Dynamics of surface catalyzed reactions; the roles of surface defects, surface diffusion, and hot electrons

The mechanism that controls bond breaking at transition metal surfaces has been studied with sum frequency generation (SFG), scanning tunneling microscopy (STM), and catalytic nanodiodes operating under the high-pressure conditions. The combination of these techniques permits us to understand the role of surface defects, surface diffusion, and hot electrons in dynamics of surface catalyzed reactions. Sum frequency generation vibrational spectroscopy and kinetic measurements were performed under 1.5 Torr of cyclohexene hydrogenation/dehydrogenation in the presence and absence of H(2) and over the temperature range 300-500 K on the Pt(100) and Pt(111) surfaces. The structure specificity of the Pt(100) and Pt(111) surfaces is exhibited by the surface species present during reaction. On Pt(100), pi-allyl c-C6H9, cyclohexyl (C6H11), and 1,4-cyclohexadiene are identified adsorbates, while on the Pt(111) surface, pi-allyl c-C6H9, 1,4-cyclohexadiene, and 1,3-cyclohexadiene are present. A scanning tunneling microscope that can be operated at high pressures and temperatures was used to study the Pt(111) surface during the catalytic hydrogenation/dehydrogenation of cyclohexene and its poisoning with CO. It was found that catalytically active surfaces were always disordered, while ordered surface were always catalytically deactivated. Only in the case of the CO poisoning at 350 K was a surface with a mobile adsorbed monolayer not catalytically active. From these results, a CO-dominated mobile overlayer that prevents reactant adsorption was proposed. By using the catalytic nanodiode, we detected the continuous flow of hot electron currents that is induced by the exothermic catalytic reaction. During the platinum-catalyzed oxidation of carbon monoxide, we monitored the flow of hot electrons over several hours using a metal-semiconductor Schottky diode composed of Pt and TiO2. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path, resulting in the ballistic transport of hot electrons through the metal. The electron flow was detected as a chemicurrent if the excess electron kinetic energy generated by the exothermic reaction was larger than the effective Schottky barrier formed at the metal-semiconductor interface. The measurement of continuous chemicurrent indicated that chemical energy of exothermic catalytic reaction was directly converted into hot electron flux in the catalytic nanodiode. We found the chemicurrent was well-correlated with the turnover rate of CO oxidation separately measured by gas chromatography.     

Electron flow generated by gas phase exothermic catalytic reactions using a platinum-gallium nitride nanodiode

We report steady-state conversion of chemical reaction energy into hot electrons by ballistic injection into a platinum-gallium nitride (Pt/GaN) nanodiode during the platinum-catalyzed oxidation of carbon monoxide. Surface catalytic reactions of molecules from the gas phase generated continuous steady-state hot electron currents with energies at least that of Schottky barrier energy ( approximately 1 eV). These hot electron currents were observed on two different nanodiodes (Pt/TiO2 and Pt/GaN) and represent a new method of chemical energy conversion.     

Chemical‐Reaction‐Induced Hot Electron Flows on Platinum Colloid Nanoparticles under Hydrogen Oxidation: Impact of Nanoparticle Size

Generation of hot electron flows and the catalytic activity of Pt nanoparticles (NPs) with different sizes were investigated using catalytic nanodiodes. We show that smaller Pt NPs lead to higher chemicurrent yield, which is associated with the shorter travel length for the hot electrons, compared with their inelastic mean free path. We also show the impact of capping on charge carrier transfer between Pt NPs and their support.     

Hot electron generation on metal catalysts under surface reaction: Principles,devices, and application

Transfer of charge through metal-support interfaces leads to an increase in the activity of mixed catalysts. In this review, we consider the main aspects of research aimed at studying processes that create and allow interphase transfer of highly excited (hot) charge carriers in supported catalysts, and discuss the effect of these phenomena on catalytic activity.     

