NH3 Molecules Research Articles

A comparative study of effects of methane and hydrogen on ammonia combustion in air via reactive molecular dynamics

Ammonia (NH3) is a promising substitute for fossil fuels to achieve the net-zero emission targets. To improve the combustion performance of NH3, reactive fuels are added to the NH3 combustion. In the present study, the combustions of NH3, CH4/NH3, and H2/NH3 in air conditions were simulated using a reactive molecular dynamics method. Results suggest that whether the addition of CH4 and H2 could accelerate the consumption of NH3 and reduce NOX emissions depends on the fuel ratio of the reactive gas (CH4/H2) and NH3 molecules. The acceleration of NH3 consumption is significant at low H2/NH3 fuel ratios and high CH4/NH3 fuel ratios, as the addition of H2 and CH4 lowers the activation energy for NH3 combustion. NOX emissions are mitigated at low H2/NH3 and CH4/NH3 fuel ratios but increase at high fuel ratios. The pathways for NOx generation and de-NOx reactions were identified. This study unveiled the mechanism via which the reactive fuels affect the NH3 combustion performance from an atomic perspective. The findings will be useful for the design of high-efficiency and low-emission combustion chambers in ammonia-powered energy systems.

Preparation and freshness detection of tofu based on In-doped CeO2 ammonia gas sensor

An ammonia (NH3) sensor with high sensitivity based on indium-doped cerium oxide (In/CeO2) was prepared by hydrothermal method, and its sensing mechanism was revealed by first-principles. Experimental results show that indium ion (In3+) doping can effectually increase the sensitivity of NH3 sensor based on CeO2, which is mainly attributed to the enhancement in the number of oxygen vacancies and oxygen free radicals on the surface of In/CeO2. In/CeO2 sensor for NH3 with a response value of 5412.93 at a concentration of 1000 ppm, which is 65 times that of CeO2 sensor. Moreover, the low detection limit (LOD) of In/CeO2 is 0.433 ppm and its response/recovery time to 5 ppm NH3 is 1.1 s/1.4 s. Furthermore, the density functional theory (DFT) calculation confirmed that NH3 has higher adsorption-induced charge transfer and adsorption energy on the surface of In/CeO2 than other gases. This makes it easier for In/CeO2 to adsorb NH3 molecules and release more conduction electrons, thus improving the performance of In/CeO2. In addition, In/CeO2 sensor can be effectively used to detect the freshness of tofu through the concentration of NH3 released by the tofu in different storage environments. This work is beneficial to the safety monitoring of high protein food.

First-principles study on the adsorption properties of NH3 and NO2 on different layers of GeSe

By means of density functional theory (DFT), the most stable structures of NH3 and NO2 molecules adsorbed by different layers of GeSe were studied. The adsorption properties of the adsorption system were studied from the aspects of adsorption energy, band gap, state density, differential charge density and recovery time. Significant adsorption energy (−1.060 eV, −1279 eV, −1.390 eV), charge transfer (−0.370e, −0.382e, −0.379e) and electron localization function (ELF) indicated that NO2 was chemisorbed on the surface of GeSe. The recovery time indicates that the mono-layer GeSe adsorption NO2 system can complete the desorption between 298 K and 398 K, and the bi-layer GeSe adsorption NO2 system can complete the desorption in a shorter time with the recovery time of 8.66S at the temperature of 498 K. Therefore, the theoretical research in this paper provides a theoretical basis for the development of GeSe gas sensors for the detection of harmful gases NH3 and NO2.

Mechanisms for deNOx and deN2O Processes on FAU Zeolite with a Bimetallic Cu-Fe Dimer in the Presence of a Hydroxyl Group-DFT Theoretical Calculations.

