Adsorption behavior and reaction properties of NO and CO on Rh(1 1 1)

Reactions between NO and CO on Rh(1 1 1) surfaces were investigated using infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption. NO adsorbed on the fcc, atop, and hcp sites in that order, whereas CO adsorbed initially on the atop sites and then on the hollow (fcc + hcp) sites. The results of experiments with NO exposure on CO-preadsorbed Rh(1 1 1) surfaces indicated that the adsorption of NO on the hcp sites was inhibited by preadsorption of CO on the atop sites, and NO adsorption on the atop and fcc sites was inhibited by CO preadsorbed on each type of site, which indicates that NO and CO competitively adsorbed on Rh(1 1 1). From a Rh(1 1 1) surface with coadsorbed NO and CO, N₂ was produced from the dissociation of fcc-NO, and CO₂ was formed by the reaction of adsorbed CO with atomic oxygen from dissociated fcc-NO. The CO₂ production increased remarkably in the presence of hollow-CO. Coverage of fcc-NO and hollow-CO on Rh(1 1 1) depended on the composition ratio of the NO/CO gas mixture, and a gas mixture with NO/CO ? 1/2 was required for the co-existence of fcc-NO and hollow-CO at 273 K.     

IR spectral shifts and adsorption potentials of CO and N2 adsorbed on LiF and LiCl

Following our recent work on IR spectra of molecules adsorbed on C₆₀ embedded in LiF and LiCl films, adsorption potentials of CO and N₂ adsorbed on LiF (100) and LiCl (100) were calculated. For CO on LiF, a value of 2.0 kcal mol⁻¹ was obtained, close to that calculated for CO adsorbed on a single C₆₀ molecule. The calculated value for CO on LiCl is much higher, 6.8 kcal mol⁻¹. It is therefore concluded that in the case of CO adsorbed on mixed LiF/C₆₀ films, the adsorbed CO molecules are distributed almost evenly on the LiF and C₆₀ single molecules, whereas in the case of CO adsorbed on mixed LiCl/C₆₀ films the salt is greatly preferred as the adsorption site. Adsorption potential calculations for a similar system, N₂ on LiF and LiCl, gave values of 1.5 and 4.4 kcal mol⁻¹, respectively. In this case, a much too large value was found for the adsorption potential on the LiCl surface. IR spectra of CO on the two substrates showed two strong absorptions for each of them. With N₂ induced spectra were obtained. Spectral shifts have been calculated for the above systems and were all toward higher frequencies, in agreement with experimental findings.     

Coadsorption of NO and other small gases (H2 and CO) on polycrystalline rhodium surface

The coadsorption of NO and other small gases (H₂ and CO) on a polycrystalline Rh filament has been studied by thermal desorption mass spectroscopy, using ¹⁵NO. The sample was exposed to a mixture of nitric oxide and other gases with various concentrations of ¹⁵NO at room temperature. It is indicated that NO, CO and H₂ coadsorbs on the rhodium surface, and NO desorbs as N₂ and O₂. NO is adsorbed mainly in the dissociation at lower coverage and molecular adsorption becomes dominant at higher coverage. But the amount of desorbed O₂ was very small. The chemisorption of CO is affected by the chemisorbed NO. Thermal desorption of hydrogen is detected when the value of P_15NO/P_CO is very small. The hydrogen adsorbed on the rhodium surface is replaced by NO with a longer exposure time.     

Formation of nanostructured carbon films in gas-discharge plasmas

Deposition of carbon materials from methane-hydrogen gas mixtures in a DC gas discharge is investigated. Parameters ensuring stable discharge conditions and synthesis of diamond and graphite-like films are determined. Optical emission spectroscopy is used to analyze the composition of the activated gas phase in the course of carbon film deposition. Synthesis of graphite-like carbon nanotubes and nanocrystallites is shown to correlate with the presence of C₂ dimers in the plasma. A noncatalytic mechanism of synthesis of nanostructured graphite in a carbon-containing gas phase is proposed.     

