Metal Surface Interaction Research Articles

Neutron Reflectivity in Corrosion Research on Metals.

Neutron reflectivity (NR) is potentially a powerful tool for characterizing chemical and morphological changes in thin films and at buried interfaces in corrosion science. While the scope of NR is limited by its inherent demands for low surface roughness and high sample planarity, these drawbacks are compensated for by the unique ability to detect light elements and distinguish between isotopes. Furthermore, the generally weak absorption of neutrons by matter allows the use of bulky sample environments and in situ experiments. In particular, the layer thickness range of 3-100 nm accessible by NR is appropriate for studying air-formed films and passive films, which are crucial for the ability of metallic materials to resist corrosion, as well as for investigating the interaction of metal surfaces with hydrogen and its compounds, e.g., water. Also, NR is suitable for studying early stages of oxide growth on metals at high temperature, including the transition from Cabrera-Mott-type films to Wagner-type growth. Here, we outline key characteristics of NR as applied to the study of corrosion of metals, exemplified by earlier work, and discuss perspectives for future work in the field. The aim of our work is to stimulate the application of the unique capabilities of NR to corrosion science.

G‐C3N4 Coating Enhanced Cu@AC for Catalytic Wet Air Oxidation of Phenol under Mild Conditions

AbstractA Cu‐based supported catalyst with g‐C3N4 coating (Cu/g‐C3N4@AC) was prepared by facile in‐situ growth over activated carbon surface with urea and Cu(NO3)2, and the catalytic performance for wet air oxidation of phenolic wastewater was investigated. The effects of different reaction conditions (catalyst, temperature, pressure and pH) were examined. The results show that under the catalysis of Cu/g‐C3N4@AC phenol could be completely oxidized at 120 °C and 0.5 MPa O2 with COD removal of 92.6 % (from 4883 mg/L to 361 mg/L). TEM, BET, XRD, FTIR and XPS characterizations showed that g‐C3N4 coating could strengthen the metal surface interaction via the Cu−N−C bonds formation, thus suppressing the aggregation of the active components on the surface and mitigating the catalyst deactivation. Moreover, the interaction between the Cu species and the g‐C3N4 structure facilitates the electron transfer and thus significantly boost up the catalytic activity. These findings help explore efficient catalysts for the wastewater treatment via wet air oxidation under mild conditions.

Experimental and computational aspects of green corrosion inhibition for low carbon steel in HCl environment using extract of Chamaerops humilis fruit waste

The inhibition effect of a methanolic extract of Chamaerops humilis (CHFE) on the corrosion of low-carbon steel in 1 M HCl solution was evaluated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy. The extract was obtained from the fruit seeds by the Soxhlet extraction method. The CHFE demonstrated promising anticorrosive performance, and the inhibition efficiency increased with increasing the concentration of the extract, peaking at 93% at only 500 ppm. Importantly, the inhibitor exhibited a remarkable stability after 48 h of immersion, reaching an efficiency of 94%. The extract revealed a mixed-type inhibitive behavior. In addition, elevating the solution temperature showed a negative influence on the inhibition efficacy. Thermodynamic parameters suggested that the steel dissolution is an endothermic, spontaneous process. In addition, the experimental findings match well with the Langmuir adsorption isotherm and physisorption of the extract prevails. Furthermore, SEM/EDX and UV-Vis analyses demonstrated that the steel surface is protected by the extract molecules, confirming the electrochemical results. Density functional theory (DFT), Fukui function and molecular dynamics (MD) calculations unraveled the nature of inhibitor—metal surface interactions and provided insights into the most favorable electrophilic and nucleophilic active sites of oleic acid, a major constituent of the extract, helping to elucidate the mechanism of corrosion inhibition at the molecular level.

Antiviral activity of copper contact surfaces against MS2 coliphage and hepatitis a virus.

Viral diseases can be indirectly transmitted by contaminated non-food contact surfaces to final food products by cross-contamination. The interaction of metal surfaces and viruses, MS2 coliphage and hepatitis A virus (HAV), was investigated for strategy development in decreasing this transmission risk. MS2 deposited onto stainless-steel surface was stable but inactivated at 0.95 log10 PFU min-1 on 99.9% copper surfaces. Greater copper-inactivation of MS2 was observed in (a) simple media (PBS) than protein-rich media (beef extract buffer), and (b) acidic than pH≥6.8 environments. Among food matrices (strawberry juices and beef broth), the greatest MS2 inactivation by copper occurred in filtered strawberry juice at pH 3.5. At a reduction of 0.17 log10 PFU min-1, HAV survived longer than MS2 on copper by FRhK-4 cell infectivity assay. The inactivation of virus on copper surfaces was greater in acidic viral surrounding environments and in simple PBS medium. In the same 99% PBS medium, MS2 may not be an appropriate surrogate for HAV when assessing viral inactivation on copper surfaces.

