TPD and FT-IRAS investigation of ethylene oxide (EtO) adsorption on a Au(211) stepped surface

Adsorption of ethylene oxide, CH(2)CH(2)O (EtO), on a Au(211) stepped surface was studied by temperature programmed desorption (TPD) and Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS). Ethylene oxide was completely reversibly adsorbed, and desorbed molecularly during TPD following adsorption on Au(211) at 85 K. EtO TPD peaks appeared at 115 K from the multilayer film and 140 and 170 K from the monolayer. Desorption at 140 K was attributed to EtO desorption from terrace sites, and that at 170 K to EtO desorption from step sites. Desorption activation energies and corresponding adsorption energies were estimated to be 8.4 and 10.3 kcal mol(-1), respectively. The EtO ring (C(2)O) deformation band appeared in IRAS at 865 cm(-1) for EtO in multilayer films and when adsorbed in the monolayer at terrace sites. The stronger chemisorption bonding of EtO at Au step sites slightly weakens the bonding within the molecule and causes a small red-shift of this band to 850 cm(-1) for adsorption at step sites. EtO presumably binds via the oxygen atom to the surface, and observation of the EtO-ring absorption band in IRAS establishes that the molecular ring plane of EtO adsorbed at step and terrace sites is nearly upright with respect to the crystal surface plane.     

氢原子在Ni(111)次表面和Ni(211)、(533)台阶面上的吸附与振动

应用原子与表面簇合物相互作用的五参数Morse势(5-MP)方法对氢原子在Ni(111)表面和次表面以及Ni(211), (533)台阶面进行了系统研究, 得到了氢原子在上述各面的吸附位、吸附几何、结合能和本征振动频率. 计算结果表明, 在Ni(111)面上, 氢原子优先吸附在三重位, 随着覆盖度的增加会吸附在次表面八面体位和四面体位. Ni(211), (533)的最优先吸附位都是四重位, 当氢原子的覆盖度增大时占据(111)平台的三重吸附位. 靠近台阶面的吸附位受台阶和平台高度的影响很大. 此外, 我们计算了氢原子在各表面的不同吸附位的扩散势垒, 获得氢原子在各表面的最低能量扩散通道.     

Site- and surface species-dependent propylene oxidation with molecular oxygen on gold surface

A complete fundamental understanding of propylene oxidation with molecular O₂ on Au surface is achieved, in which site-and surface species-dependent reaction behaviors are revealed.     

Surface electrochemistry of CO on reconstructed gold single crystal surfaces studied by infrared reflection absorption spectroscopy and rotating disk electrode

The electrooxidation of CO has been studied on reconstructed gold single-crystal surfaces by a combination of electrochemical (EC) and infrared reflection absorption spectroscopy (IRAS) measurements. Emphasis is placed on relating the vibrational properties of the CO adlayer to the voltammetric and other macroscopic electrochemical responses, including rotating disk electrode measurements of the catalytic activity. The IRAS data show that the C-O stretching frequencies are strongly dependent on the surface orientation and can be observed in the range 1940-1990 cm(-1) for the 3-fold bridging, 2005-2070 cm(-1) for the 2-fold bridging, and 2115-2140 for the terminal position. The most complex CO spectra are found for the Au(110)-(1 x 2) surface, i.e., a band near 1965 cm(-1), with the second, weaker band shifted positively by about 45 cm(-1) and, finally, a weak band near 2115 cm(-1). While the C-O stretching frequencies for a CO adlayer adsorbed on Au(111)-(1 x 23) show nu(CO) bands at 2029-2069 cm(-1) and at 1944-1986 cm(-1), on the Au(100)-"hex" surface a single CO band is observed at 2004-2029 cm(-1). In the "argon-purged" solution, the terminal nu(CO) band on Au(110)-(1 x 2) and the 3-fold bridging band on the Au(111)-(1 x 23) disappear entirely. The IRAS/EC data show that the kinetics of CO oxidation are structure sensitive; i.e., the onset of CO oxidation increases in the order Au(110)-(1 x 2) > or = Au(100)-"hex" > Au(111)-(1 x 23). Possible explanations for the structure sensitivity are discussed.     

