Interaction Of NH3 Research Articles

NH3 adsorption on PtM (Fe, Co, Ni) surfaces: Cooperating effects of charge transfer, magnetic ordering and lattice strain

Adsorption of a molecule or group with an atom which is less electronegative than oxygen (O) and directly interacting with the surface is very relevant to development of PtM (M=3d-transition metal) catalysts with high activity. Here, we present theoretical analysis of the adsorption of NH3 molecule (N being less electronegative than O) on (111) surfaces of PtM (Fe, Co, Ni) alloys using the first principles density functional approach. We find that, while NH3–Pt interaction is stronger than that of NH3 with the elemental M-surfaces, it is weaker than the strength of interaction of NH3 with M-site on the surface of PtM alloy.

Sensing of NH3 on heterogeneous nanoporous carbons in the presence of humidity

The influence of humidity on the NH3 detection capability of S- and N-containing nanoporous carbons was examined for the first time. To investigate the role of water on the electrical performance of the sensors, the sensing tests were carried out using a flow of NH3 diluted in moist air. The same tests were also carried out by performing a 2 h prehumidification prior to the exposure of the carbons to the moist gas stream. Compared to dry conditions, the presence of water in the air stream led to an enhanced response of the sensor. On the other hand, upon the prehumidification the adsorbent's surface an opposite outcome was recorded. Based on the electrical behavior of the carbons and their extensive surface characterization, a complex sensing mechanism is proposed. This mechanism includes specific interactions of NH3 and H2O molecules with surface functionalities, such as hydrogen bonding, proton transport through ionic conductivity, and electron–hole conductivity.

Approach to Multigas Sensing and Modeling on Nanostructure Decorated Porous Silicon Substrates

An approach to multiple gas sensing on decorated porous silicon (PS) substrates is presented. The simple microelectromechanical systems/nanoelectromechanical systems platform that we have developed facilitates the modeling of the interaction of nanostructured metal oxide islands with the analytes of interest, which are exemplified by NO and NH3. These conductometric sensors operate at room temperature and atmospheric pressure and, as they are forgiving, do not require film-based technology or lithography for their construction. We show that diffusion dominates the conductometric response. The direct response and the derivatives of this response are considered. The first derivative allows a quick evaluation of sensor response and the derivative is linear with concentration. The spectral simulations have been refined to include adsorption/desorption effects of the analyte gas and assess subsequent non-linear interface sensitivities. By including the physics of adsorption/desorption, the simulated sensor response is now a non-linear function of concentration. We model the absorption/diffusion through the use of the Langmuir absorption isotherm and find substantial agreement with experiment for the mixed analyte interactions of NH3 and NO combinations on several metal oxide decorated PS interfaces.

Heterogeneous reactions between ions NH3+ and NH+ and hydrocarbons adsorbed on a tungsten surface. Formation of HCN+ in NH+-surface hydrocarbon collisions

Interaction of NH3+ (ND3+) and NH+ with a hydrocarbon-covered tungsten surface kept at room temperature or heated to 150 and 300°C showed a series of reactions between the projectile ion and hydrocarbons adsorbed on the tungsten surface. Collisions with NH3+ showed formation of NH4+, HCNH+, and CH2NH2+, with NH4+ strongly prevailing at low incident energies of the projectile ion. Analogously, collisions with ND3+ showed formation of ND3H+, HCND+, and CH2ND2+ with dominant contributions of ND3H+ at low incident energies. No formation of HCN+ (DCN+) could be positively identified. In reactions with NH+, formation of HCN+ was clearly observed; the dependence of the normalized yield of HCN+ on incident energy indicated a threshold at about 40eV which might be due to an activation energy or an endothermicity of the surface reaction of about 2.4–3.2eV.

Costs and benefits of ammonia and particulate matter abatement in German agriculture including interactions with greenhouse gas emissions

