Interaction Of NH3 Research Articles

Interaction of Small Gases with the Unsaturated Metal Centers of the HKUST-1 Metal Organic Framework

The interactions of CO, CO2, OCS, SO2, NO, NO2, N2O, NH3, PH3, and other small molecules with the undercoordinated metal centers of the HKUST-1 metal organic framework are studied by means of density functional theory. These molecules are potentially harmful for humans and the environment and are widely studied because of their spectroscopic properties. In this work, the energetic and vibrational characteristics of the adsorbed species are calculated. Adsorption energies on the Cu2+ sites of the paddlewheel have been calculated, and the order is: NH3 > H2O > PH3 > H2S > SO2 > CO ∼ OCS ∼ CO2 ∼ NyOx > N2 > O2. The results show that the interactions can be classified into three categories: (1) weak physisorption, (2) polarization and electrostatics, and (3) strong acid–base. Moreover, interesting vibrational properties are calculated especially for carbonyl sulfide and dinitrogen monoxide, which can be bound via two different configurations on the metal atoms. The vibrational modes are shifting in different ...

Low Temperature Synthesis of NH3 from Atomic N and H at the Surfaces of FeS2{100} Crystals

We have investigated the interaction of H2 and NH3 with {100} surfaces of iron pyrite (FeS2) in ultrahigh vacuum (UHV) and the synthesis of NH3 from the reaction of preadsorbed atomic N with atomic H, the H either preadsorbed on or arriving at the surface, all at surface temperatures of 170 K or above. Hydrogen adsorbs and reacts only when it arrives at the surface as atomic H, after cracking at a hot filament. Recombinative desorption of H2 occurs with a peak temperature of 225 K and is accompanied by desorption of H2S, formed by surface reaction of Hads with S, with a peak temperature of 260 K. NH3 adsorbs molecularly from the gas phase, albeit with some degree of partial dissociation, and desorbs with a peak temperature of 215 K. NH3 can be synthesized when the surface, after pre-exposure to activated nitrogen, is exposed to atomic H. The synthesized NH3 desorbs with a peak temperature of 230 K, demonstrating that all hydrogenation steps are feasible under these conditions; the process appears to be de...

Molecular Dynamics Investigation of Alkali Metal Ions in Liquid and Aqueous Ammonia

A polarizable potential model for M(+)-NH3 interactions (M(+) = Li(+), Na(+), K(+), Rb(+), Cs(+)) is optimized based on the ab initio properties of the ion-ammonia dimers calculated at the MP2 level of theory. The optimized model reproduces the ab initio binding energies of M(+)(NH3)n (n = 2-4) and M(+)(NH3)n(H2O)m (n, m = 1-3 and n + m ≤ 4) clusters and gives relative solvation free energies in liquid ammonia in good agreement with experimental data, without further adjustments. It also reproduces binding cooperativity in ion-ammonia and ion-ammonia-water clusters. The model is used in molecular dynamics simulations of isolated ions in liquid ammonia and in aqueous ammonia solutions with various ammonia molar fractions (0.0 ≤ xNH3 ≤ 1.0). Simulations in liquid ammonia show coordination numbers of 4.0 for Li(+), 5.3 for Na(+), 6.1 for K(+), 6.7 for Rb(+), and 7.7 for Cs(+), in very good agreement with available experimental results. Simulations of ions in aqueous ammonia show preferential solvation by water in their first solvation shells and preferential solvation by ammonia in their second shells. Potentials of mean force are calculated between each ion and NH3 in liquid water, and between each ion and H2O in liquid ammonia. The results suggest that, in liquid water, Li(+) and Na(+) bind NH3 in their second solvation shells only, while Cs(+) binds NH3 in its first solvation shell only (K(+) and Rb(+) ions show only weak affinity for NH3 in water). In liquid ammonia, the ions bind H2O in their first solvation shells with an affinity following the trend Li(+) > Na(+) > K(+) ≈ Rb(+) > Cs(+).

