Adsorption energy

Cancer is one of the most common diseases that affects many people around the world, and one of the challenges of the scientific community in dealing with cancer is to deliver drugs to cancerous tumors. Various reports show that boron nitride nanoparticles can be effective as drug nanocarriers and drug delivery in the target cell. In the present work, capsulation of anticancer drug of mercaptopurine (MCP) upon the boron nitride (6,6) nanotube, using DFT: B3LYP/6-31G* and the natural bond orbital analysis in the gas phase was investigated for the first time. Additionally, NCI analysis is used in this study to examine interactions between MCP and boron nitride nanotubes. To ascertain the impact of MCP adsorption into the nanotube, HOMO-LUMO orbitals, DOS (Density of States) plots, and molecular electrostatic potential maps (MEPs) were used. Furthermore, the effect of the abovementioned interactions between the drug and boron nitride nanotube on the electronic characteristics, and natural charges were estimated. Based on the gained results, the thermodynamic parameters of MCP nanotube and the results of NCI analysis were in close agreement with each other and it was also shown that the MCP adsorption process on the nanotube is a physical adsorption type, and the absorption process is associated with the release of heat, and it was in a favorable state in terms of thermodynamics. Furthermore, the results of IR spectra of drug, nanotube, and drugnanotube mixture were investigated. Therefore, using boron nitride nanotube as a carrier for MCP drugs has been confirmed theoretically.

In this study, density functional theory was used to investigate the effect of adsorption process and interaction between methanol as a fuel and graphene as a catalyst. Thermodynamic studies in this field have shown that Gibb's free energy is positive in most cases. Therefore, adsorption of methanol on graphene is very low and in the physical mode. Thus, other ways are required to increase adsorption on graphene surface. Changing pristine graphene (PG) to vacancy graphene (VG) or N-doped graphene (NG) can increase absorption, and convert their adsorption into chemical adsorption. Vacancy and N-doped in electronic structure of graphene increase adsorption of methanol to graphene. Increased absorption of VG and NG, in addition to changes in charge transfer causes significant changes in the location of HOMO and LUMO, which was confirmed by adsorption energy, NBO, QTAIM, and DOS.

A detailed understanding of the organic molecule/substrate interface is of crucial importance for the design of organic semiconducting devices, as the interface determines the contact resistance and the charge injection. Generally, two different adsorption situations are considered: physisorption and chemisorption. For small molecular adsorbates like CO or N 2 , the adsorption energy alone can be used as a criterion to classify the adsorption in chemisorption (adsorption energies larger than 1 eV) and physisorption (few tens of meV). This classification fails for complex π-conjugated organic molecules. Here we discuss on the basis of a pentacene/Cu(110) model system a different set of criteria to distinguish between chemisorption and physisorption beyond the total bond energy argument. We analyze the bonding situation on the basis of density functional theory (DFT) calculations and photoelectron spectroscopy. Theory predicts (i) a significant bending of the molecule after adsorption, (ii) a buckling of the top layer Cu atoms, (iii) the emergence of new hybrid states, and (iv) a substantial charge redistribution and accompanying charge transfer. Photoemission confirms the energies of the 3 topmost molecular orbitals with an almost "half-filled" lowest unoccupied molecular orbital (LUMO). The four criteria are used to qualify the adsorption mechanism in the pentacene/Cu(110) system as chemisorption. This set of criteria is indicative of chemisorption also in the case of other noncovalently coupled large adsorbates, far beyond the pentacene/Cu(110) case.

A detailed understanding of the organic molecule/substrate interface is of crucial importance for the design of organic semiconducting devices, as the interface determines the contact resistance and the charge injection. Generally, two different adsorption situations are considered: physisorption and chemisorption. For small molecular adsorbates like CO or N 2 , the adsorption energy alone can be used as a criterion to classify the adsorption in chemisorption (adsorption energies larger than 1 eV) and physisorption (few tens of meV). This classification fails for complex π-conjugated organic molecules. Here we discuss on the basis of a pentacene/Cu(110) model system a different set of criteria to distinguish between chemisorption and physisorption beyond the total bond energy argument. We analyze the bonding situation on the basis of density functional theory (DFT) calculations and photoelectron spectroscopy. Theory predicts (i) a significant bending of the molecule after adsorption, (ii) a buckling of the top layer Cu atoms, (iii) the emergence of new hybrid states, and (iv) a substantial charge redistribution and accompanying charge transfer. Photoemission confirms the energies of the 3 topmost molecular orbitals with an almost "half-filled" lowest unoccupied molecular orbital (LUMO). The four criteria are used to qualify the adsorption mechanism in the pentacene/Cu(110) system as chemisorption. This set of criteria is indicative of chemisorption also in the case of other noncovalently coupled large adsorbates, far beyond the pentacene/Cu(110) case.