The abatement of ammonia (NH3) and particulate matter (PM) emissions in agriculture reduces damages to human health and biodiversity and provides benefits for society, but also imposes costs on farmers. As NH3 and PM emissions partly originate from the same activities as greenhouse gases, interactions may exist between NH3 and PM emission abatement and greenhouse gas emissions. This study is aimed at estimating the costs and benefits of NH3 and PM emission abatement measures, considering interactions with agricultural greenhouse gas emissions in Germany. We combined an economic-ecological farm model for estimating emission reductions and abatement costs with an integrated environmental impact assessment model for estimating the benefits for human health and biodiversity, with applications to three Federal States in Germany. We reasoned that benefits exceed costs and that synergies with greenhouse gas reduction exist. All NH3 and PM emission abatement measures affected greenhouse gases. In crop production, conservation tillage increased farmers' gross margins and reduced both PM emissions and, via soil carbon sequestration, also greenhouse gas emissions. The benefits depended on the soil type and its carbon sequestration potential, which differ across regions. The substitution of urea fertiliser for calcium ammonium nitrate reduced both NH3 and greenhouse gas emissions. In livestock production, the measures with the highest net benefits were chemical washers for exhaust-air purification, injection or cultivator manure application and concrete manure storage cover. Low-protein pig feeding increased farmers' gross margins and also achieved high net benefits, with the benefits of greenhouse gas emission reduction exceeding those of NH3 emission reduction. Low-protein poultry feeding and biofilters for air purification yielded negative net benefits and were therefore not recommended for implementation. The results confirm interactions of NH3 and PM emission abatement measures with greenhouse gas emissions and suggest that all relevant emission types be integrated in an analysis. Air pollution abatement and climate change mitigation have mainly been addressed in separate policies. Our results suggest that these policies are better integrated so as to stimulate synergies and to define the appropriate ambition level of emission reduction targets.

Insight into ammonia sensing on heterogeneous S- and N- co-doped nanoporous carbons

The design of S- and N-dual-doped carbon-based ammonia sensors is reported for the first time. The materials are exposed to NH3 concentrations varying from 45 ppm to 500 ppm in dry air and normalized resistance changes are recorded. The response time is 40 s and the chips exhibit excellent reversibility and repeatability of the signal after continuous NH3/air cycles. The synergistic effect of N- and S- functional groups enhances the response. This behavior is governed by physical interactions of NH3 with surface groups, pore-filling, and hole depletion/formation in the carbon matrix. The texture and the degree of carbon graphitization also contribute to the magnitude of the observed signal. The results show that heteroatom containing nanoporous carbons can both detect NH3 and protect against its exposure.

From the (NH3)2–5 clusters to liquid ammonia: Molecular dynamics simulations using the NVE and NpT ensembles

A force field for the intermolecular NH3–NH3 interaction has been constructed and applied to characterize in detail the ammonia behavior in different environments. In particular, the dynamics of the (NH3)2-5 small clusters have been investigated and the isomerization processes analyzed as a function of the temperature considering a microcanonical (NVE) ensemble. The predicted (NH3)2-5 binding energies are in good agreement with experimental data and/or ab initio calculations. Liquid ammonia has been studied, by considering an isothermic–isobaric ensemble (NpT) of 512 molecules at different conditions of temperature and pressure. In particular, the temperature dependence of the density and of the mean diffusion coefficients has been analyzed at 1atm of pressure. Six different p-T conditions, at which the coexistence of vapor and liquid is possible, have been also taken into account. Finally, the radial distribution functions and the coordination number have been calculated at the same conditions used in neutron diffraction experiments. The model predictions have been compared successfully with experimental results, confirming the reliability of the force field formulation.

Preparation of polyelectrolyte complex nanoparticles of chitosan and poly(2-acry1amido-2-methylpropanesulfonic acid) for doxorubicin release

A new kind of polyelectrolyte complex (PEC) based on cationic chitosan (CS) and anionic poly(2-acry1amido-2-methylpropanesulfonic acid) (PAMPS) was prepared using a polymer–monomer pair reaction system. Chitosan was mixed with 2-acry1amido-2-methylpropanesulfonic acid) (AMPS) in an aqueous solution, followed by polymerization of AMPS. The complex was formed by electrostatic interaction of NH3+ groups of CS and SO3− groups of AMPS, leading to a formation of complex nanoparticles of CS-PAMPS. A series of nanoparticles were obtained by changing the weight ratio of CS to AMPS, the structure and properties of nanoparticles were investigated. It was observed that the nanoparticles possessed spherical morphologies with average diameters from 255nm to 390nm varied with compositions of the nanoparticles. The nanoparticles were used as drug vehicles for doxorubicin, displaying relative high drug loading rate and encapsulation rate. The vitro release profiles revealed that the drug release could be controlled by adjusting pH of the release media. The nanoparticles demonstrated apparent advantages such as simple preparation process, free of organic solvents, size controllable, good biodegradability and biocompatibility, and they could be potentially used in drug controlled release field.

