碱性介质中CO对甲醇在PtAu(111)和Pt(111)表面氧化生成甲酸的影响的第一性原理研究

采用密度泛函理论计算研究了碱性介质中甲醇在清洁的PtAu(111)和Pt(111)表面、及有CO存在的PtAu(111)和Pt(111)表面的氧化。计算结果表明,在碱性介质中,预吸附的CO促进了甲醇在PtAu(111)和Pt(111)表面氧化的每一步反应,这与其在Au(111)表面的作用相似。究其原因,是由于CO的吸附增强了OH的稳定性和碱性,从而增强了OH夺取氢原子的能力。     

Self-assembly of mixed Pt and Au nanoparticles on PDDA-functionalized graphene as effective electrocatalysts for formic acid oxidation of fuel cells

Pt and Au nanoparticles with controlled Pt?:?Au molar ratios and PtAu nanoparticle loadings were successfully self-assembled onto poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene (PDDA-G) as highly effective electrocatalysts for formic acid oxidation in direct formic acid fuel cells (DFAFCs). The simultaneously assembled Pt and Au nanoparticles on PDDA-G showed superb electrocatalytic activity for HCOOH oxidation, and the current density associated with the preferred dehydrogenation pathway for the direct formation of CO(2) through HCOOH oxidation on a Pt(1)Au(8)/PDDA-G (i.e., a Pt?:?Au ratio of 1?:?8) is 32 times higher than on monometallic Pt/PDDA-G. The main function of the Au in the mixed Pt and Au nanoparticles on PDDA-G is to facilitate the first electron transfer from HCOOH to HCOO(ads) and the effective spillover of HCOO(ads) from Au to Pt nanoparticles, where HCOO(ads) is further oxidized to CO(2). The Pt?:?Au molar ratio and PtAu nanoparticle loading on PDDA-G supports are the two critical factors to achieve excellent electrocatalytic activity of PtAu/PDDA-G catalysts for the HCOOH oxidation reactions.     

Facile Synthesis of Quasi‐One‐Dimensional Au/PtAu Heterojunction Nanotubes and Their Application as Catalysts in an Oxygen‐Reduction Reaction

An intermediate‐template‐directed method has been developed for the synthesis of quasi‐one‐dimensional Au/PtAu heterojunction nanotubes by the heterogeneous nucleation and growth of Au on Te/Pt core–shell nanostructures in aqueous solution. The synthesized porous Au/PtAu bimetallic nanotubes (PABNTs) consist of porous tubular framework and attached Au nanoparticles (AuNPs). The reaction intermediates played an important role in the preparation, which fabricated the framework and provided a localized reducing agent for the reduction of the Au and Pt precursors. The Pt₇Au PABNTs showed higher electrocatalytic activity and durability in the oxygen‐reduction reaction (ORR) in 0.1 M HClO₄ than porous Pt nanotubes (PtNTs) and commercially available Pt/C. The mass activity of PABNTs was 218 % that of commercial Pt/C after an accelerated durability test. This study demonstrates the potential of PABNTs as highly efficient electrocatalysts. In addition, this method provides a facile strategy for the synthesis of desirable hetero‐nanostructures with controlled size and shape by utilizing an intermediate template.     

Pt (111)面和Pt14团簇上肉桂醛吸附及选择性加氢机理研究

利用密度泛函理论研究了Pt（111）面及Pt₁₄团簇对肉桂醛（CAL）的吸附作用和不完全加氢的反应机理。分析吸附能结果表明,肉桂醛分子以C=O与C=C键协同吸附在Pt（111）面上的六角密积（Hcp）位最稳定,以C=C键吸附在Pt₁₄团簇上最稳定,且在Pt₁₄团簇上的吸附作用较Pt（111）面更强。由过渡态搜索并计算得到的反应能垒及反应热可知,肉桂醛在Pt（111）面和Pt₁₄团簇上均较容易对C=O键加氢得到肉桂醇（COL）。其中,优先加氢O原子为最佳反应路径,即Pt无论是平板还是团簇对肉桂醛加氢均有较好的选择性。同时发现,肉桂醛分子在Pt（111）面的加氢反应能垒较Pt₁₄团簇上更低,即Pt的催化活性及对肉桂醛加氢产物选择性与其结构密切相关,其中,Pt（111）面对生成肉桂醇更加有利。     

Screening by kinetic Monte Carlo simulation of Pt-Au(100) surfaces for the steady-state decomposition of nitric oxide in excess dioxygen