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DFT calculations on sensor-drug interactions are necessary for understanding binding mechanisms, predicting sensor performance, evaluating stability and reactivity, and rational design of sensor materials. We scrutinized the adsorption of amphetamine (AFE) on the pure magnesium oxide nano-cage (MgONC) by applying density functional theory. All geometries and single point energy computations were optimized at M06-2X/6-311 G (d, p). Furthermore, we performed an analysis of the natural bond orbital (NBO) and evaluated the values of partial natural charges. Additionally, we investigated donor-acceptor (D-A) interactions and examined the Wiberg bond index (WBI) in greater depth. The MgONC was capable of adsorbing AFE with greater strength with the energy of adsorption (E ads) of − 48.19 kcal/mol (for stable configurations). Moreover, the NBO method demonstrated more effective D-A interactions between AFE and the MgONC. Based on the computations, for the most stable configuration, there was a substantial alteration in the HOMO-LUMO gap of the MgONC following the drug adsorption, thus increasing the electrical conductance (EC) of the MgONC. The sensing mechanism is related to the gap difference, which depends on the change in the EC. We adopted the conventional transition state theory for the prediction of recovery time. The computations indicated that the MgONC+ AFE configuration had a short recovery time for the desorption of AFE. Finally, based on our findings, we could conclude that the MgONC is an appropriate choice for the improvement of effective AFE sensors. DFT study of drug sensors will focus on enhancing sensitivity, selectivity, and stability while exploring novel materials and optimizing performance through theoretical simulations and analysis.

The critical conductivity regime of carbon nanotube strongly depends on the its chirality and symmetry after the adsorption of various gas molecules. a) Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) parameters, including isotropic and anisotropic chemical shielding parameters, were calculated to study the adsorption of N 2 , O 2 , CO, and CO 2 on pristine SWCNTs by DFT technique. b) Bond lengths, bond angles, tip diameters, dipole moments, energy levels, highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), band gaps, and electronic chemical potential (μ) for the lowest energy that is derived to estimate the structural stability of the composites, were also investigated for the sensitivity of the composites' electronic properties for application in gas sensors. c) It is more pronounced that molecule-induced modification of the density of states close to the Fermi level, charge transfer and gas-induced charge fluctuation might significantly affects the transport properties of nanotubes. d) The adsorption properties and NMR and NQR of zigzag (5, 0) and armchair (4, 4) SWCNTs with the optimal lengths of 7.1 Å and 8.6 Å, respectively, as a gas sensor and the optimized adsorption rates were calculated.

Molecular dynamics (MD) and Born-Oppenheimer MD simulations (BOMD) were employed to investigate adsorption of aqueous triethylene glycol (TEG) on a hydrated {1014} calcite surface at 298K. We analyzed the orientation of TEG adsorbed on calcite, as well as the impact of TEG on water density and adsorption free energy. Adsorption energies of TEG, free energy profiles for TEG, the details of hydrogen bonding between water and adsorbed TEG, as well as dihedral angle distribution of adsorbed TEG were estimated. We found that while the first layer of water was mostly unaffected by presence of adsorbed TEG, the density of the second water layer was decreased by 71% at 75% surface coverage of TEG. TEG primarily attached to the calcite surface via two adjacent adsorption sites. Hydrogen bonds between water and adsorbed TEG in the second layer almost exclusively involved the hydroxyl oxygen of TEG. The adsorption energy of TEG on calcite in a vacuum environment calculated by classical MD amou...

The adsorption of CO on a reduced 3.5%Ru/Al 2 O 3 catalyst has been studied by means of FTIR spectroscopy between 298 and 740 K at a constant partial pressure P a =1000 Pa. At 300 K, three adsorbed species were detected on the Ru particles: a linear CO species (strong IR band at 2047 cm −1), a bridged CO species (weak IR band at 1750 cm −1) and a gem-dicarbonyl species (weak IR bands at 2135 and 2080 cm −1). The FTIR spectra show how the coverage θ of the linear CO species evolves with the adsorption temperature T a. This cannot be achieved for the bridged CO species or for the gem-dicarbonyl species due to the weak intensities of their IR bands. At T a >600 K, the curve θ=f (T a) is in very good agreement with Temkin's adsorption model. Moreover, it is shown that, in the range 300-720 K, the curve agrees well with an adsorption model considering (a) an immobile adsorbed species; and (b) a linear decrease in the heat of adsorption with the increase in θ. This leads for the linear CO species to the heat of adsorption E θ , at various coverages θ: from E 0 =175 kJ mol −1 at θ=0 to E 1 =115 kJ mol −1 at θ =1. This procedure for the determination of the heat of adsorption of CO on Ru particles is simple (it requires a single isobar) and accurate (≈±5 kJ mol −1). It constitutes a well adapted tool to study the modifications of this parameter with the method of preparation of the catalyst (precursor, support, particle size).