Adsorption of CO, CO2 and NO molecules on a BaTiO3 (0 0 1) surface

Since the development of Scanning Tunnelling Microscopy (STM) technique, considerable attention has been devoted to various molecules adsorbed on various surfaces. Also, a new concept emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale are thus particularly invaluable. The present work describes the first Density Functional Theory (DFT) study of adsorption of CO, CO₂ and NO molecules on a BaTiO₃ surface following a first preliminary calculation of O and O₂ adsorption on the same surface. In the previously considered work, we found that a (0 0 1) surface with BaO termination is more stable than the one with TiO₂-termination. Consequently, we extended our study to CO, CO₂ and NO molecules adsorbed on a (0 0 1) surface with BaO termination. The present calculation was performed on a (1 × 1) cell with one monolayer of adsorbed molecules. Especially, a series of cases implying CO molecules adsorbed in various geometrical configurations has been examined. The corresponding adsorption energy varies in the range of −0.17 to −0.10 eV. The adsorption energy of a CO₂ molecule directly located above an O surface atom (called O_s) is of the order of −0.18 eV. The O-C distance length is then 1.24 Å and the O-C-O and O-C-O_s angles are 134.0° and 113.0°, respectively. For NO adsorption, the most important induced structural changes are the followings: (i) the N-O bond is broken when a NO molecule is absorbed on a Ba-O_s bridge site. In that case, N and O atoms are located above an O and a Ba surface atom, respectively, whereas the O-Ba-O_s and N-O_s-Ba angles are 106.5° and 63.0°, respectively. The N-O distance is as large as 2.58 Å and the adsorption energy is as much as −2.28 eV. (ii) In the second stable position, the NO molecule has its N atom adsorbed above an O_s atom, the N-O axis being tilted toward the Ba atom. The N-O_s-Ba angle is then 41.1° while the adsorption energy is only −0.10 eV. At last, the local densities of states around C, O as well as N atoms of the considered adsorbed molecules have also been discussed.     

AES and LEED studies of xenon adsorption on (100)NaCl

The thermal and electro impact behaviour of NO adsorbed on Pt(111) and Pt(110) have been studied by LEED, Auger spectroscopy, and thermal desorption. NO was found to adsorb non-dissociatively and with very similar low coverage adsorption enthalpies on the two surfaces at 300 K. In both cases, heating the adlayer resulted in partial dissociation and led to the appearance of N₂ and O₂ in the desorption spectra. The (111) surface was found to be significantly more active in inducing the thermal dissociation of NO, and on this surface the molecule was also rapidly desorbed and dissociated under electron impact. Cross sections for these processes were obtained, together with the desorption cross section for atomically bound N formed by dissociation of adsorbed NO. Electron impact effects were found to be much less important on the (110) surface. The results are considered in relation to those already obtained by Ertl et al. for NO adsorption on Ni(111) and Pd(111), and in particular, the unusual desorption kinetics of N₂ production are considered explicitly. Where appropriate, comparisons are made with the behaviour of CO on Pt(111) and Pt(110), and the adsorption kinetics of NO on the (110) surface have been examined.     

Theoretical studies of CO and NO on CuO and Cu2O(110) surfaces

The characteristics of CO and NO adsorption on surfaces of CuO(110) and Cu₂O(110) have been studied by using the self-consistent-charge discrete variational X_a method (SCC-DV-X_a). The calculated results show that the CO and NO molecules are perpendicularly adsorbed on cuprous ions of Cu₂O and cupric ions of CuO, respectively and with oxygen pointing upward in both cases. The order of chemisorption energy of the four adsorbed systems is: CuO-NO > Cu₂O-CO > Cu₂O-NO > CuO-CO. In all chemisorptions discussed d orbitals of Cu do play an important role.     

Au/TiO2/Ru(0 0 0 1) model catalysts and their interaction with CO

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 TiO_x, 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 TiO_x 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.     

Nitric oxide reduction by CO ON Rh(111): Temperature programmed reaction

The reaction of NO with CO on Rh(111) has been studied with temperature programmed reaction (TPR). Comparisons are made with the reaction of O₂ with CO and the reaction of NO with H₂. The rate-determining step for both CO oxidation reactions is CO(a) + O(a) → CO₂(g). Repulsive interactions between adsorbed CO and adsorbed nitrogen atoms lead to desorption of CO in a peak at 415 K which is in the temperature range where the reaction between CO(a) and O(a) produces CO₂(g). Thus the extent of reaction of CO(a) with NO(a) is less than that between CO(a) and O(a) due to the lower coverage of CO caused by adsorbed N atoms and NO. A similar repulsive interaction between NO(a) and H(a) suppresses the NO + H₂ reaction. CO + NO reaction behavior on Rh(111) is compared to that observed on Pt(111).     