Charge transport and ammonia sensing properties of flexible polypyrrole nanosheets grown at air–liquid interface

Flexible polypyrrole nanosheets (thickness ∼150 nm) grown at the air–liquid interface have been investigated for charge transport and NH3 sensing application. Polypyrrole nanosheets films exhibited a uniform and dense morphology. Temperature dependent charge transport measurements revealed that the PPy films obey Mott's 3-D variable range hopping mechanism. The mobility values calculated using temperature dependent current voltage characteristics indicated them to obey Arrhenius behaviour. These films exhibited a reversible response towards NH3 at room temperature. The sensor exhibited a sensitivity of ∼12% with a typical response and recovery times of 240 s and 50 min, respectively towards 50 ppm of NH3. Raman studies indicated that there is an increase in the antisymmetrical C–N stretching upon exposure to higher concentration of NH3 (500 ppm) and could be assigned to the interaction of NH3 with the carbon backbone of PPy film. Our results clearly emphasize that these flexible PPy films could be used to realize flexible sensors.

Reverse selective NH3/CO2 permeation in fluorinated polymers using membrane gas separation

The analysis of the process of gas and vapour permeation through dense polymers is of primary importance for packaging, controlled release and membrane separation processes. A significant amount of polymer permeability data has already been reported, especially for permanent gases, such as N2, O2, H2, CH4 and CO2, although a very small amount of data is available for ammonia (NH3). In this case, the experimental results show the faster permeation of NH3 in comparison to CO2, which is in agreement with the solution diffusion model predictions. NH3 is smaller and more condensable than CO2. In this study, the solubility, diffusion coefficient and permeability of NH3, CO2 and N2 in ten different polymers were investigated between 5 and 50°C. A reverse NH3/CO2 permeation selectivity is occasionally observed for dense fluorinated polymers (PTFE, FEP, Hyflon AD and Teflon AF). This unusual behaviour is interpreted in the light of the diffusion and sorption coefficients obtained from time lag experiments which tend surprisingly to show in fluorinated polymers: a NH3/CO2 solubility selectivity systematically lower than expected by the usual correlations and, in some cases, lower diffusion coefficients for NH3 than for CO2. This peculiar result is interpreted from the differences between NH3 and CO2 interactions with fluorine atoms, similarly to the differential solubility phenomena of these two species which have previously been clearly established in fluorinated liquids.

Density Functional Theory Study of the Interaction of Arginine-Glycine-Aspartic Acid with Graphene, Defective Graphene, and Graphene Oxide

This study investigated the interaction between carbon nanostructures, including pristine graphene, defective graphene with monovacancy, graphene oxide (GO), and tripeptide arginine-glycine-aspartic acid (RGD), by density functional theory. The results from the adsorption energy analysis show that the strongest adsorption is observed when RGD is parallel to graphene surfaces, in which graphene interacts with all three functional groups of RGD, including NH3+, COO–, and guanidine. The interaction of NH3+···π was stronger than that of guanidine–NH2···π and COO–···π. The vacancy improves the ability of graphene to attract RGD because of active dangling C atoms. GO has a stronger interaction with RGD than the pristine and defective graphene because of O-containing groups. The comparison of the GO model with the OH, epoxy, and mixed OH/epoxy groups reveals that various O-containing groups have distinguishing binding abilities with RGD. Water molecules strengthen the interactions between graphene and RGD, where...

A Modeling Study of NH3 Slip Catalysts: Analysis of the SCR/PGM Interactions

We present a simulation study which comparatively analyzes the performances of four configurations of NH3 slip catalysts (ASC) for automotive NH3–SCR based Diesel aftertreatment systems. The comparison in terms of NH3 conversion and N2 selectivity over a wide range of operating conditions highlights the positive interaction of NH3–SCR and PGM oxidation chemistries, which is best exploited by a dual-layer configuration with the SCR catalyst on top. This study also emphasizes the key role of modeling and simulation tools in the development of complex exhaust aftertreatment systems as well as the importance of a clear understanding of the catalytic chemistry involved in automotive deNOx converters.