Graphene has been proposed to be either fully transparent to van der Waals interactions to the extent of allowing to switch between hydrophobic and hydrophilic behaviour, or partially transparent (translucent), yet there has been considerable debate on this topic, which is still ongoing. In a combined experimental and theoretical study we investigate the effects of different metal substrates on the adsorption energy of atomic (argon) and molecular (carbon monoxide) adsorbates on high-quality epitaxial graphene. We demonstrate that while the adsorption energy is certainly affected by the chemical composition of the supporting substrate and by the corrugation of the carbon lattice, the van der Waals interactions between adsorbates and the metal surfaces are partially screened by graphene. Our results indicate that the concept of graphene translucency, already introduced in the case of water droplets, is found to hold more generally also in the case of single polar molecules and atoms, which are apolar.

Here we demonstrate a ternary Cu2NiZn alloy substrate for controllably synthesizing monolayer graphene using a liquid carbon precursor cyclohexane via a facile CVD route. In contrast with elemental metal or bimetal substrates, the alloy-induced synergistic effects that provide an ideal metallic platform for much easier dehydrogenation of hydrocarbon molecules, more reasonable strength of adsorption energy of carbon monomer on surface and lower formation energies of carbon chains, largely renders the success growth of monolayer graphene with higher electrical mobility and lower defects. The growth mechanism is systemically investigated by our DFT calculations. This study provides a selective route for realizing high-quality graphene monolayer via a scalable synthetic method by using economic liquid carbon supplies and multialloy metal substrates.

Carbon monoxide oxidation on the surface of in-situ prepared direct and inverse model Au/TiO2 catalyst have been studied in ultra-high vacuum condition by a set of surface science analytical techniques. It is found that a metal/oxide perimeter interface is an active area for CO to CO2 transformation. Measurements with isotopically labeled O2 reveal that carbon dioxide is formed over Au/titania via the participation of oxygen specie of titanium oxide. Efficiency of the process is higher for the system consisting of reduced titania (TiOx, x<2) compared to TiO2. Results offer a number of possibilities to improve the performance of real Au/TiO2 catalyst.

The deactivation of unconditioned Au/TiO 2 catalysts during CO oxidation at different reaction temperatures (30 and 80 • C) and in different reaction atmospheres was investigated. Kinetic and in situ IR spectroscopic measurements revealed a close correlation between the exponentially decreasing CO 2 formation rate and the CO ad coverage (decreasing) and carbonate coverage (increasing) during deactivation, whereas transmission electronic microscopy imaging revealed no significant changes in Au particle size. Consequences for the deactivation mechanism are discussed.

The adsorption of cytosine on Au(111) is investigated using density functional theory with the nonlocal van der Waals density functional. Test calculations performed on the benzene stacked dimer and on a benzene molecule adsorbed on Au(111) allow us to assess the methodology and reveal the accuracy and predictivity of the van der Waals density funcional relative to experimental outcome. Our results for cytosine on Au(111) indicate that the inclusion of dispersion interactions is crucial for the treatment of this system. In fact, such terms enhance the value of the adsorption energy and also affect the cytosine bonding geometry: in particular, we find that a tilted geometry is always favorable relative to a parallel geometry, which was not found in standard density functional theory investigations. The combined new data for energetics and geometry lead to conclusions that contrast the common opinion that the surface−molecule interaction is negligible in the process of monolayer formation.

Au/Ti0 2 catalysts are active for CO oxidation at room temperature and lower. To probe the surfaces of these catalysts, CO and 02 adsorption and coadsorption on model Au-Ti0 2 systems were examined under UHV conditions using TPD, ASE and XPS. No chemisorption ofmolecular 02 was detected, as previously reported for clean Au single-crystal surfaces. A low concentration of CO adsorption sites associated with Au was observed; however, no unique interfacial sites could be unambiguously identified on these surfaces.