Enhanced low-temperature CO oxidation on a stepped platinum surface for oxygen pressures above 10(-5) Torr

The rate of CO oxidation has been characterized on the stepped Pt(411) surface for oxygen pressures up to 0.002 Torr, over the 100-1000 K temperature range. CO oxidation was characterized using both temperature-programmed reaction spectroscopy (TPRS) and in situ soft X-ray fluorescence yield near-edge spectroscopy (FYNES). New understanding of the important role surface defects play in accelerating CO oxidation for oxygen pressure above 10(-5) Torr is presented in this paper for the first time. For saturated monolayers of CO, the oxidation rate increases and the activation energy decreases significantly for oxygen pressures above 10(-5) Torr. This enhanced CO oxidation rate is caused by a change in the rate-limiting step to a surface reaction limited process above 10(-5) Torr oxygen from a CO desorption limited process at lower oxygen pressure. For example, in oxygen pressures above 0.002 Torr, CO(2) formation begins at 275 K even for the CO saturated monolayer, which is well below the 350 K onset temperature for CO desorption. Isothermal kinetic measurements in flowing oxygen for this stepped surface indicate that activation energies and preexponential factors depend strongly on oxygen pressure, a factor that has not previously been considered critical for CO oxidation on platinum. As oxygen pressure is increased from 10(-6) to 0.002 Torr, the oxidation activation energies for the saturated CO monolayer decrease from 24.1 to 13.5 kcal/mol for reaction over the 0.95-0.90 ML CO coverage range. This dramatic decrease in activation energy is associated with a simple increase in oxygen pressure from 10(-5) to 10(-3) Torr. Activation energies as low as 7.8 kcal/mol were observed for oxidation of an initially saturated CO layer reacting over the 0.4-0.25 ML coverage range in oxygen pressure of 0.002 Torr. These dramatic changes in reaction mechanism with oxygen pressure for stepped surfaces are consistent with mechanistic models involving transient low activation energy dissociation sites for oxygen associated with step sites. Taken together these experimental results clearly indicate that surface defects play a key role in increasing the sensitivity of CO oxidation to oxygen pressure.     

Hot Electrons at Solid–Liquid Interfaces: A Large Chemoelectric Effect during the Catalytic Decomposition of Hydrogen Peroxide

The study of energy and charge transfer during chemical reactions on metals is of great importance for understanding the phenomena involved in heterogeneous catalysis. Despite extensive studies, very little is known about the nature of hot electrons generated at solid–liquid interfaces. Herein, we report remarkable results showing the detection of hot electrons as a chemicurrent generated at the solid–liquid interface during decomposition of hydrogen peroxide (H₂O₂) catalyzed on Schottky nanodiodes. The chemicurrent reflects the activity of the catalytic reaction and the state of the catalyst in real time. We show that the chemicurrent yield can reach values up to 10^?1 electrons/O₂ molecule, which is notably higher than that for solid–gas reactions on similar nanodiodes.     

Oscillatory reactions on single crystal surfaces

Heterogeneous catalytic reactions exhibit under certain conditions kinetic oscillations which have been investigated both with polycrystalline materials and with single crystal surfaces as catalysts. The present paper reviews single-crystal experiments conducted under isothermal, low pressure conditions (p < 10^-3 mbar). Two different reaction systems have been investigated: catalytic CO oxidation on various Pt and Pd orientations and catalytic NO reduction on Pt(100) using CO, H₂, or NH₃ as the reducing agent. The different reaction systems exhibit a wide variety of interesting phenomena which are well-known in nonlinear dynamics, for example, such as spatiotemporal pattern formation, the existence of Turing structures and the appearance of deterministic chaos, and chemical turbulence. The mechanistic steps leading to the observed phenomena have been investigated and appropriate mathematical models have been formulated and analyzed using bifurcation theory. The driving force for the rate oscillations has been shown to result from structural changes of the substrate in the case of catalytic CO oxidation on Pt surfaces, subsurface oxygen formation in the case of catalytic CO oxidation on Pd surfaces, and in the chemical reaction network described by a vacancy model in the case of the NO reduction reactions.     

Evolution of the surface science of catalysis from single crystals to metal nanoparticles under pressure

Vacuum studies of metal single crystal surfaces using electron and molecular beam scattering revealed that the surface atoms relocate when the surface is clean (reconstruction) and when it is covered by adsorbates (adsorbate-induced restructuring). It was also discovered that atomic steps and other low coordination surface sites are active for breaking chemical bonds (H-H, O=O, C-H, C=O, and C-C) with high reaction probability. Investigations at high reactant pressures using sum frequency generation-vibrational spectroscopy and high pressure scanning tunneling microscopy revealed bond breaking at low reaction probability sites on the adsorbate-covered metal surface and the need for adsorbate mobility for continued turnover. Since most catalysts (heterogeneous, enzyme, and homogeneous) are nanoparticles, colloid synthesis methods were developed to produce monodispersed metal nanoparticles in the 1-10 nm range and controlled shapes to use them as new model catalyst systems in two-dimensional monolayer film or deposited in mesoporous three-dimensional oxides. Studies of reaction selectivity in multipath reactions (hydrogenation of benzene, cyclohexene, and crotonaldehyde) showed that the reaction selectivity depends on both nanoparticle size and shape. The oxide-metal nanoparticle interface was found to be an important catalytic site that is associated with the hot electron flow induced by exothermic reactions such as carbon monoxide oxidation.     