Insights into Adsorption of NH3 on HKUST-1 Metal–Organic Framework: A Multitechnique Approach

We report a careful characterization of the interaction of NH3 with the Cu(II) sites of the [Cu2C4O8] paddle-wheel cornerstone of the HKUST-1 metallorganic framework, also known as Cu3(BTC)2. The general picture emerging from combining XRPD, EXAFS, XANES, mid- and far-IR, DRUV–vis, and EPR techniques is that the presence of traces of water has relevant consequences on the effect of ammonia on the MOF framework. NH3 adsorption on the dry system results in a strong chemisorption on Cu(II) sites that distorts the framework, keeping the crystallinity of the material. Perturbation observed upon NH3 adsorption is analogous to that observed for H2O, but noticeably enhanced. When the adsorption of ammonia occurs in humid conditions, a time-dependent, much deeper modification of the system is observed by all of the considered techniques. On a methodological ground, it is worth noticing that we used the optimization of XANES spectra to validate the bond distance obtained by EXAFS.

Photoinduced Radical Processes on the Spinel (MgAl2O4) Surface Involving Methane, Ammonia, and Methane/Ammonia

The present study explored photoinduced radical processes caused by interaction of CH(4) and NH(3) with a photoexcited surface of a complex metal oxide: magnesium-aluminum spinel (MgAl(2)O(4); MAS). UV irradiation of MAS in vacuo yielded V-type color centers as evidenced by the 360 nm band in difference diffuse reflectance spectra. Interaction of these H-bearing molecules with photogenerated surface-active hole states (O(S)(-)•) yielded radical species which on recombination produced more complex molecules (including heteroatomic species) relative to the initial molecules. For the MAS/CH(4) system, photoinduced dissociative adsorption of CH(4) on surface-active hole centers produced •CH(3) radicals that recombined to yield CH(3)CH(3). For MAS/NH(3), a similar dissociative adsorption process led to formation of •NH(2) radicals with formation of NH(2)NH(2) as an intermediate product; continued UV irradiation ultimately yielded N(2). For the mixed MAS/CH(4)/NH(3) system, however, interaction of adsorbed NH(3) and CH(4) on the UV-activated surface of MAS yielded •NH(2) and •CH(3) radicals, respectively, which produced CH(3)-NH(2) followed by loss of the remaining hydrogens to form a surface-adsorbed cyanide, CN(S), species. Recombination of photochemically produced radicals released sufficient energy to re-excite the solid spinel, generating new surface-active sites and a flash luminescence (emission decay time at 520 nm, τ ~ 6 s for the MAS/NH(3) case) referred to as the PhICL effect.

The effect of oxygen vacancies on the binding interactions of NH3 with rutile TiO2(110)-1 × 1

A series of NH(3) temperature-programmed desorption (TPD) spectra were taken after dosing NH(3) at 70 K on rutile TiO(2)(110)-1 × 1 surfaces with oxygen vacancy (V(O)) concentrations of ~0% (p-TiO(2)) and 5% (r-TiO(2)), respectively, to study the effect of V(O)s on the desorption energy of NH(3) as a function of coverage, θ. Our results show that in the zero coverage limit, the desorption energy of NH(3) on r-TiO(2) is 115 kJ mol(-1), which is 10 kJ mol(-1) less than that on p-TiO(2). The desorption energy from the Ti(4+) sites decreases with increasing θ due to repulsive NH(3)-NH(3) interactions and approaches ~55 kJ mol(-1) upon the saturation of Ti(4+) sites (θ = 1 monolayer, ML) on both p- and r-TiO(2). The absolute monolayer saturation coverage is determined to be about 10% smaller on r-TiO(2) than that on p-TiO(2). Additionally, the trailing edges of the NH(3) TPD spectra on the hydroxylated TiO(2)(110) (h-TiO(2)) appear to be the same as that on r-TiO(2) while those on oxidized TiO(2)(110) (o-TiO(2)) shift to higher temperatures. We present a detailed analysis of the results and reconcile the observed differences based on the repulsive adsorbate-adsorbate dipole interactions between neighboring NH(3) molecules and the surface charge associated with the presence of V(O)s.