Surface bonding and dynamical behavior of the CH3SH molecule on Au(111)

The chemisorption of the undissociated CH3SH molecule on the Au(111) surface has been studied at 5 K using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The molecule was found to adsorb on atop Au sites on the defect-free surface. CH3SH undergoes hindered rotation about the Au-S bond on the defect-free surface which is seen in STM as a time-averaged 6-fold pattern. The pattern suggests that the potential minima directions occur for the rotating molecule at the six hollow sites surrounding the atop adsorption site. The barrier for rotation, obtained by DFT calculations, is approximately 0.1 kcal.mol(-1). At low coverages, preferential adsorption occurs at defect sites in the surface, namely, the herringbone "elbows" and random atomic step sites. Molecules adsorbed on these sites do not exhibit rotational freedom.     

Stripping voltammetry of carbon monoxide oxidation on stepped platinum single-crystal electrodes in alkaline solution

The electrochemical oxidation of a CO adlayer on Pt[n(111)x(111)] electrodes, with n = 30, 10, and 5, Pt(111), Pt(110) as well as a Pt(553) electrode (with steps of (100) orientation) in alkaline solution (0.1 M NaOH) has been studied using stripping voltammetry. On these electrodes, it is possible to distinguish CO oxidation at four different active oxidation sites on the surface, i.e. sites with (111), (110) and (100) orientation, and kink sites. The least active site for CO oxidation is the (111) terrace site. Steps sites are more active than the (111) terrace sites, the (110) site oxidizing CO at lower potential than the (100) site. The CO oxidation feature with the lowest overpotential (oxidation potential as low as 0.35 V vs. RHE) was ascribed to oxidation of CO at kink sites. The amount of CO oxidized at the active step or kink sites vs. the amount of CO oxidized at the (111) terrace sites depends on the concentration of the active sites and the time given for the terrace-bound CO to reach the active site. By performing CO stripping on the stepped surfaces at different scan rates, the role of CO surface diffusion is probed. The possible role of electronic effects in explaining the unusual activity and dynamics of CO adlayer oxidation in alkaline solution is discussed.     