In this paper, a detailed mechanism is discussed for two processes: deNOx and deN2O. An FAU catalyst was used for the reaction with Cu-Fe bimetallic adsorbates represented by a dimer with bridged oxygen. Partial hydration of the metal centres in the dimer was considered. Ab initio calculations based on the density functional theory were used. The electron parameters of the structures obtained were also analysed. Visualisation of the orbitals of selected structures and their interpretations are presented. The presented research allowed a closer look at the mechanisms of processes that are very common in the automotive and chemical industries. Based on theoretical modelling, it was possible to propose the most efficient catalyst that could find potential application in industry-this is the FAU catalyst with a Cu-O-Fe bimetallic dimer with a hydrated copper centre. The essential result of our research is the improvement in the energetics of the reaction mechanism by the presence of an OH group, which will influence the way NO and NH3 molecules react with each other in the deNOx process depending on the industrial conditions of the process. Our theoretical results suggest also how to proceed with the dosage of NO and N2O during the industrial process to increase the desired reaction effect.

DFT-D3 and TD-DFT Studies of the Adsorption and Sensing Behavior of Mn-Phthalocyanine toward NH3, PH3, and AsH3 Molecules.

This study employs density functional theory (DFT) calculations at the B3LYP/6-311+g(d,p) level to investigate the interaction of XH3 gases (X = N, P, As) with the Mn-phthalocyanine molecule (MnPc). Grimme's D3 dispersion correction is applied to consider long-range interactions. The adsorption behavior is explored under the influence of an external static electric field (EF) ranging from -0.514 to 0.514 V/Å. Chemical adsorption of XH3 molecules onto the MnPc molecule is confirmed. The adsorption results in a significant decrease in the energy gap (Eg) of MnPc, indicating the potential alteration of its optical properties. Quantum theory of atoms in molecules (QTAIM) analysis reveals partially covalent bonds between XH3 and MnPc, and the charge density differenc (Δρ) calculations suggest a charge donation-back donation mechanism. The UV-vis spectrum of MnPc experiences a blue shift upon XH3 adsorption, highlighting MnPc's potential as a naked-eye sensor for XH3 molecules. Thermodynamic calculations indicate exothermic interactions, with NH3/MnPc being the most stable complex. The stability of NH3/MnPc decreases with increasing temperature. The direction and magnitude of the applied electric field (EF) play a crucial role in determining the adsorption energy (Eads) for XH3/MnPc complexes. The Eg values decrease with an increasing negative EF, which suggests that the electrical conductivity (σ) and the electrical sensitivity (ΔEg) of the XH3/MnPc complexes are influenced by the magnitude and direction of the applied EF. Overall, this study provides valuable insights into the suggested promising prospects for the utilization of MnPc in sensing applications of XH3 gases.

Preparation of amino cellulose aerogel and its formaldehyde adsorption properties

The aerogel prepared from cellulose has the advantages of low density, high porosity, large specific surface area, good gas diffusion and adsorption space, which is a good gas adsorption material. In this study, microcrystalline cellulose was used as raw material, and LiBr ionic liquid was used as a solvent system. In addition, cellulose aerogel was modified by polyethyleneimine, which retained three-dimensional network structure and had excellent formaldehyde adsorption capacity. The adsorption capacity of polyethyleneimine-modified cellulose aerogel (PCA) to formaldehyde can reach 12.3 mg/g at 25 ℃. It was found that the adsorption capacity of PCA aerogel for formaldehyde changed with the increase in nitrogen content. The adsorption of formaldehyde was mainly through the chemical adsorption of the Schiff base reaction between NH2 and formaldehyde molecules in polyethylenimine (PEI).

Photocatalytic degradation of ammonia to nitrogen by anatase TiO2 under microwave discharge electrodeless lamp irradiation

In this study, a microwave discharge electrodeless lamp (MDEL) photo-degradation system coupled with anatase TiO2 (P25) was constructed to improve the selective degradation of NH3 to N2. The MDEL system can generate abundant reactive oxygen species (ROS) with ultraviolet radiation at 185 nm and 254 nm during gas phase reaction. The species and content of ROS generated in the reaction system were determined by oxidation extraction spectrophotometry, and the effects of residence time, temperature, and relative humidity on the production of reactive oxygen species were investigated. In addition, the removal efficiency under different conditions such as initial ammonia concentration, relative humidity and residence time was explored. It was found that the removal rate could reach 83% when the initial ammonia concentration was 100 ppm, relative humidity was 55% and gas residence time was 5.16 s. The high-energy ultraviolet at 185 nm from MDEL could break NH3 molecules in advance and produced a large amount of ·NH2. Besides, NH3 was converted to N2 by generating large amounts of ROS, reducing NOx and nitrate generation. Our work presents a novel approach to construct a photocatalytic system for high efficiency degradation of NH3.