Catalytic Oxidation of CO on a Curved Pt(111) Surface: Simultaneous Ignition at All Facets through a Transient CO-O Complex**

The catalytic oxidation of CO on transition metals, such as Pt, is commonly viewed as a sharp transition from the CO-inhibited surface to the active metal, covered with O. However, we find that minor amounts of O are present in the CO-poisoned layer that explain why, surprisingly, CO desorbs at stepped and flat Pt crystal planes at once, regardless of the reaction conditions. Using near-ambient pressure X-ray photoemission and a curved Pt(111) crystal we probe the chemical composition at surfaces with variable step density during the CO oxidation reaction. Analysis of C and O core levels across the curved crystal reveals that, right before light-off, subsurface O builds up within (111) terraces. This is key to trigger the simultaneous ignition of the catalytic reaction at different Pt surfaces: a CO-Pt-O complex is formed that equals the CO chemisorption energy at terraces and steps, leading to the abrupt desorption of poisoning CO from all crystal facets at the same temperature.     

单原子催化剂M1/FeOx(M=Pt,Fe)的理论研究:CO氧化反应

负载型纳米贵金属催化剂是用于多相催化反应的重要的催化剂之一,也是各国催化科学与技术研发的重点,其工业应用也越来越广泛.理论和实验的研究结果均表明,当载体表面的金属粒子尺寸减小至亚纳米级乃至更小的低配位、不饱和的原子团簇时,它们常常成为诱发催化反应的活性中心,呈现更高的催化活性和选择性.将负载的金属尺寸由纳米量级减小至分散的金属团簇甚至单原子而使每个原子成为反应的活性位点已成为研究的重点.最近,由张涛等首次合成的单原子催化剂(SAC)Pt1/FeOx引起了国内外催化及表面科学工作者的极大关注.单原子催化剂作为连接均相催化剂和多相催化剂的桥梁,不仅具有非均相催化剂的稳定、易于与反应体系分离、易表征等优点,而且具有均相催化剂活性中心结构均一、活性中心原子利用率百分之百等优点.一方面,单原子催化剂给多相催化领域注入了新的活力,另一方面也更有利于运用量子与计算化学的研究方法建立与实验相匹配的理论模型并从原子水平上进一步理解多相催化反应的微观作用机理.实验和理论的研究结果表明,其它单原子催化剂如Ir1/FeOx,Au1/FeOx和Ni1/FeOx催化CO氧化反应表现出不同的活性.然而,底物FeOx中的Fe同样是第VIII族中的3d过渡金属,却在低温下对CO氧化反应没有催化活性.我们围绕这一问题,重点研究了底物FeOx在负载单原子Pt1前后催化CO氧化的反应机理和活性,解释了单原子催化剂Pt1/FeOx相比于底物FeOx为何具有如此高的催化活性的原因.我们采用Vienna Ab-initio Simulation Package(VASP)从头算模拟软件和密度泛函理论(DFT)的广义梯度近似(GGA)进行了理论计算.其中,选择PBE泛函描述体系的交换关联相互作用,用投影缀加波(PAW)赝势基组方法描述体系中的电子和离子实之间的相互作用,对Fe原子采用了DFT+U方法进行d电子强相关校正,并使用Dimer计算方法搜寻反应过渡态.研究结果表明,底物FeOx中氧空位的再生伴随第二个CO2分子从催化剂表面脱附的过程需要较高的活化势垒(1.09 eV),这一过程是整个CO氧化反应的决速步.与此相比较,Pt1/FeOx催化剂中,由于Pt原子代替了表面Fe原子,导致电子结构及性质的显著变化,有利于CO的活化、氧化和CO2的脱附.我们从电子能量态密度(DOS)和Bader电荷分析及模型分子团簇的轨道相互作用的角度进一步分析了两种催化剂存在差异的本质;揭示了单原子催化剂Pt1/FeOx中Pt1和底物FeOx之间的相互作用的机理及催化剂表面Pt单原子在催化反应过程中的关键作用.     

