Coadsorption Of O2 Research Articles

FTIR Study of Carbon Monoxide Oxidation and Scrambling at Room Temperature over Copper Supported on ZnO and TiO2. 1

An FTIR and quadrupole mass spectroscopic study of CO adsorption and oxidation with 16O2 and 18O2 on copper supported on ZnO and TiO2 is presented. The experimental results indicate that CO is adsorbed on the metallic particles dispersed on both oxides on two kinds of sites, on the normal terrace sites and on sites at the borderline of the particles. Moreover, on titania, a band at 2126 cm-1, assigned to CO adsorbed on isolated Cu atoms and/or on two-dimensional small clusters, is detected. A frequency shift of the bands of CO adsorbed on the metallic particles observed in the CO−O2 coadsorption experiments and the occurrence of a scrambling reaction between CO and 18O2 reveal that on all these samples, there are metallic sites which are able to adsorb at the same time oxygen atoms and carbon monoxide. Carbon dioxide and carbonate-like species are formed: the asymmetric stretching frequencies of CO2 and the quadrupole mass spectroscopic analysis reveal that with 18O2, different isotopic molecular CO2's a...

Photoemission and HREELS study of K adsorption on TiO2(100)

The adsorption of K and coadsorption of O2 on TiO2(100) have been studied using photoemission and high resolution electron energy-loss spectroscopy (HREELS). We compare our results with those of earlier studies of potassium oxides. The energy separations of peaks appearing in photoemission spectra indicate the formation of a peroxide or superoxide at the surface following adsorption of > 1 monolayer of potassium. HREELS results are consistent with this conclusion.

Catalytic oxidation of CO on Pt(335): A study of the active site

The catalytic reaction CO(a)+O(a)→CO2(g) has been studied on Pt(335) using infrared reflection absorption spectroscopy (IRAS) and temperature programmed reaction (TPR) methods. Both dissociative O2 adsorption and CO adsorption occur preferentially on the step sites. It has been found that chemisorbed CO on the (111) terrace sites is more reactive than chemisorbed CO on the (100) step sites. In contrast, chemisorbed O on the step sites is more reactive at high CO coverages than chemisorbed O on the terrace sites. The results indicate that at high CO coverages the most reactive geometry involves step site O[O(S)] interacting with terrace sites CO [CO(T)]. This new information provides a conceptual basis for understanding the interplay between geometrical and energetic factors influencing the CO oxidation reaction.

Calorimetric Investigations of Processes at the Solid/Gas Interphase

AbstractAdsorption calorimetry, partially combined with thermal desorption spectroscopy and isotope exchange measurements, has been used to study the adsorption and coadsorption of gases on metal films under ultrahigh vacuum conditions. It has proved to be possible to get detailed information on both the primary adsorption step and the consecutive reaction in the adsorbed layer. Adsorption of CO and CO2 on Fe are treated as examples with subsequent decomposition reactions. In the case of the coadsorption of CO and O2 and of H2 and CO on Fe the mutual interaction of the gases including replacement processes are studied.

Co-adsorption of CO and O2on Fe

A combination of calorimetric measurement of heat of adsorption and of thermal desorption spectroscopy (TDS) is used to study the adsorption of CO and O2 as well as co-adsorption of both gases on Fe films. There is a strong influence of the sequence of admission of the gases on their adsorption behaviour. Oxygen is able to block adsorption sites of CO as well as to replace CO from the surface. Generally, TDS is not able to give information on the situation at the adsorption temperature, neither in the case of CO adsorption, nor in the case of co-adsorption of CO and O2. The use of labelled oxygen (18O2) improves the value of TDS experiments in such systems.

Coadsorption of CO and O2 on Fe(111): III. Thermal desorption spectroscopy, comparison with adsorption on Fe films and heats of adsorption

TDS was used to study the influence of oxygen on the adsorption of CO on Fe(111). There is clear evidence the oxygen blocks adsorption sites for CO and hinders the decomposition of CO. This statement is confirmed by very similar adsorption studies on Fe films in which TDS was combined with calorimetric determination of heats of adsorption. The decomposition of CO mainly occurs during the heating at TDS.