甲酸在Au（997）台阶表面的氧化反应

金催化是纳米催化的代表性体系之一,但对金催化作用的理解还存在争议,特别是金颗粒尺寸对其催化作用的影响.金颗粒尺寸减小导致的表面结构主要变化之一是表面配位不饱和金原子密度的增加,因此研究金原子配位结构对其催化作用的影响对于理解金催化作用尺寸依赖性具有重要意义.具有不同配位结构的金颗粒表面可以利用金台阶单晶表面来模拟.我们研究组以同时具有Au(111)平台和Au(111)台阶的Au(997)台阶表面为模型表面,发现Au(111)台阶原子在CO氧化、NO氧化和NO分解反应中表现出与Au(111)平台原子不同的催化性能.负载型Au颗粒催化甲酸氧化反应是重要的Au催化反应之一.本文利用程序升温脱附/反应谱(TDS/TPRS)和X射线光电子能谱(XPS)研究了甲酸在清洁的和原子氧覆盖的Au(997)表面的吸附和氧化反应,观察到Au(111)台阶原子和Au(111)平台原子不同的催化甲酸根氧化反应行为.与甲酸根强相互作用的Au(111)台阶原子表现出比与甲酸根弱相互作用的Au(111)平台原子更高的催化甲酸根与原子氧发生氧化反应的反应活化能.在清洁Au(997)表面,甲酸分子发生可逆的分子吸附和脱附.甲酸分子在Au(111)台阶原子的吸附强于在Au(111)平台原子的吸附. TDS结果表明,吸附在Au(111)台阶原子的甲酸分子的脱附温度在190 K,吸附在Au(111)平台原子的甲酸分子的
　　脱附温度在170 K. XPS结果表明,分子吸附甲酸的C 1s和O 1s结合能分别位于289.1和532.8 eV.利用多层NO2的分解反应在Au(997)表面控制制备具有不同原子氧吸附位和覆盖度的原子氧覆盖Au(997)表面,包括氧原子吸附在(111)台阶位的0.02 ML-O(a)/Au(997)、氧原子同时吸附在(111)台阶位和(111)平台位的0.12 ML-O(a)/Au(997)、氧原子和氧岛吸附在(111)平台位和氧原子吸附在(111)台阶位的0.26 ML-O(a)/Au(997). TPRS和XPS结果表明,甲酸分子在105 K与Au(997)表面原子氧物种反应生成甲酸根和羟基物种,但甲酸根物种的进一步氧化反应依赖于Au原子配位结构和各种表面物种的相对覆盖度.在0.02 ML-O(a)/Au(997)表面暴露0.5 L甲酸时, Au(111)台阶位氧原子完全反应,甲酸过量.表面物种是Au(111)台阶位吸附的甲酸根、羟基和甲酸分子.在加热过程中,甲酸分子与羟基在181 K反应生成甲酸根和气相水分子(HCOOH(a)+ OH(a)= H2O + HCOO(a)),甲酸根在340 K发生歧化反应生成气相HCOOH和CO2分子(2HCOO(a)= CO2+ HCOOH).在0.12 ML-O(a)/Au(997)和0.26 ML-O(a)/Au(997)表面暴露0.5 L甲酸时,甲酸分子完全反应,原子氧过量.表面物种是Au(111)平台位和Au(111)台阶位吸附的甲酸根、羟基和原子氧.在加热过程中, Au(111)平台位和Au(111)台阶位的甲酸根分别在309和340 K同时发生氧化反应(HCOO(a)+ O(a)= H2O + CO2)和歧化反应(2HCOO(a)= CO2+ HCOOH)生成气相CO2, H2O和HCOOH分子.在0.26 ML-O(a)/Au(997)表面暴露10 L甲酸时,甲酸分子和原子氧均未完全消耗.表面物种是Au(111)平台位和Au(111)台阶位吸附的甲酸根、羟基、甲酸分子和原子氧.在加热过程中,除了上述甲酸根的氧化反应和歧化反应,还发生171 K的甲酸分子与羟基的反应(HCOOH(a)+ OH(a)= H2O + HCOO(a))和216 K的羟基并和反应(OH(a)+ OH(a)= H2O + O(a)).     

Ethanol electrooxidation onto stepped surfaces modified by Ru deposition: electrochemical and spectroscopic studies

Oxidation of ethanol on ruthenium-modified Pt(775) and Pt(332) stepped electrodes has been studied using electrochemical and FTIR techniques. It has been found that the oxidation of ethanol on these electrodes takes place preferentially on the step sites yielding CO(2) as the major final product. The cleavage of the C-C bond, which is the required step to yield CO(2), occurs only on this type of site. The presence of low ruthenium coverages on the step sites promotes the complete oxidation of ethanol since it facilitates the oxidation of CO formed on the step from the cleavage of the C-C bond. However, high ruthenium coverages have an important inhibiting effect since the adatoms block the step sites, which are required for the cleavage of the C-C bond. Under these conditions, the oxidation current diminishes and the major product in the oxidation process is acetic acid, which is the product formed preferentially on the (111) terrace sites.     

Application of the site blocking method to the investigation of the kinetics of carbon monoxide electrooxidation on nanostructured Pt

In this work, we apply a recently developed selective site blocking with gold adatoms (Kuznetsov et al. Electrocatal 3:211–220, 2012) for studying the electrooxidation of adsorbed carbon monoxide on electrodeposited Pt. The reaction is studied using chronoamperometry, and the obtained current transients are fitted with a nucleation-and-growth model in order to determine the characteristic kinetic parameters on defect and terrace (facet) sites. We conclude that Au selectively blocks defect sites up to very high coverages of 0.42 MLs, strongly slowing down the reaction kinetics. Blocking of defect sites with Au adatoms also results in an increase of the packing density of CO on terrace sites. The rate constant of CO oxidation on defects is higher than that on terraces and exhibits higher Tafel slope.     