Rational Design of Novel Reaction Pathways and Tailor-Made Catalysts for Value-Added Chemicals Synthesis from CO2 Hydrogenation

Abstract The highly effective transformation of CO2 into targeted chemicals has attracted significant attention due to greenhouse gas utilization and value-added chemical synthesis functions. Among all of the proposed CO2 transformation pathways, e.g., electrolytic CO2 reduction, photocatalytic CO2 conversion, and thermal-catalytic CO2 utilization, the latter, especially the thermal-catalytic hydrogenation process with renewable energy-driven H2 supply, is the most promising strategy owing to its high efficiency, fast reaction rate, controllable product selectivity, and industrial application potential. In recent years, our research group has made great efforts to realize various chemical syntheses from CO2 hydrogenation technology, such as production of methanol, ethanol, liquid petroleum gas (LPG), alkenes, aromatics (especially para-xylene, PX), etc. In this account, we summarize the main achievements of our laboratory in the rational design of novel heterogeneous catalysts and innovative reaction pathways for CO2 hydrogenation, including reaction pathway design for new low-temperature methanol synthesis, catalytic metal-surface interaction tailoring to boost methanol synthesis performance, tandem reaction network fabrication for the synthesis of ethanol, LPG, or aromatics, a capsule catalyst concept for tandem reaction, etc. In this account, we want to inspire new ideas and methodologies for the rational design of novel catalysts and reaction pathways for CO2 hydrogenation into value-added chemicals.

Improvement of the environmental safety of weaving equipment by reducing the wear of contact surfaces

The purpose of the work is improvement of the environmental safety of weaving equipment by reducing the wear of contact surfaces. For the environment, minimizing the wear during the operation of weaving equipment is of great importance. Nevertheless, the physical-chemical interaction of metal surfaces with the environment in its individual sections is uneven due to its polycrystalline structure and heterogeneity. At the same time, the value of their residual stresses (microstresses), the degree of plastic deformation, etc., have a significant effect on the physical and chemical activity of separate surface grains. The article covers the causes of wear of the batten mechanism of a shuttleless loom because of friction. In order to ensure the environmental safety of weaving equipment, methods of increasing the wear resistance of the batten mechanisms of shuttleless looms have been proposed. The article substantiates that an effective method for improving the efficiency of the batten mechanisms of shuttleless looms can be the method of surface plastic deformation of the inner surface of the batten teeth shed. As a result, the uniformity of the physical-chemical interaction of metal surfaces with the environment is ensured, as the resistance to wear and fatigue failure increases.

Corrosion inhibitory potential of selected flavonoid derivatives: Electrochemical, molecular⋅⋅⋅Zn surface interactions and quantum chemical approaches

Zinc metal corrosion inhibitor potential of some flavonoid derivatives, namely, naringenin (NRNG), morin hydrate (MNHD), and 6-hydroxyflavone (6-HFN), was investigated by measuring their inhibitory activities, determining their thermodynamic and kinetic adsorption mechanistic properties as well as comparing their molecular⋅⋅⋅Zn metal surface interaction strengths. The inhibition efficiencies were evaluated in 1.5 M hydrochloric acid (HCl) environment and different concentrations of the inhibitors (from 2.0 × 10−4 – 1.8 × 10−3 M) using gravimetric and various electrochemical methods at 30–60 °C. The molecular···metal surface interactions were determined using the density functional theory method by using the GGA/RPBE/DNP approach. Electrochemical studies show that 6-HFN and NRNG are the most and least effective corrosion inhibitors, with 77.54 and 70.46 maximum percentage inhibition efficiency, respectively. Atomic Absorption Spectroscopy technique was used to compare the concentration of the zinc ions that remained in the solution after gravimetric analysis in the absence and presence of the inhibitors at 30 °C; it was found that the inhibited solution contained less concentrations of zinc ions as compared to the uninhibited solution. Surface morphology techniques (e.g., 3D microscope) suggest that a localised type of corrosion took place on the metals, and the corrosion damage was minimal in the presence of the inhibitors. FT-IR showed a strong adsorption of the functional groups found in the inhibitor compounds, with CC functional group being strongly retained by all three inhibitors. The flavonoid inhibitor compounds were found to absorb chemically at low temperatures and physically at high temperatures. Langmuir adsorption isotherm was obeyed. The trend for molecular···metal surface interaction strengths follows the trend obtained from experimental findings on inhibition efficiency. Overall, the results suggest that all the molecules investigated are good corrosion inhibitors with a preference for those compounds in which there exists extended electron delocalization through the aromatic rings and in which there are minimal electron-withdrawing groups on the aromatic rings.