An ab initio-based kinetic Monte Carlo algorithm was developed to simulate the direct decomposition of NO over Pt and different PtAu alloy surfaces. The algorithm was used to test the influence of the composition and the specific atomic surface structure of the alloy on the simulated activity and selectivity to form N2. The apparent activation barrier found for the simulation of lean NO decomposition over Pt(100) was 7.4 kcal/mol, which is lower than the experimental value of 11 kcal/mol that was determined over supported Pt nanoparticles. Differences are likely due to differences in the surface structure between the ideal (100) surface and supported Pt particles. The apparent reaction orders for lean NO decomposition over the Pt(100) substrate were calculated to be 0.9 and -0.5 for NO and O2, respectively. Oxygen acts to poison Pt. Simulations on the different Pt-Au(100) surface alloys indicate that the turnover frequency goes through a maximum as the Au composition in the surface is increased, and the maximum occurs near 44% Au. Turnover frequencies, however, are dictated by the actual arrangements of Pt and Au atoms in the surface rather than by their overall composition. Surfaces with similar compositions but different alloy arrangements can lead to very different activities. Surfaces composed of 50% Pt and 50% Au (Pt4 and Au4 surface ensembles) showed very little enhancement in the activity over that which was found over pure Pt. The Pt-Pt bridge sites required for NO adsorption and decomposition were still effectively poisoned by atomic oxygen. The well-dispersed Pt(50%)Au(50%) alloy, on the other hand, increased the TOF over that found for pure Pt by a factor of 2. The most active surface alloy was one in which the Pt was arranged into "+" ensembles surrounded by Au atoms. The overall composition of this surface is Pt(56.2%)Au(43.8%). The unique "+" ensembles maintain Pt bridge sites for NO to adsorb on but limit O2 as well as NO activation by eliminating next-nearest neighbor Pt-bridge sites. The repulsive interactions between two adatoms prevent them from sharing the same metal atoms. The decrease in the oxygen coverage leads to a greater number of vacant sites available for NO adsorption. This increases the NO coupling reaction and hence N2 formation. The inhibition of the rate of N2 formation by O2 is therefore suppressed. The coverage of atomic oxygen decreases from 53% on the Pt(100) surface down to 19% on the "+" ensemble surface. This increases the rate of N2 formation by a factor of 4.3 over that on pure Pt. The reaction kinetics over the "+" ensemble Pt(56.2%)Au(43.8%) surface indicate apparent reaction orders in NO and oxygen of 0.7 and 0.0, respectively. This suggests that oxygen does not poison the PtAu "+" alloy ensemble. The activity and selectivity of the PtAu ensembles significantly decrease for alloys that go beyond 60% Au. Higher coverages of Au shut down sites for NO adsorption and, in addition, weaken the NO and O bond strengths, which subsequently promotes desorption as well as NO oxidation. The computational approach identified herein can be used to more rapidly test different metal compositions and their explicit atomic arrangements for improved catalytic performance. This can be done "in silico" and thus provides a method that may aid high-throughput experimental efforts in the design of new materials. The synthesis and stability of the metal complexes suggested herein still ultimately need to be tested.     

A first principles study of oxygen reduction reaction on a Pt(111) surface modified by a subsurface transition metal M (M = Ni, Co, or Fe)

We have performed first-principle density functional theory calculations to investigate how a subsurface transition metal M (M = Ni, Co, or Fe) affects the energetics and mechanisms of oxygen reduction reaction (ORR) on the outermost Pt mono-surface layer of Pt/M(111) surfaces. In this work, we found that the subsurface Ni, Co, and Fe could down-shift the d-band center of the Pt surface layer and thus weaken the binding of chemical species to the Pt/M(111) surface. Moreover, the subsurface Ni, Co, and Fe could modify the heat of reaction and activation energy of various elementary reactions of ORR on these Pt/M(111) surfaces. Our DFT results revealed that, due to the influence of the subsurface Ni, Co, and Fe, ORR would adopt a hydrogen peroxide dissociation mechanism with an activation energy of 0.15 eV on Pt/Ni(111), 0.17 eV on Pt/Co(111), and 0.16 eV on Pt/Fe(111) surface, respectively, for their rate-determining O2 protonation reaction. In contrast, ORR would follow a peroxyl dissociation mechanism on a pure Pt(111) surface with an activation energy of 0.79 eV for its rate-determining O protonation reaction. Thus, our theoretical study explained why the subsurface Ni, Co, and Fe could lead to multi-fold enhancement in catalytic activity for ORR on the Pt mono-surface layer of Pt/M(111) surfaces.     