NH3 adsorption and competition with H2O on a hydroxylated aluminosilicate surface.

The interaction between ammonia (NH3) and (alumino)silicates is of fundamental and applied importance, yet the specifics of NH3 adsorption on silicate surfaces remain largely unexplored, mainly because of experimental challenges related to their electrically insulating nature. An example of this knowledge gap is evident in the context of ice nucleation on silicate dust, wherein the role of NH3 for ice nucleation remains debated. This study explores the fundamentals of the interaction between NH3 and microcline feldspar (KAlSi3O8), a common aluminosilicate with outstanding ice nucleation abilities. Atomically resolved non-contact atomic force microscopy, x-ray photoelectron spectroscopy, and density functional theory-based calculations elucidate the adsorption geometry of NH3 on the lowest-energy surface of microcline, the (001) facet, and its interplay with surface hydroxyls and molecular water. NH3 and H2O are found to adsorb molecularly in the same adsorption sites, creating H-bonds with the proximate surface silanol (Si-OH) and aluminol (Al-OH) groups. Despite the closely matched adsorption energies of the two molecules, NH3 readily yields to replacement by H2O, challenging the notion that ice nucleation on microcline proceeds via the creation of an ordered H2O layer atop pre-adsorbed NH3 molecules.

High switching characteristics and sensing-performance improvement of two-dimensional MN4 (M = Be, Mg, Ga) monolayer based nanodevices

Beryllium tetrazolium nitride (BeN4) has recently been synthesized under high pressure by laserheated diamond anvil electrodes as a new class of two-dimensional layered materials. Inspired by this, we perform first-principles calculations to investigate the electronic transport properties of MN4 (M = Be, Mg and Ga) monolayers and their gas sensing properties towards nitride-gases (NH3, NO2, NO). The obtained results show that BeN4 exhibits semi-metallic properties, MgN4 is a semiconductor with a bandgap of 0.13 eV, and the GaN4 monolayer presents strong metallic properties. Interestingly, the BeN4 and MgN4 monolayers are found to have anisotropic Dirac cones. The MN4-based 2D devices all exhibit excellent conductance as well as strong anisotropic transport, with maximum switching ratios of 107 and 104 for MgN4 and BeN4, respectively. The adsorption properties indicate that the adsorption of NH3, NO2, and NO molecules on MN4 monolayers are all chemisorptions, with the system owning much larger adsorption energies and bader charge transfers of the NO2 and NO molecules than those for the NH3 molecules, suggesting the MN4 monolayer has strong selective adsorption and responsiveness to NO2 and NO molecules. The designed gas sensor based on MgN4 show good response characteristics for NO molecules, as evidenced by the maximum current changes before and after adsorption of 30.31 µA, respectively. In summary, MN4 (M = Be, Mg and Ga) monolayers can be important candidates for high switching ratio devices and for the detection and trapping of toxic gas molecules NO.