Effect of adsorbed oxygen on the properties of ytterbium nanofilms

The effect of O₂ molecules adsorbed on the surface of ytterbium nanofilms on the properties of the volume and surface of these films has been studied. It has been shown that the dependence of the work function of the films on the concentration of O₂ adsorbed molecules exhibits a nonmonotonic behavior: originally, the work function decreases, to start increasing again on passing through a minimum. At high oxygen doses, this increase stops. Adsorption of oxygen brings about a fundamental rearrangement of the Auger spectra of ytterbium; indeed, the Auger peaks observed before oxygen adsorption disappear completely after its deposition on the surface, to become replaced by other ones. The results obtained qualitatively agree with similar observations amassed by the present authors in studies of adsorption of CO molecules on the surface of ytterbium films. These results should be ascribed to a manifestation of complex processes of electron exchange between these films and adsorbed O₂ molecules. These processes end up in a qualitative rearrangement of the electronic structure of the part of film volume that borders the surface, where ytterbium transforms into the d metal.     

Molecular simulation of adsorption of NO and CO2 mixtures by a Cu-BTC metal organic framework

Environmental problems due to the discharge of gases, including NO and CO₂, in addition, diseases caused by improper concentration of NO and CO₂ in vivo must be resolved. In this study, Grand canonical Monte Carlo (GCMC) simulations are combined with density functional theory (DFT) to calculate the adsorption of NO and CO₂ from a dual-component mixture to the Cu-BTC metal organic framework. The results show that the adsorption isotherms for various molar ratios of the gaseous mixture followed a Langmuir distribution. At higher pressures more CO₂ than NO was adsorbed by Cu-BTC, with NO showing a tendency to desorb. However, better results for adsorption of NO were observed at lower pressures. For the different pressure and molar ratios of the gaseous mixture examined, more CO₂ than NO was always adsorbed. Compared with three-way catalysts, Cu-BTC offers benefits to adsorption of CO₂ and NO from gaseous mixtures without increased durability problems.     

The temperature dependence of the interaction of NO + CO on Pt{1 0 0}

Infrared reflection absorption spectroscopy together with mass spectrometry has been used to investigate the interaction of NO and CO on Pt{1 0 0}, initially prepared in the reconstructed ‘hex’ phase, under ambient pressures of these gases, in the temperature range 300-500 K. The results allow the local and total coverages of adsorbed CO and NO to be related to the rate of reaction to produce gas phase CO₂, and provide insight into the species present on the surface during the so-called low temperature oscillatory reaction regime of this process. At temperatures below that at which NO dissociation occurs (approximately 390-400 K) adsorption is controlled by the non-reactive displacement of NO by CO and results in a CO-poisoned surface. Above 400 K when significant CO₂ production occurs, the NO coverage increases to produce a surface with NO and CO fully intermixed; the increase in NO coverage is attributed to the higher rate of NO arrival from the gas phase (with a partial pressure ratio of P_NO:P_CO>1) at free surface sites created by NO dissociation and subsequent reaction with CO. The competition between these two processes of non-reactive NO displacement by CO and reactive displacement of CO by NO is proposed to determine the parameter space of the low temperature oscillatory regime. Rapid equilibration between bridged and atop CO species leads to them appearing to exhibit identical reaction behaviour. Particularly at the lowest reaction temperatures (around 400 K), islands of pure CO may coexist on the surface but not participate in the reaction. Under conditions corresponding to the high temperature oscillatory regime, small quantities of absorbed CO, but no NO, are seen on the surface.     

Adsorption properties of CO on low-index Pt3Sn surfaces

The adsorption properties of CO on Pt₃Sn were investigated by utilizing quantum mechanical calculations. The (1 1 1), (1 1 0) and (0 0 1) surfaces of Pt₃Sn were generated with all possible bulk terminations, and on these terminations all types of active sites were determined. The adsorption energies and the geometries of the CO molecule at those sites were found. Those results were compared with the results obtained from the adsorption of CO on similar sites of Pt(1 1 1), Pt(1 1 0) and Pt(0 0 1) surfaces. The comparison reveals that adsorption of CO is stronger on Pt surfaces; this may be the reason why catalysts with Pt₃Sn phase do not suffer from CO posioning in experimental works. Aiming to understand the interactions between CO and the metal adsorption sites in detail, the local density of states (LDOS) profiles were produced for atop-Pt adsorption, both for the carbon end of CO for its adsorbed and free states, and for the Pt atom of the binding site. LDOS profiles of C of free and adsorbed CO and Pt for corresponding pure Pt surfaces, Pt(1 1 1), Pt(1 1 0) and Pt(0 0 1) were also obtained. The comparison of the LDOS profiles of Pt atoms of atop adsorption sites on the same faces of bare Pt₃Sn and Pt surfaces showed the effect of alloying with Sn on the electronic properties of Pt atoms. Comparison of LDOS profiles of the C end of CO in its free and atop adsorbed states on Pt₃Sn and LDOS of Pt on bare and CO adsorbed Pt₃Sn surface were used to clear out the electronic changes occurred on CO and Pt upon adsorption. The study showed that (i) inclusion of a Sn atom at the adsorption site structure causes dramatic decrease in stability which limits the number of possible CO adsorption sites on Pt₃Sn surface, (ii) the presence of Sn causes angles different from 180° for M-C-O orientation, (iii) the presence of Sn in the neighborhood of Pt on which CO is adsorbed causes superposition of the 5σ/1π derived-state peaks at the carbon end of CO and changes in adsorption energy of CO, (iv) Sn present beneath the adsorption site strengthens the CO adsorption, whereas neighboring Sn on the surface weakens it for all Pt₃Sn surfaces tested and (v) the most stable site for CO adsorption is the atop-Pt site of the mixed atom termination of Pt₃Sn(1 1 0).     

