Adsorbed Nitrogen Atoms Research Articles

Inverse kinetic isotope effect of ammonia decomposition over Ru/CeO2 using deuterated ammonia.

This study investigated the ammonia decomposition mechanism over Ru/CeO2. Isotopic tests using ND3 revealed that the rate-determining step involves adsorbed nitrogen atoms on Ru. Moreover, an inverse kinetic isotope effect where ND3 decomposition was faster than NH3 was clearly observed. The origin of the inverse effect was explained by the lower D coverage on the catalyst surface compared to H coverage for mitigating the inhibition of ND3 activation.

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Plasma-Assisted Dinitrogen Activation via Dual Platinum Cluster Catalysis: A Strategy for Ammonia Synthesis under Mild Conditions

Neural-network assisted study of nitrogen atom dynamics on amorphous solid water – II. Diffusion

ABSTRACT The diffusion of atoms and radicals on interstellar dust grains is a fundamental ingredient for predicting accurate molecular abundances in astronomical environments. Quantitative values of diffusivity and diffusion barriers usually rely heavily on empirical rules. In this paper, we compute the diffusion coefficients of adsorbed nitrogen atoms by combining machine learned interatomic potentials, metadynamics, and kinetic Monte Carlo simulations. With this approach, we obtain a diffusion coefficient of nitrogen atoms on the surface of amorphous solid water of merely $(3.5 \pm 1.1)\, \times 10^{-34}$ cm2 s−1 at 10 K for a bare ice surface. Thus, we find that nitrogen, as a paradigmatic case for light and weakly bound adsorbates, is unable to diffuse on bare amorphous solid water at 10 K. Surface coverage has a strong effect on the diffusion coefficient by modulating its value over 9–12 orders of magnitude at 10 K and enables diffusion for specific conditions. In addition, we have found that atom tunnelling has a negligible effect. Average diffusion barriers of the potential energy surface (2.56 kJ mol−1) differ strongly from the effective diffusion barrier obtained from the diffusion coefficient for a bare surface (6.06 kJ mol−1) and are, thus, inappropriate for diffusion modelling. Our findings suggest that the thermal diffusion of N on water ice is a process that is highly dependent on the physical conditions of the ice.

Deuterium fractionation of nitrogen hydrides: detections of NHD and ND2

ABSTRACT Although ammonia is an abundant molecule commonly observed towards the dense interstellar medium, it has not yet been established whether its main formation route is from gas-phase ion–molecule reactions or grain-surface hydrogen additions on adsorbed nitrogen atoms. Deuterium fractionation can be used as a tool to constrain formation mechanisms. High abundances of deuterated molecules are routinely observed in the dense interstellar medium, with the ratio between deuterated molecules and the main isotopologue enhanced by several orders of magnitude with respect to the elemental D/H ratio. In the case of ammonia, the detection of its triply deuterated isotopologue hints at high abundances of the deuterated intermediate nitrogen radicals, ND, NHD, and ND2. So far however, only ND has been detected in the interstellar medium. In this paper, to constrain the formation of ammonia, we aim at determining the NHD/NH2 and ND2/NHD abundance ratios, and compare them with the predictions of both pure gas-phase and grain-surface chemical models. We searched for the fundamental rotational transitions of NHD and ND2 towards the class 0 protostar IRAS16293−2422, towards which NH, NH2 and ND had been previously detected. Both NHD and ND2 are detected in absorption towards the source. The relative abundance ratios NH2:NHD:ND2 are close to 8:4:1. These ratios can be reproduced by our gas-phase chemical model within a factor of 2–3. Statistical ratios as expected from grain-surface chemistry are also consistent with our data. Further investigations of the ortho-to-para ratio in ND2 , both theoretical and observational, could bring new constraints to better understand nitrogen hydride chemistry.

Caprylamidopropyl Betaine as a highly efficient eco-friendly corrosion inhibitor for API X120 steel in 1 M H2SO4

CORROSION inhibition of API X120 steel in a 1M sulfuric acid solution at altered temperatures was investigated utilizing a new eco-friendly surfactant (Caprylamidopropyl Betaine (CAPB)) by Gravimetric and electrochemical test (containing potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS). Surface characterization tests containing scanning electron microscopy (SEM), and atomic force microscopy (AFM) are utilized in the study. In addition, kinetic and thermodynamic parameters were measured and discussed. The overall results displayed that the corrosion rate of API X120 steel was significantly lowered with improving the temperature. The polarization curves lead to the CAPB inhibitor is influenced both anodic and cathodic reactions (mixed type inhibitor). Analyses of the surface topography designated an appreciable decrease in the surface roughness as the dose of the inhibitor in the solution improved. Energy-dispersive X-ray and X-ray photoelectron spectroscopy revealed the presence of adsorbed nitrogen atoms on the API X 120 steel surfaces. This work provides a promising eco-friendly inhibitor for mitigating the corrosion of API X120 steel in highly acidic brine environments.

