Chemisorption Of Nitric Oxide Research Articles

Efficient electrocatalytic reduction of nitric oxide (NO) to ammonia (NH3) on metal-free B4@g-C3N4 nanosheet

The combustion of fossil fuels releases substantial amounts of nitric oxide (NO), posing serious environmental and health risks. Addressing NO pollution effectively is, therefore, a pressing need. Conversion of NO into valuable chemicals is an appealing strategy with dual benefits, including waste utilization and sustainable energy transformation. In this study, we investigate the metal-free electrocatalytic reduction of NO (NORR) to NH3 on a B4 atomic cluster supported by a g-C3N4 nanosheet (B4@g-C3N4) using density functional theory (DFT). Our findings reveal that NO is efficiently activated on the B4@g-C3N4 catalyst, favoring side-on and N end-on adsorption configurations. Significant electron transfer and strong adsorption energies confirm the chemisorption of NO. The NORR exhibits an impressively low limiting potential (UL) of −0.29 V in the gas phase, which decreases further under solvent effects and varying charge states (−2e-, −1e-, +1e-, +2e-). Additionally, the high negative UL values for competing side reactions such as H2 (−0.42 V), N2 (−0.29 V), and N2O (−0.72 V) underscore the selectivity of B4@g-C3N4 for ammonia synthesis. These results highlight the promising potential of B4@g-C3N4 nanosheets for eco-friendly ammonia production from NO, providing a theoretical basis for future experimental efforts to combat NO pollution.

Density functional theory study on the catalytic reduction of nitric oxide over the bio-char surface during biomass reburning: The influence of inherent potassium

Active sites on char surface have been proven to be effective for nitric oxide (NO) reduction. In this work, density functional theory was used to study the catalytic reduction of NO over the zigzag char surface. Two bio-char models with or without potassium were established and the reaction paths during char-NO interaction were built. The effect of inherent potassium and active sites on NO reduction was taken into consideration. Mulliken charge results showed that the migration of electron from potassium(K) atom to carbon atom would increase the electron density on char surface, which further improved the electron-donating capacity. Orbital electron distribution and ESP results proved that char(K) was more likely to donate electron to NO than char-1 during char-NO interaction. Reaction potential energy results indicated that the bonded K atom on char surface would enhance the chemisorption of NO via electrical charge transfer and reduced energy barriers from 173.7 kJ/mole to 31.6 kJ/mole, which was consistent with the kinetic analysis results. The bonding of –O-K to carbon atoms on char surface greatly activated the NO reduction during char-NO interaction, which enhanced the adsorption and reduction of NO.

Photo-induced reversible nitric oxide capture by Fe-M(CO2H)4 (M = Co, Ni, Cu) as a building block of mixed-metal BTC-based MOFs.

Metal-organic frameworks incorporating mixed-metal sites (MM-MOFs) have emerged as promising candidates in the development of sensing platforms for the detection of paramagnetic species. In this context, the present study explores the photo-induced switching behavior of mixed-metal Fe-M (M = Co, Ni, Cu) formate (Fe-M(CO2H)4), as an experimentally feasible strategy for the reversible capture of nitric oxide (NO). Using Fe-M(CO2H)4 as a building block of synthesized MOFs based on BTC (benzene-1,3,5-tricarboxylic acid), molecular simulations of NO adsorption on Fe-M(CO2H)4 were conducted to provide a template for evaluating the behavior of BTC-based MOFs towards NO. Accordingly, the relationship between the magnetic properties and adsorption behaviors of Fe-M(CO2H)4 towards NO gas molecules was evaluated before and after photoexcitation. We show that the photo-induced effect on the magnetic properties of Fe-M(CO2H)4 changes the interaction strength between NO and the Fe-M(CO2H)4 systems. NO chemisorption over Fe-Ni(CO2H)4 indicates that nickel-doped Fe-BTC MOFs can be efficiently applied for capturing purposes. Moreover, our calculations show a switching behavior between physisorption and chemisorption of the NO molecules over Fe-Co(CO2H)4, occurring through magnetic modulation under UV-Vis irradiation. As far as we know, this is the first study that proposes light-controlled reversible NO capture using MOFs. The present study provides a promising platform for reversible NO capture using MM-MOF-incorporated BTC building blocks.

