Adsorption of hydrogen and carbon monoxide on nickel

Ion induced desorption was used to examine the emission of secondary ion clusters during coadsorption of H₂ and CO on nickel. In addition to the expected CO bearing species, a significant NiOH⁺ signal was observed. It is suggested that the source of this cluster ion may be interaction of the parent adsorbed H₂ and CO. Evidence was also found for emission of a negative species of mass 26, presumably C₂H^?₂.     

Coadsorption of carbon monoxide and hydrogen on polycrystalline rhodium

The coadsorption of carbon monoxide and hydrogen on polycrystalline rhodium filament has been studied by thermal desorption mass spectrometry. From a series of thermal desorption spectra of CO and H₂ from rhodium as a function of the exposure time to the gas mixture of CO and H₂, it is indicated that there are a single broad peak for CO and three peaks designated as β₁, β₂, β₃ for hydrogen. Thermal desorption of hydrogen is complex. CO and β₁-hydrogen coadsorb on the rhodium surface with their partial pressures in the initial stage of the exposure to the gas mixture and then the β₁ -hydrogen adsorbed on the surface is replaced by CO with the further exposure time. The kinetics for the replacement of β₁-hydrogen by CO may be discussed from the standpoint of the L-H reaction process. The β₂-and β₃-hydrogen are observed with a longer exposure time after the elimination of β₁ -hydrogen. It may be suggested that the β₃-hydrogen peak is attributed to the desorption of hydrogen absorbed in the bulk. The nature of β₂ -hydrogen is also briefly mentioned in possible implications.     

Adsorption-desorption kinetics of carbon monoxide on rhodium polycrystalline surfaces

Adsorption isotherms, the absolute adsorption rate, and the absolute desorption rate of carbon monoxide on rhodium polycrystalline surfaces were measured in the same manner as in our previous work on palladium. The absolute adsorption rate was proportional to pressure, independent of temperature and was a slightly non-linear function of the coverage of CO. The absolute desorption rate was proportional to the coverage and was an increasing function of temperature and pressure. These results are similar to those of palladium.     

Dissociation of carbon monoxide on stepped nickel surfaces

Field emission microscopy with photometric measurements has been applied to investigate the adsorption of carbon monoxide on various crystal planes of a nickel field emitter. Upon heating the CO-covered surface, the work function drastically decreased during desorption of CO molecules into the gas phase and exhibited almost the value of the clean surface at 450 K. However, part of the CO molecules adsorbed on the stepped planes such as (510) and (310) were found to dissociate upon heating at 450–470 K, which was accompanied by an increase of the work function of ～0.2 eV.     

Adsorption of hydrogen and carbon monoxide on platinum

TDS spectra and ESD ion energy distributions have been measured for coadsorption of H₂ and CO on recrystallized platinum. Sample exposure to a 90% H₂?10% CO gas mixture results in appearance of structurein both TDS spectra of H₂ and CO. Coadsorption also results in an O⁺ ion energy distribution which is much narrower compared to the distribution resulting from pure CO adsorption. These results are interpreted as evidence for the formation of an HCO surface complex.     

Infrared spectra of carbon monoxide on evaporated nickel films: A low temperature thermal detection technique

A novel thermal detection scheme has been developed and combined with the techniques of rapid scan Fourier transform infrared spectroscopy to make sensitive, high resolution measurements of the vibrational spectrum of carbon monoxide molecules on evaporated nickel films. Adsorbed molecules are detected by attaching a germanium resistance thermometer to the sample, cooling the assembly to liquid helium temperatures, and measuring the temperature changes which occur when infrared radiation is absorbed. Spectra are presented for a range of CO coverages on an evaporated nickel film and a film damaged by ion bombardment. The positions, shapes, and intensities of the spectral lines from linear and bridge bonded CO molecules give information about the surface structure of the metal films and about the different ordered phases of the adsorbed molecules.     

