and use the knowledge obtained from these studies to design optimal electrolytic conditions to produce NH3 through NRR.

Fe Doped CoS2 Nanoarrays: Efficient Electrocatalytic Nitrate Reduction to Ammonia under Ambient Conditions.

The electrocatalytic nitrate reduction reaction (NO3-RR) enables the reduction of nitrate to ammonium ions under ambient conditions. It was considered as an alternative reaction for the production of ammonia (NH3) in recent years. In this paper, we report that the Fe doping CoS2 nanoarrays can effectively catalyze the formation of NH3 from nitrate (NO3-) under ambient conditions. This is mainly due to the increase of the NO3- reaction active site by Fe doping and the porous nanostructure of the catalyst, which greatly improves the catalytic activity. Specifically, at -0.9 V vs. RHE, the NH3 yield rate (RNH3) of Fe-CoS2/CC is 17.8 × 10-2 mmol h-1 cm-2 with Faraday Efficiency (FE) of 88.93%. Besides, such catalyst shows good durability and catalytic stability, which provides the possibility for the future application of electrocatalytic NH3 production.

Discovering a catholyte free design for gas phase electrocatalytic NO gas reduction to NH3 at room temperature

Nitric oxide (NOx) is one of the most contributors to the health risks associated with breathing in flue gases and it is crucial to eliminate this pollutant from the air when solid waste is burned. Electrochemical gas phase reduction of NO to NH3 is the promising method to mitigating the accumulation of NO gas pollutants and producing a valuable NH3 as a product at room temperature. In this investigation, for the first time, we designed a catholyte-free cell for gas phase electrochemical NO to NH3 conversion using K2[Ni(CN)4] coated carbon felt (CF) electrode as a electrocatalyst at room temperature. Herein, K2[Ni(CN)4] heterogeneous mediator transfers the electron between the NO gas molecule and electrode. The NO removal efficiency and NH3 formation were simultaneously monitored by using online gas phase FTIR spectroscopy. In the catholyte-free gas phase NORR process, the K2[Ni(CN)4]/CF electrode exhibits excellent NORR performance, with a high NH3 yield rate of 1128.9 µmol h−1 cm−2, an excellent 89.5 % NH3 faradaic efficiency at − 1 V vs quasi reference Ag and enhanced long term NORR durability. It is noteworthy that, this is the highest yield rate and faradaic efficiency of NH3 during gas phase NORR at room temperature. In addition, K2[Ni(CN)4]/CF electrocatalyst exhibits 99 % of NO removal efficiency with the formation of value-added product (NH3). Moreover, the proposed electrocatalyst shows excellent chemical, and morphological stability after long durability NORR operations. Furthermore, the detailed electrode-electrolyte free cell, NORR reduction mechanism was proposed. Present discovery provides great insights for sustainable NORR operations in real-site applications.

Effect of NaCl/MgCl2 on generation of NOx precursors during aspartic acid pyrolysis: A experimental and theoretical study

This work studied the effect of NaCl/MgCl2 on the evolution of nitrogen during aspartic acid pyrolysis, focusing on the transformation pathways in molecular level. The generation of NOX precursors and other volatiles were detected by TG-FTIR, UV, and GC–MS. Notably, density functional theory was used to evaluate energy barrier and rate-determining step during pyrolysis. The yields of NH3, HCN, and HNCO were inhibited by NaCl/MgCl2 addition, especially on the second releasing stage (333–468 °C). The result of theoretical simulations showed that the rate-determining step in six pathways of aspartic acid pyrolysis was changed by NaCl/MgCl2 addition, especially for MgCl2, and the optimum generation pathway for nitrogen–containing products changed from NH3 formation to DKP formation. The highest energy barrier of NH3 and HCN generation increased to 327 kJ/mol and 432 kJ/mol after the addition of NaCl and MgCl2, respectively, leading to their lower release than raw aspartic acid. In addition, the presence of NaCl/MgCl2 decreased the energy barrier for the substitution of the amino group with the hydroxyl group, especially for NaCl, resulting in the fact that more nitrogen was retained in the char. The results first revealed how the NaCl/MgCl2 affected the nitrogen transformation during aspartic acid pyrolysis under molecular level.

The formation mechanism of N2O and NH3 on PtRh three-way catalyst of natural gas vehicles

The mechanism of the NO conversion to poisonous substrates, such as NH3 and N2O on a model Pt/CeO2+Rh/LA three-way catalyst (TWC) during the treatment of exhaust emission from natural gas vehicles (NGVs) was investigated. The in situ DRIFTS results showed that the main pathway of NO reduction is the reaction of nitrite/nitrate species formed by NO adsorbed on CeO2 with CH4. It was further elucidated by O1s and DRIFTS that the formation of N2O at low temperature is ascribed to competitive reactions of cyanide (-CN) species with O2 and NOx. Specifically, for Pt/Ce catalysts, N2 and CO2 are formed due to the preferential reaction of -CN species with the surface adsorbed oxygen (Oads) species on the catalyst. While for Pt/Ce-Rh/LA550 and Pt/Ce-Rh/LA600 catalysts, N2O is formed due to the easier reaction of -CN with NOx. At high temperature, the catalyst mechanically mixed with Rh/LAx increased the concentration of Oads, which promoted CH4 oxidation and inhibited the reaction of NO with C-containing compounds to isocyanate (NCO*), thus reducing NH3 formation. Our work may provide new ideas for developing advanced TWC for NGVs with lower emission of NH3 and N2O.