Counterpoise-corrected energies, NBO, HOMO–LUMO and interaction energies of poly(o-aminophenol) for ammonia sensing by DFT methods

The response of poly(o-aminophenol) (POAP) both in doped and undoped forms toward NH3 gas was investigated on the basis of density functional theory (DFT) at B3LYP and UB3LYP/6-31G* level of theory. POAP is unique due to the presence of two potential interactive sites, i.e., NH and O. The sensing ability of both of these interactive sites was investigated. Change in geometric parameters, and interaction energy analysis provide an effective evidence for the sensing ability of POAP for NH3 gas. Further support to the sensing response was obtained by natural bond orbital (NBO) and Mulliken charge analysis. Density of state spectra also show the interaction of NH3 with POAP and provide an understanding of the response mechanism of POAP toward NH3. Greater interaction was observed for the NH site of POAP as compared to O site, illustrating that NH site is the actual interactive site of POAP in both doped/undoped forms. The response became more sophisticated in the doped form of POAP.

Nature of Acid Sites in Silica-Supported Zirconium Oxide: A Combined Experimental and Periodic DFT Study

A combined experimental and DFT study was carried out to investigate the acidity of silica-supported zirconium oxide synthesized via the grafting method. XRD results show the crystal phase of ZrO2 is tetragonal. Sample acidity was characterized via ammonia adsorption microcalorimetry and DRIFTS pyridine desorption. Theoretical results predict that on a vacancy-free surface of t-ZrO2 at low coverage NH3 binds preferentially to Lewis acid sites with an adsorption energy up to 120 kJ/mol and that ammonia adsorption energies below 100 kJ/mol calculated at higher coverage can be well explained by lateral NH3–NH3 interactions. Higher differential heats of adsorption at low coverage (up to 190 kJ/mol) on both the (101) and (201) crystal planes of t-ZrO2 are in agreement with dissociative adsorption of ammonia near an oxygen vacancy site. The theoretical results are in good agreement with our findings in ammonia adsorption microcalorimetry and DRIFTS pyridine desorption on the ZrO2/SiO2 sample.

Theoretical study of the interaction of electron donor and acceptor molecules with monolayer WS2

With the aim of understanding recent experimental data concerning molecular doping in WS2-based FET gas sensors, we have investigated the interaction of NH3 and H2O molecules with monolayer WS2, by means of first-principles calculations. The structural relaxations and total energy calculations are performed to determine the preferential binding configurations and it is found that both NH3 and H2O molecules are physisorbed on monolayer WS2. The Bader analysis combined with the plane-averaged differential charge density results indicate that NH3 acts as the electron donor, while H2O acts as the electron acceptor, leading to n- and p-type doping of WS2, respectively. The charge transfer mechanism is discussed in light of the mixing of the molecular highest occupied molecular orbital and lowest unoccupied molecular orbital with the underlying WS2 orbitals. In addition, the modification of the work function is found to be almost linearly dependent on the total charge transfer. The modification of the work function and the carrier concentration can be obtained by tuning the molecule coverages, without destroying the band structure of monolayer WS2. The electrical sensitivities to the gas adsorption make WS2 a gas sensor that promises wide-ranging applications.

Air quality and the selective detection of ammonia in the presence of carbon monoxide, toluene, benzene, and xylene

Air quality is an important factor especially in areas where humans are exposed to animal excrement. The selective detection of NH3, especially in the presence of CO provides an important means of protecting the health of workers in the dairy, swine, and poultry industries especially in enclosed barn areas. In addition, selective non-invasive detection of NH3 can play an important role in breath analysis especially for asthmatics. We assess the sensitivity of a variety of untreated and decorated porous silicon (PS) interfaces to NH3 at room temperature in the presence of carbon monoxide, toluene, benzene, and xylene. Interfaces, selective ranging from 102 105 for NH3, are demonstrated. The reversible interaction of NH3 with a PS interface completely overwhelms that for CO. A SnOx-decorated PS interface is used to evaluate the NH3-toluene system as the much weaker toluene signal corresponds to that of a weak base. SnOx and AuxO(x> > 1) decorated and PS interfaces are used to evaluate the NH3-benzene system as a much weaker benzene signal corresponds to that of a weak acid. A SnOx decorated PS interface is used to evaluate the NH3-xylene system as a much weaker xylene signal corresponds to that of a weak base.

Potential energy surface and bound states of the NH3-Ar and ND3-Ar complexes.

A new, four-dimensional potential energy surface for the interaction of NH3 and ND3 with Ar is computed using the coupled-cluster method with single, double, and perturbative triple excitations and large basis sets. The umbrella motion of the ammonia molecule is explicitly taken into account. The bound states of both NH3-Ar and ND3-Ar are calculated on this potential for total angular momentum values from J = 0 to 10, with the inclusion of Coriolis interactions. The energies and splittings of the rovibrational levels are in excellent agreement with the extensive high-resolution spectroscopic data accumulated over the years in the infrared and microwave regions for both complexes, which demonstrates the quality of the potential energy surface.