Electrochemical and FTIRS characterisation of NO adlayers on cyanide-modified Pt(111) electrodes: the mechanism of nitric oxide electroreduction on Pt

We report here a study, using cyclic voltammetry and FTIRS, of NO irreversibly adsorbed on a cyanide-modified Pt(111) electrode. NO adlayers were formed by immersion of the cyanide-modified Pt(111) electrode in an acidic solution of KNO(2). The behaviour of NO adsorbed on the cyanide-modified electrode is very similar to that of NO on the clean Pt(111) surface, suggesting that adsorbed cyanide (saturation coverage theta(CN) = 0.5) behaves simply as a third body, blocking some of the surface sites but leaving the free Pt sites unaffected. Comparison of the voltammetric profile for NO electroreduction on Pt(111) and on cyanide-modified Pt(111) electrodes has allowed us: (i) to confirm that the reduction of three-fold hollow NO and atop NO on Pt(111) electrodes occurs in two distinct reduction peaks, as previously proposed by Rosca et al. (Langmuir, 2005, 21, 1448); (ii) to suggest that the reduction of irreversibly adsorbed NO layers on Pt electrodes can proceed through two possible paths, one involving an EE mechanism in which the rate-determining step (rds) is an Eley-Rideal reaction, with a direct proton transfer from the solution to adsorbed NO, and the other involving an EC mechanism in which the rds is a Langmuir-Hinshelwood reaction of adsorbed NO with adsorbed H. The availability of adsorbed hydrogen determines which path is followed by the reaction; (iii) to identify the smallest atomic ensemble for the reduction of NO on Pt as being composed of two adjacent Pt atoms.     

Structure sensitivity of methanol electrooxidation pathways on platinum: an on-line electrochemical mass spectrometry study

By monitoring the mass fractions of CO(2) (m/z 44) and methylformate (m/z 60, formed from CH(3)OH + HCOOH) with on-line electrochemical mass spectrometry (OLEMS), the selectivity and structure sensitivity of the methanol oxidation pathways were investigated on the basal planes--Pt(111), Pt(110), and Pt(100)--and the stepped Pt electrodes--Pt(554) and Pt(553)--in sulfuric and perchloric acid electrolytes. The maximum reactivity of the MeOH oxidation reaction on Pt(111), Pt(110), and Pt(100) increases in the order Pt(111) < Pt(110) < Pt(100). Mass spectrometry results indicate that the direct oxidation pathway through soluble intermediates plays a pronounced role on Pt(110) and Pt(111), while, on Pt(100), the indirect pathway through adsorbed carbon monoxide is predominant. In 0.5 M H(2)SO(4), introducing steps in the (111) plane increases the total reaction rate, while the relative importance of the direct pathway decreases considerably. In 0.5 M HClO(4), however, introducing steps increases both the total reaction rate and the selectivity toward the direct oxidation pathway. Anion (sulfate) adsorption on (111) leads to a more prominent role of the direct pathway, but, on all the other surfaces, (bi)sulfate seems to block the formation of soluble intermediates. For both electrolytes, increasing the step density results in more methylformate being formed relative to the amount of CO(2) detected, indicating that the [110] steps themselves catalyze the direct oxidation pathway. A detailed reaction scheme for the methanol oxidation mechanism is suggested based on the literature and the results obtained here.     

Influence of coadsorbed hydrogen on ethylene adsorption and reaction on a (radical3 x radical3)R30 degrees-Sn/Pt(111) surface alloy

The effect of surface-bound hydrogen adatoms on adsorption, desorption, and reaction of ethylene (CH(2)=CH(2)) on a (radical3 x radical3)R30 degrees-Sn/Pt(111) surface alloy with theta(Sn) = 0.33 was investigated by using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Preadsorbed H decreased the saturation coverage of chemisorbed ethylene and less H was required to completely block ethylene chemisorption on this alloy than that on Pt(111). This is also the first report of extensive H site-blocking of ethylene chemisorption on Pt(111). Preadsorbed H also decreased the desorption activation energy of ethylene on the alloy surface. The reaction chemistry of ethylene on this Sn/Pt(111) alloy is dramatically different than on the Pt(111) surface: the H-addition reaction channel taking ethylene to ethane on Pt(111) is totally inhibited on the alloy. This is important information for advancing understanding of the surface chemistry involved in hydrogenation and dehydrogenation catalysis.     