Adsorption of carbon monoxide on tungsten (210)

Thermal desorption spectra taken after adsorption of carbon monoxide at room temperature on W(210) show sequential formation with increasing coverage of strongly bound β₂ and β₁ binding states, correlated to the sequential formation of P(2 × 1) and (1 × 1) adsorbate structures as observed by LEED. Adsorption at room temperature gives a poorly ordered arrangement of adsorbed CO molecules, but well-ordered structures are produced by subsequent anneal. For adsorption without anneal the work function increases monotonically with coverage to a maximum of Δφ = + 0.70 eV at saturation coverage of 1 monolayer. For adsorption followed by anneal the work function dependence upon coverage is less simple, with even a decrease of work function at coverages less than a quarter monolayer. LEED intensity-voltage measurements from P(2 × 1)CO and P(2 × 1)N structures suggest that CO molecules occupy the sites of 4-fold symmetry upon which nitrogen is believed to be adsorbed. The distinction between the β₂ and β₁ states of adsorbed CO is attributed to heterogeneity induced by the reduction in binding energy of a CO molecule when its nearest-neighbor sites are occupied.     

Adsorption of carbon monoxide on silver/palladium alloys

The adsorption of carbon monoxide on epitaxial (100) and (111) planes of Ag/Pd alloys with definite surface compositions has been studied by means of LEED, Auger electron spectroscopy and work function measurements. The formation of ordered adsorbed structures is prevented by even small amounts of silver in the surfaces. The maximum variation of the work function with CO adsorption bears no simple relationship to the surface composition. From measured adsorption isotherms the isosteric heats of adsorption have been evaluated. For CO adsorption on pure Pd planes the adsorption energies E_ad are either constant or decrease slowly up to high coverages, whereas a continuous decrease was observed with the alloys indicating the energetical heterogeneity. The results are discussed on the basis of our knowledge about the nature of the CO chemisorption and about the electronic structure of Ag/Pd alloys.     

Bulk-to-surface precipitation and surface diffusion of carbon on polycrystalline nickel

The time evolution of the KLL Auger spectrum of carbon as a function of temperature is used to derive the kinetics of the surface diffusion and bulk-to-surface precipitation of carbon on polycrystalline nickel. The results show that the activation energy for the surface diffusion of carbon atoms on polycrystalline nickel is 6.9 ± 0.6 $\text{kcal}\text{mole}$, and the activation energy for bulk-to-surface precipitation is 9.4 ± 0.6 $\text{kcal}\text{mole}$. The dependence on the surface diffusion coefficient D_s (cm²s^?1), on the absolute temperature T can be represented, over the experimental temperature range, 350–425° C, by: $\text{ln}\text{D}{}_{\mathrm{s}}\text{= 10.27 ?}\text{3568}\text{T}$.     

Bistability of the reaction rate in the oxidation of carbon monoxide by nitrogen monoxide on polycrystalline platinum

Multiplicity of the stationary reaction rate of CO oxidation by NO is observed under reducing conditions at pressures below 4×10^?4 mbar in the temperature range 500<T<525 K. The two branches of the reaction rate coalesce at a point where sustained oscillations are observed.     

Decomposition of carbon monoxide on a (110) nickel surface

New investigations of the (110) nickel/carbon monoxide system have been made using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), mass spectroscopy and work function measurements. Room temperature adsorption of CO on the surface was reversible with the CO easily removable by heating in vacuum to 450°K. The CO formed a double-spaced structure on the surface which, however, was unstable at room temperature for CO pressures less than 1×10^?7 torr. Work function changes greater than + 1.3 eV accompany this reversible CO adsorption. Irreversible processes leading to the build-up of carbon, and under certain circumstances oxygen, on the surface were the primary concern of the measurements reported here. These processes could be stimulated by the electron beams used in LEED and AES, or by heating the clean surface in CO. The results of AES investigations of this carbon (and oxygen) build-up, together with CO desorption results could be explained on the basis of two surface reactions. The primary reaction was the dissociation of chemisorbed CO leaving carbon and oxygen atomically dispersed on the surface. The second reaction was the reduction of the surface oxygen by CO from the gas phase. The significance of the dissociation reaction to COdesorption studies is discussed.     

Adsorption of oxygen molecules and carbon monoxide molecules on tin dioxide

The effect of oxygen and carbon oxide on the SnO₂ surface conductivity is considered in the framework of the early model of gas adsorption on semiconductor oxides. A change in the work function of the adsorption system is calculated.     

Adsorption of carbon monoxide on the molybdenum (100) surface

The interaction of CO with Mo(100) has been studied by means of thermal desorption spectrometry, work function measurements and electron stimulated desorption, in conjunction with LEED and AES. Results have been obtained for adsorption at room temperature and at temperatures down to 200 K. The study confirms previous results, showing that the β-states formed at room temperature are atomic. The thermal desorption data for the β-states are analyzed to give directly the desorption activation energy as a function of coverage. This energy is found to vary smoothly from an initial value of 3.7 to a final value of 2.9 eV molecule, indicating an average repulsive interaction between a pair of adjacent adatoms of 0.2 eV. The data at low temperature indicate that a molecular state, virgin-CO, is produced in competition with β-CO and probably one other state, from a common precursor. The step leading to virgin-CO has both a low activation energy and a low pre-exponential factor, suggesting that a reorientation of the molecule is required.     