Physicochemical and functional properties of modified tin dioxide

Specimens of tin dioxide with modifying Sb and Pt additives are synthesized. Their physicochemical properties (specific surface area, porosity, and conductivity), chemisorption and catalytic activity in the model reaction of CO oxidation are studied. A considerable chemisorption of CO on SnO₂ and SnO₂-SbO _x is observed at 150–180°C. The oxidation of CO in the flow of gases starts in the same temperature range. An addition of platinum leads to a significant increase in the rate of CO oxidation, the reaction starts at 80°C. It is proposed that the process proceeds at the SnO₂/Pt interface.     

可见光诱导提升Pt/g-C3N4纳米片甲酸氧化性能的研究

以半导体材料类石墨氮化碳纳米片(g-C₃N₄纳米片)为载体,通过微波-多元醇法构筑了Pt/g-C₃N₄纳米片催化剂. 通过TEM、XRD、XPS、紫外-可见吸收光谱等方法对Pt/g-C₃N₄纳米片催化剂的粒径尺寸、组成、结构、光学等性质进行分析. 通过对比可见光照和暗室条件下的甲酸电氧化活性,Pt/g-C₃N₄纳米片催化剂在可见光照射下展现出良好的催化性能. 该性能的提高一方面可能是由于g-C₃N₄纳米片在可见光照射下加速了电子从Pt转移给g-C₃N₄纳米片,Pt处于“电子匮乏”状态,可削弱CO与Pt之间的化学键能,减弱CO在Pt表面的吸附能力,促进了CO的氧化,提高了催化剂抗中毒能力;另一方面,g-C₃N₄纳米片在光照条件下分离出的空穴可有效氧化甲酸分子,提高甲酸氧化活性. 因此,可见光条件下可有效提高Pt/g-C₃N₄纳米片催化剂甲酸催化氧化活性,这为直接甲酸燃料电池的发展提供了新思路.     

Experimental study of intermediates and wave phenomena in co oxidation on platinum metal (Pt,Pd) surfaces

The mechanism of catalytic CO oxidation on Pt(100) and Pd(110) single-crystal surfaces and on Pt and Pd sharp tip (～10³ Å) surfaces has been studied experimentally by temperature-programmed reaction, temperature desorption spectroscopy, field electron microscopy, and molecular beam techniques. Using the density functional theory the equilibrium states and stretching vibrations of oxygen atoms adsorbed on the Pt(100) surface have been calculated. The character of the mixed adsorption layer was established by high resolution electron energy loss spectroscopy—molecular adsorption (O_2ads, CO_ads) on Pt(100)-hex and dissociative adsorption (O_ads, CO_ads) on Pt(100)-(1×1). The origin of kinetic self-oscillations for the isothermal oxidation of CO in situ was studied in detail on the Pt and Pd tips by field electron microscopy. The initiating role of the reversible phase transition (hex) ? (1 × 1) of the Pt(100) nanoplane in the generation of regular chemical waves was established. The origination of self-oscillations and waves on the Pt(100) nanoplane was shown to be caused by the spontaneous periodical transition of the metal from the low-active state (hex) to the highly active catalytic state (1 × 1). A relationship between the reactivity of oxygen atoms (O_ads) and the concentration of CO_ads molecules was revealed for the Pd(110) surface. Studies using the isotope label ¹⁸O_ads demonstrated that the low-temperature formation of CO₂ at 150 K is a result of the reaction of CO with the highly reactive state of atomic oxygen (O_ads). The possibility of the low-temperature oxidation of CO via interaction with the so-called “hot” oxygen atoms (O_hot) appearing on the surface at the instant of dissociation of O_2ads molecules was studied by the molecular beam techniques.     