The influence of metal cluster size on adsorption energies: CO adsorbed on Au clusters supported on TiO2

Infrared reflection absorption spectroscopy (IRAS) has been used to study CO adsorption on Au clusters ranging in size from 1.8 to 3.1 nm, supported on TiO(2). The adsorbed CO vibrational frequency blue-shifts slightly (approximately 4 cm(-)(1)) compared to that adsorbed on bulk Au, whereas the heats of adsorption (-DeltaH(ads)) increase sharply with decreasing cluster size, from 12.5 to 18.3 kcal/mol.     

Adsorption of carbon monoxide on Pd (210) and (510) surfaces

Adsorption of carbon monoxide on Pd (210) and (510) stepped surfaces has been investigated by the extended London‐Eyring‐Polyani‐Sato method constructed using a five‐parameter Morse potential. Pd (210) and (510) stepped surfaces consist of terrace with (100) structure and step with (110) character. These results show that there exist common characteristics of CO adsorption on these two surfaces. At low coverage, CO adsorbs in twofold bridge site of the (100) terrace. The critical characteristics inherit that of CO molecule adsorbed in twofold bridge site of (100) original surface. When the coverage is increased, the top site of (110) step is occupied. The critical characteristics resemble that of CO molecule adsorbed in top site of (110) original surface. A number of new sites are exposed on the boundary regions, for example, the fivefold hollow site (H) of these two surfaces. There are stable adsorption sites at high coverage. Because of the different length of the (100) terrace, the (210) and (510) stepped surfaces have some different characteristics. First, CO is tilted adsorption on bridge site of terrace of (210), but perpendicular on terrace of (510) surface. Second, the bridge site (B₁) where one Pd atom at the top of the step and the other at the bottom of the step is a stable adsorption site on (210), but the same type of site on Pd (510) surface is not. Copyright © 2012 John Wiley & Sons, Ltd.     

Kinetic studies of adsorbed CO electrochemical oxidation on Pt(335) at full and sub-saturation coverages

Electrochemical measurements were performed to characterize the kinetics of adsorbed CO oxidation on the surface of the stepped Pt(s)-[4(111)x(100)][triple bond, length half m-dash]Pt(335) single crystal electrode. For CO adsorbed to full coverage at 0.1 V (versus the reversible hydrogen electrode, RHE) in 0.5 M H(2)SO(4) at ambient temperature (23 degrees C), oxidation of the layer gave 7.6 x 10(14) +/- 0.3 CO/cm(2) as the saturation CO coverage, just below the average value reported for CO on Pt(335) in ultra high vacuum (8.3 x 10(14) +/- 0.6 CO/cm(2)). In potential step measurements carried out between 0.75 and 0.9 V, the peak region in the current-time transient was consistent with the surface reaction between adsorbed CO and adsorbed oxide as rate limiting. Plotting the log of the rate constant for the surface reaction versus potential gave a Tafel slope of 79 mV per decade, consistent with responses for CO electrochemical oxidation on structurally related stepped Pt electrodes. For CO coverages below saturation, current-time transients were more stable in 0.05 M H(2)SO(4) than in the higher concentration electrolyte. Numerically solving the rate equations to the Langmuir-Hinshelwood model of adsorbed CO electrochemical oxidation reproduced the main features in current-time transients measured at 0.7 V in 0.05 M H(2)SO(4) for sub-saturation CO coverages. The results provide new insights into CO oxidation on Pt at sub-saturation coverage and confirm that anions play a role in CO surface chemistry.     