Promoting effect of polyoxometallic acid modification on the NH3-SCR performance of Mn-based catalysts

The strong oxidation capabilities of Mn sites render Mn-based catalysts showing high activities of selective catalytic reduction (SCR) at temperatures < 250℃, but simultaneously lead to the generation of by-product N2O with strong greenhouse effect. The activity-N2-selectivity trade-off was a prevalent observation in the development of Mn-based SCR catalysts. Here, a polyoxometallic acid enhancement strategy was devised to simultaneously promote the N2 selectivity and low-temperature SCR (LT-SCR) activity of Mn-based metal oxide catalysts, where the introduction of uniformly dispersed phosphomolybdic acid (HPMo) tuned the oxidation capabilities and enhanced NH3 adsorption-storage capability of catalysts. The combination of transient reaction, in-situ DRIFTS analysis and DFT calculations revealed that the main origin of N2O on the Mn-based catalysts was the deep oxidation of NH3, which was inhibited by the interaction between HPMo and Mn sites. Additional NH3 molecules adsorbed by the abundant acid sites supplied by HPMo further facilitated the SCR reaction. This strategy could guide the design of high-activity and high-selectivity LT-SCR catalysts for industrial denitration.

Cooperativity between Intermolecular Hydrogen and Carbon Bonds in ZY···CH3CN/CH3NC···HX Trimers (ZY = H2O, H2S, HF, HCl, HBr, NH3, and H2CO; HX = HF, HCl, and HBr).

Hydrogen-bonding and carbon-bonding interactions are widespread in nature. We studied the cooperativity between these interactions in 42 trimeric complexes ZY···CH3CN/CH3NC···HX, where ZY molecules are H2O, H2S, HF, HCl, HBr, NH3, and H2CO, and HX molecules are HF, HCl, and HBr. Acetonitrile (CH3CN) and isoacetonitrile (CH3NC) act as hydrogen bond acceptors as well as carbon bond donors in these trimers. Various theoretical methods, such as electronic structure calculations, quantum theory of atoms in molecule (QTAIM), natural bond orbital (NBO), and reduced density gradient analysis, are employed to study these trimers, and the results are compared with the corresponding ZY···CH3CN/CH3NC and CH3CN/CH3NC···HX dimers. Electronic structure calculations are performed at the second-order Mo̷ller-Plesset perturbation theory using the 6-311++G(2d,2p) basis set. We show that both the interactions act synergistically in these trimers leading to an increase in their bond strength as compared to the strength in the individual dimers. The cooperative energies for these trimers are in the range of 0.69 to 3.22 kJ/mol. It is seen that the carbon bonds benefit more from the cooperativity than the hydrogen bonds. The trends of cooperativity and correlations of interaction energies and cooperative energies with relevant QTAIM and NBO parameters are reported.

Enhancing proton conduction of MOF-74(Co) by encapsulating NH3 molecules

The functional design of efficient and stable proton exchange membrane materials is an important research direction in the field of proton exchange membrane fuel cells (PEMFCs). In this work, ammonia molecules were successfully encapsulated into the one-dimensional pores of MOF-74(Co) through fumigation with ammonia vapor. Alternating current (AC) impedance tests showed that the proton conductivity of NH3 modified NH3@ MOF-74(Co) reaches an impressive value of 6.8 × 10−3 S/cm, being 10000 times that of the pristine MOF-74(Co) at 98% relative humidity (RH) and 50 °C. Various and abundant hydrogen bonds can improve the proton conduction of NH3 modified compound. This strategy provides an efficient and convenient way to construct high proton conducting porous MOFs materials by attaching NH3 molecules.

Selective adsorption and sensing mechanism of ZnFe2O4 (111) surface towards toxic gases:A first-principles study

ZnFe2O4 possesses an excellent gas-sensing performance, but its sensing mechanism towards different toxic gas molecules requires further exploration. In this study, the competitive adsorption and sensing properties of several toxic gases (NO2, NO, SO2, CO, H2S, and NH3) on the ZnFe2O4 (111) surface were investigated using density functional theory (DFT) calculations. The adsorption energy, charge transfer (QT), occupation function, adsorption free energy, charge density difference (CDD), and density of states (DOS) were compared. The results reveal that the ZnFe2O4 (111) surface exhibits obvious adsorption for NH3, H2S, NO2, and H2O, besides the selectivity of NH3 molecule is highest. Strong chemical interactions exist between these harmful gas molecules and the ZnFe2O4 (111) surface. This study offers valuable theoretical insights into the selective adsorption and sensing mechanism, contributing to the development of high-performance gas sensors to detect toxic gases.

