Coadsorption Of Carbon Monoxide Research Articles

Characterization of CO Adsorbed to Clean and Partially Oxidized Cu(211) and Cu(111).

Copper-based catalysts gain activity through the presence of poorly coordinated Cu atoms and incomplete oxidation at the surface. The catalytic mechanisms can in principle be observed by controlled dosing of reactants to single-crystal substrates. However, the interconnected influences of surface defects, partial oxidation, and adsorbate coverage present a large matrix of conditions that have not been fully explored in the literature. We recently characterized oxygen and carbon monoxide coadsorption on Cu(111), a nominally defect-free surface, and now extend our study to the stepped surface Cu(211). Temperature-programmed desorption of CO adsorbed to bare metal surfaces confirms that two sites dominate desorption from a saturated layer: atop terrace atoms of local (111) character and atop step edge atoms with CO bound more strongly to the latter. At low coverage, discrete CO resonances in reflection adsorption infrared spectra can be assigned to these sites: 2077 cm-1 for extended (111) terraces, 2093 cm-1 for step sites, and additional kink-adsorbed molecules at 2110 cm-1. With increasing coverage, in contrast to Cu(111), the infrared spectral features on Cu(211) evolve and shift as a consequence of dipole-dipole coupling between differentially occupied types of sites. Auger electron spectroscopy shows that exposure to background O2 oxidizes the (211) surface at a rate nearly 1 order of magnitude greater than (111); we argue that the resulting surface is stoichiometric Cu2O, as previously found for Cu(111). This oxide binds CO less strongly than the bare metal and the underlying crystal cut continues to influence the adsorption sites available to CO. On oxidized (111) terraces, broad absorption peaks at 2115-2120 cm-1; on oxidized Cu(211), CO adsorbed to step sites appears as a resolved secondary peak at 2144 cm-1. This suite of spectroscopic signatures, obtained under carefully controlled conditions, will help to determine the origin and fate of adsorbed species in future studies of reaction mechanisms on copper.

Enhancing the Catalytic Activity of Mo(110) Surface via Its Alloying with Submonolayer to Multilayer Boron Films and Oxidation of the Alloy: A Case of (CO + O2) to CO2 Conversion

In-situ formation of boron thin films on the Mo(110) surface, as well as the formation of the molybdenum boride and its oxide and the trends of carbon monoxide catalytic oxidation on the substrates formed, have been studied in an ultra-high vacuum (UHV) by a set of surface-sensitive characterization techniques: Auger and X-ray photoelectron spectroscopy (AES, XPS), low-energy ion scattering (LEIS), reflection-absorption infrared spectroscopy (RAIRS), temperature-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and work function measurements using the Anderson method. The boron deposited at Mo(110) via electron-beam deposition at a substrate temperature of 300 K grows as a 2D layer, at least in submonolayer coverage. Such a film is bound to the Mo(110) via polarized chemisorption bonds, dramatically changing the charge density at the substrate surface manifested by the Mo(110) surface plasmon damping. Upon annealing of the B-Mo(110) system, the boron diffuses into the Mo(110) bulk following a two-mode regime: (1) quite easy dissolution, starting at a temperature of about 450 K with an activation energy of 0.4 eV; and (2) formation of molybdenum boride at a temperature higher than 700 K with M-B interatomic bonding energy of 3.8 eV. The feature of the formed molybdenum boride is that there is quite notable carbon monoxide oxidation activity on its surface. A further dramatic increase of such an activity is achieved when the molybdenum boride is oxidized. The latter is attributed to more activated states of molecular orbitals of coadsorbed carbon monoxide and oxygen due to their enhanced interaction with both boron and oxygen species for MoxByOz ternary compound, compared to only boron for the Mox'By' double alloy.

RAIRS Characterization of CO and O Coadsorption on Cu(111).

In a study preliminary to investigating CO2 dissociation, we report our results on oxygen and carbon monoxide coadsorption on Cu(111). We use reflection adsorption infrared spectroscopy and Auger electron spectroscopy to characterize and quantify adsorbed species. On clean Cu(111), the CO internal stretch mode appears initially at 2077 cm–1 for a surface temperature of ∼80 K. We accurately reproduce the previously determined redshift of the absorption band with increasing CO coverage. We subsequently oxidize the surface by exposure to O2 at 300 K to ensure O2 dissociation. The band’s frequency and line shape of subsequently adsorbed CO at ∼80 K are not affected. However, the maximum absorbance and integrated peak intensities drop with increasing O coverage. The data suggest that CO is not adsorbed near O, likely as a consequence of the mechanism of Cu(111) surface oxidation by O2 at 300 K. We discuss whether our RAIRS results may be used to quantify CO2 dissociation in the zero-coverage limit.