Structural and electronic properties of the adsorption of nitric oxide molecule on copper clusters CuN(N = 1–7): A DFT study

The interconversion between different isomers of copper clusters has been investigated using density functional theory. Seven distinct transition states have been located for the isomerization of the Cu3, Cu4, Cu5, Cu6 and Cu7 clusters. The chemisorption of nitric oxide on copper clusters has been studied and the approach of nitric oxide to produce either the nitrosyl (–NO) or the isonitrosyl (–ON) complexes has been compared. The interaction of NO with the copper cluster complexes leads to significant odd–even oscillations of the spin density differences (ΔSD), mean polarizability (α¯) and HOMO-LUMO gaps. The computed binding energies and ionization potentials of the copper clusters are in excellent agreement with the experimental values. The binding energy, charge transfer, forward donation, υ(NO) and bond ellipticity values are higher in the nitrosyl complexes than their isonitrosyl counterparts. The relationship between the ΔSD and the NO stretching frequencies is approximately linear with high correlation coefficients of R2 = 0.94 and 0.96 for nitrosyl and isonitrosyl complexes, respectively. The stable copper clusters have been reoptimized at couple cluster singles and doubles method with Dunning double-ζ basis sets (CCSD/cc-pVDZ level).

Effect of Alkali Metal Elements on Nitric Oxide Chemisorption at the edge of Char: A DFT study

The effect of alkali metal elements on nitric oxide (NO) heterogeneous adsorption on the surface of char was investigated by density functional theory (DFT) calculations. Geometries of reactants and products are optimized at B3LYP/6-31G(d) level. Adsorptions of alkali metal atoms on the "defective" activate sites of char is chemical adsorption with lots of energies released. Energies released from adsorption of alkali metal atoms on char is Li>K>Na. It is found that chemisorption of NO could be enhanced by loading alkali metal atoms on char as the absolute value of adsorption energy increases. The catalytic activity for NO chemisorption is K>Na>Li.

Nitric Oxide Adsorption in Cu3btc2-Type MOFs—Physisorption and Chemisorption as NONOates

The adsorption of the biologically important signaling molecule nitric oxide (NO) on two metal–organic frameworks (MOFs), Cu3btc2 and Cu3(NHEtbtc)2, has been studied by multinuclear solid-state NMR. N-Diazenium diolate (NONOate) formation as primary mode of NO adsorption in the latter MOF is concluded from 15N, 1H, and 13C NMR spectra together with analysis of the 1H spin–lattice relaxation time (T1). Furthermore, NO adsorption at the open metal site of Cu3btc2 as well as Cu3(NHEtbtc)2 is also evident, indicating both physisorption and chemisorption of nitric oxide.

Detoxification of NO and CO gases over effectively substituted Pd and Rh in cupric oxide catalysts

Precious metals like Pd and Rh mixed with metal oxides exhibit a superior CO adsorption capacity, and thus their substitution has considerable effect on surface property of cupric oxide. This communication focuses on Pd and Rh substitution in cupric oxide and their catalytic application in detoxification of both nitric oxide (NO) and carbon monoxide (CO) gases by redox reaction. The synthesised catalysts were characterised by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and Brunauer–Emmett–Teller. In our study, we discovered that when doped with not more than 5% concentration of Pd and Rh the catalytic activity of cupric oxide was found to be increased. These electron-rich metals have a promotional effect on the catalytic activity for detoxification reactions. Effect of partial pressures of O2 and CO on the CO–O2 and NO–CO redox reactions was studied. Chemisorption of CO and NO was investigated using pulse titrations. Pd-doped CuO gave good catalytic reaction and showed better reaction stability in the presence and absence of the moisture.

Remarkably Strong Chemisorption of Nitric Oxide on Insulating Oxide Films Promoted by Hybrid Structure

The remarkably strong chemical adsorption behaviors of nitric oxide on magnesia (001) film deposited on metal substrate have been investigated by employing periodic density functional calculations with Van der Waals corrections. The molybdenum supported magnesia (001) show significantly enhanced adsorption properties and the nitric oxide is chemisorbed strongly and preferably trapped in flat adsorption configuration on metal supported oxide film, due to the substantially large adsorption energies and transformation barriers. The analysis of Bader charges, projected density of states, differential charge densities, electron localization function, highest occupied orbital and particular orbital with largest Mg-NO-Mg bonding coefficients, are applied to reveal the electronic adsorption properties and characteristics of bonding between nitric oxide and surface as well as the bonding within the hybrid structure. The strong chemical binding of nitric oxide on magnesia deposited on molybdenum slab offers new opportunities for toxic gas detection and treatment. We anticipate that hybrid structure promoted remarkable chemical adsorption of nitric oxide on magnesia in this study will provide versatile strategy for enhancing chemical reactivity and properties of insulating oxide.