Dynamics of CO at the solid/liquid interface studied by modeling and simulation of CO electro-oxidation on Pt and PtRu electrodes

We consider theoretical models for CO monolayer oxidation on stepped Pt single-crystal electrodes and Ru-modified Pt(111) electrodes. For both systems, our aim is to assess the importance of CO surface diffusion in reproducing the experimental chronoamperometry or voltammetry. By comparing the simulations with the experimental chronoamperometric transients for CO oxidation on a series of stepped Pt surfaces, it was concluded that mixing of CO on the Pt(111) terrace is good, implying rapid diffusion (N. P. Lebedeva, M. T. M. Koper, J. M. Feliu and R. A. van Santen, J. Phys. Chem. B, submitted). We discuss here a more detailed model in which the CO adsorbed on steps is converted into CO adsorbed on terraces as the oxygen-containing species occupy the steps (as observed experimentally on stepped Pt in UHV), followed by a subsequent oxidation of the latter, to reproduce the observed chronoamperometry on stepped surfaces with a higher step density. On Ru-modified Pt(111), the experimentally observed splitting of the CO stripping voltammetry into two stripping peaks, may suggest a slow diffusion of CO on Pt(111). This apparent contradiction with the conclusions of the experiments on stepped surfaces, is resolved by assuming a weaker CO binding to a Pt atom which has Ru neighbors than to "bulk" Pt(111), in agreement with recent quantum-chemical calculations. This makes the effective diffusion from the uncovered Pt(111) surface to the perimeter of the Ru islands, which are considered to be the active sites in CO oxidation electrocatalysis on PtRu surfaces, very slow. Different models for the reaction are considered, and discussed in terms of their ability to explain experimental observations.     

In situ infrared reflection absorption spectroscopy of carbon monoxide adsorbed on Pt(S)-[n(100)x(110)] electrodes

Structural effects on the adsorption of CO have been studied using infrared reflection absorption spectroscopy (IRAS) on Pt(S)-[n(100)x(110)] surfaces (n = 2, 5, 9) that have densely packed kink atoms in the step. Coverage and potential dependence of the IRAS spectra are scrutinized. On-top and bridge-bonded CO are found on all of the surfaces examined. CO is adsorbed on only kink at low coverage (thetaCO < or = 0.2). Adsorbed CO on kink gives an IR band at lower frequency than that on step. CO is adsorbed on both kink and terrace at 0.3 < or = thetaCO. Water is adsorbed on the terrace of Pt(510) n = 5 and Pt(910) n = 9 at low CO coverage, but water is not found on Pt(210) n = 2 of which the first layer is composed of only kink atoms. It is suggested that coadsorbed water on the terrace enhances the activity for the oxidation of adsorbed CO on the kink remarkably.     

氧原子在Pt(s)-[n(111)×(100)]型台阶面上的吸附和振动

应用原子和表面簇合物相互作用的5-参数Morse势(简称5-MP)方法系统地研究了氧-铂台阶面体系.理论结果表明:在Pt(s)-[n(111)×(100)]型台阶面上，氧原子吸附在台阶下的四重位，对应稳定吸附态β2；平台上靠近四重位的三重吸附态被湮灭，其它三重位对应吸附态β1；而且平台的长度对四重吸附态有影响.     

DFT investigation of CO adsorption on Pt(211) and Pt(311) surfaces from low to high coverage

Adsorption of CO on Pt(211) and Pt(311) surfaces has been investigated by the density functional theory (DFT) method (periodic DMol3) with full geometry optimization. Adsorption energies, structures, and C-O stretching vibrational frequencies are studied by considering multiple possible adsorption sites and comparing them with the experimental data. The calculated C-O stretching frequencies agree well with the experimental ones, and precise determination of adsorption sites can be carried out. For Pt(211), CO adsorbs at the atop site on the step edge at low coverage, but CO adsorbs at the atop and bridge sites simultaneously on both the step edge and the terrace with further increasing CO coverage. The present results interpret the reflection adsorption infrared (RAIR) spectra of Brown and co-workers very well from low to high coverage. For Pt(311), CO adsorbs also at the atop site on the step edge at low coverage. The lifting of reconstruction by CO adsorption occurs also for Pt(311), whereas the energy gain for lifting the reconstruction of the Pt(311) surface is smaller than that for Pt(110). The largest difference between the stepped Pt(211)/Pt(311) and Pt(110) surfaces is the occupation on the edge sites at higher coverage. For the stepped surfaces, the bridge site begins to be occupied at higher coverage, whereas the atop site is always occupied for the Pt(110) surface.     