Transition metals doped Zr2CF2 as promising sensor and adsorbent for NH3

The effective adsorption and treatment of toxic gases have attracted great attention amongst researchers, particularly the use of new two-dimensional materials for achieving the adsorption of toxic gases. We applied the density functional theory to investigate the stability, geometric structural, electrical, and magnetic properties of NH3 molecules adsorbed on pristine, F-vacancy defected, and transition-metals (V, Cr, Mn, Y, Nb, and Mo) doped Zr2CF2. The charge transfer and adsorption energy of the original substrate were low, indicating that the interaction between NH3 and Zr2CF2 was primarily physical adsorption. After introducing F-vacancy and TM-doping, the adsorption stability was enhanced, with the large charge transfer and high adsorption energies indicating that the adsorption of NH3 transitioned to chemisorption. Electronic density of state diagrams suggested that the enhanced interaction was mainly caused by the hybridization of the d orbitals of dopants and p orbitals of the adsorbed NH3 molecules. The adsorption energy of NH3 molecules on Y-doped Zr2CF2 was the highest at a value of −1.425eV, and the material was also explored as an adsorbent for NH3 gas. After adsorbing six NH3 molecules, the Y-doped substrate had an average adsorption energy of −1.350eV and still maintained a good thermal stability at a temperature of 300 K. These results can provide insights into the development of sensors and adsorbents based on MXenes.

Role of methane in ammonia combustion in air: From microscale to macroscale

Ammonia (NH3) has gained increasing recognition as a carbon-free fuel. To enhance NH3 combustion, reactive gases, like methane (CH4), are usually added to the combustion system. In this work, the role of CH4 in NH3 combustion is systematically studied. A series of reactive force field molecular dynamic (ReaxFF MD) simulations are implemented to investigate effects of CH4 addition on the consumption of NH3 and the yields of nitrogen oxides (NOx) from the atomic perspective: CH4 accelerates the consumption of NH3 by shortening the decomposition time of the first NH3 molecule and increasing the translational kinetic energy of the system; CH4 modifies the yield of NOx by complicating the elementary reactions and introducing additional intermediates. The fuel ratio of CH4 and NH3 between 0.5 and 1 is suggested for a cleaner and enhanced NH3 combustion. By summarising the findings from the latest publications and the present work, the role of CH4 in NH3 combustion is comprehensively analysed from the macroscale and microscale perspectives: CH4 accelerates the progress of NH3 combustion flame, activates chemical reactions, and aggravates NOx emissions at a low CH4 content. Taking the NH3/CH4 combustion as an example, this study provides an exclusive perspective to understand combustion phenomena from the microscale events to macroscale observations.

The study of NH3‐SCR mechanism on γFe2O3 supported LaMnO3 catalyst based on DFT

AbstractFe2O3 supported LaMnO3 is an effective selective catalytic reduction (SCR) denitrification catalyst, but its reaction mechanism has not been reported yet. This article is based on the density functional theory (DFT) method to study the denitrification reaction mechanism of LaMnO3/Fe2O3 catalyst, in order to guide the development and application of denitrification catalysts. The conclusion is as follows: NH3, NO, and O2 molecules can form stable adsorption on the surface of La MnO3/γFe2O3 catalysts, and NH3 molecules are more likely to be adsorbed on Mn ions. Under the oxidation of lattice oxygen, NH3 will gradually dehydrogenate to form NH2, and then will react with NO in the air to form the transitional intermediate NH2NO, to produce N2 and H2O. The mechanisms are same on Mn and Fe sites. The dehydrogenate of NH3 to form NH2 is rate determining step. Compared with pure γFe2O3, the energy barrier decreases to promote the SCR process.