Adsorption of ammonia on vanadium–antimony mixed oxides

We analyzed the adsorption of ammonia (NH3) on the VSbO4(110) catalyst surface using density functional theory (DFT) calculations. We followed the evolution of the chemical bonds between different atoms of the resulting NH3/VSbO4 system and the changes in the electronic structure of the catalyst. NH3 preferential adsorption geometries were analyzed through the crystal orbital overlap population (COOP) concept and the density of states (DOS) curves. The VSbO4(110) surface exhibits Lewis and Brønsted acid sites on which the ammonia molecule can interact. On the Lewis acid site, NH3 adsorption resulted in the interaction between the N and a surface V-isolated cation. On Brønsted acid site, N interacted with a surface H coming from the chemical dissociation of water. The COOP analysis indicate that NH3 interaction on the VSbO4(110) surface is weak. In addition, the DOS curves show more developed electronic interactions for NH3 adsorption on Lewis acid site than over Brønsted acid site.

Adsorption of NO and NH3 over CuO/γ-Al2O3 catalyst

The selective catalytic reduction reaction belongs to the gas-solid multiphase reaction, and the adsorption of NH3 and NO on CuO/γ-Al2O3 catalysts plays an important role in the reaction. Performance of the CuO/γ-Al2O3 catalysts was explored in a fixed bed adsorption system. The catalysts maintain nearly 100% NO conversion efficiency at 350 °C. Comprehensive tests were carried out to study the adsorption behavior of NH3 and NO over the catalysts. The desorption experiments prove that NH3 and NO are adsorbed on CuO/γ-Al2O3 catalysts. The adsorption behaviors of NH3 and NO were also studied with the in-situ diffusion reflectance infrared Fourier transform spectroscopy methods. The results show that NH3 could be strongly adsorbed on the catalysts, resulting in coordinated NH3 and NH 4 + NO adsorption leads to the formation of bridging bidentate nitrate, chelating bidentate nitrate, and chelating nitro. The interaction of NH3 and NO molecules with the Cu2+ present on the CuAl2O4 (100) surface was investigated by using a periodic density functional theory. The results show that the adsorption of all the molecules on the Cu2+ site is energetically favorable, whereas NO bound is stronger than that of NH3 with the adsorption site, and key information about the structural and energetic properties was also addressed.

Molecular chemisorption on open metal sites in Cu3(benzenetricarboxylate)2: A spatially periodic density functional theory study

Chemical interactions of H(2)O, CO, NO, pyridine, C(2)H(2), H(2)S, and NH(3) with open metal sites in the metal-organic framework (MOF) Cu(3)(benzenetricarboxylate)(2) are examined using plane wave periodic density functional theory (DFT). In the case of single molecule adsorption on a Cu dimer, NH(3) and pyridine have the strongest binding, while NO binds weakly. Binding of pairs of molecules on a Cu dimer shows significant interaction energies, that is, the binding energy of the pair of molecules is not a simple summation of the binding energies of each molecule. The effect of molecular adsorption on the magnetic moments of Cu atoms in the MOF is also examined. Using the binding energies from DFT calculations, the effects of the pressure and temperature on the chemisorbed species are investigated. Finally the effect of water adsorption on the elastic behavior of Cu(3)(BTC)(2) is described.