纳米Pd和Au催化CO2还原粒径效应的密度泛函理论计算研究

以可再生能源为能量来源,在水溶液中进行的光(电)催化CO₂还原生成高附加值化学品和燃料是解决能源危机与环境污染的有效途径之一.CO是一种简单却很重要的CO₂还原产物,它可以作为水煤气变换反应与费托合成的重要原料.具有较高CO选择性的贵金属纳米颗粒催化剂(如Au和Pd)一直受到研究者的广泛关注.一般来说,金属颗粒催化剂的催化性能与粒径大小密切相关,即所谓的粒径效应.然而在实际的理论计算研究中,由于受到计算能力的限制,催化剂模型都仅局限于简单的周期性模型或小的金属团簇模型,无法准确描述真实颗粒上复杂的反应位点的性质,导致了对催化行为的误解.因此,建立更加真实的颗粒模型对探究纳米颗粒催化剂上活性位点的性质,解释其粒径效应至关重要.本文旨在阐述Au与Pd纳米颗粒催化剂不同活性位点上CO₂还原反应与产H2副反应的竞争机制,并解释Au与Pd纳米颗粒催化剂在CO₂电还原中表现出不同粒径效应的原因.本文基于密度泛函理论,采用VASP软件,BEEF-vdW泛函进行计算.分别建立了原子数为55,147,309和561的颗粒模型和高CO^*覆盖度模型,避免了传统周期性模型的局限性,探究了金属颗粒催化剂不同反应位点上的CO选择性.结果表明,对于颗粒模型来说,(100)位点对CO的选择性优于边缘位点;但对于周期性模型来说,Au(211)对CO的选择性则优于Au(100).产生这种反差的主要原因在于Au颗粒的边缘位点对H*的吸附过强.通过对比,我们直观地展现了颗粒模型上平面位点和Edge位点与相对应的周期性模型上CO选择性的区别,突出了模型选择对揭示活性位点性质的重要性.在此基础上,通过计算理论CO法拉第效率,发现Au颗粒随着粒径的减小,CO选择性降低,与实验的趋势一致.对于Pd催化剂来说,低覆盖度模型无法正确预测活性位点的性质;而高CO覆盖度的情况下,Pd颗粒的边缘位点对COOH^*吸附能更强,这是导致边缘位点上CO选择性更高的主要原因.同样通过计算理论CO法拉第效率,发现随着粒径的减小,Pd颗粒上CO选择性升高.本文不仅成功揭示了Au与Pd颗粒催化剂上活性位点的性质,对粒径效应做出了合理解释,也强调了合理的计算模型是理论研究的基础.     

Comprehensive mechanism and structure-sensitivity of ethanol oxidation on platinum: new transition-state searching method for resolving the complex reaction network

Ethanol oxidation on Pt is a typical multistep and multiselectivity heterogeneous catalytic process. A comprehensive understanding of this fundamental reaction would greatly benefit design of catalysts for use in direct ethanol fuel cells and the degradation of biomass-derived oxygenates. In this work, the reaction network of ethanol oxidation on different Pt surfaces, including close-packed Pt{111}, stepped Pt{211}, and open Pt{100}, is explored thoroughly with an efficient reaction path searching method, which integrates our new transition-state searching technique with periodic density functional theory calculations. Our new technique enables the location of the transition state and saddle points for most surface reactions simply and efficiently by optimization of local minima. We show that the selectivity of ethanol oxidation on Pt depends markedly on the surface structure, which can be attributed to the structure-sensitivity of two key reaction steps: (i) the initial dehydrogenation of ethanol and (ii) the oxidation of acetyl (CH3CO). On open surface sites, ethanol prefers C-C bond cleavage via strongly adsorbed intermediates (CH2CO or CHCO), which leads to complete oxidation to CO2. However, only partial oxidizations to CH3CHO and CH3COOH occur on Pt{111}. Our mechanism points out that the open surface Pt{100} is the best facet to fully oxidize ethanol at low coverages, which sheds light on the origin of the remarkable catalytic performance of Pt tetrahexahedra nanocrystals found recently. The physical origin of the structure-selectivity is rationalized in terms of both thermodynamics and kinetics. Two fundamental quantities that dictate the selectivity of ethanol oxidation are identified: (i) the ability of surface metal atoms to bond with unsaturated C-containing fragments and (ii) the relative stability of hydroxyl at surface atop sites with respect to other sites.     