Effect of the Surface Oxidation of Molybdenum Boride on the Adsorption and Interaction of Carbon Oxide and Oxygen Molecules

Surface analysis conducted under ultrahigh vacuum conditions shows that the oxidation of a B‒Mo(110) alloy with a submonolayer concentration of boron atoms dramatically improves the efficiency of conversion of co-adsorbed carbon monoxide and oxygen molecules to carbon dioxide. It is established that this effect is associated with differences between the properties of the adsorbed particles before and after molybdenum boride oxidation, particularly an increase in the slope of the CO molecular axis to the plane of the adsorbent surface and the weakening of the chemisorptive bonds of oxygen with the substrate on the surface of the MoxByOz ternary compound. It is concluded that this substrate can be considered a model system and an alternative to the currently available catalysts for CO oxidation based on noble metals.

Coadsorption of CO and H2 on an Iron Surface and Its Implication on the Hydrogen Embrittlement of Iron

We investigated the competitive coadsorption of carbon monoxide and hydrogen gas on an iron surface with a 110 facet using density functional theory. Our study discusses the hydrogen dissociation r...

Adsorption and Interaction of CO and NO Molecules on Pure and Oxidized Surfaces of Al−Mo(110) Alloy

The coadsorption of carbon-monoxide- and nitric-oxide molecules and their interactions on surfaces of Al−Mo(110) alloy and the system resulting from its oxidation (Al−Mo−O) are investigated using an array of spectroscopic techniques (X-ray photoelectron, Auger electron, infrared, and thermal-desorption spectroscopies), low-energy electron diffraction, and work-function measurements in ultra-high vacuum. Al−Mo(110) alloy is fabricated by the thermal annealing (at 800 K) of an aluminum film several layers thick deposited onto the Mo(110) surface. Aluminum atoms diffuse into the substrate to yield a surface alloy of hexagonal structure characteristic of stoichiometric Al2Mo alloy. Unlike dissociative adsorption on both Mo(110) and Al(111) surfaces, CO and NO adsorb molecularly at the surface of Al−Mo(110) alloy. At 200 K, the adsorption of CO molecules on the Al−Mo(110) surface containing pre-adsorbed NO molecules has a dramatic effect on the latter by displacing them to higher-coordinated adsorption sites and at the same time causing their molecular axis to tilt toward the adsorbent surface plane. Heating this system to 320 K results in the reduction of nitric oxide by carbon monoxide to yield CO2 and surface nitrides. This can be a consequence of surface reconstruction that leads to the formation of additional adsorption/reaction sites at the Al/Mo interface and to changes in the substrate’s d-band filling as a result of alloying. The oxidation of CO by NO proceeds with a markedly higher efficiency at the surface of the Al−Mo−O system; this system results from oxidation of the Al−Mo(110) alloy by oxygen at 700 K and exposure up to 1500 L.

Electron density topological and adsorbate orbital analyses of water and carbon monoxide co-adsorption on platinum.

The electron density topology of carbon monoxide (CO) on dry and hydrated platinum is evaluated under the quantum theory of atoms in molecules (QTAIM) and by adsorbate orbital approaches. The impact of water co-adsorbate on the electronic, structural, and vibrational properties of CO on Pt are modelled by periodic density functional theory (DFT). At low CO coverage, increased hydration weakens C-O bonds and strengthens C-Pt bonds, as verified by changes in bond lengths and stretching frequencies. These results are consistent with QTAIM, the 5σ donation-2π* backdonation model, and our extended π-attraction σ-repulsion model (extended π-σ model). This work links changes in the non-zero eigenvalues of the electron density Hessian at QTAIM bond critical points to changes in the π and σ C-O bonds with systematic variation of CO/H2O co-adsorbate scenarios. QTAIM invariably shows bond strengths and lengths as being negatively correlated. For atop CO on hydrated Pt, QTAIM and phenomenological models are consistent with a direct correlation between C-O bond strength and CO coverage. However, DFT modelling in the absence of hydration shows that C-O bond lengths are not negatively correlated to their stretching frequencies, in contrast to the Badger rule: When QTAIM and phenomenological models do not agree, the use of the non-zero eigenvalues of the electron density Hessian as inputs to the phenomenological models, aligns them with QTAIM. The C-O and C-Pt bond strengths of bridge and three-fold bound CO on dry and hydrated platinum are also evaluated by QTAIM and adsorbate orbital analyses.