Interactions between NO and CO on Pt(111)

Temperature programmed desorption (TPD) of coadsorbed NO and CO on Pt(111) shows that no reaction occurs (less than 2%) up to the desorption temperature of NO. At 100 K, adsorption is competitive, but neither gas displaces the other from the surface. Coadsorbed CO causes the NO desorption temperature to be lowered by as much as 100 K, but NO does not affect the CO desorption temperature. TPD spectra for NO depend on which gas is adsorbed first, indicating that equilibrium between species is not established on the surface during desorption. Electron energy loss spectra show that the vibrational spectrum of each gas is only weakly affected by the other. When NO is adsorbed first, CO does not affect the ratio of bridged and terminal NO but lowers the frequencies of the bridged NO by approximately 50 cm^?1 and lowers the intensities of vibrational peaks of both species by a factor of about four. When CO is adsorbed first, the ratio of terminal to bridged NO increases for given coverage of NO, and the frequency of the bridged NO remains at the pure NO value. These results are explained in terms of CO island formation, repulsive interactions between NO and CO, and low adsorbate mobilities.     

Sensing charged macromolecules with nanocrystalline diamond-based field-effect capacitive sensors

The possibility of a label-free electrical detection of layer-by-layer adsorbed polyelectrolyte (PE) multilayers using a field-effect capacitive electrolyte-diamond-insulator-semiconductor (EDIS) structure is investigated. Positively charged synthetic polyelectrolyte PAH (Poly (allylamine hydrochloride)) and negatively charged PSS (Poly (sodium 4-styrene sulfonate)) have been used as a model system. Nanocrystalline diamond films were grown on p-Si-SiO₂ substrates by a microwave plasma-enhanced chemical vapor deposition from a mixture of methane and hydrogen. The EDIS sensors functionalized with charged macromolecules have been characterized by means of capacitance-voltage and constant-capacitance methods. Alternating shifts in the capacitance-voltage and constant-capacitance curves have been observed after the adsorption of each polyanion and polycation layer, respectively. The effect of the number of the adsorbed PE layers and polarity of the outermost layer on the sensor response is discussed.     

Adsorption of NO and CO on a Ru(1010) surface

A combination of modern surface measurement techniques such as LEED, AES and Thermal Desorption Spectroscopy were used to study the chemisorptive behavior of NO and CO on a $\text{(10}\text{1}\text{0)Ru}$ surface. The experimental evidence strongly favors a model in which NO adsorbs and rapidly dissociates into separate nitrogen and oxygen adsorbed phases, each exhibiting ordered structures: the C(2 × 4) and (2 × 1) structures at one-half and full saturation coveilage, respectively. At temperatures as low as 200°C, the nitrogen phase begins to desorb, and continuous exposure to NO in this temperature range results in an increasing oxygen coverage until the surface is saturated with oxygen and no further NO dissociation can take place. The nitrogen desorption spectrum depends strongly on coverage and exhibits several peaks which are related to structure of the adsorbed phase. There is evidence that once the surface is saturated with the dissociated NO phase further NO adsorption occurs in a molecular state. Carbon monoxide adsorbs in a molecular state and does not exhibit an ordered structure. The implications of the results with respect to the catalytic reduction of NO by H₂ and CO and the N₂ selectivity of Ru catalysts are discussed.     