铂族金属催化剂低温 CO氧化研究近期进展

CO氧化可能是多相催化领域最常见的反应,它不仅能作为探针反应研究催化剂结构、反应活性位等,而且在诸多实际过程如空气净化、汽车尾气污染物控制、燃料电池所用氢源净化等扮演重要角色.最早的 CO氧化催化剂为霍加拉特剂,其组分主要为 CuO与 MnO2混合氧化物,然而在实际应用过程中存在低温活性低、吸湿易失活等缺点.1987年, Haruta等发现湿化学法制备的氧化物负载 Au催化剂表现出非常高的低温 CO氧化活性及耐水稳定性,其 Au粒子以纳米尺度分散,进而引发了催化研究领域的“淘金热”及纳米催化研究热潮.而 CO氧化通常作为考察 Au催化剂结构性质的探针反应,也成为考核其它金属催化剂是否具有高活性的判据之一. Pt族金属上 CO氧化反应从 Langmuir等研究开始至今已有100多年,然而低温下该金属催化剂活性与 Au催化剂相比要低一个数量级.本质原因为 Pt族金属上 CO吸附较强, O2吸附与活化受到抑制,而该步骤被认为是 CO氧化的速控步,因而表现出较低的催化活性.通常 Pt族金属催化剂需要100oC以上 CO才能脱附, O2进而得以吸附.目前研究人员采取多种策略,其基本原则为削弱 Pt族金属上 CO吸附强度或者提供其它活性位供 O2吸附与活化.本综述将概括近十年来Pt族金属催化剂 CO氧化研究进展,主要总结室温甚至超低温条件下的研究成果.高活性 CO氧化催化剂主要是通过采用可还原氧化物为载体或助剂,或者改变催化剂表面性质如使表面富 OH基物种来形成. Au催化剂的研究发现,改变金属粒子尺寸极有可能获得不同寻常的催化性能,而常规的 Pt族金属催化剂研究主要是在纳米尺度.近期人们发现逐渐减小 Pt族金属粒子尺寸,从纳米到亚纳米甚至单原子时,其电荷状态逐渐呈正价形式,这有利于削弱其 CO吸附强度.此外,可通过增强金属载体间的相互作用,改变金属载体接触方式,如从核壳到交叉结联结构,构筑出更多的金属载体界面,使得 O2更容易吸附与活化或稳定更多的 OH基物种进而在此界面与吸附的 CO反应.伴随着表征技术的发展, CO氧化机理的认识也更加深入,这给催化剂的设计带来更多新的思路.(1)改变 CO吸附活化位,将 CO吸附活化位从金属转移到载体上,从而大大降低 CO吸附强度,活化的 CO物种在反应过程中容易溢流到金属载体界面处,这甚至有利于超低温度下(–100oC左右) CO氧化.(2)改变 O2活化形式. O2通常在 Pt族金属上容易以解离氧原子形式存在,通过改变载体、金属载体界面性质使得 O2以分子氧形式活化,如形成超氧或过氧物种,这有利于降低 CO氧化的活化能垒,进而提高其低温甚至超低温下 CO氧化活性.今后,设计并合成出在超低温度下能够氧化 CO的 Pt族金属催化剂将成为 CO氧化催化剂研究的重要方向之一.     

Effects of reduction temperature and metal-support interactions on the catalytic activity of Pt/gamma-Al2O3 and Pt/TiO2 for the oxidation of CO in the presence and absence of H2

TiO2- and gamma-Al2O3-supported Pt catalysts were characterized by HRTEM, XPS, EXAFS, and in situ FTIR spectroscopy after activation at various conditions, and their catalytic properties were examined for the oxidation of CO in the absence and presence of H2 (PROX). When gamma-Al2O3 was used as the support, the catalytic, electronic, and structural properties of the Pt particles formed were not affected substantially by the pretreatment conditions. In contrast, the surface properties and catalytic activity of Pt/TiO2 were strongly influenced by the pretreatment conditions. In this case, an increase in the reduction temperature led to higher electron density on Pt, altering its chemisorptive properties, weakening the Pt-CO bonds, and increasing its activity for the oxidation of CO. The in situ FTIR data suggest that both the terminal and bridging CO species adsorbed on fully reduced Pt are active for this reaction. The high activity of Pt/TiO2 for the oxidation of CO can also be attributed to the ability of TiO2 to provide or stabilize highly reactive oxygen species at the metal-support interface. However, such species appear to be more reactive toward H2 than CO. Consequently, Pt/TiO2 shows substantially lower selectivities toward CO oxidation under PROX conditions than Pt/gamma-Al2O3.     

The impact of geometric and surface electronic properties of pt-catalysts on the particle size effect in electrocatalysis

The particle size effect on the formation of OH adlayer, the CO bulk oxidation, and the oxygen reduction reaction (ORR) have been studied on Pt nanoparticles in perchloric acid electrolyte. From measurements of the CO displacement charge at controlled potential, the corresponding surface charge density versus potential curves yielded the potentials of total zero charge (pztc), which shifts approximately 35 mV negative by decreasing the particle size from 30 nm down to 1 nm. As a consequence, the energy of adsorption of OH is more enhanced, that is, at the same potential the surface coverage with OH increases by decreasing the particle size, which in turn affects the catalytic reactions thereon. The impact of the electronically induced potential shift in the OH adsorption is demonstrated at the CO bulk oxidation, in which adsorbed OH is an educt species and promotes the reaction, and the ORR, where it can act as a surface site blocking species and inhibits the reaction.     