Adsorption of hydrogen sulphide over rhodium/silica and rhodium/alumina at 293 and 873\xa0K, with co-adsorption of carbon monoxide and hydrogen

In this study, we have examined the adsorption of hydrogen sulphide and carbon monoxide over rhodium/silica and rhodium/alumina catalysts. Adsorption of hydrogen sulphide was measured at 293 and 873 K and at 873 K in a 1:1 ratio with hydrogen. At 293 K, over Rh/silica, hydrogen sulphide adsorption capacity was similar to that of carbon monoxide; however, over Rh/alumina, the carbon monoxide adsorption capacity was higher, probably due to the formation of RhI(CO)2. Over Rh/silica, the primary adsorbed state was HS(ads), in contrast to Rh/alumina, where the H2:S ratio was 1:1 indicating that the adsorbed state was S(ads). Competitive adsorption between CO and H2S over Rh/silica and Rh/alumina revealed adsorption sites on the metal that only adsorbed carbon monoxide, only adsorbed hydrogen sulphide or could adsorb both species. At 873 K, hydrogen sulphide adsorption produced the bulk sulphide Rh2S3; however, when a 1:1 H2:H2S mixture was used formation of the bulk sulphide was inhibited and a reduced amount of hydrogen sulphide was adsorbed.

The Effect of Carbon Monoxide Co-Adsorption on Ni-Catalysed Water Dissociation

The effect of carbon monoxide (CO) co-adsorption on the dissociation of water on the Ni(111) surface has been studied using density functional theory. The structures of the adsorbed water molecule and of the transition state are changed by the presence of the CO molecule. The water O–H bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking O–H bond in the transition state structure has a larger imaginary frequency in the presence of CO. In addition, the distances between the Ni surface and H2O reactant and OH and H products decrease in the presence of the CO. The changes in structures and vibrational frequencies lead to a reaction energy that is 0.17 eV less exothermic in the presence of the CO, and an activation barrier that is 0.12 eV larger in the presence of the CO. At 463 K the water dissociation rate constant is an order of magnitude smaller in the presence of the CO. This reveals that far fewer water molecules will dissociate in the presence of CO under reaction conditions that are typical for the water-gas-shift reaction.

Adsorption and Reactions of Carbon Monoxide and Oxygen on Bare and Au-Decorated Carburized W(110)

Adsorption and coadsorption of carbon monoxide and oxygen on different types of Au clusters on R(15 × 3)C/W(110) and R(15 × 12)C/W(110), respectively, are studied with respect to the catalytic behavior for oxidation of CO as well as of surface carbon. Carburization of the W(110) surface results in a weakening of the adsorption bond for molecularly adsorbed CO. Dissociation of carbon monoxide, which occurs on W(110), is reduced on the low-carbon coverage R(15 × 12) surface and completely suppressed on the carbon-saturated R(15 × 3) phase. Deposition of gold results in a blocking of adsorption sites for molecularly adsorbed CO and reopening of the dissociation channel. Probably the latter is associated with the existence of double-layer gold clusters and islands. At room temperature the gold clusters on both carburized templates are stable in CO atmosphere as shown by in-situ STM measurements. In contrast, exposure to oxygen alters the clusters on the R(15 × 12) surface, implying dissociation of oxygen not only on the substrate but also on or in immediate vicinity of the gold clusters. On the Au-free carburized templates oxygen adsorbs dissociatively and is released as CO at temperatures beyond 800 K due to reaction with carbon atoms from the templates. Deposition of gold enhances the desorption rate of the formed CO at the low-temperature end of the recombinative CO desorption range, indicating a promoting effect of gold for oxidation of surface carbon. In contrast, low-temperature CO oxidation catalyzed by the deposited Au clusters is not observed. Two reasons could be identified: (1) weakly bound CO with desorption temperatures between 100 and 200 K (as reported for other related systems) is not observed, and (2) oxygen atoms are bonded too strongly to the templates.