Methanol oxidation on a Pt(111)-OH/O surface

The methanol oxidation on a hydroxylated Pt (Pt(111)-OH) surface has been investigated by means of infrared reflection absorption spectroscopy (IRAS) in ultra-high vacuum (UHV) and in acidic solution. The Pt(111)-OH surface in UHV was prepared by introducing water molecules on a Pt(111)-(2 x 2)-O surface and annealed at temperature higher than 160 K. Methanol was then, introduced to the Pt(111)-OH surface to show the dependence of the reaction intermediate on the annealing temperature. At an annealing temperature below 160 K, IR bands assignable to methanol overlayer were observed and no detectable intermediates, such as CO, formaldehyde and formate, were formed, suggesting that methanol molecules remain stable on Pt(111) surface without dissociation at this temperature region. At an annealing temperature above 160 K, on the other hand, CO and formate were observed. In addition, the oxidation of CO on Pt(111)-OH showed no sign of formate formation, indicating that formate is not derived from CO, but from a direct oxidation of methanol. Methanol oxidation was carried out in 0.1 mol dm(-3) HClO(4) solution on Pt(111) with a flow cell configuration and showed the formation of formate. These results indicate that the formate is the dominant non-CO intermediate both in UHV and in acidic solution, and the preadsorbed oxygen-containing species, in particular OH adsorbates, on Pt(111) surface plays a very important role in the formate formation process in methanol oxidation reaction.     

Computational study of the adsorption and dissociation of phenol on Pt and Rh surfaces

The adsorption of phenol on flat and stepped Pt and Rh surfaces and the dissociation of hydrogen from the hydroxyl group of phenol on Pt(111) and Rh(111) were studied by density functional calculations. On both Pt(111) and Rh(111), phenol adsorbs with the aromatic ring parallel to the surface and the hydroxyl group tilted away from the surface. Furthermore, adsorption on stepped surfaces was concluded to be unfavourable compared to the (111) surfaces due to the repulsion of the hydroxyl group from the step edges. Transition state calculations revealed that the reaction barriers, associated with the dissociation of phenol into phenoxy, are almost identical on Pt and Rh. Furthermore, the oxygen in the dissociated phenol is strongly attracted by Rh(111), while it is repelled by Pt(111).     

Electrochemistry of iridium single crystal surfaces: Part I. Structural effect on formic acid oxidation and poison formation on Ir (111), (100) and (110)

The geometrical arrangement of Ir sites favourable for the main oxidation reaction and the poison formation reaction in formic acid oxidation is determined on Ir (111), (100) and (110). The order of catalytic activity is (111) > (100) > (100) for the main oxidation and that for the poison formation is (111) < (110) < (100). This order is different from that on Pt single crystal planes, the order of which is (111) > (100) > (110) for the main oxidation and (111) < (100) < (110) for poison formation. Since the order is different on Pt and Ir, the chemical property determines the order. On both Ir and Pt, poison formation occurs independently of the existence of adsorbed hydrogen.     

Adsorption and dissociation of O2 on Pt-Co and Pt-Fe alloys

Self-consistent periodic density functional theory calculations (GGA-PW91) have been performed to study the adsorption of O and O(2) and the dissociation of O(2) on the (111) facets of ordered Pt(3)Co and Pt(3)Fe alloys and on monolayer Pt skins covering these two alloys. Results are compared with those obtained on two Pt(111) surfaces, one at the equilibrium lattice constant and the other laterally compressed by 2% to match the strain in the Pt alloys. The absolute magnitudes of the binding energies of O and O(2) follow the same order in the two alloy systems: Pt skin < compressed Pt(111) < Pt(111) < Pt(3)Co(111) or Pt(3)Fe(111). The reduced activity of the compressed Pt(111) and Pt skins for oxygen can be rationalized as being due to the shifting of the d-band center increasingly away from the Fermi level. We propose that an alleviation of poisoning by O and enhanced rates for reactions involving O may be some of the reasons why Pt skins are more active for the oxygen reduction reaction in low-temperature fuel cells. Finally, a linear correlation between the transition-state and final-state energies of O(2) dissociation on monometallic and bimetallic surfaces is revealed, pointing to a simple way to screen for improved cathode catalysts.     