Characterizing a Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of atmospheric ammonia

Abstract. A compact, fast-response Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS) for measurements of ammonia (NH3) has been evaluated under both laboratory and field conditions. Absorption of radiation from a pulsed, thermoelectrically cooled QC laser occurs at reduced pressure in a 0.5 L multiple pass absorption cell with an effective path length of 76 m. Detection is achieved using a thermoelectrically-cooled Mercury Cadmium Telluride (HgCdTe) infrared detector. A novel sampling inlet was used, consisting of a short, heated, quartz tube with a hydrophobic coating to minimize the adsorption of NH3 to surfaces. The inlet contains a critical orifice that reduces the pressure, a virtual impactor for separation of particles, and additional ports for delivering NH3-free background air and calibration gas standards. The level of noise in this instrument has been found to be 0.23 ppb at 1 Hz. The sampling technique has been compared to the results of a conventional lead salt Tunable Diode Laser Absorption Spectrometer (TDLAS) during a laboratory intercomparison. The effect of humidity and heat on the surface interaction of NH3 with sample tubing was investigated at mixing ratios ranging from 30–1000 ppb. Humidity was seen to worsen the NH3 time response and considerable improvement was observed when using a heated sampling line. A field intercomparison of the QC-TILDAS with a modified Thermo 42CTL chemiluminescence-based analyzer was also performed at Environment Canada's Centre for Atmospheric Research Experiments (CARE) in the rural town of Egbert, ON between May–July 2008. Background tests and calibrations using two different permeation tube sources and an NH3 gas cylinder were regularly carried out throughout the study. Results indicate a very good correlation at 1 min time resolution (R2 = 0.93) between the two instruments at the beginning of the study, when regular background subtraction was applied to the QC-TILDAS. An overall good correlation of R2 = 0.85 was obtained over the entire two month data set, where the majority of the spread can be attributed to differences in inlet design and background subtraction methods.

DFT study of NH3(H2O)n=0,1,2,3 complex adsorption on the (8,0) single-walled carbon nanotube

Abstract Theoretical study of NH3(H2O)n=0,1,2,3 adsorption on (8, 0) carbon nanotube was performed at the X3LYP/6–31G* level of density functional theory (DFT). The tube–NH3 interaction was discussed in the terms of binding energy (EB), coupling energy (EC), charge density, molecular orbitals, and dipole moments. The results reveal that addition of water molecules to tube–NH3 system increases the interaction between tube and ammonia molecule.

Fabrication of Poly(p-Phenylene)/Zeolite Composites and Their Responses Towards Ammonia

Poly(p-phenylene) (PPP) was chemically synthesized via oxidative polymerization using benzene and doped with FeCl3. The electrical conductivity response of the doped PPP (dPPP) towards CO, H2 and NH3 is investigated. dPPP shows no electrical conductivity response towards the first two gases (CO and H2), but it shows a definite negative response towards NH3. The electrical conductivity sensitivity of dPPP increases linearly with increasing NH3 concentration. To improve the sensitivity of the sensor towards NH3, ZSM-5 zeolite is added into the conductive polymer matrix. The electrical sensitivity of the sensor increases with increasing zeolite content up to 30%. The effect of the type of cation in the zeolite pores is investigated: namely, Na+, K+, NH4+ and H+. The electrical conductivity sensitivity of the composites with different cations in the zeolite can be arranged in this order: K+ < no zeolite < Na+ < NH4+ < H+. The variation in electrical sensitivity with cation type can be described in terms of the acid-base interaction, the zeolite pore size and surface area. The PPP/Zeolite composite with H+ possesses the highest electrical sensitivity of −0.36 since H+ has the highest acidity, the highest pore volume and surface area, which combine to induce a more favorable NH3 adsorption and interaction with the conductive polymer.