The oxidation of carbon monoxide on polycrystalline rhodium under knudsen conditions: II. Reaction with nitrogen monoxide

The reaction between carbon monoxide and nitrogen monoxide on a polycrystalline rhodium ribbon under stationary conditions is followed by mass spectrometry. In the temperature range 300 to 1100 K the ratio of the partial pressures of the reactants varies between 0.1 < p_NO/p_CO < 100 at values of the total pressure in the reactor from 10^?4 to 10^?5 Torr. The results can be interpreted qualitatively by a simple elementary reaction sequence. Simulation using literature values of the kinetic constants leads to semi-quantitative agreement with experimental results. No isothermal oscillations of the reaction rate could be observed under the stated conditions.     

The rate of formation of nickel carbonyl from carbon monoxide and nickel single crystals

We have measured the rate of Ni(CO)_i formation at a total pressure of 1 atm on Ni(100), (110) and (111) single crystals cleaned by argon ion bombardment and UHV annealing. The (111) surface reacts significantly faster than the other two surfaces. The partial pressure dependence of the reaction and the effect of impurities are also discussed.     

Carbon monoxide dissociation on polycrystalline cobalt

The dissociation reaction of carbon monoxide was studied on a polycrystalline cobalt foil between room temperature and 470 K, at pressures below 10^-5 Torr. Dissociation kinetics were monitored mainly by the variation of the work function, while the surface composition was studied with AES, UPS and TDS. Kinetics of oxygen uptake at 300 and 470 K were also obtained in order to ascertain the state of surface oxygen. The dissociation of CO on polycrystalline material is well detectable above 350 K and leads to a surface covered by both carbon and oxygen atoms in a 1:1 atomic ratio, each atomic species reaching about half the coverage corresponding to saturation of the chemisorption when adsorbed separately. Adsorbed oxygen atoms do not react with CO in the range of temperatures and pressures investigated. The rate of the dissociation process is determined by the coverage of CO molecules adsorbed in equilibrium with the gas and by the availability of active sites for the dissociation of adsorbed CO molecules, which are mobile on the surface. Values of the rate constant of the dissociation process were obtained for different temperatures and pressures, from which an activation energy of 17±2 kcal/mol was derived.     

Effect of grain boundary on electrical properties of polycrystalline lanthanum nickel oxide thin films

In the present work, lanthanum nickel oxide (LNO) thin films were prepared by the sol-gel method. Microstructures of the films were tailored by changing sol concentration so as to investigate the effect of grain boundary on the transport properties of electrons in the polycrystalline LNO films. Based on the temperature dependence of the resistivity and the magnetic field dependence of the magnetoresistance (MR) at various temperatures, the factors that dominate the transport behavior in the polycrystalline LNO films were explored in terms of weak localization and strong localization. The results show that the grain boundary has a significant influence on the transport behavior of the electrons in LNO films at a low-temperature region, which can be captured by a variable-range hopping (VRH) model. The increase of metal–insulator (M–I) transition temperature is ascribed to Anderson localization in grain boundary. At a high-temperature region, electron–electron scattering and electron–phonon scattering predominates in the films. In this case, the existence of more grain boundary shows a minor effect on the transport behavior of the electrons but elevates the residual resistivity of the films.     

An investigation of the high-frequency form of carbon monoxide chemisorbed on nickel oxide

Semi-empirical calculations have been carried out with the aim of achieving a better understanding of the CO-NiO interaction which results in an absorption band at a frequency higher than that of gaseous CO. It was concluded that the adsorbed form responsible for this band bonds through the carbon to a nickel ion of the oxide. Rearrangements of both σ and π electronic charge occur which strengthen the C-O bond and increase its vibration frequency (as measured by the C-O overlap population). Charge transfer takes place between the CO and the nickel ion, σ charge shifting to the ion and π charge to the CO. In the cases of Ni (II) and Ni (III), the σ shift considerably outweighs the π, resulting in net transfers of approximately 0.3 electrons from the CO to the Ni (II) and 0.6 electrons from the CO to the Ni(III).