Enhanced reactivity of Pt nanoparticles supported on ceria thin films during ethylene dehydrogenation

The adsorption and reaction of ethylene on Pt/CeO(2-x)/Cu(111) model catalysts were studied by means of high resolution photoelectron spectroscopy (HR-PES) in conjunction with resonant photoemission spectroscopy (RPES). The dehydrogenation mechanism is compared to the HR-PES data obtained on a Pt(111) single crystal under identical conditions. It was found that the Pt nanoparticle system shows a substantially enhanced reactivity and several additional reaction pathways. In sharp contrast to Pt(111), partial dehydrogenation of ethylene on the supported Pt nanoparticles already starts at temperatures as low as 100 K. Similar to the single crystal surface, dehydrogenation occurs via the isomer ethylidene (CHCH(3)) and then mainly via ethylidyne (CCH(3)). In the temperature region between 100 and 250 K there is strong evidence for spillover of hydrocarbon fragments to the ceria support. In addition, splitting of ethylene to C(1) fragments is more facile than on Pt(111), giving rise to the formation of CH species and CO in the temperature region between 250 and 400 K. Upon further annealing, carbonaceous deposits are formed at 450 K. By heating to 700 K, these carbon deposits are completely removed from the surface by reaction with oxygen, provided by reverse spillover of oxygen from the ceria support.     

Ni/Pt(111) bimetallic surfaces: unique chemistry at monolayer ni coverage.

We have utilized the dehydrogenation and hydrogenation of cyclohexene as probe reactions to compare the chemical reactivity of Ni overlayers that are grown epitaxially on a Pt(111) surface. The reaction pathways of cyclohexene were investigated using temperature-programmed desorption, high-resolution electron energy loss (HREELS), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our results provide conclusive spectroscopic evidence that the adsorption and subsequent reactions of cyclohexene are unique on the monolayer Ni surface as compared to those on the clean Pt(111) surface or the thick Ni(111) film. HREELS and NEXAFS studies show that cyclohexene is weakly pi-bonded on monolayer Ni/Pt(111) but di-sigma-bonded to Pt(111) and Ni(111). In addition, a new hydrogenation pathway is detected on the monolayer Ni surface at temperatures as low as 245 K. By exposing the monolayer Ni/Pt(111) surface to D2 prior to the adsorption of cyclohexene, the total yield of the normal and deuterated cyclohexanes increases by approximately 5-fold. Furthermore, the reaction pathway for the complete decomposition of cyclohexene to atomic carbon and hydrogen, which has a selectivity of 69% on the thick Ni(111) film, is nearly negligible (<2%) on the monolayer Ni surface. Overall, the unique chemistry of the monolayer Ni/Pt(111) surface can be explained by the weaker interaction between adsorbates and the monolayer Ni film. These results also point out the possibility of manipulating the chemical properties of metals by controlling the overlayer thickness.     

Reforming of oxygenates for H2 production: correlating reactivity of ethylene glycol and ethanol on Pt(111) and Ni/Pt(111) with surface d-band center

The dehydrogenation and decarbonylation of ethylene glycol and ethanol were studied using temperature programmed desorption (TPD) on Pt(111) and Ni/Pt(111) bimetallic surfaces, as probe reactions for the reforming of oxygenates for the production of H2 for fuel cells. Ethylene glycol reacted via dehydrogenation to form CO and H2, corresponding to the desired reforming reaction, and via total decomposition to produce C(ad), O(ad), and H2. Ethanol reacted by three reaction pathways, dehydrogenation, decarbonylation, and total decomposition, producing CO, H2, CH4, C(ad), and O(ad). Surfaces prepared by deposition of a monolayer of Ni on Pt(111) at 300 K, designated Ni-Pt-Pt(111), displayed increased reforming activity compared to Pt(111), subsurface monolayer Pt-Ni-Pt(111), and thick Ni/Pt(111). Reforming activity was correlated with the d-band center of the surfaces and displayed a linear trend for both ethylene glycol and ethanol, with activity increasing as the surface d-band center moved closer to the Fermi level. This trend was opposite to that previously observed for hydrogenation reactions, where increased activity occurred on subsurface monolayers as the d-band center shifted away from the Fermi level. Extrapolation of the correlation between activity and the surface d-band center of bimetallic systems may provide useful predictions for the selection and rational design of bimetallic catalysts for the reforming of oxygenates.     