Adsorption and oxidation of NH3 over V2O5/AC surface

V2O5/AC has been reported to be active for selective catalytic reduction (SCR) of NO with NH3 at around 200°C and resistant to SO2 deactivation. To elucidate its SCR mechanism, adsorption and oxidation of NH3 over V2O5/AC are studied in this paper using TG, MS and DRIFTS techniques. It is found that the adsorption and oxidation of NH3 take place mainly at VO bond of V2O5. A higher V2O5 loading results in more NH3 adsorption on the catalyst. V2O5 contains both Brϕnsted and Lewis acid sites; NH4+ on Brϕnsted acid sites is less stable and easier to be oxidized than NH3 on Lewis acid sites. Gaseous O2 promotes interaction of NH3 with AC and oxidation of NH3 over V2O5/AC. NH3 is oxidized into NH2 and acylamide structures and then to isocyanate species, which is an intermediate for N2 formation.

Experimental and theoretical Raman and surface‐enhanced Raman scattering study of cysteine

AbstractRaman spectra in solid and 1 M solution of L‐cysteine and surface‐enhanced Raman scattering (SERS) spectra of this molecule in the zwitterionic form, by using colloidal silver nanoparticles, have been recorded. Density functional theory with the B3LYP functional was used for the optimizations of the ground state geometries and simulation of the vibrational spectrum of this amino acid. The SERS spectrum with a large silver cluster as a model metallic surface was simulated for the first time. Taking into account the experimental and calculated Raman and SERS vibrations and the corresponding assignments, as well as a comparison of force constants and geometrical parameters between the free zwitterion cysteine and the one in the presence of the colloidal silver nanoparticles, we can confirm the presence of gauche (PH) and trans (PN) rotamers in the solid state, the formation of a SS bond in the solution state, the dissociation of the peptide bond and mixing of rotamers because of the SERS effect, and the relative importance of the interaction of sulphyldryl, NH3+, and carboxylate groups with the metallic surface. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Reactivity of (TiO2)N Clusters (N = 1−10): Probing Gas-Phase Acidity and Basicity Properties

We present B3LYP calculations on a selection of small-size clusters with (TiO2)N stoichiometry (N = 1−10) built on previous works on TiO2 and SiO2 or derived by kinship with stable clusters of different sizes. Their reactivity is analyzed as a function of size and electronic structure. Gas-phase acidity is probed by H+ interaction with the oxygen sites, while basicity is tested by interaction of molecular NH3 with titanium sites. Correlation with size, topology, or electronic properties is observed for some systems. In general, the correlation with electronic levels (highest occupied and lowest unoccupied molecular orbitals, HOMO and LUMO) is good criteria of reactivity, although this is not always observed. The calculated values generally decrease with the size. The HOMO−LUMO gaps show oscillations and a general decrease with the size. Coordination of the active site influences both the levels of the frontier orbitals and their effect upon reactivity. The protonation testing the cluster basicity is found...

Influence of Ion Pairing on the UV-Spectral Behavior of KI Dissolved in Supercritical NH3: From Vapor Phase to Condensed Liquid

The UV-spectroscopic behavior of KI dissolved in supercritical ammonia enabled us to identify two species that contribute to the optical absorption depending on the fluid density rho1 and the temperature T. At low rho1 and high T, contact ion pairs (CIPs) prevail, while at high density of ammonia, solvent separated ion pairs (SSIPs) and free iodide ions dominate the optical absorption of the solute. The features of the electron excitation process depend on the state of the K+ I- species present. Starting with isolated KI in the vapor, where the process is an interionic charge transfer, when the CIP becomes solvated the UV absorption shifts strongly to the blue. As rho1 increases, the amounts of SSIP and of free iodide increase progressively and their electronic excited states become those characteristic of the charge-transfer-to-solvent process. This study suggests there is a strong influence of the cation on the electronic transition of dissolved iodide when it is forming CIPs. Moreover, the fact that K+-NH3 interaction is much larger than that of I(-)-NH3 suggests that the electronic photoinduced excited state of CIPs is similar to the ground state observed for alkali metals in NH3 clusters.