Supported Co catalysts prepared as thin films by magnetron sputtering for sodium borohydride and ammonia borane hydrolysis

Supported Co catalysts were prepared for sodium borohydride and ammonia borane hydrolysis by magnetron sputtering for the first time under different conditions. Ni foam was selected as support. Deposition conditions (time, pressure, and power) were varied to improve catalytic activity. A decrease in deposition power from 200 to 50W, leads to a decrease in crystallite and column size and a higher activity of catalysts. The increase in deposition pressure from 1.5×10−2 to 4.5×10−2mbar produces same effect but in this case the enhancement in activity is higher because amorphous materials were obtained. The highest activity for SB hydrolysis was 2650mlmin−1gcat−1 for the 50W Co 4.5 (4h) sample (Ea=60±2kJmol−1). For AB hydrolysis activity for the 50W Co 3.2 (4h) sample was similar. Durability of the thin films was tested for both reactions upon cycling (14 cycles). Diluted acid washing was effective to recover the activity for sodium borohydride reaction but not for ammonia borane hydrolysis. The strong Co–NH3 interactions explain the non-efficiency of the acid washing.

Interaction of NH3 with Cu-SSZ-13 Catalyst: A Complementary FTIR, XANES, and XES Study.

In the typical NH3-SCR temperature range (100-500 °C), ammonia is one of the main adsorbed species on acidic sites of Cu-SSZ-13 catalyst. Therefore, the study of adsorbed ammonia at high temperature is a key step for the understanding of its role in the NH3-SCR catalytic cycle. We employed different spectroscopic techniques to investigate the nature of the different complexes occurring upon NH3 interaction. In particular, FTIR spectroscopy revealed the formation of different NH3 species, that is, (i) NH3 bonded to copper centers, (ii) NH3 bonded to Brønsted sites, and (iii) NH4(+)·nNH3 associations. XANES and XES spectroscopy allowed us to get an insight into the geometry and electronic structure of Cu centers upon NH3 adsorption, revealing for the first time in Cu-SSZ-13 the presence of linear Cu(+) species in Ofw-Cu-NH3 or H3N-Cu-NH3 configuration.

Catalytic roles of substrate-binding residues in coenzyme B12-dependent ethanolamine ammonia-lyase.

Ethanolamine ammonia-lyase (EAL) catalyzes the adenosylcobalamin-dependent conversion of ethanolamine to acetaldehyde and ammonia. 1-OH of the substrate is hydrogen-bonded with Gluα287, Argα160, and Asnα193 and 2-NH2 with Gluα287, Glnα162, and Aspα362. The active site somewhat resembles that of diol dehydratase. All five residues were important for the high-affinity binding of the substrate and for catalysis. The -COO(-) group at residue α287 was absolutely required for activity and coenzyme Co-C bond cleavage, and there was a spatially optimal position for it, suggesting that Gluα287 contributes to Co-C bond homolysis, stabilizes the transition state for the migration of NH2 from C2 to C1 through partial deprotonation of spectator OH, and functions as a base in the elimination of ammonia. A positive charge and/or the hydrogen bond at position α160 and the hydrogen bonds at positions α162 and α193 with the substrate are important for catalysis and for preventing a radical intermediate from undergoing side reactions. Argα160 would stabilize the trigonal transition state in NH2 migration by electrostatic catalysis and hydrogen bonding with spectator OH. Asnα193 would contribute to maintaining the appropriate position and direction of the guanidinium group of Argα160, as well. Hydrogen bond acceptors were necessary at position α162, but hydrogen bond donors were rather harmful. Glnα162 might stabilize the trigonal transition state by accepting a hydrogen bond from migrating NH3(+). The activity was very sensitive to the position of -COO(-) at α362. Aspα362 would assist Co-C bond homolysis indirectly and stabilize the trigonal transition state by accepting a hydrogen bond from migrating NH3(+) and electrostatic interaction.

Ab initio calculations of the effect of impurity iron ions on the interaction of CH4 and NH3 with nanoporous silicates

The interaction of CH4 and NH3 molecules with the surface of pure and iron-doped nanoporous SiO2 has been simulated by ab initio calculations. The energetically favorable positions for adsorbate molecules have been found and the variation of the local atomic structure of SiO2 has been studied in detail. It was shown that the adsorption energy of CH4 and NH3 molecules on the surface of nanoporous SiO2 was 0.16 and 0.51 eV, respectively.