Effects of nitrogen impurity on zno crystal growth on Si substrates

ABSTRACTEffects of nitrogen impurity on ZnO crystal growth on Si substrates have been investigated. The quantitative analysis on the surface morphology deriving height-height correlation function indicates that adsorbed nitrogen atoms suppress the secondary nucleation and enhance adatom migration. The resultant films have smooth surface as well as large grain size up to 24 nm even for small thickness of 10 nm. ZnO films fabricated by using such films as buffer layers possess high crystal quality, where the full width at half maximum of (002) rocking curve is 0.68°, one-fourth of that for films fabricated without nitrogen.

Nitrogen Atom Abstraction of Nitrogen Chemisorbed on W(100) Surface

We have computed the probability of N2 formation and the partitioning of the reaction exothermic energy of the product N2 molecule in the reaction N(g) + N(ad)/W → N2(g) + W. The N2 formation probability at the on‐top sites of the W(100) surface is approximately 0.01 at a gas temperature of 1800 K and surface temperature of 300 K. The total cross‐section of N2 formation at the on‐top sites of the W(100) surface as a function of the collision energy is significantly smaller than that at the hollow sites of the W(100) surface. The majority of the reaction energy is shared by the vibrational and translational motions of the newly produced N2. The vibrational excitations of the adsorbed nitrogen atom from the ground state to the higher levels 1, 2, and 3, do not significantly alter the energy shared by the product. In addition, strong vibrational excitation in N2 causes population inversion for the vibrational population. The energy transferred to the heat bath is negative, which denotes an energy transfer from the surface to the desorbed product. While the N2 formation probabilities do not depend significantly on the surface temperature (0–1500 K), they depend strongly on the gas temperature, which is consistent with the Eley‐Rideal reaction.

N2 emission in steady-state N2O + CO and NO + CO reactions on Ir(110) by means of angle-resolved desorption

This paper confirms the intermediate N2O(a) pathway to N2 in the NO reduction on iridium surfaces. The spatial distributions of desorbing product N2 have been compared with each other in steady-state N2O+CO and NO+CO reactions on Ir(110) by means of angle-resolved desorption. In the former reaction, the N2 emission is fairly concentrated on the normally directed plane in the [001] direction and split into two-directional ways, being collimated at 46–58° off normal. In the latter reaction, the N2 desorption consists of a normally directed component and two-directional components. The former component shows remarkable anisotropy; i.e., the distribution is sharp on the normally directed plane in the [001] direction and broad on the plane perpendicular to it. This component originates from the association of adsorbed nitrogen atoms. The other components are collimated at around 54° off normal towards the [001] and [001¯] directions and they come from the decomposition of intermediate N2O(a). The off-normal components significantly share the total N2 emission below approximately 550K. At higher temperatures, these become minor and mostly invisible above 650K. The desorption of counter-product CO2 is normally directed and shows anisotropy in both reactions.

Effect of the size and distribution of supported Ru nanoparticles on their activity in ammonia synthesis under mild reaction conditions

Ru/γ-Al2O3 catalysts were prepared using three different methods: wet impregnation, colloidal method and microemulsion. Ru-supported nanoparticles with different average sizes and distribution of sizes were obtained. The catalysts were tested in ammonia synthesis under mild reaction conditions, namely low temperature (100°C) and low pressure (4bar), and characterized by N2 adsorption, XRD, XPS, TEM and TPR techniques. The results indicate that a good catalytic performance can be achieved by Ru supported nanoparticles fulfilling two requirements: (i) a relatively high average size (despite the usual assertion that only small particles are required) and (ii) a broad distribution of sizes that ensures the presence of both small particles, containing highly active sites, and large nanoparticles, which are shown to promote the reaction on small particles. This promotion results from a cooperative effect between small and large nanoparticles in good contact, which also allows keeping a highly reduced surface of ruthenium.It is proposed that, under mild reaction conditions, large Ru nanoparticles promote the ammonia synthesis reaction by allowing a more effective activation and transfer of hydrogen atoms, able to hydrogenate strongly adsorbed nitrogen atoms, and thus to release active sites for the activation of N2.

Investigation into the adsorption of atomic nitrogen on an Al2O3 (0001) surface

Computer simulation of sapphire nitridation used to obtain nitride-based heterostructures (GaN) on an Al2O3 substrate has been performed. The adhesion of atomic nitrogen to the sapphire (0001) surface is investigated ab initio. The possibility of replacing surface-layer oxygen atoms with nitrogen atoms has been examined. The calculated results indicate that adsorbed nitrogen atoms occupy the most stable positions above surface oxygen atoms at different nitrogen concentrations. The changes in the total system energy after replacement of surface oxygen atoms with nitrogen atoms have been calculated. It turns out that oxygen replacement is energetically unfavorable for a single nitrogen adatom. However, this process becomes energetically favorable if the concentration of nitrogen atoms increases. This outcome, obtained for the first time, enables better understanding of the atomic-scale mechanism of sapphire nitridation.