CO organization at ambient pressure on stepped Pt surfaces: first principles modeling accelerated by neural networks

Step and kink sites at Pt surfaces have crucial importance in catalysis. We employ a high dimensional neural network potential (HDNNP) trained using first-principles calculations to determine the adsorption structure of CO under ambient conditions (T = 300 K and P = 1 atm) on these surfaces. To thoroughly explore the potential energy surface (PES), we use a modified basin hopping method. We utilize the explored PES to identify the adsorbate structures and show that under the considered conditions several low free energy structures exist. Under the considered temperature and pressure conditions, the step edge (or kink) is totally occupied by on-top CO molecules. We show that the step structure and the structure of CO molecules on the step dictate the arrangement of CO molecules on the lower terrace. On surfaces with (111) steps, like Pt(553), CO forms quasi-hexagonal structures on the terrace with the top site preferred, with on average two top site CO for one multiply bonded CO, while in contrast surfaces with (100) steps, like Pt(557), present a majority of multiply bonded CO on their terrace. Short terraced surfaces, like Pt(643), with square (100) steps that are broken by kink sites constrain the CO arrangement parallel to the step edge. Overall, this effort provides detailed analysis on the influence of the step edge structure, kink sites, and terrace width on the organization of CO molecules on non-reconstructed stepped surfaces, yielding initial structures for understanding restructuring events driven by CO at high coverages and ambient pressure.

A neural network potential trained using first-principles calculations enables to understand the adsorption configurations of carbon monoxide on stepped Pt surfaces at ambient pressure.     

Adsorption/oxidation of CO on highly dispersed Pt catalyst studied by combined electrochemical and ATR-FTIRAS methods: oxidation of CO adsorbed on carbon-supported Pt catalyst and unsupported Pt black

ATR-FTIRAS measurements combined with linear potential sweep voltammetry were conducted to investigate oxidation of CO adsorbed on a highly dispersed Pt catalyst supported on carbon black, Pt/C, and carbon-unsupported Pt black catalyst, Pt-B. Bands nu(CO) of atop- and bridge-bonded COs were resolved into those of COs adsorbed at terrace and step edge sites by curve-fitting analysis. At the high coverage near the saturation, a band around 1950-1960 cm(-1) assigned to asymmetric bridge-bonded CO, CO(B)(asym), was observed to develop on both Pt/C and Pt-B, which was the predominant type on the latter. Preferential oxidation of atop-CO adsorbed at the step edge site was commonly observed on both Pt/C and Pt-B during the potential sweep from 0.05 to 1.2 V. However, it has been found that CO(B)(asym) is the most reactive species. The high reactivity of the CO(B)(asym) on Pt/C and Pt-B is demonstrated for the first time in the present report. Adsorption of CO on the Pt/C and Pt-B resulted in growth of a sharp nu(OH) band around 3642-3645 cm(-1) which is assigned to non-hydrogen-bonded water molecules coadsorbed with CO. The nu(OH) band frequency exhibits a linear increase with potential with a Stark tuning rate of ca. 20 cm(-1)/V. Analysis of the potential dependence of this band in the CO oxidation potential region led us to conclude that this is the oxygen-containing species to oxidize adsorbed CO. Stark tuning rates of nu(CO) bands for the COs at the terrace and step edge sites on both Pt/C and Pt-B are almost independent of the adsorption sites for both atop- and bridge-bonded COs. However, CO(B)(asym) exhibits tuning rates of 41 cm-1/V and 37 cm-1/ V on Pt/C and Pt-B, respectively, which is in between the rates of atop and symmetric bridge-bonded COs.