Here we demonstrate a ternary Cu2NiZn alloy substrate for controllably synthesizing monolayer graphene using a liquid carbon precursor cyclohexane via a facile CVD route. In contrast with elemental metal or bimetal substrates, the alloy-induced synergistic effects that provide an ideal metallic platform for much easier dehydrogenation of hydrocarbon molecules, more reasonable strength of adsorption energy of carbon monomer on surface and lower formation energies of carbon chains, largely renders the success growth of monolayer graphene with higher electrical mobility and lower defects. The growth mechanism is systemically investigated by our DFT calculations. This study provides a selective route for realizing high-quality graphene monolayer via a scalable synthetic method by using economic liquid carbon supplies and multialloy metal substrates.

We present ab initio study using dispersion-corrected density functional theory calculations to investigate the hydrogen interaction with Ti-coated, one end closed, single-walled carbon nanotube (SWCNT). Our results demonstrate that a single Ti atom binds up to five hydrogen molecules on SWCNT cap top, whereas adsorption of four hydrogen molecules is energetically more favourable. The analyses from adsorption energy profile, highest occupied molecular orbital-lowest unoccupied molecular orbital gap and Mulliken charge distribution show contrast in first hydrogen molecule adsorption compared with the rest of four configurations. This is clearly due to the strongly different bonding nature of first hydrogen adsorption among others, between hydrogen molecules and Ti-coated SWCNT. These results not only support our understanding of adsorption nature of hydrogen in Ti-coated SWCNTs but also suggest new directions for smart storage techniques.

Full DFT-D2 calculations were carried out to study the interactions between single wall (10,10) boron nitride nanotubes (BNNTs) and different molecules, such as azomethine (C2H5N) and an anticancer agent (Pt(IV) complex) linked to an amino-derivative chain. The geometry of the (10,10) BNNT-azomethine and the BNNT-amino derivative system was optimised by considering different molecular configurations on the inner and outer surfaces of the nanotube. Simulation results showed that the most stable physisorption state for both molecules was located inside the nanotube in a parallel configuration. We showed also that the molecular chemisorption was possible only when the azomethine was present above two adjacent B and N atoms of a hexagon. The attachment of an azomethine plus a subsequent drug did not perturb the cycloaddition process. Moreover, all theoretical results showed that the therapeutic agent complex was not affected when it was attached onto BNNTs.

Using the density functional theory approach and pseudopotentials we studied energetics and electron structures of metal layers (Al, Cu, Ni, and Cr) deposited on a cristobalite surface. We have found that the properties of the first adsorbed layers decide by interaction of metal atoms with oxygen atoms of a substrate surface. Aluminum as an easily oxidized metal, is characterized by the high adhesion, it is followed by nickel and chromium, and copper closes the studied group of metals. Further plating is characterized by significant reduction of binding energy; the properties of films tend to properties of bulk metals.

Using the density functional theory approach and pseudopotentials we studied energetics and electron structures of metal layers (Al, Cu, Ni, and Cr) deposited on a cristobalite surface. We have found that the properties of the first adsorbed layers decide by interaction of metal atoms with oxygen atoms of a substrate surface. Aluminum as an easily oxidized metal, is characterized by the high adhesion, it is followed by nickel and chromium, and copper closes the studied group of metals. Further plating is characterized by significant reduction of binding energy; the properties of films tend to properties of bulk metals.

Using the density functional theory approach and pseudopotentials we studied energetics and electron structures of metal layers (Al, Cu, Ni, and Cr) deposited on a cristobalite surface. We have found that the properties of the first adsorbed layers decide by interaction of metal atoms with oxygen atoms of a substrate surface. Aluminum as an easily oxidized metal, is characterized by the high adhesion, it is followed by nickel and chromium, and copper closes the studied group of metals. Further plating is characterized by significant reduction of binding energy; the properties of films tend to properties of bulk metals.

Herein, the interaction of hydrogen sulfide with inside and outside single-wall carbon nanotube of (5,0) and (5,5) is investigated using density functional theory at B3LYP/6-31G* level of theory in the gaseous phase by Gaussian 09. The adsorption energies, thermodynamic properties, highest occupied molecular orbital, lowest unoccupied molecular orbital, energy gaps, and partial charges of the interacting atoms are also studied during two kinds of rotation of hydrogen sulfide (H 2 S) molecules as vertical and horizontal to the main axes of the nanotube. For these systems, the binding energy of H 2 S-single-wall carbon nanotubes is low and the process is thermodynamically near-simultaneous.