Identification of nitrogen-containing species obtained by nitric oxide adsorption on the surface of model gold catalysts

Nitric oxide adsorption at 300–500 K on gold particles supported on an alumina film has been investigated for the first time by in situ X-ray photoelectron spectroscopy. Two nitrogen-containing adsorption species can form on the surface of gold particles. By test experiments on NO adsorption on the stepped face (533) of a gold single crystal, these species have been identified as adsorbed nitrogen atoms (which are detected throughout the temperature range examined) and a surface complex with N2O stoichiometry (which is stable in a narrow temperature range of 325–425 K).

In situ measurement of adsorbed nitrogen atoms for PA‐MBE growth of group III nitrides on Si

AbstractAn atom probe of two parallel electrodes is proposed to monitor adsorbed (ADS) nitrogen atoms in situ during growth of β‐Si3N4 using indirect exposure of effusing active nitrogen beam from the radio frequency induction coupled plasma cell. The β‐Si3N4 film is a component of a double buffer layer (DBL) AlN(0001)/β‐Si3N4/Si(111) to grow high quality the group III nitrides and their alloys on Si. Atom current between the parallel electrodes corresponds to flux of the ADS nitrogen atoms on the inside surface at the atom potential, VA. The ADS atom current received influence of wall and shutter of the cell, because adsorption of nitrogen atom depended wall condition such as temperature and the concentration of adatoms on the wall (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Control of active nitrogen species used for PA-MBE growth of group III nitrides on Si

A new spiral parallel mesh electrode (PME) is presented to control active nitrogen species in plasma-assisted molecular beam epitaxial (PA-MBE) growth of group III nitrides and their alloys. Direct flux of active nitrogen from radio frequency inductive coupled plasma (rf-ICP) discharge was able to be measured using a mesh electrode for filtering charge particles and electron emission due to the self-ionization of nitrogen atoms on a negatively biased electrode. In situ measurement of direct nitrogen atom fluxes using the spiral PME during PA-MBE growth of GaN and AlN on Si substrates is investigated. A linear rf power dependence of direct flux of active species on atoms such as nitrogen (N+N⁎), where N and N⁎ were ground and excited atoms, respectively, from a rf-ICP was confirmed by the spiral PME. An indirect flux of nitrogen adsorbed (ADS) atoms (N+N⁎) during discharge was also monitored by the spiral PME and received influence of the wall surface of the growth chamber. ADS nitrogen atoms are able to be used for nitridation of Si surface to grow a double buffer layer (DBL) AlN/β-Si3N4/Si.

Origination of N2O from NO reduction by NH3 over β-MnO2 and α-Mn2O3

Selective catalytic reduction (SCR) of NO with NH3 was studied on β-MnO2 and α-Mn2O3 catalysts at 150°C and the formation of N2O from SCR was mainly investigated. The activity evaluation showed that the rates of both NO conversion and N2O formation per unit surface area on β-MnO2 were much higher than the corresponding values on α-Mn2O3, while two catalysts gave same generated rate of N2. Transient reactions of NO with NH3 showed that N2O predominantly originated from direct reaction of NO and NH3 via an Eley–Rideal mechanism. β-MnO2 gave higher generated rate of N2O in transient reaction of NH3 and more desorption amount of N2O in temperature-programmed desorption of NH3 than α-Mn2O3. The results of temperature-programmed reduction of H2 exhibited that oxygen species on β-MnO2 are more active than α-Mn2O3. Therefore, β-MnO2 had higher selectivity to N2O in SCR reaction than α-Mn2O3, predominantly resulting from higher activated capability to NH3, and β-MnO2 can cleave more N–H bonds in NH3 molecules to give more adsorbed nitrogen atom species, which reacted with gaseous NO to form more N2O.

Electrochemical formation of AlN in molten LiCl–KCl–Li 3N systems

Electrochemical formation of aluminum nitride was investigated in molten LiCl–KCl–Li 3N systems at 723 K. When Al was anodically polarized at 1.0 V (versus Li +/Li), oxidation of nitride ions proceeded to form adsorbed nitrogen atoms, which reacted with the surface to form AlN film. The obtained nitrided film had a thickness of sub-micron order. The obtained nitrided layer consisted of two regions; the outer layer involving AlN and aluminum oxynitride and the inner layer involving metallic Al and AlN. When Al electrode was anodically polarized at 2.0 V, anodic dissolution of Al electrode occurred to give aluminum ions, which reacted with nitride ions in the melt to produce AlN particles (1–5 μm of diameter) of wurtzite structure.