Study on alkylated Schiff base of a triazole with 3, 5-di-tert-butyl-4-hydroxybenzaldehyde as a novel multifunctional lubricant additive

A novel triazole derived multifunctional lube additive (MFA) denoted as TBB was designed and synthesized for improved metal surface interaction properties and inhibiting lubricant degradation. At first, two hindered phenolic moieties were coupled with the heterocyclic 3,5-diamino-1,2,4-triazole framework by the reaction with 3, 5-di-tert-butyl-4-hydroxybenzaldehyde to give the intermediate Schiff base followed by alkylation through the reaction of bromododecane for better solubility in polyol base oil. After molecular characterization, the TBB performance evaluation for the lubricity and antioxidant characteristics was done following the standard test methods in the polyol. At a low concentration of 1000 ppm, the average wear scar diameter and average friction coefficient was reduced by 16.92% and 64.39% respectively while the RBOT time was increased by 70.76% at 5000 ppm concentration with respect to polol base oil. The standard corrosion testing procedures were used for evaluating the anti-corrosion potential of additive TBB in terms of weight loss, corrosion rate, and penetration rate which were found to be reduced at 5000 ppm concentration to the values as 0.01 ± 0.01 mg, 0.01 ± 0.005 mdd, and 0.001 ± 0.001 mpy from the 0.60 ± 0.04 mg, 0.62 ± 0.03 mdd, and 0.114 ± 0.009 mpy respectively for blank polyol. So TBB showed moderate efficiency as a lubricity improver but showed excellent antioxidant and anti-corrosion additive properties.

Phosphonium-based ionic liquids as additives in calcium/lithium greases

This work studies the performance of three phosphonium-based ionic liquids ([P6,6,6,14][BEHP], [P6,6,6,14][TCM] and [P6,6,6,14][DEC]) when used separately as additives on the thermal conductivity, thermal stability and tribological properties of two non-additised greases (a lithium-based and a calcium-based grease). The main results confirmed that the [P6,6,6,14][TCM] improved the thermal stability of both greases. Only the mixtures G1 + 5%[P6,6,6,14][BEHP] and G2 + 5%[P6,6,6,14][TCM] showed a slight increase in thermal conductivity. In general, the addition of the ILs to the lithium-based grease increased the friction coefficient in both the four-ball tests and the reciprocating tests, while the friction coefficient decreased with the addition of the ILs to the calcium-based grease in the four-ball tests. The addition of the [P6,6,6,14][BEHP] and [P6,6,6,14][TCM] improved the antiwear behavior of the lithium-based grease under both tribological tests, whereas all the ionic liquids worsened the antiwear behavior of the calcium-based grease in the four-ball tests. The [P6,6,6,14][BEHP] had the best antiwear behavior due to the higher interaction of phosphorous with the metal surface. A possible interference of the calcium thickener with the ionic liquid–metal surface interaction was found, resulting in lower antiwear behavior of the mixtures with the calcium-based grease.

Improving LC/MS/MS-based bioanalytical method performance and sensitivity via a hybrid surface barrier to mitigate analyte – Metal surface interactions

The accurate determination of the pharmacokinetics (PK) of a candidate drug molecule is critical in both drug discovery and development. Over the last 30 years, the sensitivity and selectivity of LC/MS has resulted in it being established as the technology of choice for these studies. However, unwanted chemical interactions between analyte(s) and the metal components in a chromatography system can result in poor peak shape and reduction in signal response, which can adversely affect the analysis of low concentrations of drugs and their metabolites in biological samples. This study evaluated the benefits of employing an inert hybrid surface technology (HST) applied to the metallic components in the LC flow path, column frits and column wall to mitigate these interactions. The results obtained were compared with that of an identical conventional LC for the bioanalysis of two steroid phosphate drugs (dexamethasone phosphate and hydrocortisone phosphate) and an epidermal growth factor receptor (EGFR) inhibitor (gefitinib) in human plasma. The results showed that for the two steroid phosphates, the peak width was reduced by 20%, peak tailing factors reduced by up to 30% and the assay sensitivity improved by factors of 7.5 and 10. This resulted in a significant improvement in the limit of detection. The new LC system also improved the reproducibility of peak integration for gefitinib, thereby reducing assay coefficients of variation (%CV) from greater than 10% to less than 5% at the lower limit of quantification.

