Adsorption of carbon oxide and nitrogen oxide molecules on the surface of the Ni/MgO(111) system

The coadsorption of carbon oxide (CO) and nitrogen oxide (NO) molecules on the surface of nickel nanoclusters formed on a thin magnesium oxide MgO(111) film grown on the Mo(110) face in an ultrahigh vacuum is studied by reflective infrared spectroscopy and thermodesorption spectroscopy (TDS). The adsorption of NO molecules is found to substantially change the state of the initially adsorbed CO molecules. The TDS and IR spectra suggest that the adsorption of NO molecules stimulates the surface migration of CO molecules from the surface of metallic clusters to the cluster-oxide interface, which is accompanied by a decrease in the angle of inclination of the molecular axis to the surface.     

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.     

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.     

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.     

Adsorption and valence electronic states of nitric oxide on metal surfaces

Among fundamental diatomic molecules, the adsorption of carbon monoxide (CO) and nitric oxide (NO) on metal surfaces has been a subject of intensive research in the surface science community, partly owing to its relevance to heterogeneous catalysis used for environmental control. Compared to the rather well-defined adsorption mechanism of CO, that of NO is less understood because the adsorption results in much more complex reactions. The complexity is ascribed to the open-shell structure of valence electrons, making the molecule readily interact with the metal surface itself as well as with co-adsorbed molecules. Furthermore, the interaction crucially depends on the local structure of the surface. Therefore, to elucidate the interaction at the molecular scale, it is essential to study the valence state as well as the bonding geometry for individual NO molecules placed in a well-defined environment on the surface. Scanning tunneling microscopy (STM) is suitable for this purpose. In this review, we summarize the knowledge about the interaction of NO with metal surfaces, mainly focused on the valence electronic states, followed by recent studies using STM and atomic force microscopy (AFM) at the level of individual molecules.     

A transient study of the co-adsorption and reaction of CO and oxygen on Ir(110)

The heterogeneously catalyzed reaction of CO and O₂ to form CO₂ over Ir(110) has been studied through measurements of the transient kinetics of the various elementary reactions that may limit the steady state rate. Rate expressions for these elementary reactions — the desorption of CO, the oxidation of CO via the Langmuir-Hinshelwood mechanism, the adsorption of CO and the adsorption of oxygen — were developed using thermal desorption mass spectrometry. Several phenomena were observed: (1) the activation energies for CO desorption and CO oxidation depend markedly upon the composition of the adlayer; (2) diffusion in the adlayer may limit the rates of CO desorption and CO oxidation; (3) the formation of a surface oxide modifies these four rate processes; and (4) chemisorbed CO blocks sites for oxygen adsorption, but chemisorbed oxygen does not block sites for CO adsorption.     

TiO2表面氧空位对NO分子吸附的作用

采用程序升温热脱附(TPD)实验方法测定了NO在TiO2表面吸附后的脱附谱，利用分子轨道理论研究了TiO2吸附NO的原子簇模型及吸附前后的原子簇能级变化．结果表明，NO在TiO2表面吸附后可在两个峰值温度450和980K脱附出N2．TiO2表面经预覆氧处理后，N2的脱附量降低．吸附时NO中的O能够占据TiO2表面氧空位并与N脱离，而N原子则相互结合成为N2脱附．分子轨道理论计算证明在TiO2(110)表面能够存在氧空位并具备吸附NO的结构条件．     

LEED and thermal desorption studies of small molecules (H2, O2, CO,CO2, NO,C2H4, C2H2 and C) chemisorbed on the stepped rhodium (755) and (331) surfaces

The chemisorption of H₂, O₂, CO, CO₂, NO, C₂H₂, C₂H₄ and C has been studied on the clean stepped Rh(755) and (331) surfaces. Low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) were used to determine the size and orientation of the unit cells, desorption temperatures and decomposition characteristics for each adsorbate. All of the molecules studied readily chemisorbed on both stepped surfaces and several ordered surface structures were observed. The LEED patterns seen on the (755) surface were due to the formation of surface structures on the (111) terraces, while on the (331) surface the step periodicity played an important role in the determination of the unit cells of the observed structures. When heated in O₂ or C₂H₄ the (331) surface was more stable than the (755) surface which readily formed (111) and (100) facets. In the CO and CO₂ TDS spectra a peak due to dissociated CO was observed on both surfaces. NO adsorption was dissociative at low exposures and associative at high exposures. C₂H₄ and C₂H₂ had similar adsorption and desorption properties and it is likely that the same adsorbed species was formed by both molecules.     