The effects of oxygen and metal oxide catalysts on the reduction reaction of NO with lignite char during combustion flue gas cleaning

The development of lignite-char-supported metal oxide catalyst for reduction of nitric oxide (NO) is investigated in this paper. The characteristics of NO reduction by copper and iron oxide catalysts supported on activated lignite chars (ALC) was studied using a fixed-bed reactor at 300°C. The results showed that the impregnation of Cu on ALC resulted in higher catalytic reactivity during NO reduction compared with that of Fe. Chemisorption of O2 and NO on Cu/ALC catalyst was found to play an important role in denitrification. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses showed that chemically adsorbed oxygen facilitates the formation of C(O) complex and oxidation of Cu0 to Cu+ for Cu/ALC catalyst. The C(O) intermediates and C* production formed due to the fact that C/O2 reaction promoted the reduction of NO. It is suggested that the catalytic reaction of NO in this case comprised of C/O2 reaction, C(O)/NO reaction and formation of N2 and CO2. Cu seemed to have significantly promoted the C(O) formation and CO oxidation compared with Fe. The catalytic reactivity of Cu species for C(O) formation and CO oxidation followed the order of Cu0>Cu+>Cu2+. Fe3O4 was believed to be the active phase in Fe catalyst. The oxygen and char-supported metal catalysts significantly promoted C/NO reaction, and therefore may lead to a lower operation temperature of NOx removal.

Effects of synthesis conditions on structure and surface properties of SmMn2O5 mullite-type oxide

A mixed-phase compound that contains SmMn2O5 mullite-type oxides has been reported to display excellent catalytic activity for nitric oxide (NO) oxidation. Here we investigate the effects of calcination temperature and precipitation pH on structural, physical, chemical, and surface properties of SmMn2O5. As the calcination temperature increases from 750°C to 1000°C, mullite phase purity increases from 74% to 100%, while specific surface area (SSA) decreases from 23.6m2/g to 5.1m2/g with particle size increases correspondingly. Mullite phase purity (87%) is independent of pH between 8.5–10.4, whereas SSA monotonically increases from 12.5m2/g at pH 8.1 to 27.4m2/g at pH 13. X-ray photoelectron spectroscopy (XPS) studies reveal that the surface Mn/Sm ratio is similar to the bulk value and is unaffected by calcination temperature and pH values up to 10.4, whereas sample precipitated at pH 13 is surface-rich in Sm. NO chemisorption studies show that the SSA and surface Mn/Sm ratio determine NO uptake by SmMn2O5 mullite oxides.

Thermodynamic and kinetic evaluation of the reaction between NO (nitric oxide) and char(N) (char bound nitrogen) in coal combustion

Using pyridine nitrogen as representative of nitrogen-containing char model, detailed theoretical calculations based on DFT (density functional theory) and conventional TST (transition state theory) are carried out to investigate the thermodynamics and kinetics of the heterogeneous interaction between NO (nitric oxide) and char(N) (char bound nitrogen) during coal combustion. Focus is directed on NO chemisorption of direct nitrogen–nitrogen interaction and N2 desorption from medium chemisorbed surface. It is suggested that side-on chemisorption is a low barrier (2.3 kJ/mol) and high exothermic (178.5 kJ/mol) step, while N-down chemisorption is a high barrier (105.2 kJ/mol) and moderate exothermic (64.4 kJ/mol) step. Worth noticing is that NO chemisorption on char(N) surface is different from that on char surface, largely because there is no unpaired σ electrons located at N atom. After chemisorption, four stepwise reactions with the highest energy barrier of 266.3 kJ/mol are found to produce separated N2. The overall NO reduction rate is expressed as 7.6×105×exp(−9606T). Reaction rate of rate-limiting step involved in N2 desorption is 2 × 100 s−1 at 1000 K, indicating it can tempestuously take place above 1000 K. The calculated results lend credit to previous experimental phenomenon.

Nitric Oxide Chemisorption in a Postsynthetically Modified Metal−Organic Framework

Postsynthetic metal-organic framework (MOF) derivatization introduces accessible secondary amine functionalities that react with nitric oxide (NO) to form N-diazenium diolates. This is in contrast to the parent MOF that binds NO essentially irreversibly at open metal coordination sites.