Experimental and theoretical study on the corrosion inhibitor potential of quinazoline derivative for mild steel in hydrochloric acid solution

Interaction of metal surfaces with organic molecules has a significant role in corrosion inhibition of metals and alloys. More clarification, from both experimental and computa­tional view is needed in describing the application of inhibitors for protection of metal surfaces. In this study, the surface adsorption and corrosion inhibition behavior of metol­azone, a quinazoline derivative, on mild steel in 0.02, 0.04, 0.06, and 0.08 M HCl solutions were investigated. Weight loss, potentiodynamic polarization and electrochemical impe­dance spectroscopy techniques were used. The optimum inhibition efficiencies of 75, 82 and 83 % were found by these three techniques at the optimum inhibitor concentration of 500 mg/L and 303 K. Scanning electron microscopy (SEM) was used to confirm adsorption of quinazoline derivative on the surface of the mild steel. Computational simulations were additionally used to give insights into the interaction between quinazoline inhibitor and mild steel surface. Thermodynamic parameters of mild steel corrosion showed that quinazoline derivative functions as an effective anti-corrosive agent that slows down corrosion process. Potentiodynamic polarization results revealed a mixed-type inhibitor, while the result of the adsorption study suggests that adsorption of the inhibitor on the mild steel surface obeys the physical adsorption mechanism and follows Langmuir adsorption isotherm model.

Plant Extracts as Green Corrosion Inhibitors for Different Metal Surfaces and Corrosive Media: A Review

Natural extracts have been widely used to protect metal materials from corrosion. The efficiency of these extracts as corrosion inhibitors is commonly evaluated through electrochemical tests, which include techniques such as potentiodynamic polarization, electrochemical impedance spectroscopy, and weight loss measurement. The inhibition efficiency of different extract concentrations is a valuable indicator to obtain a clear outlook to choose an extract for a particular purpose. A complementary vision of the effectiveness of green extracts to inhibit the corrosion of metals is obtained by means of surface characterizations; atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy analysis are experimental techniques widely used for this purpose. Moreover, theoretical studies are usually addressed to elucidate the nature of the corrosion inhibitor—metal surface interactions. In addition, calculations have been employed to predict how other organic substances behave on metal surfaces and to provide experimental work with fresh proposals. This work reports a broad overview of the current state of the art research on the study of new extracts as corrosion inhibitors on metal surfaces in corrosive media. Most constituents obtained from plant extracts are adsorbed on the metal, following the Langmuir adsorption model. Electron-rich regions and heteroatoms have been found to be responsible for chemisorption on the metal surface, whereas physisorption is due to the polar regions of the inhibitor molecules. The plant extracts compiled in this work obtained corrosion inhibition efficiencies above 60%, most of them around 80–90%. The effect of concentration, extraction solvent, temperature, and immersion time were studied as well. Additional studies regarding plant extracts as corrosion inhibitors on metals are needed to produce solutions for industrial purposes.

Selective suppression of amplitudes of frictional oscillations

Maintenance of sanitary codes and standards during operation of railway sorting sta-tions, in particular, standards which concern noise levels, is now the most pressing task. The analysis of noise has been carried out during operation of brake beams of car hump retarders with car wheelsets; the most problem frequency ranges have been revealed. On the basis of mod-elling bench tests with application of techniques of physical and mathematical modelling and tribospectral identification of friction processes we carried out selection of noise-suppressing cladding material which would reduce the level of acoustic noise at interaction of metal surfaces. Results of operational trials have confirmed efficiency of the chosen material in noise reduction.