铂、钯负载型活性催化剂的制备及其对一氧化碳的催化氧化活性

用浸渍法分别将铂、钯负载在铝柱撑蒙脱石载体上,制备了铂、钯负载铝柱撑蒙脱石催化剂。运用X射线衍射(XRD)、原子吸收光谱(AAS)、透射电镜(TEM)等分析方法对样品的性能和结构进行了表征,并考察了不同铂、钯负载量的催化剂对一氧化碳的催化氧化性能。结果表明,铂、钯均以高度分散的纳米粒子状态均匀分布在载体表面,并表现出良好的CO催化氧化活性。铂、钯在铝柱撑蒙脱石载体表面的有效负载率在70%~76%之间,在相同的设计负载量条件下,铂的实际负载量和有效负载率均略大于钯。CO催化氧化试验结果表明,相对于负载前,负载后催化剂的催化活性明显增加,且其催化活性随着铂、钯负载量的增加而不断增强。在相同温度和负载量条件下,钯负载型催化剂的催化活性明显高于铂负载型催化剂。     

Inhibition at perimeter sites of Au/TiO2 oxidation catalyst by reactant oxygen

TiO(2)-supported gold nanoparticles exhibit surprising catalytic activity for oxidation reactions compared to noble bulk gold which is inactive. The catalytic activity is localized at the perimeter of the Au nanoparticles where Au atoms are atomically adjacent to the TiO(2) support. At these dual-catalytic sites an oxygen molecule is efficiently activated through chemical bonding to both Au and Ti(4+) sites. A significant inhibition by a factor of 22 in the CO oxidation reaction rate is observed at 120 K when the Au is preoxidized, caused by the oxygen-induced positive charge produced on the perimeter Au atoms. Theoretical calculations indicate that induced positive charge occurs in the Au atoms which are adjacent to chemisorbed oxygen atoms, almost doubling the activation energy for CO oxidation at the dual-catalytic sites in agreement with experiments. This is an example of self-inhibition in catalysis by a reactant species.     

Highly active platinum nanoparticles on graphene nanosheets with a significant improvement in stability and CO tolerance

Graphene nanosheets (GNS) supporting Pt nanoparticles (PNs) are prepared using perfluorosulfonic acid (PFSA) as a functionalization and anchoring agent. Transmission electron microscope (TEM) results indicate that the prepared Pt NPs are uniformly deposited on GNS with a narrow particle size ranging from 1 to 4 nm in diameter. A high catalytic activity of this novel catalyst is observed by both cyclic voltammetry and oxygen reduction reaction (ORR) measurements due to the increasing of proton (H(+)) transmission channels. Significantly, this novel PFSA-functionalized Pt/GNS (PFSA-Pt/GNS) catalyst reveals a better CO oxidation and lower loss rate of electrochemical active area in comparison with that of the plain Pt/GNS and conventional Pt/C catalysts, indicating our PFSA-Pt/GNS catalysts hold much higher stability and CO tolerance by virtue of introduction of PFSA.     

Modification of a Pt surface by spontaneous Sn deposition for electrocatalytic applications. 2. Oxidation of CO,formaldehyde, formic acid,and methanol

The electrocatalytic activity of a spontaneously tin-modified Pt catalyst, fabricated through a simple dip-coating method under open-circuit conditions and characterized using surface analysis methods, was studied in electrooxidation reactions of a preadsorbed CO monolayer and continuous oxidation of methanol, formic acid, and formaldehyde in the potentiodynamic and potentiostatic modes. The catalytic activity of the tin-modified Pt surface is compared with that of a polycrystalline Pt electrode. Spontaneously Sn-modified Pt catalyst shows a superior activity toward adsorbed CO oxidation and thus can be promising for PEFC applications. The methanol oxidation rate is not enhanced on the Sn-modified Pt surface, compared to the Pt electrode. Formic acid oxidation is enhanced in the low potential region on the Sn-modified surface, compared to the Pt electrode. The formaldehyde oxidation rate is dramatically increased by modifying tin species at the most negative potentials, where anodic formaldehyde oxidation is completely suppressed on the pure Pt electrode. The results are discussed in terms of poisoning CO intermediate formation resulting from dehydrogenation of organic molecules on Pt sites, and oxidation of poisoning adsorbed CO species via the surface reaction with OH adsorbed on neighboring Sn sites.