Alkali metal induced effects on coadsorbed carbon monoxide on Co(0 0 0 1): A density functional theory study

The coadsorption of CO on alkali metal (AM=Li, Na and K) precovered-Co(0001) are studied b density functional theory. Calculations indicate that the presence of AM atom strongly enhances the stabilization of CO with substrate surface, lowers the surface potential around CO molecule and weakens C–O bond. These findings are compared with the increasing coverage of CO and it is demonstrated that CO adsorption is affected by a short-range AM–CO electrostatic attraction interaction at a short distance (less than 3Å), particularly an ionic bonding trend between AMδ+ and Oδ− attraction in a p(2×2)–(AM+2CO) overlayer.

Cyclic voltammetric and <italic>in situ</italic> FTIR spectroscopic studies of redox of nitric oxide and carbon monoxide coadlayers on Pt electrode

The coadsorption behavior of nitric oxide (NO) and carbon monoxide (CO) on the polycrystalline Pt electrode and the influence of CO on the oxidation-reduction reactions of coadsorbed NO were studied by using cyclic voltammetric (CV) and <italic>in situ</italic> FTIR spectroscopy in acid media. The results demonstrated that the NO/CO adlayers can be adsorbed on the Pt electrode stably at 0.20 V (vs. SCE). CO existed with linear adsorption state (CO_L), and NO were coadsorded with both bridged adsorption state (NO_B) and linear adsorption state (NO_L). Due to the coadsorption of CO_L, the reduction peak potentials of NO were negatively shifted about 0.024 V, and NO_B which should have been not accessible to be oxidized were oxidized at 0.93 V. <italic>in situ</italic> FTIRS further indicated that NO can replace CO which is pre-adsorbed on the Pt electrode, and it is a competitive adsorption process between NO and CO. Both NO and CO can be converted into environment- friendly species, which are NO₃^- and CO₂ respectively. The quantity of NO₃^- depends on the adsorption quantity of CO on the Pt electrode.

A bonding study of CO–benzene co-adsorption on Rh(1 1 1)

The co-adsorption of carbon monoxide and benzene on Rh(1 1 1) has been studied using density functional calculations. We used the ordered p(3 × 30) surface unit cell for the study. Besides, a comparison of the co-adsorption with CO and benzene two-dimensional networks is also given. The hydrogen of the benzene ring presents a bonding angle of 26°. The electronic structure reveals that the CO does not interact with benzene. Regarding the bonding, the Rh–Rh overlap population decreases 36.7% after co-adsorption, which is almost, the same decrease after CO adsorption. The CO–benzene interaction is very weak and a small H benzene–C CO OP of 0.001 is detected.

Coadsorption of CO and NO on the Cu2O(111) surface: A periodic density functional theory study

Coadsorption of carbon monoxide (CO) and nitric oxide (NO) on the Cu(2)O(111) surface was studied using periodic density functional theory calculations. It is interesting to find that CO+NO on Cu(2)O(111) could react to form adsorbed NCO surface species. Coadsorption of CO and NO could give rise to the formation of a O-C...N-O complex well bound to the Cu(2)O(111) surface, in which both the C-O and N-O bonds are greatly activated and the C-N bond is formed. Consequently, the reaction of CO with NO to form adsorbed NCO and CNO species may occur, for which it is disclosed that NCO formation is more possible than CNO formation both thermodynamically and kinetically. In addition, our calculations of searching transition states reveal that it is facile for NCO formation both kinetically and thermodynamically when CO+NO reaction takes place at Cu(CUS) site, and is impossible when this reaction takes places at O(vac) site. Moreover, CO(2) species cannot form when CO+NO reaction occurs at O(vac) site. Therefore, oxygen vacancy on Cu(2)O(111) does not play a positive role on CO+NO reaction to forming NCO, CNO, or CO(2) species.

THE CO-ADSORPTION OF BENZENE ANDCOONCo(0001)

The co-adsorption of carbon monoxide and benzene on Co (0001) has been studied using density functional calculations. We used the ordered [Formula: see text] surface unit cell. A comparison of the co-adsorption with CO and benzene two-dimensional networks is also given. The electronic structure reveals that the CO orbitals interact with benzene and Co layer. Regarding the bonding, the Co–Co overlap population decrease 18% after benzene adsorption and increase a little after CO adsorption with a net 14.6% decrease in the co-adsorption system. The CO –benzene interaction is shown by the changes in the C – O ( CO ) and C – H (benzene) bonds.