原位漫反射FTIR研究Fe改性的Cu-Mn/ZrO_2催化剂上CO的吸附行为

利用原位漫反射傅里叶变换红外光谱(FTIR)技术,研究了Fe改性的Cu-Mn/ZrO_2催化剂的CO吸附行为。通过测定单组元及其不同组合催化剂的CO吸附以及催化剂的CO-TPD-IR特征、不同温度CO吸附的红外光谱,研究了Fe助剂对催化剂上CO吸附行为的影响,发现Fe通过提高铜的分散度,改变铜的化学环境,影响催化剂上CO线式吸附的特征,而且形成CO桥式吸附中心,从而提供了低碳醇合成的催化剂表面,并探讨了催化剂上CO吸附形式变化的规律。     

原位漫反射FTIR研究Fe改性的Cu-Mn/ZrO2催化剂上CO的吸附行为

利用原位漫反射傅里叶变换红外光谱(FTIR)技术，研究了Fe改性的Cu—Mn／ZrO2催化剂的CO吸附行为。通过测定单组元及其不同组合催化剂的CO吸附以及催化剂的CO-TPD-IR特征、不同温度CO吸附的红外光谱，研究了Fe助剂对催化剂上CO吸附行为的影响，发现Fe通过提高铜的分散度，改变铜的化学环境，影响催化剂上CO线式吸附的特征，而且形成CO桥式吸附中心，从而提供了低碳醇合成的催化剂表面，并探讨了催化剂上CO吸附形式变化的规律。     

Leed and thermal desorption studies of small molecules (H2, O2, CO,CO2, NO,C2H4, C2H2 AND C) chemisorbed on the rhodium (111) and (100) surfaces

The chemisorption of H₂, O₂, CO, CO₂, NO, C₂H₄, C₂H₂ and C has been studied on the clean Rh(111) and (100) surfaces. LEED, AES and thermal desorption were used to determine the surface structures, disordering and desorption temperatures, displacement and decomposition characteristics for each species. All of the molecules studied readily chemisorbed on both surfaces. A large variety of ordered structures was observed, especially on the (111) surface. The disordering temperatures of most ordered surface structures on the (111) surface were below 100°C. It was necessary to adsorb the gases at 25° C or below in order to obtain well-ordered surface structures. Chemisorbed oxygen was readily removed from the surface by H₂ or CO gas at crystal temperatures above 50°C. CO₂ appears to dissociate to CO upon adsorption on both rhodium surfaces as indicated by the identical ordering and desorption characteristics of these two molecules. C₂H₄ and C₂H₂ also had very similar ordering and desorption characteristics and it is likely that the adsorbed species formed by both molecules is the same. Decomposition of ethylene produced a sequence of ordered carbon surface structures on the (111) face as a result of a bulk-surface carbon equilibrium. The chemisorption properties of rhodium appear to be generally similar to those of iridium, nickel and palladium.     

ITO负载单原子钇吸附NO和CO的第一性原理研究

基于密度泛函理论,对氧化铟锡(Indium Tin Oxide,ITO)表面负载单原子Y模型的表面性能进行了第一性原理计算.根据表面能计算结果可知,单原子Y最稳定负载位置为空位(H),即确定了ITO负载单原子钇(Single-atom Y supported on ITO,Y/ITO)稳定模型.对ITO和Y/ITO表面吸附气体分子(NO和CO)模型的吸附性能进行了第一性原理计算.根据对比ITO和Y/ITO表面的吸附能和态密度计算结果可知,单原子钇负载提高了ITO表面的稳定性和吸附性能.根据对比Y/ITO表面吸附NO和CO气体分子的吸附能和态密度计算结果可知,NO和CO气体分子吸附均为自发行为,过程放热.且NO气体分子更容易吸附在Y/ITO表面,即Y/ITO对NO气体分子更敏感.     

Investigation of the role of oxygen in NO reduction by C2H4 on the surface of stepped Pt(3 3 2)

The influence of pre-dosed oxygen on NO–C₂H₄ interactions on the surface of stepped Pt(3 3 2) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of oxygen significantly suppresses the adsorption of NO on the steps of Pt(3 3 2), leading to a very specific adsorption state for NO molecules when oxygen–NO co-adlayers are annealed to 350 K (assigned as atop NO on step edges). An oxygen-exchange reaction also takes place between these two kinds of adsorbed molecules, but there appears to be no other chemical reaction, which can result in the formation of higher-valence NOx.