Modelling nitrogen atom flux in post-discharge nitriding processes

Nitriding of pure iron using microwave N 2–H 2 post-discharges is modelled by coupling kinetics of the gas phase, surface processes and solid diffusion. Despite basic data are missing for iron and are thus estimated, the description of the interface phenomena provides a clear understanding of the material response to a given gas-phase composition. The most important aspect presented deals with the dissolution of nitrogen atoms into the iron nitride ɛ-Fe 2N 1− x at the topmost surface of the sample. As chemically adsorbed nitrogen atoms are involved in both the Langmuir–Hinshelwood and the Eley–Rideal loss mechanisms of N atoms into N 2, their dissolution implies a subsequent decrease of the loss probability of N atoms at the surface. This is the main reason why post-discharge nitriding works at high temperature. The consumption of the nitrogen atoms at the surface of the sample limits considerably their loss by recombination. A first comparison with experimental results of nitriding at 723 K shows that the nitrogen profile along the post-discharge does not exhibit any change of slope from the Pyrex surface to the nitrided iron foil. The time evolution of the nitrogen density in the middle of the iron foil is either weak or null, showing that the loss of N atoms by solid diffusion at 723 K in iron is probably very weak with respect to other loss processes to be monitored by optical emission spectroscopy (OES).

Electrochemical Nitriding of Cobalt by Molten Salt Electrochemical Process

Electrochemical nitriding of Co was achieved by potentiostatic electrolysis at 0.80 and 1.20 V (vs. in LiCl-KCl eutectic melt containing at 723 K. From X-ray photoelectron spectroscopy and X-ray diffraction analyses, it was confirmed that the obtained nitrided layer consisted of the free energies of formation of this nitride is positive and the equilibrium nitrogen partial pressure of those are of the order of atm at 723 K. This result suggests an equivalent nitrogen pressure of at least the order of atm was imposed by the adsorbed nitrogen atoms formed by anodic oxidation of nitride ion at Co electrode surface. © 2004 The Electrochemical Society. All rights reserved.

Removal Pathways of Surface Nitrogen in a Steady-State NO + CO Reaction on Pd(110) and Rh(110): Angular and Velocity Distribution Studies

The angular and velocity distributions of desorbing products N2 and CO2 were studied in a steady-state NO + CO reaction on Pd(110) and Rh(110) by cross-correlation time-of-flight techniques. The CO2 desorption sharply collimated along the surface normal on both surfaces. On the other hand, N2 desorption on Pd(110) sharply collimated along about 40° off the surface normal in the plane along the [001] direction below around 650 K, yielding a translational temperature of about 3600 K. At higher temperatures, the normally directed desorption was relatively enhanced. On Rh(110), desorbing N2 sharply collimated along the surface normal, yielding a translational temperature of about 2500 K. The inclined desorption was assigned to the decomposition of the intermediate, N2O(a) → N2(g) + O(a), and the normally directed component was proposed to be due to the associative desorption of adsorbed nitrogen atoms, 2N(a) → N2(g). The branching of these pathways was analyzed on Pd(110).

Electrochemical surface nitriding of pure iron by molten salt electrochemical process

Electrochemical surface nitriding of pure iron was investigated in molten LiCl–KCl–Li 3N systems at 773 K. An outer compound layer and an inner diffusion layer were obtained by means of potentiostatic electrolysis at 1.00 V (versus Li +/Li). From XRD and SEM analyses, it was confirmed that the obtained compound layer consisted of ε-Fe 2–3N and γ′-Fe 4N; the free energies of formation of the two nitrides are positive and the equilibrium nitrogen partial pressure of those are of the order of 10 4 atm at 773 K. This result suggests that an apparent nitrogen partial pressure of at least the order of 10 4 atm was imposed by the adsorbed nitrogen atoms (N ads) formed by anodic oxidation of nitride ion (N 3−) at the iron electrode surface.

Theoretical study on the initial processes of nitridation of silicon thin film

The initial processes of nitridation of silicon thin film have been examined by means of the first-principle calculations. The nitrogen atom on the bare silicon(1 0 0) surface stays around the surface due to the dangling bond of the first-layer silicon, and the large stabilization on the bare silicon surface raises the energy barrier of the penetration of the nitrogen atom into the surface. The nitrogen atom on the H-terminated silicon surface can penetrate into the surface by crossing over the small energy barrier. In the nitridation by using nitrous oxide (N 2O) molecule, N 2O can be adsorbed only with the large NN bond length, and then an exothermic elimination of nitric oxide (NO) molecule from the adsorbed nitrogen atom on the bare silicon surface takes place. The electronic processes have been discussed in terms of the quantum mechanical energy densities, which give new images of microscopic electronic stresses in the interaction system.