Selection of iron precursor for preparation of 3D-solids of hydrophobic composites with γ-alumina and carbon nanostructured materials

An easy handling formulation of hybrid material, which could approach carbon nanomaterials application to industrial catalysts, of carbon nanofibers (CNF) and carbon nanotubes (CNT) over γ-alumina, C@alumina is described. The study discussed the selection of iron precursor to obtain mechanical stable hybrids by analysis of coverage effect of process preparation of seminal γ-alumina pellets, in order to evaluate the yield of carbon nanomaterials (CNFs/CNTs) coverage on the alumina pellets. Each C@alumina series were synthetized by catalytic vapor decomposition of acetylene at 1023 K, and were studied according to the nature of active phase, the iron precursor, by the light of characterization results obtained by thermogravimetric analysis and Scanning Electron Microscopy. Besides, ethanol reaction is employed as chemical reaction test for acid-base surface distribution analysis. Finally, the hydrophobic behavior of every precursor hybrid sample is discussed attending to contact angle. So, it was discussed from de nature of iron precursors of acetylacetonate, chloride, sulfate, cyanide, pentacarbonyl, phthalocyanine, 1,10-phenanthroline, ferrocene the surface structure of 3d-solids obtained, and it is correlated with the effects of iron precursor loading, pKa, and polar surface area (PSA) and metal-surface interaction. It was evidenced the effect of iron precursor selection over the C@alumina hybrid hydrophobic properties.

Computational design of metal-supported molecular switches: transient ion formation during light- and electron-induced isomerisation of azobenzene

In molecular nanotechnology, a single molecule is envisioned to act as the basic building block of electronic devices. Such devices may be of special interest for organic photovoltaics, data storage, and smart materials. However, more often than not the molecular function is quenched upon contact with a conducting support. Trial-and-error-based decoupling strategies via molecular functionalisation and change of substrate have in many instances proven to yield unpredictable results. The adsorbate-substrate interactions that govern the function can be understood with the help of first-principles simulation. Employing dispersion-corrected density-functional theory (DFT) and linear expansion delta-self-consistent-field DFT, the electronic structure of a prototypical surface-adsorbed functional molecule, namely azobenzene adsorbed to (1 1 1) single crystal facets of copper, silver and gold, is investigated and the main reasons for the loss or survival of the switching function upon adsorption are identified. The light-induced switching ability of a functionalised derivative of azobenzene on Au(1 1 1) and azobenzene on Ag(1 1 1) and Au(1 1 1) is assessed based on the excited-state potential energy landscapes of their transient molecular ions, which are believed to be the main intermediates of the experimentally observed isomerisation reaction. We provide a rationalisation of the experimentally observed function or lack thereof that connects to the underlying chemistry of the metal-surface interaction and provides insights into general design strategies for complex light-driven reactions at metal surfaces.

Dry reforming of methane for syngas production over Ni\u2013Co-supported Al2O3\u2013MgO catalysts

This research project focuses on the development of catalysts for syngas production by synthesizing Ni–Co bimetallic catalyst using aluminum oxide (Al2O3) and magnesium oxide (MgO) as the catalyst support. Ni/Al2O3 (CAT-1), Ni–Co/Al2O3 (CAT-2) and Ni–Co/Al2O3–MgO (CAT-3) nanocatalysts were synthesized by sol–gel method with citric acid as the gelling agent, and used in the dry reforming of methane (DRM). The objective of this study is to investigate the effects of Al2O3 and MgO addition on the catalytic properties and the reaction performance of synthesized catalysts in the DRM reactions. The characteristics of the catalyst are studied using field emission scanning electron microscope (FESEM), Brunauer–Emmett–Teller (BET), X-ray powder diffraction (XRD), transmission electron microscopy, H2-temperature programmed reduction, CO2-temperature programmed desorption and temperature programmed oxidation analysis. The characteristics of the catalyst are dependent on the type of support, which influences the catalytic performances. FESEM analysis showed that CAT-3 has irregular shape morphology, and is well dispersed onto the catalyst support. BET results demonstrate high surface area of the synthesized catalyst due to high calcination temperature during catalysts preparation. Moreover, the formation of MgAl2O4 spinel-type solution in CAT-3 is proved by XRD analysis due to the interaction between alumina lattice and magnesium metal which has high resistance to coke formation, leading to stronger metal surface interaction within the catalyst. The CO2 methane dry reforming is executed in the tubular furnace reactor at 1073.15 K, 1 atm and CH4/CO2 ratio of unity to investigate the effect of the mentioned catalysts. Ni–Co/Al2O3–MgO gave the highest catalyst performance compared to the other synthesized catalysts owning to the strong metal–support interaction, high stability and significant resistance to carbon deposition during the DRM reaction.