A Molecular Beam Study of the NO + CO Reaction on Pd(111) Surfaces

Nitric oxide (NO) reduction with carbon monoxide (CO) on the Pd(111) surface was studied under isothermal conditions by molecular beam techniques as a function of temperature, NO:CO beam composition, and beam flux. Systematic experiments were performed under transient and steady state conditions. Displacement of adsorbed CO by NO in the transient state of the reaction was observed at temperatures between 375 and 475 K for all the NO:CO compositions studied. NO accumulation occurs on Pd(111) surface under steady state conditions, below 475 K, due to stronger chemisorption of NO. The steady state reaction rates attain a maximum at about 475 K, nearly independent of beam composition. N2 was found to be the major product of the reduction, along with a minor production of N2O. The production of N2 and N2O indicates molecular and dissociative adsorption of NO on Pd(111) at temperatures up to 525 K. Postreaction TPD measurements were performed in order to determine the nitrogen coverage under steady-state conditions. Finally, the results are discussed with respect to the rate-controlling character of the different elementary steps of the reaction system.

Performance of fluorine-added, sonochemically prepared MoS2/Al2O3 catalysts in the hydrodesulfurization of dibenzothiophene compounds

The performance of MoS2/Al2O3 catalysts, prepared by a sonochemical method and containing different amounts of fluorine, was investigated for hydrodesulfurization (HDS), using dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) as model compounds. The activity of sonochemically synthesized MoS2 catalysts was higher than that of impregnated ones due to the improved dispersion of the Mo species. The addition of fluorine to the catalyst further increased the activity, reaching a maximum at the optimum fluorine content, due to an increase in acidity at the catalyst surface. The optimum amount of fluorine for maximum HDS activity was higher for the sonochemically prepared catalysts than for impregnated ones and, therefore, the activity of the former catalysts can be enhanced by fluorine addition to a greater extent than that of the latter types. The two promoting factors, sonochemical synthesis and fluorine addition, led to an increase in the hydrogenation (HYD) rates, compared to the direct-desulfurization (DDS) rates, in the HDS of both DBT and 4,6-DMDBT. However, the enhancement in overall activity was greater for the HDS of 4,6-DMDBT, which proceeds mainly via the HYD route, than for the HDS of DBT. The above reaction results, obtained using different catalysts, can be explained based on the surface properties of the catalysts, as characterized by X-ray photoelectron spectroscopy (XPS), nitric oxide chemisorption and infrared spectra of adsorbed pyridine.

Oxygen States at Magnesium and Copper Surfaces Revealed by Scanning Tunneling Microscopy and Surface Reactivity

By a combination of STM and XPS a study of the dynamics of oxygen chemisorption at Mg(0001) at 295 K has revealed oxygen states involving nucleation sites and the development of hexagonal and square lattice structures; the hexagonal structures develop epitaxially with the Mg(0001) surface. There is extensive surface mobility with, at the early stage of chemisorption, oxygen states being observed at steps at the (1 x 1)-O adlayer and overlapping magnesium atoms. These are active in ammonia and hydrocarbon oxidation whereas at higher oxygen coverage the surface is inactive. The dissociative chemisorption of nitric oxide generates a surface characterized by the hexagonal oxide structure; nitrogen adatoms known to be present from the N(Is) spectra are disordered. The chemisorption of hydrogen chloride at a Cu(110) surface results in a c(2 x 2)-Cl structure with at high coverage domains 1.8 nm wide. A sub-surface oxygen state at Cu(110), although unreactive to ammonia, undergoes a chemisorption replacement (corrosive chemisorption) reaction with HCl at 295 K.

Tuning the chemistry of metal surfaces: I. Adsorption and reaction of NO and N 2O on ultrathin Pd films on Ta(1 1 0)