Temperature dependence of co-adsorption of carbon monoxide and water on highly dispersed Pt/C and PtRu/C electrodes studied by in-situ ATR-FTIRAS

ATR-FTIRAS measurements were conducted to investigate nature of water molecules co-adsorbed with CO on highly dispersed PtRu alloy and Pt catalysts supported on carbon black in the temperature range between 23 °C and 60 °C. Each catalyst was uniformly dispersed and fixed by Nafion ® film of 0.0125 μm thickness on a chemically deposited gold film. Adsorption of CO was conducted and monitored by ATR-FTIRAS for 30 min in 1% CO saturated 0.1 M HClO 4 after stepping the potential from 1.2 V and 1.0 V to 0.05 V on Pt/C and PtRu/C, respectively. Similar atop and bridge bonded CO bands were observed on both PtRu/C and Pt/C, but a smaller relative band intensity, bridge bonded vs. atop CO, was observed on PtRu/C compared to Pt/C. A distinct O–H stretching band was found around 3643 cm −1 and 3630 cm −1 on PtRu/C and Pt/C, respectively, upon CO adsorption. They are assigned to non-hydrogen bonded water molecules co-adsorbed with CO on these catalysts. We found that the number of non-hydrogen bonded water molecules co-adsorbed with a given number of CO molecules decreases with increasing temperature and is higher on PtRu/C than Pt/C at each temperature. We interpret the higher ability of water co-adsorption at PtRu/C over Pt/C is due to stronger H 2O–metal interactions on the alloy surface. We present a model of the CO–H 2O co-adsorbed layer based on the bilayer model of water on metal surfaces.

First-principles study on the geometry and stability of CO and hydrogen coadsorption on the Ni(1 1 1)2 × 2 surface

Periodic, self-consistent, density functional theory (GGA-PW91) calculations are performed for hydrogen and carbon monoxide coadsorption on Ni(1 1 1). It was found that the hollow sites are energetically preferred in pure H/CO adsorption system. In the co-adsorbed phase, the best-fit geometry is that CO molecule sits in hcp hollow and hydrogen atom occupies fcc site. The adsorption states and the optimized geometries are found to be in excellent agreement with experimental results. In coadsorption system, the calculations show a blue shift of 36 cm −1 relative to the pure CO adsorption phase for the CO stretching frequency. The calculated Ni–C stretching frequency shift directions in Ni(1 1 1) and Ni(1 0 0) are reversed. The Density of State (DOS) analysis has shown that there is charge redistribution in coadsorption system upon hydrogen adsorption on the CO/Ni(1 1 1) surface.

Effect of Oxygen Adsorption on the Chiral Pt{531} Surface

The adsorption of oxygen on the chiral Pt{531} surface was studied by high-resolution X-ray photoelectron spectroscopy (HRXPS) and low energy electron diffraction (LEED). After the surface is annealed in oxygen (3 x 10(-7) mbar), three O 1s peaks are observed in XPS. One peak, at 529.5 eV, is assigned to chemisorbed oxygen; it disappears after annealing in vacuo to temperatures above 900 K. The other two peaks at 530.8 and 532.3 eV are stable up to at least 1250 K. They are associated with oxide clusters on the surface. These clusters readily react with coadsorbed carbon monoxide at temperatures between 315 and 620 K.

Coadsorption of carbon monoxide and copper atoms on rhodium electroplates

The partial removal of copper atoms from a preliminarily formed Cuad layer and the adsorption of Cu2+ cations in the presence of a COads monolayer were demonstrated for Rh/Pt electrodes by means of transients of current and potentiodynamic and analytical measurements. The electrooxidation of the mixed COads + Cuad layer in the course of anodic potential scans is shown to be accompanied by simultaneous removal of both species in a wide potentials range.

Benzene and carbon monoxide co-adsorption on Pt(1 1 1): a theoretical study

The co-adsorption of carbon monoxide and benzene on Pt(111) has been studied by theoretical tight-binding calculations. We used the ordered (23×4) rect-2C6H6+4CO superlattice. The computed energies for the adsorption sequences agrees with the experimental fact that CO displaces benzene. A comparison of the co-adsorption with CO and benzene 2D networks and both, CO and benzene 2D, adsorbed alone on Pt(111) is also given. An important H–H intermolecular interaction between benzenes is reinforced when CO is added to the surface. In addition, the Pt–C6H6 overlaps population decrease while a bonding interaction is developed between carbon from benzene and the C and O atoms from carbon monoxide.The density of states (DOS) and crystal orbital overlap population (COOP) curves clearly show this behavior.