Full DFT-D2 calculations were carried out to study the interactions between single wall (10,10) boron nitride nanotubes (BNNTs) and different molecules, such as azomethine (C2H5N) and an anticancer agent (Pt(IV) complex) linked to an amino-derivative chain. The geometry of the (10,10) BNNT-azomethine and the BNNT-amino derivative system was optimised by considering different molecular configurations on the inner and outer surfaces of the nanotube. Simulation results showed that the most stable physisorption state for both molecules was located inside the nanotube in a parallel configuration. We showed also that the molecular chemisorption was possible only when the azomethine was present above two adjacent B and N atoms of a hexagon. The attachment of an azomethine plus a subsequent drug did not perturb the cycloaddition process. Moreover, all theoretical results showed that the therapeutic agent complex was not affected when it was attached onto BNNTs.

The adsorption of NO 2 , NH 3 , H 2 O, CO 2 and H 2 gases on the undoped, Zn-, Pd-and Os-doped armchair (5,5) single-walled carbon nanotubes (SWCNTs) were studied using density functional method. The adsorptions of these five gases on the Zn-, Pd-and Os-doped SWCNTs are obviously stronger than on the undoped SWCNT and their adsorption abilities are in the same order: NO 2 > NH 3 > H 2 O > CO 2 > H 2. Adsorption energies for all the studied gases on the undoped, Zn-, Pd-and Os-doped SWCNTs computed at the B3LYP/LanL2DZ level are reported.

In this article, the electronic and stability features of indium nitride (InN) nanotubes have been studied by density functional theory. The results show that the stability of nanotubes increases with increasing diameter. The band structure calculations indicate that the nanotubes have indirect gaps. Also, the band gap of InN nanotubes increases with increasing diameter and it can be modify by changing the diameter of nanotube. InN nanotubes have different applications due to small bandages and indirect gaps such as solar cells and lightemitting devices.

Geometrical structure, nuclear magnetic resonance (NMR) chemical shielding tensors, and chemical shifts of silicon and carbon nuclei are investigated for two finite size zigzag and armchair single-walled silicon carbide nanotubes (SiCNTs). Geometrical structures of SiCNTs, Si-C bonds and bond angles of Si and C vertices in both zigzag and armchair nanotubes, indicate that bond lengths are approximately constant in the armchair model but vary in the zigzag model. The NMR parameters of C nuclei change more in the zigzag model as compared to the armchair model in agreement with geometrical structure changes. The calculations were performed with B3LYP DFT method and 6-31G (d) standard basis sets using the Gaussian 03 package. Gaussian 03 package.

Aiming at model systems with close-to-realistic transport properties, we have prepared and studied planar Au/TiO 2 thin-film model catalysts consisting of a thin mesoporous TiO 2 film of 200-400 nm thickness with Au nanoparticles, with a mean particle size of 2 nm diameter, homogeneously distributed therein. The systems were prepared by spin-coating of a mesoporous TiO 2 film from solutions of ethanolic titanium tetraisopropoxide and Pluronic P123 on planar Si(100) substrates, calcination at 350 °C and subsequent Au loading by a deposition-precipitation procedure, followed by a final calcination step for catalyst activation. The structural and chemical properties of these model systems were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N 2 adsorption, inductively coupled plasma ionization spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The catalytic properties were evaluated through the oxidation of CO as a test reaction, and reactivities were measured directly above the film with a scanning mass spectrometer. We can demonstrate that the thin-film model catalysts closely resemble dispersed Au/TiO 2 supported catalysts in their characteristic structural and catalytic properties, and hence can be considered as suitable for catalytic model studies. The linear increase of the catalytic activity with film thickness indicates that transport limitations inside the Au/TiO 2 film catalyst are negligible, i.e., below the detection limit.

The ability of soluble surfactants to form liquid expanded (LE) phase is investigated. The experimental surface tension isotherms are divided into two well-defined types: cohesive (with LE phase) and non-cohesive (without LE phase). The effect of surfactant structure and the properties of the medium on the adsorption parameters of both adsorption types are analyzed. A model of the adsorption constant is proposed, which compares well to the experimental data.

Behavior of a single NH 3 molecule adsorbed on external surface of H-capped (5,5), (6,6), (5,0), and (8,0) single-walled carbon nanotubes (SWCNTs) is studied via DFT calculations. Binding energies clearly exhibit adsorption dependence on tube diameter. 13 C, 15 N and 1 H chemical shielding tensors are calculated at the B3LYP level using GIAO method. NMR calculations reveal that 13 C chemical shielding of (8,0) is more sensitive to NH 3 adsorption compared to (5,5), (6,6) and (5,0) tubes. 15 N and 1 H chemical shielding correlate noticeably with diameter of the nanotubes. 14 N and 2 H nuclear quadrupole coupling constants, C Q , and asymmetry parameter, Z, reveal the remarkable effect of NH 3 adsorption on electronic structure of the SWCNTs.