Azardirachta Indica Leaves Ark’s as Green Corrosion Inhibitor for Aluminum in HCl Solutions

The purpose of this paper to find out the effect of Azardirachta indica (Neem) leaves ark’s on the corrosion of aluminum in 0.4, 0.5 and 0.6M hydrochloric acid (HCl), and elucidates the mechanism of the inhibition system. Gravimetric and galvanostatic polarization methods were used to investigate the effect of aluminum corrosion in HCl solutions. The outcome revealed that maximum inhibitor efficiency which corresponds to the lowest corrosion rate was obtained at most favorable inhibitor concentration of 1.25% with reduction in the corrosion rate observed to follow in order of increasing extract concentration. The adsorption study promote that Langmuir isotherm best described the metal surface interaction with the Azardirachta indica (Neem) leaves ark’s with the best exposure time for the Azardirachta indica (Neem) leaves ark’s to adsorb to the metal surface at all concentrations. Polarization study reveals that the inhibitors functions as a mixed inhibitor.

Modeling of solid-liquid interfaces using scaled charges: rutile (110) surfaces.

Electronic continuum correction (ECC) has been proven to bring significant improvement in the modeling of interactions of ions (especially multivalent) in aqueous solutions. We present a generalization and the first application of this approach to modeling solid-liquid interfaces, which are omnipresent in physical chemistry, geochemistry, and biophysics. Scaling charges of the top layer of surface atoms makes the existing solid models compatible with the ECC models of ions and molecules, allowing the use of modified force fields for a more accurate investigation of interactions of various metal and metal-oxide surfaces with aqueous solutions, including complex biomolecules and multivalent ions. We have reparametrized rutile (110) models with different surface charge densities (from 0 to -0.416 C m-2) and adopted/developed scaled charge force fields for ions, namely Na+, Rb+, Sr2+, and Cl-. A good agreement of the obtained molecular dynamics (MD) data with X-ray experiments and previously reported MD results was observed, but changes in the occupancy of various adsorption sites were observed and discussed in detail.

Green synthesis of surface-passivated carbon dots from the prickly pear cactus as a fluorescent probe for the dual detection of arsenic(iii) and hypochlorite ions from drinking water.

Efforts were made to develop a simple new approach for the green synthesis of surface-passivated carbon dots from edible prickly pear cactus fruit as the carbon source by a one-pot hydrothermal route. Glutathione (GSH) was passivated on the surface of the CDs to form a sensor probe, which exhibited excellent optical properties and water solubility. The prepared sensor was successfully characterized by UV-visible spectrophotometry, fluorescence spectrophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The simple sensing platform developed by the GSH-CDs was highly sensitive and selective with a “turn-off” fluorescence response for the dual detection of As3+ and ClO− ions in drinking water. This sensing system exhibited effective quenching in the presence of As3+ and ClO− ions to display the formation of metal complexes and surface interaction with an oxygen functional group. The oxygen-rich GSH-CDs afforded a better selectivity for As3+/ClO− ions over other competitive ions. The fluorescence quenching measurement quantified the concentration range as 2–12 nM and 10–90 μM with the lower detection limit of 2.3 nM and 0.016 μM for the detection of As3+ and ClO− ions, respectively. Further, we explored the potential applications of this simple, reliable, and cost-effective sensor for the detection of As3+/ClO− ions in environmental samples for practical analysis.

Water and CO (co-)adsorption on pseudomorphic Pt films on Ru(0001) - a low-temperature scanning tunneling microscopy study.

Coadsorption of CO and water under ultrahigh vacuum (UHV) conditions can be considered as a model system for the interaction of metal surfaces with CO in an aqueous electrochemical environment. Nevertheless, this has rarely been investigated, and in particular for catalytically relevant bimetallic systems, there is hardly any information available. Here we report results of a low-temperature scanning tunneling microscopy (STM) study on the adsorption and coadsorption of CO and water on a Ru(0001) surface covered with a pseudomorphic Pt film of 2 or 3 monolayers thickness. The role of kinetic effects introduced by the sequence of adsorption, either pre-adsorption of CO followed by water adsorption or pre-adsorption of water followed by CO adsorption, on the adlayer structure formation will be demonstrated and discussed. Furthermore, the data show a distinct influence of the thickness of the Pt film, reflecting changes in the chemistry of the Pt surface due to electronic interactions with the underlying Ru(0001) substrate ('vertical ligand effects'). Implications of the present findings on the interaction of CO with these bimetallic PtRu surfaces under electrochemical conditions will be discussed.