Nitric oxide (NO) chemisorption is a sensitive chemical probe of the electronic structure and reactivity of metal surfaces. We have used NO, in conjunction with temperature programmed desorption and high resolution electron energy loss spectroscopy, to explore the altered reactivity of ultrathin (monolayer, bilayer, trilayer) Pd films deposited on Ta(1 1 0). The reactivity of the Pd-monolayer film is strongly altered from that of bulk-terminated Pd surfaces. NO is molecularly adsorbed on the Pd monolayer at 95 K, but the desorption activation energy is decreased to only 8 kcal/mol, and N 2O is the primary desorption product. At low initial NO coverages, N 2O desorbs in a reaction rate-limited peak at 129 K, which grows and shifts up in temperature, with increasing coverage, to 159 K at saturation. NO desorption occurs at 135 K, in addition to N 2O, at high coverages. Separate N 2O adsorption experiments show that N 2O is weakly and reversibly bound to the Pd monolayer film, desorbing by 115 K. NO chemisorption and reaction was independent of the initial geometric structure of the Pd monolayer, i.e., nearly identical results were obtained when using a pseudomorphic-bcc(1 1 0) or incommensurate-fcc(1 1 1) Pd monolayer. However, the chemical properties and reactivity of the Pd films rapidly returned to that of bulk Pd(1 1 1) surfaces as the Pd film thickness was increased above one monolayer. “Tuning” of NO chemistry on these Pd films was possible for initial thicknesses of 2–3 layers. The interaction of NO with a Pd monolayer on Ta(1 1 0) closely resembles that of NO with a Ag(1 1 1) surface, supporting the interpretation that Pd–Ta bonding interactions lead to a filled Pd d-band resulting in more noble metal-like properties.

Field-dependent chemisorption of carbon monoxide and nitric oxide on platinum-group (111) surfaces: Quantum chemical calculations compared with infrared spectroscopy at electrochemical and vacuum-based interfaces

Density Functional Theory (DFT) is utilized to compute field-dependent binding energies and intramolecular vibrational frequencies for carbon monoxide and nitric oxide chemisorbed on five hexagonal Pt-group metal surfaces, Pt, Ir, Pd, Rh, and Ru. The results are compared with corresponding binding geometries and vibrational frequencies obtained chiefly from infrared spectroscopy in electrochemical and ultrahigh vacuum environments in order to elucidate the broad-based quantum-chemical factors responsible for the observed metal- and potential-dependent surface bonding in these benchmark diatomic chemisorbate systems. The surfaces are modeled chiefly as 13-atom metal clusters in a variable external field, enabling examination of potential-dependent CO and NO bonding at low coverages in atop and threefold-hollow geometries. The calculated trends in the CO binding-site preferences are in accordance with spectral data: Pt and Rh switch from atop to multifold coordination at negative fields, whereas Ir and Ru exhibit uniformly atop, and Pd hollow-site binding, throughout the experimentally accessible interfacial fields. These trends are analyzed with reference to metal d-band parameters by decomposing the field-dependent DFT binding energies into steric (electrostatic plus Pauli) repulsion, and donation and back-donation orbital components. The increasing tendency towards multifold CO coordination seen at more negative fields is due primarily to enhanced back-donation. The decreasing propensity for atop vs multifold CO binding seen in moving from the lower-left to the upper-right Periodic corner of the Pt-group elements is due to the combined effects of weaker donation, stronger back-donation, and weaker steric repulsion. The uniformly hollow-site binding seen for NO arises from markedly stronger back-donation and weaker donation than for CO. The metal-dependent zero-field DFT vibrational frequencies are in uniformly good agreement with experiment; a semiquantitative concordance is found between the DFT and experimental frequency-field (“Stark-tuning”) slopes. Decomposition of the DFT bond frequencies shows that the redshifts observed upon chemisorption are due to donation as well as back-donation interactions; the metal-dependent trends, however, are due to a combination of several factors. While the observed positive Stark-tuning slopes are due predominantly to field-dependent back-donation, their observed sensitivity to the binding site and metal again reflect the interplay of several interaction components.

A general model for both three-way and deNO x catalysis: dissociative or associative nitric oxide adsorption, and its assisted decomposition in the presence of a reductant : Part I. Nitric oxide decomposition assisted by CO over reduced or oxidized rhodium species supported on ceria