Rh/SiO 2 model catalyst surfaces are prepared under ultra-high vacuum conditions and examined in situ using scanning tunneling microscope and CO infrared reflection absorption techniques, to quantify the number and kinds of active Rh surface sites available for kinetic reaction (CO oxidation) as a function of Rh particle size. The results are compared against CO desorption measurements and elevated pressure CO oxidation reaction kinetics, to evaluate the extent of the correlation between the low and elevated pressure site characterization techniques. Data demonstrate that estimates of Rh active sites exhibit good agreement between the characterization methods and illustrate the utility of low pressure surface science characterization techniques in understanding elevated pressure reaction kinetics on model catalyst surfaces.

Au is usually viewed as an inert metal, but surprisingly it has been found that Au nanoparticles less than 3-5 nm in diameter are catalytically active for several chemical reactions. We discuss the origin of this effect, focusing on the way in which the chemical activity of Au may change with particle size. We find that the fraction of low-coordinated Au atoms scales approximately with the catalytic activity, suggesting that atoms on the corners and edges of Au nanoparticles are the active sites. This effect is explained using density functional calculations.

Elucidation of complex heterogeneous catalytic mechanisms at the molecular level is a challenging task due to the complex electronic structure and the topology of catalyst surfaces. Heterogeneous catalyst surfaces are often quite dynamic and readily undergo significant alterations under working conditions. Thus, monitoring the surface chemistry of heterogeneous catalysts under industrially relevant conditions such as elevated temperatures and pressures requires dedicated in situ spectroscopy methods. Due to their photons-in, photons-out nature, vibrational spectroscopic techniques offer a very powerful and a versatile experimental tool box, allowing real-time investigation of working catalyst surfaces at elevated pressures. Infrared reflection absorption spectroscopy (IRAS or IRRAS), polarization modulation-IRAS and sum frequency generation techniques reveal valuable surface chemical information at the molecular level, particularly when they are applied to atomically well-defined planar model catalyst surfaces such as single crystals or ultrathin films. In this review article, recent state of the art applications of in situ surface vibrational spectroscopy will be presented with a particular focus on elevated pressure adsorption of probe molecules (e.g. CO, NO, O 2 , H 2 , CH 3 OH) on monometallic and bimetallic transition metal surfaces (e.g. Pt, Pd, Rh, Ru, Au, Co, PdZn, AuPd, CuPt, etc.). Furthermore, case studies involving elevated pressure carbon monoxide oxidation, CO hydrogenation, Fischer-Tropsch, methanol decomposition/partial oxidation and methanol steam reforming reactions on single crystal platinum group metal surfaces will be provided. These examples will be exploited in order to demonstrate the capabilities, opportunities and the existing challenges associated with the in situ vibrational spectroscopic analysis of heterogeneous catalytic reactions on model catalyst surfaces at elevated pressures.

Density functional theory (DFT) calculations were performed to calculate nitrogen-14 and oxygen-17 Nuclear magnetic resonance (NMR) spectroscopy parameters in the representative considered models of zigzag and armchair single wall nanotubes (SWNTs) for the first time. The considered models consisting of 7.1 and 4.8nm length of H-capped (5,0) and (4,4) single-walled nanotube respectively, At first, the structural models were optimized and then the chemical-shielding (CS) tensors were computed in the optimized structures. Finally, the CS tensors were converted to isotropic chemical-shielding (ICS) and anisotropic chemical-shielding (ACS) parameters. The calculations were performed based on the B3LYP DFT method and 6-311G* standard basis set using the Gaussian 98 package of program.

Infrared reflection absorption spectroscopy (IRAS) has been used to study CO adsorption on Au clusters ranging in size from 1.8 to 3.1 nm, supported on TiO2. The adsorbed CO vibrational frequency blue-shifts slightly (approximately 4 cm -1 ) compared to that adsorbed on bulk Au, whereas the heats of adsorption (-∆Hads) increase sharply with decreasing cluster size, from 12.5 to 18.3 kcal/mol.