Investigating the adsorption performance of CO, NO, NO2, NH3, and H2S molecules on C9N4 through DFT for potential gas sensor applications

In this work, the feasibility of using transition metal doped C9N4 as an efficient gas sensor is comprehensively investigated by density functional theory methods. Firstly, the calculated Ef and Udiss values show that most of M-C9N4 and M2-C9N4 have good thermodynamic and electrochemical stability. Secondly, for CO, NO, NO2, NH3, and H2S on Cr-C9N4, the Eads values are −2.07, −3.05, −2.53, −1.76, and −2.14 eV, respectively. For these gases on Fe2-C9N4, the Eads values are −2.60, −3.07, −2.45, −2.39, and −2.21 eV, respectively. The results show that Cr-C9N4 and Fe2-C9N4 have good adsorption strengths for all gases, which can provide good theoretical guidance for the design of excellent sensing materials. Finally, by calculating band structures of all catalysts, they all have small band gap values, such as, Fe2-C9N4 with the 0.10 eV, which all shows stable catalysts possess good conductive properties. The DOS results show that there is an obvious orbital hybridization between metal, N, C, and O atoms, indicating that there is a certain interaction between them, which is an important factor leading to the good adsorption of the catalyst to the molecular gas. This work can provide theoretical guidance for searching efficient sensor materials.

DFT study of adsorption properties of the ammonia on both pristine and Si-doped graphene nanoflakes

Investigation of the interactions between nanomaterials and molecules at the molecular level is a crucial factor in the design of novel materials for nanosensor applications. In this study, we used the chemical calculations based on density functional theory calculations to evaluate the adsorption properties for the NH3 molecule (ammonia) over the surface of the pristine graphene nanoflakes (PGNFs) and Si-doped graphene nanoflakes (Si-GNFs). The results show that NH3 molecules are physically adsorbed onto the surface of PGNFs, while it is significantly chemisorbed onto the surface of Si-GNFs, with an adsorption energy of -1.561 eV. The recovery time for NH3/PGNF after adsorption process is very small, so the detection of the NH3 molecule is practically impossible even it has high electronic sensitivity of PGNF to the NH3 molecule. When a Si atom was substituted for a carbon atom, the adsorption characteristics of GNF improved. This, in turn, reduced the stability of the Si-GNF cluster, increasing its activity significantly relative to that of PGNF. When the Si-GNF cluster interacted with the NH3 molecule, its electrical conductivity increased significantly, and there was a large change in the energy gap. It follows that the Si-GNF cluster is an excellent candidate for use as a nanosensor for NH3 molecule detection due to its high electrical sensitivity to the above molecules. Therefore, the presence of silicon considerably promotes the NH3 chemisorption onto the GNFs and therefore significantly increases their sensitivity performance. In conclusion, the Si-GNF clusters could be employed as effective nanosensors for NH3 molecule detection.

A functionalised interface for controllable decomposition of ammonium perchlorate by a self-assembly method

A functionalised interface construction strategy was developed by coating an ammonium perchlorate (AP) surface with quaternary ammonium cation surfactants using a self-assembly method. The functionalised interface transforms AP decomposition from high temperature decomposition into low temperature decomposition, and provides pressure-sensitive control over the mass ratio of AP decomposition in the two stages. Further study using molecular dynamics simulations and density functional theory reveal that the functionalised interface hinders the adsorption of NH3 molecules and promote the adsorption and decomposition of ClO4 on the AP surface, all of which could contribute to controlling AP decomposition.

Mechanistic Inquisition on the Reduction of C17Si(NH2)2 to NH3: A DFT Study.

Activation of molecular nitrogen by silicon-substituted cyclo[18]carbon and its ability to produce the C17Si-(NH2)2 derivative, as the precursor of NH3, has been recently reported. This specific acquisition has piqued an interest to investigate the possibility of NH3 formation with further addition of H2 molecules in the gaseous reaction media. The current investigations reported in this article show that two moles of molecular H2 generate two molecules of NH3 and a C17Si-H2 byproduct from its precursor. The catalyst gets restored by an in situ reaction between some unreacted C17Si-N2 and the byproduct in the media. This reaction also produces the next C17Si-(NH)2 adduct, which restarts the catalytic cycle for NH3 production again.