Interaction of Nitrogen Oxide and Carbon Molecules Adsorbed on Ni Clusters Formed on the MgO(111) Thin Film Surface

The joint adsorption of CO and NO molecules on the surface of nanodimensional nickel clusters formed on the Mo(110) face of a thin MgO(111) magnesium oxide film under conditions of ultrahigh vacuum is investigated by methods of infrared reflection and thermal desorption spectroscopy. It is revealed that the adsorption of the NO molecules changes significantly the state of the adsorbed CO molecules. Based on an analysis of thermal desorption and IR spectra, a conclusion can be drawn that the adsorption of the NO molecules stimulates the migration of the CO molecules from the metal cluster surface to the boundary between the cluster and oxide accompanied by a decrease in the tilt angle of the molecular axis to the surface. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 85–89, May, 2005.     

原位红外光谱法研究大气颗粒物表面非均相反应

大气污染物之间可能发生协同作用,造成严重的二次污染,产生次生环境问题.本实验通过原位红外光谱分析方法研究气态污染物和碳颗粒物之间的吸附过程,发现大气中CO2和NO极易在颗粒物表面发生吸附;CO2在颗粒物表面达到吸附平衡时间很短,NO的吸附平衡时间较长;CO2和SO2会影响NO在颗粒物表面的吸附,CO2在颗粒物表面的吸附几乎不受NO和SO2的影响.     

Site-specific core level spectroscopy of CO and NO adsorption on Pt(110)(1×2) and (1×1) surfaces

The adsorption of CO and NO on the (1×2) and (1×1) modifications of the Pt(110) surface was studied by x-ray photoemission spectroscopy, LEED and work-function change measurements. The O(1s) binding energy of adsorbed CO is site-specific and differentiates between on-top and bridge adsorbed species. CO adsorption on Pt(110)(1×2) at 120 K occurred sequentially into on-top and bridge sites yielding an orderedc(8×4) layer at the maximum coverage. At 300 K only on-top bonded CO was present after CO adsorption on the (1×2) surface. CO adsorption on the (1×1) surface at 120 K showed a transient bridge adsorbed CO and on-top CO at saturation, with an ordered (2×1)p1g1 LEED pattern. Heating the (2×1)p1g1 CO layer to 400 K also showed this transient bridge CO species. Work function changes generally correlated with the appearance of different CO species but were complex in detail. The findings for CO adsorption are consistent with the missing row model of the (1×2) surface.Parallel data for NO adsorption on (1×2) and (1×1) surfaces at 120 K were less informative than those for CO because O(1s) spectra showed single broad peaks. Peak contributions due to bridge and on-top bonded NO could be estimated.     

Characterisation of the Ru/MgF2 catalyst with adsorbed O2, NO, CO probe molecules by EPR and IR spectroscopy

Electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy were used to study the formation of ruthenium and adsorbed species appearing on the catalyst during O₂, NO, and CO adsorption at room temperature on 1 wt% Ru/MgF₂ catalysts prepared from Ru₃(CO)₁₂ . Both EPR and IR results provided clear evidence for the interaction between surface ruthenium and probe molecules. No EPR signals due to ruthenium (Ru) species were recorded at 300 and 77 K after H₂-reduction of the catalyst at 673 K. However, at 4.2 K a very weak EPR spectrum due to low-spin (4d⁵) Ru³⁺ complexes was detected. A weak anisotropic O₂^- radicals signal with g_∣∣=2.017 and g_⊥=2.003 superimposed on a broad (ΔB_pp=120 mT), slightly asymmetric line at g=2.45(1) was identified after O₂ admission to the reduced sample. Adsorption of NO gives only a broad, Gaussian-shaped EPR line at g=2.43(1) indicating that the admission of NO, similarly to O₂ adsorption, brings about an oxidation of Ru species in the course of the NO decomposition reaction. Introduction of NO over the CO preadsorbed catalyst leads to EPR spectrum with parameters g_⊥=1.996, g_∣∣=1.895, and A_⊥^N=2.9 mT assigned to surface NO species associated with Ru ions. The IR spectra recorded after adsorption of NO or CO probe molecules showed the bands in the range of frequency characteristic of ruthenium nitrosyl, nitro, and nitrate/nitrite species and the bands characteristic of ruthenium mono-and multicarbonyls, respectively. Addition of CO after NO admission to the catalyst leads to appearance in the IR spectrum, beside the ones characteristic of NO adsorption, the bands which can be attributed to Ru-CO₂ and Ru-NCO species, indicating that the reaction between NO and CO occurs. These species were also detected after CO adsorption followed by NO adsorption, additionally to the band at 1850 cm⁻¹ being due to cis-type species.