The correlation between structural and chemical properties of bimetallic PtRu/Ru(0001) model catalysts and their modification upon stepwise annealing of a submonolayer Pt-covered Ru(0001) surface up to the formation of an equilibrated
Pt_x Ru_{1-x} /Ru(0001) monolayer surface alloy was investigated by scanning tunneling microscopy and by the adsorption of CO and D_2 probe molecules. Both temperature-programmed desorption and IR measurements demonstrate the influence of the surface structure on the adsorption properties of the bimetallic surface, which can be explained by changes of the composition of the adsorption ensembles (ensemble effects)
for D adsorption and by changes in the electronic interaction
(ligand effects, strain effects) of the metallic constituents for
CO and D adsorption upon alloy formation.

The coadsorption of CO and hydrogen on a structurally well-defined Pt 35 Ru 65 /Ru monolayer surface alloy and, for comparison, on Ru(0001) were investigated by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). The data reveal distinct modifications in the hydrogen adsorption behavior and also in the CO adsorption properties compared to adsorption of the individual components both on the monometallic and on the bimetallic surface. These modifications are discussed on an atomic scale, in a picture that involves adsorbate -adsorbate interactions and site-specific variations in the (local) adsorption properties of the bimetallic surface, due to electronic ligand and strain effects and geometric ensemble effects.

In this study sensing capability of single walled carbon nanotubes (SWCNTs), of both zigzag (5, 0) and armchair (4, 4) models were investigated for adsorption of O 2 and N 2 molecules were investigated using density functional theory (DFT) method. Using this computational method, it is possible to obtain much more data to apply in medical science and industrial technologies. Geometrical optimization have carried out using standard set and B3LYP/6-311G* basis set of Gaussian 98 program. Those parts of SWCNT which have demonstrated more contribution in adsorption energy, ΔE ads (eV) were studied and compared. Electronic configurations were discussed and the results were interpreted.

Behavior of a single NH 3 molecule adsorbed on external surface of H-capped (5,5), (6,6), (5,0), and (8,0) single-walled carbon nanotubes (SWCNTs) is studied via DFT calculations. Binding energies clearly exhibit adsorption dependence on tube diameter. 13 C, 15 N and 1 H chemical shielding tensors are calculated at the B3LYP level using GIAO method. NMR calculations reveal that 13 C chemical shielding of (8,0) is more sensitive to NH 3 adsorption compared to (5,5), (6,6) and (5,0) tubes. 15 N and 1 H chemical shielding correlate noticeably with diameter of the nanotubes. 14 N and 2 H nuclear quadrupole coupling constants, C Q , and asymmetry parameter, Z, reveal the remarkable effect of NH 3 adsorption on electronic structure of the SWCNTs.

Theoretical study of NH 3 (H 2 O) n=0,1,2,3 adsorption on (8, 0) carbon nanotube was performed at the X3LYP/ 6-31G Ã level of density functional theory (DFT). The tube-NH 3 interaction was discussed in the terms of binding energy (E B ), coupling energy (E C ), charge density, molecular orbitals, and dipole moments. The results reveal that addition of water molecules to tube-NH 3 system increases the interaction between tube and ammonia molecule.

Behavior of a single NH 3 molecule adsorbed on external surface of H-capped (5,5), (6,6), (5,0), and (8,0) single-walled carbon nanotubes (SWCNTs) is studied via DFT calculations. Binding energies clearly exhibit adsorption dependence on tube diameter. 13C, 15N and 1H chemical shielding tensors are calculated at the B3LYP level using GIAO method. NMR calculations reveal that 13C chemical shielding of (8,0) is more sensitive to NH 3 adsorption compared to (5,5), (6,6) and (5,0) tubes. 15N and 1H chemical shielding correlate noticeably with diameter of the nanotubes. 14N and 2H nuclear quadrupole coupling constants, C Q, and asymmetry parameter, η, reveal the remarkable effect of NH 3 adsorption on electronic structure of the SWCNTs.

The adsorption of CO on planar Au/TiO2 model catalysts was studied by polarization-modulation infrared reflection–absorption spectroscopy (PM-IRAS) under catalytically relevant pressure (10–50 mbar) and temperature (30–120?°C) conditions, both in pure CO and in CO/O2 reaction gas mixtures. The adsorption energy of CO on the Au particles was determined by a quantitative analysis of the temperature dependence of the CO absorption intensity in adsorption isobars. The data reveal considerable effects of the Au particle size when pure CO is used; the initial adsorption energy decreases from 74 kJ/mol (2 nm mean Au particle diameter) to 62 kJ/mol (4 nm). For CO/O2 gas mixtures, the initial CO adsorption energy is, irrespective of the Au particle size, constant at 63 kJ/mol (i.e., the CO adsorption energy is reduced for smaller Au particles), but this effect vanishes for larger Au particles.