A selective overview of recent studies on both three-way and deNO x catalysis (we shall note ‘deNO x ’, the removal of NO in the presence of an excess of oxygen) leads to an unique and general model of these reactions, based on kinetic concepts. Two kinds of active sites have to be first defined: cationic and zero-valent metal ones. The first type can form either through the reduction of the support ( V)-Ce 3+-( V) or (ii) a strong metal-support interaction ( V)-Rh +-( V)/CeO 2, both linked to adjacent oxygen vacancies ( V) of the reducible support, or (iii) a surface transition metal (TM) complex (TM in zeolite for instance). The second kind of sites are accessible supported-zero-valent noble metal atoms. These two kinds of sites are involved in three-way Catalysts (TWC), whereas only the cationic ones concern deNO x reactions. Therefore, nitric oxide chemisorption can be either ‘associative’ on the first kind of sites — leading to dinitrosyl or hyponitrite species — or ‘dissociative’, on the second ones, leading to oxygen and nitrogen atoms adsorbed on the sites. Two different catalytic sequences of elementary steps can then be defined. On cationic sites, successive N–O bond scissions of dinitrosyl or hyponitrite species occur, potentially able to produce intermediate N 2O, and in all cases leaving oxygen atoms adsorbed on the active site, and inhibiting a further adsorption of NO. A reductant is then necessary to remove these oxygen atoms and permit the reaction to proceed further. On zero-valent metallic sites, at the temperature of reaction, NO suffers a dissociative chemisorption leading again to surface oxygen atoms. Again, a reductant is necessary to remove these oxygen species and permit the reaction to proceed again. In this first paper, TWC are considered and the reductant is CO. Two catalytic cycles are considered based on our results on temperature-programmed desorption and surface reactions of NO in a stoichiometric CO/NO/O 2 mixture.

Adsorption, diffusion, and dissociation of NO, N and O on flat and stepped Ru(0001)

The chemisorption, diffusion and dissociation of nitric oxide, NO, on flat and stepped Ru(0001) surfaces are investigated using density functional theory. In the Perdew–Wang-91 GGA approximation (PW91) for the exchange-correlation energy, the NO chemisorption potential energy (calculated relative to the gas-phase NO) is −2.73 and −3.10 eV on flat and stepped Ru(0001), respectively. The NO(a) experiences a diffusion energy barrier of 0.33 eV on the flat Ru(0001) terrace, while the barrier for diffusion across the steps is 0.9–1.1 eV. The barriers for attachment to and detachment from the steps are in the range of 0.4–0.8 eV. A number of strongly inclined, but metastable, NO configurations are found. The NO dissociation is calculated to be highly activated ( E a≃1.3 eV) on the flat Ru(0001) but is found to be only slightly activated ( E a≃0.1–0.5 eV) when monatomic Ru steps are present at the surface. The product N and O atoms prefer chemisorption in two- and threefold configurations right behind, or at, the step edges. The reason for this is the energetically higher Ru 4d-band positions at the step edges. The N and O atoms are subject to considerable energy barriers for diffusion over the Ru(0001) terraces ( E N d=0.79 eV and E O d=0.54 eV), and they experience even larger barriers for interlayer diffusion. Combining the NO dissociation and the N plus O chemisorption results, two mechanisms are found to cause the higher reactivity of the step edges in terms of NO-bond activation. The main mechanism is the ability of the reaction site to provide rebonding of the non-interacting reaction products. The other mechanism is the minimization of the degree of repulsive interaction of the N and O atoms in the transition state. Chemisorption energies, and diffusion and dissociation energy barriers are further calculated in the PBE and RPBE exchange-correlation descriptions. The PBE results are, as expected, very close to the PW91 results. The RPBE results, however, show largely reduced bonding energies and energy barriers that vary by ±0.2 eV, depending on the reaction geometry.

The chemisorption of nitric oxide and the oxidation of ammonia at Cu(110) surfaces: a X-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM) study

The dissociative chemisorption of nitric oxide at Cu(110) has been shown to result in rapid ordering of oxygen adatoms as (2×1)O chains oriented along the 〈100〉 direction while the associated nitrogen adatoms are mainly disordered at 295 K. Surface diffusion of the N adatoms, following bond cleavage, is activated and ordering of the (2×3)N strings occurs on heating to 430 K. A number of distinct reaction pathways have been isolated during the oxidation of ammonia resulting in the formation of either chemisorbed imide or nitrogen adatoms. The latter depending on temperature, may exhibit a (2×3)N, a (3×3)N or both structures may exist simultaneously. The concentration of nitrogen in the complete (2×3)N structure has been determined to be 6.6×1014 cm-2, with only a 25% decrease in nitrogen concentration leading to the transformation to the (3×3)N structure. The oxygen atoms at a Cu(110)–O overlayer, and present at the ends of the (2×1) strings terminating in steps, show specific reactivity when exposed to ammonia at 375 K resulting in the “decoration” of the steps with imide species while the oxygens within the (2×1) strings remain unreactive.