Coadsorption of Cu and O2 on a Ru(0001) surface

The adsorption behavior of oxygen on Cu submonolayer, monolayer and multilayer films epitaxially grown on a Ru(0001) substrate is studied by AES, LEED, TDS and Δφ-measurements. In the presence of coadsorbed oxygen and below 500 K the Cu films preserve a layered structure. In the case of θCu < 1 ML the interaction is dominated by the free Ru(0001) sites. Annealing of the Cu film after adsorption of oxygen destabilizes the Cu structure and Cu clusters are formed; the O atoms are then distributed among the free Ru areas and the Cu clusters. Up to ∼ 6 ML the adsorption of oxygen is influenced by the presence of the underlying Ru(0001) substrate, possibly in two ways: (a) by direct mutual influence between both metals and (b) by the presence of relatively high oxygen concentration within the thin Cu films (Ru acts at this temperature as diffusion barrier for oxygen). The adsorption is accompanied by diffusion into the Cu overlayer as evidenced by a comparison of AES and TDS data for θCu≥6 ML.

Coadsorption of CO and O2 on Fe(111)

Coadsorption of CO and O2 on Fe(111)

Coadsorption of CO and O2 on Fe(111): I. Photoelectron spectroscopy and changes in work function

UPS and changes in work function are used to study adsorption of CO and O2 as well as coadsorption of both gases on Fe(111) in the temperature range between 77 and 350 K. Oxygen influences the polarization of CO at 77 K and partially blocks the sites on which CO can decompose at temperatures above 300 K. At 273 K O2 can replace adsorbed CO.

Electronic structure and photon stimulated desorption of ions from V3Si

We present results of synchrotron radiation studies of photon stimulated desorption (PSD) from the (100) surface of V3Si. Kinetic energy distributions and photon energy dependence are presented for positive ions desorbed as a result of exposures of V3Si surface to H2, O2, C2H4, as well as for co-adsorption of O2 plus H2 and O2 plus C2H4, respectively. Desorption of ions and several simple chemical reactions are associated with excitation of V3p core level.

Comparison of oxygen and sulphur adsorption on the (0001) surface of zirconium

Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) have been used to compare the adsorption and coadsorption of O2 and H2S on the (0001) surface of zirconium where exposures are in the one to five Langmuir regime. The new observations made are as follows: (i) that sulphur forms a stable (3 × 3) surface structure after heating to 600° C; (ii) that the Zr(0001) surface with high O coverage adsorbs H2S, whereas the surface with high S coverage does not adsorb oxygen in detectable amounts; and (iii) that for surfaces with adsorbed H2S a sudden increase in the 150 eV to 92 eV Auger peak ratio occurs on heating to 530° C.

The interaction of CO, NO, and O2 with sodium-promoted Rh(100) surfaces

The promotor effect of Na on the dissociative adsorption of CO, NO, and O2 at 300 K on Rh(100) has been studied by work function measurements and photoemission spectroscopy using synchrotron radiation in the photon energy range hν=15–35 eV. Preadsorption of Na lowers the work function up to −4.2 eV. Below a critical Na concentration, the work function increases again by ∼0.9 eV by coadsorption of CO, NO, and O2. Compared to clean Rh(100), the saturation exposure of the dissociative adsorption of NO and O2 is about ten times greater for Na/Rh(100). The promotional effect of Na is less pronounced for the coadsorption of CO, which shows only fractional dissociation at 300 K.