Au/TiO2/Ru(0 0 0 1) model catalysts and their interaction with CO were investigated by scanning tunneling microscopy and different surface spectroscopies. Thin titanium oxide films were prepared by Ti deposition on Ru(0 0 0 1) in an O2 atmosphere and subsequent annealing in O2. By optimizing the conditions for deposition and post-treatment, smooth films were obtained either as fully oxidized TiO2 or as partly reduced TiOx, depending on the preparation conditions. CO adsorbed molecularly on both oxidized and reduced TiO2, with slightly stronger bonding on the reduced films. Model catalyst surfaces were prepared by depositing submonolayer quantities of Au on the films and characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy. From X-ray photoelectron spectroscopy, a weak interaction between the Au and the TiO2 substrate was found. At 100 K CO adsorption occurred on both the TiO2 film and on the Au nanoparticles. CO desorbed from the Au particles with activation energies between 53 and 65 kJ/mol, depending on the Au coverage. If the Au deposit was annealed to 770 K prior to CO exposure, the CO adsorption energy decreased significantly. STM measurements revealed that the Au particles grow upon annealing, but are not encapsulated by TiOx suboxides. The higher CO adsorption energy observed for smaller Au coverages and before annealing is attributed to a significantly stronger interaction of CO with mono- and bilayer Au islands, while for higher particles, the adsorption energy becomes more bulk-like. The implications of these effects on the known particle size effects in CO oxidation over supported Au/TiO2 catalysts are discussed.

The coadsorption of CO and hydrogen on a structurally well-defined Pt35Ru65/Ru(0001) monolayer surface alloy and, for comparison, on Ru(0001) were investigated by temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). The data reveal distinct modifications in the hydrogen adsorption behavior and also in the CO adsorption properties compared to adsorption of the individual components both on the mono-metallic and on the bimetallic surface. These modifications are discussed on an atomic scale, in a picture that involves adsorbate–adsorbate interactions and site-specific variations in the (local) adsorption properties of the bimetallic surface, due to electronic ligand and strain effects and geometric ensemble effects.

Different types of planar Au/TiO2 model catalysts are produced on TiO2(110) single-crystal substrates and thin TiO2 films on Ru(0001) by physical vapor deposition of gold under ultrahigh-vacuum (UHV) conditions or by micelle-based chemical routes. Both the Au nanoparticles and the support are characterized by surface-science-based methods (such as atomic force microscopy and X-ray photoelectron spectroscopy) as well as by transmission electron microscopy. Finally, the activity of the model catalysts in the CO oxidation reaction is analyzed in a microflow reactor. Au/TiO2(110) model catalysts with a stoichiometric TiO2(110) support exhibit only a low catalytic activity compared to those with a reduced crystal and Au/TiO2 model catalysts with thin TiO2 films on Ru(0001) as a substrate. The possible influence of Ti interstitials in the reduced TiO2(110) substrates on the CO oxidation activity is discussed.

The results of an IR study on the interaction of CO/O2 gas mixtures with planar Au/TiO2 model catalysts at elevated pressures and at room temperature are presented. The model catalysts were prepared by deposition of a flat titania film on a Ru(0 0 0 1) substrate and subsequent evaporation of gold on the titania film. In the presence of the gas mixtures, an IR band in the CO stretching region was formed, pointing to linearly adsorbed CO. The position of this band is nearly independent of the Au coverage employed. Compared to pure CO, the IR band is shifted to higher wave numbers when CO/O2 gas mixtures are used. Although the production of CO2 was detected in the CO oxidation reaction on the model catalysts, the formation of other IR bands, revealing the build-up of carbonates or other side-products which is usually observed for Au/TiO2 real powder catalysts, was very weak.

The interaction of CO with structurally well-defined, planar Au/TiO2 model catalysts at elevated pressures (up to 50 mbar) was studied in-situ by polarization-modulated infrared reflection absorption spectroscopy and ex-situ by X-ray photoelectron spectroscopy performed before and after CO exposure. The results indicate a CO-induced partial reduction of the oxide surface, which is evidenced by a low frequency C–O vibration at 2060 cm-1, combined with a spreading of the Au nanoparticles due to a modification of the Au-oxide interface energy. In a 2:1 CO:O2 atmosphere, TiO2 support reduction was not observed, and a pre-reduced surface was re-oxidized. The consequences of these results for the understanding of the CO oxidation mechanism on Au/TiO2 (model) catalysts are discussed.