C₂H₄ molecules which are post-dosed at 250 K to adlayers consisting of ¹⁸O and NO do not have strong interactions with either the NO or the ¹⁸O atoms. In particular, interactions which may result in the formation of new surface species that are intermediates for N₂ production appear to be absent. However, C₂H₄ is oxidized to C¹⁸O₂ by ¹⁸O atoms at higher annealing temperature. This reaction scavenges surface ¹⁸O atoms quickly, and the adsorption of NO molecules on step sites is therefore quickly restored. As a consequence, NO dissociation on steps proceeds very effectively, giving rise to N₂ desorption which closely resembles that following only NO exposure on a clean Pt(3 3 2), both in peak intensity and desorption temperature. It is concluded that the presence of ¹⁸O₂ in the selective catalytic reduction (SCR) of NO with C₂H₄ on the surface of Pt(3 3 2) does not play a role of activating reactants.     

NO adsorption and thermal behavior on Pd surfaces. A detailed comparative study

The adsorption and thermal behavior of NO on ‘flat’ Pd(111) and ‘stepped’ Pd(112) surfaces has been investigated by temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and electron stimulated desorption ion angular distribution (ESDIAD) techniques. NO is shown to molecularly adsorb on both Pd(111) and Pd(112) in the temperature range 100–373 K. NO thermally desorbs predominantly molecularly from Pd(111) near 500 K with an activation energy and pre-exponential factor of desorption which strongly depend on the initial NO surface coverage. In contrast, NO decomposes substantially on Pd(112) upon heating, with relatively large amounts of N₂ and N₂O desorbing near 500 K, in addition to NO. The fractional amount of NO dissociation on Pd(112) during heating is observed to be a strong function of the initial NO surface coverage. HREELS results indicate that the thermal dissociation of NO on both Pd(111) and Pd(112) occurs upon annealing to 490 K, forming surface-bound O on both surfaces. Evidence for the formation of sub-surface O via NO thermal dissociation is found only on Pd(112), and is verified by dissociative O₂ adsorption experiments. Both surface-bound O and sub-surface O dissolve into the Pd bulk upon annealing of both surfaces to 550 K. HREELS and ESDIAD data consistently indicate that NO preferentially adsorbs on the (111) terrace sites of Pd(112) at low coverages, filling the (001) step sites only at high coverage. This result was verified for adsorption temperatures in the range 100–373 K. In addition, the thermal dissociation of NO on Pd(112) is most prevalent at low coverages, where only terrace sites are occupied by NO. Thus, by direct comparison to NO/Pd(111), this study shows that the presence of steps on the Pd(112) surface enhances the thermal dissociation of NO, but that adsorption at the step sites is not the criterion for this decomposition.     

Effect of the electronic structure of a substrate on the photoinduced behavior of adsorbed NO and CO molecules

Photoprocesses in systems produced by adsorption of NO and CO molecules on the Pt(111) and Ni(111) surfaces, as well as on the (111) surface of Pt-Ge alloy, is studied by the IR absorption spectroscopy, resonant multiphoton ionization, and UV photoelectron spectroscopy methods. The energy of photons varies between 2.3 and 6.4 eV. The character of the processes depends on the type of the metallic substrate. On the Pt(111) surface, NO molecules dissociate or are desorbed, depending on the degree of coverage. On the Ni(111) surface, the molecules only dissociate. Conversely, NO molecules adsorbed on the (111) surface of the Pt-Ge alloy are only desorbed from the surface. In the CO/Pt(111) and CO/Pt(111)-Ge systems, CO molecules adsorbed on on-top adsorption sites are desorbed under the action of the photons, while those occupying bridging adsorption sites change their properties insignificantly. A model of photoinduced processes is suggested. According to this model, the lifetime of a state excited by charge transfer between the valence band of the metal and the 2π-antibonding molecular orbital plays a decisive part in the occurrence of one or the other of these processes.     