Coadsorption of CO and O2 on rhodium

Coadsorption of CO and O2 on rhodium

Electronic properties of the Cs and O co-adsorption on Mo(100) at room temperature

Room-temperature co-adsorption of Cs and O2 on Mo(100) is studied by ELS, UPS and work function changes. The authors use a constant amount of caesium (4.3*1014 atoms cm-2) which corresponds to a monolayer on clean Mo(100). The loss peak at 1.65 eV observed for the Cs monolayer disappears for an oxygen exposure L of 0.28 L (Langmuir) and is replaced by a loss peak at 1.2 eV. Both losses are attributed to interband transitions. Above 2 L several O2p states are observed in UPS, indicating that O is bonded to the substrate and to the Cs. These spectra differ significantly from those obtained for Cs deposited on an Mo surface with various oxygen coverages. The differences observed with respect to Cs on Cu(111) are attributed to a substrate effect.

Chemisorption of sulfur dioxide on tungsten and platinum surfaces

AbstractThe chemisorption of SO2 on a W and a Pt surface has been investigated by flash desorption mass spectrometry (FDMS) and AES. AES data indicate that the chemisorbed sulfur dioxide molecules oxidized the W surface, and produced a stable tungsten oxide during the heating (up to 1400 K) process. FDMS data indicate that the decomposition of SO2 yielded elemental and molecular sulfur during the desorption process. FDMS data show that SO2 exists in four binding states (α1, α2, α3 and α4) on a clean Pt surface and in three binding states (α5, α6 and α7) on an oxidized Pt surface. In addition, the coadsorption of SO2 and O2 was carried out on a Pt surface. The coadsorption process can produce SO3 which exists in two different binding states on a Pt surface. The data indicate that the oxidation of SO2 to form SO3 on a Pt surface occurs by means of a Langmuir–Hinshelwood mechanism.

Carbon monoxide adsorption and hydrogen-oxygen titration on Ru/Al2O3

Hydrogen-oxygen titration and carbon monoxide adsorption on Ru/Al2O3 samples were employed to determine metal dispersity values. To avoid Ru−CO polycarbonyl formation, before CO adsorption, the ruthenium surface was precovered with hydrogen. By this procedure, good agreement between H2−O2 titration, CO adsorption and electron microscopy is obtained.

A molecular beam investigation of the catalytic oxidation of CO on Pd (111)

A detailed investigation of the steady-state and nonsteady-state reaction CO+1/2O2→CO2 on Pd (111) has been carried out with the molecular beam technique. It could be shown conclusively that the reaction proceeds between two adsorbed species (Langmuir–Hinshelwood mechanism) throughout the temperature and pressure range investigated. For low CO coverages, the activation energy of the reaction was determined to be 25 kcal/mole, whereas at moderate CO coverages, a rearrangement of the oxygen adlayer takes place resulting in a reduction of the activation energy to 14 kcal/mole. It is not possible to formulate a simple kinetic expression for the reaction rate which is valid over the entire range of temperatures and pressures due to changes in the adsorption rate for O2, coadsorption of CO and O2, to diffusion in the adlayer, and to changes in the geometrical arrangement within the adlayer with varying coverage.

Coadsorption of CO2 and O2 on MgO: An experimental and theoretical ESR study

A paramagnetic species attributed to an anionic coadsorbate of CO2 and O2 has been identified on an uv irradiated MgO surface. Its ESR parameters are as follows: gx=g1=2.040±0.001, gy=g2=2.0072±0.0005, and gz=2.0015±0.0005; Cx ?4 Oe, Cy=3.5±0.5 Oe, and Cz=2.8±0.3 Oe for 13C hyperfine tensor, and Caz=100 Oe and Cbz=50 Oe for 17O hyperfine splittings from molecular oxygen; the corresponding Cy and Cx components were too small to be determined. A theoretical approach to such a species has been made using the CNDO II/SP method. We have studied first the direct interaction of CO2 with O−2 in the gas phase, and then various models for the adsorbed species. The one that best fitted the experimental data corresponded to a species parallel to the surface with a CO2–O2 distance equal to 1.5 Å. We suggest that interaction of the O−2 unit with both CO2 and surface ions is necessary in order to obtain theoretical results in qualitative agreement with experimental data.