Structure, ligands and substrate coordination of the oxygen-evolving complex of photosystem II in the S2 state: a combined EPR and DFT study

The S2 state of the oxygen-evolving complex of photosystem II, which consists of a Mn4O5Ca cofactor, is EPR-active, typically displaying a multiline signal, which arises from a ground spin state of total spin ST = 1/2. The precise appearance of the signal varies amongst different photosynthetic species, preparation and solvent conditions/compositions. Over the past five years, using the model species Thermosynechococcus elongatus, we have examined modifications that induce changes in the multiline signal, i.e. Ca(2+)/Sr(2+)-substitution and the binding of ammonia, to ascertain how structural perturbations of the cluster are reflected in its magnetic/electronic properties. This refined analysis, which now includes high-field (W-band) data, demonstrates that the electronic structure of the S2 state is essentially invariant to these modifications. This assessment is based on spectroscopies that examine the metal centres themselves (EPR, (55)Mn-ENDOR) and their first coordination sphere ligands ((14)N/(15)N- and (17)O-ESEEM, -HYSCORE and -EDNMR). In addition, extended quantum mechanical models from broken-symmetry DFT now reproduce all EPR, (55)Mn and (14)N experimental magnetic observables, with the inclusion of second coordination sphere ligands being crucial for accurately describing the interaction of NH3 with the Mn tetramer. These results support a mechanism of multiline heterogeneity reported for species differences and the effect of methanol [Biochim. Biophys. Acta, Bioenerg., 2011, 1807, 829], involving small changes in the magnetic connectivity of the solvent accessible outer MnA4 to the cuboidal unit Mn3O3Ca, resulting in predictable changes of the measured effective (55)Mn hyperfine tensors. Sr(2+) and NH3 replacement both affect the observed (17)O-EDNMR signal envelope supporting the assignment of O5 as the exchangeable μ-oxo bridge and it acting as the first site of substrate inclusion.

Exploring and rationalising effective n-doping of large area CVD-graphene by NH3

Despite the large number of papers on the NH3 doping of graphene, the achievement of stable n-doped large area CVD (chemical vapor deposition) graphene, which is intrinsically p-doped, is still challenging. A control of the NH3 chemisorption and of the N-bond configuration is still needed. The feasibility of a room temperature high pressure NH3 treatment of CVD graphene to achieve n-type doping is shown here. We use and correlate data for (a) sheet resistance, R(sh), and the Hall coefficient, R(H), in van der Pauw configuration, acquired in real time during the NH3 doping of CVD-graphene on a glass substrate, (b) optical measurements of the effect of doping on the graphene Van Hove singularity point at 4.6 eV in the dielectric function spectra by spectroscopic ellipsometry, and of (c) N-bond configuration by XPS to better understand and, finally, control the NH3 doping of graphene. The discussion is focused on the thermal and time stability of the n-doping after air exposure. A chemical rationale is provided for the NH3 n-doping based on the interaction of (i) NH3 with intrinsic oxygen functionalities and defects of CVD graphene and of (ii) C-NH2 doping centers with acceptor species present in the air.

A DFT study on doping assisted changing of B80 electronic structure: Promising candidates for NH3 sensor

Density functional theory calculations at the B3LYP with 6-31G(d), 6-311++G(d,p), and LANL2DZ basis sets were carried out to investigate the adsorption of NH3 on the series of B79X structures with X={B, Al, Ga, N, F}. In order to go further and gain insight into the binding features of doped B80 complexes with NH3, the structural and electronic parameters as well as the Atoms in Molecules (AIM) properties were examined. The parameters and the obtained results by AIM were regarded as powerful tools to reveal some unknown aspects of electronic structures of the boron buckyballs upon the adsorption when they were exposed to doping. According to our results, the interaction of NH3 with the external wall of pristine and doped B80 leads to the remarkable differences in their structures and conductivities. The results show that B79X with X={B, Al, Ga} kept their original structure greatly while the structure of B79X with non-metal dopants, particularly fluorine, were changed dramatically. For instance, when F was substituted as a dopant on cap site, the F atom was projected inside the buckyball. It is clarified that B79Al, B79Ga and B79F complexes gain noticeable response to NH3 by locating the dopants in the cap site. Therefore, it is concluded that they can potentially regard as NH3 sensors. In addition, AIM based analyses indicated a partial covalent nature for all the complexes except NH3–B80 and frame–NH3–B79F. Moreover, it was found that the covalent nature of the NX bonds is decreased by increasing of metallic characteristic of X atom.