Surface structure effects in the reactions of nitric oxide with hydrogen and carbon monoxide on rhodium: A comparison with the surface structure effects observed for the hydrogen-oxygen and carbon monoxide-oxygen reactions

Using field electron microscopy (FEM) and thermal desorption and reaction spectroscopy (TDS) the behaviour of various Rh single crystal surfaces towards reactions involving NO has been studied. If, after NO adsorption up to saturation at 77 K, the temperature is slowly raised the FEM results suggest that dissociation of NO starts at the (321), (331) and (533) surfaces. The reaction of NO_ads with hydrogen starts also at these surfaces (at about 360 K) suggesting that NO bond scission initiates the reaction. After initiation a surface explosion is observed. Depending on the heating rate either a clean surface or a N_ads covered surface is obtained after completion of the reaction. Apparently, the reduction of adsorbed N_ads by hydrogen can occur at a significant rate at this temperature. At a higher heating rate the formed N adatoms do not react with hydrogen and are readily desorbed as N₂ at 600 K. The reaction of NO_ads with CO starts again on the (321) and (331) surfaces. The rate of the reaction with CO is, however, much lower than that with hydrogen. For the reaction of CO_ads with NO, desorption of CO is the initiation step. The mechanisms of the reactions and the dependence of the reaction on the surface structure are discussed in relation to literature data.     

The adsorption of CO on clean and potassium promoted FeO surfaces

The adsorption of CO on a FeO (wustite) surface was investigated using UPS, AES and temperature programmed desorption. These results are compared to those obtained from the same sample following addition of potassium from the decomposition of KOH. CO adsorption was identified following exposure at 300 K to the potassium free surface. The adsorbed species readily desorbs below 500 K. CO adsorption was poisoned by pre-exposure to oxygen at 300 K. This suggests CO is adsorbed at surface oxygen vacancies. CO induced UPS emission features are different from those typically found for CO chemisorbed on transition metal surfaces. The presence of potassium alters the adsorption behavior of CO. The thermal desorption maximum shifts to 625 K. UPS results indicate molecular CO adsorption at 300 K and upon heating to 470 K CO dissociates. The presence of potassium thus promotes CO dissociation on FeO.     

Nickel carbonyl adsorption on the Ni(111) surface

Overlayers formed by the adsorption of Ni(CO)₄ in CO on the Ni(111) surface at 100 K were characterized using high resolution electron energy loss spectroscopy and thermal desorption spectroscopy. At temperatures below 135 K, molecular nickel carbonyl adsorbs on the CO saturated Ni(111) surface as suggested by several observations. Vibrational transitions characteristic of molecular Ni(CO)₄ are dominant. The energy dependence of both the elastic and inelastic electron scattering cross sections are dramatically altered by Ni(CO)₄ adsorption. All of the mass spectrometer ionization fragments typical of molecular Ni(CO)₄ are observed in the narrow thermal desorption peak at 150 K. The inelastic scattering cross sections for both adsorbed nickel carbonyl and adsorbed CO on the Ni(111) surface suggest that a nonresonant dipole scattering mechanism is dominant.     

Adsorption, reaction and desorption of hydrogen on modified Pd(1 1 1) surfaces

The interaction of hydrogen (deuterium) with different modified Pd(1 1 1) surfaces has been investigated. The focus was put on the energy and angel dependence of the desorbing molecules from oxygen covered, potassium covered and vanadium oxide covered surfaces. Conventional adsorption/desorption as well as permeation/desorption experiments were performed. For the oxygen covered surface optimum reaction rates for water production and the energy distribution of the reaction products were determined, both for the reaction of oxygen with molecular hydrogen as well as with atomic hydrogen. Potassium on the surface enhances the activation barrier for hydrogen adsorption resulting in a hyper-thermal desorption flux and a forward focused angular distribution of desorption. Permeation/desorption of deuterium from ultra-thin vanadium oxide films yield mainly thermalized desorbing molecules or slightly hyper-thermal, depending on the oxidation state of the surface oxide.     

Computational study of CO and NO adsorption on magnesium oxide nanotubes

The adsorption of CO and NO molecules on the MgO nanotubes was investigated using density functional theory calculations. The adsorption energies of CO and NO were estimated to ranging from −0.35 to −0.16 eV and −0.28 to −0.13 eV, respectively. The most stable adsorption configurations are those in which the C or N atoms the adsorbates are close to the Mg atom of the tube surface. It was found that the MgO nanotubes selectively act against the CO and NO gaseous molecules. Their electrical conductivity are sensitive to NO gaseous molecule while is not to CO one, indicating that they may be potential sensors for NO molecule. These findings are characterized by analyzing the features in the electron density of states.