Theoretical study of CCl(4) adsorption and hydrogenation on a Pt (111) surface

The adsorption and hydrogenation of carbon tetrachloride (CCl(4)) on a Pt (111) surface have been investigated using density functional theory (DFT). We have performed calculations on the adsorption energies and structures of CCl(4) on four different adsorption sites of a Pt (111) surface using the full adsorbate geometry optimization method. The results show that the adsorption energy of all of the potential sites is less than -17 kcal/mol, which indicates that CCl(4) is physiosorbed on a Pt (111) surface through van der Waals interactions. The dissociation and hydrogenation pathways were investigated by a transition state search. For the Pt(15), Pt(19), and Pt(25) cluster surfaces, the activation energies of dissociation obtained in this work are 15.69, 16.94, and 16.77 kcal/mol, respectively. The hydrogenation of CCl(3). was studied at the on-top site of the Pt(15) cluster, and the calculated activation energy is 5.06 kcal/mol. The small activation energies indicate that the Pt (111) surface has high catalytic activity for the CCl(4) hydrogenation reaction. In addition, the Hirshfeld population analysis reveals that the charge transfer from the Pt (111) surface to the adsorbates occurs in both the dissociation and hydrogenation pathways.     

At least three contiguous atoms are necessary for CO formation during methanol electrooxidation on platinum

We have used cyanide-modified Pt(111) electrodes to investigate the size and geometry of the minimum atomic ensemble necessary for the oxidation of methanol on Pt electrodes. Poison formation on cyanide-modified Pt(111) is completely inhibited, the corresponding electrooxidation reaction proceeding, hence, exclusively through the reactive intermediate pathway. These results suggest that formation of adsorbed CO would require the presence of at least three contiguous Pt atoms.     

First principles based mean field model for oxygen reduction reaction

A first principles-based mean field model was developed for the oxygen reduction reaction (ORR) taking account of the coverage- and material-dependent reversible potentials of the elementary steps. This model was applied to the simulation of single crystal surfaces of Pt, Pt alloy and Pt core-shell catalysts under Ar and O(2) atmospheres. The results are consistent with those shown by past experimental and theoretical studies on surface coverages under Ar atmosphere, the shape of the current-voltage curve for the ORR on Pt(111) and the material-dependence of the ORR activity. This model suggests that the oxygen associative pathway including HO(2)(ads) formation is the main pathway on Pt(111), and that the rate determining step (RDS) is the removal step of O(ads) on Pt(111). This RDS is accelerated on several highly active Pt alloys and core-shell surfaces, and this acceleration decreases the reaction intermediate O(ads). The increase in the partial pressure of O(2)(g) increases the surface coverage with O(ads) and OH(ads), and this coverage increase reduces the apparent reaction order with respect to the partial pressure to less than unity. This model shows details on how the reaction pathway, RDS, surface coverages, Tafel slope, reaction order and material-dependent activity are interrelated.     

Kinetics of CO oxidation on high-concentration phases of atomic oxygen on Pt(111)

Temperature-programmed reaction spectroscopy (TPRS) and direct, isothermal reaction-rate measurements were employed to investigate the oxidation of CO on Pt(111) covered with high concentrations of atomic oxygen. The TPRS results show that oxygen atoms chemisorbed on Pt(111) at coverages just above 0.25 ML (monolayers) are reactive toward coadsorbed CO, producing CO(2) at about 295 K. The uptake of CO on Pt(111) is found to decrease with increasing oxygen coverage beyond 0.25 ML and becomes immeasurable at a surface temperature of 100 K when Pt(111) is partially covered with Pt oxide domains at oxygen coverages above 1.5 ML. The rate of CO oxidation measured as a function of CO beam exposure to the surface exhibits a nearly linear increase toward a maximum for initial oxygen coverages between 0.25 and 0.50 ML and constant surface temperatures between 300 and 500 K. At a fixed CO incident flux, the time required to reach the maximum reaction rate increases as the initial oxygen coverage is increased to 0.50 ML. A time lag prior to the reaction-rate maximum is also observed when Pt oxide domains are present on the surface, but the reaction rate increases more slowly with CO exposure and much longer time lags are observed, indicating that the oxide phase is less reactive toward CO than are chemisorbed oxygen atoms on Pt(111). On the partially oxidized surface, the CO exposure needed to reach the rate maximum increases significantly with increases in both the initial oxygen coverage and the surface temperature. A kinetic model is developed that reproduces the qualitative dependence of the CO oxidation rate on the atomic oxygen coverage and the surface temperature. The model assumes that CO chemisorption and reaction occur only on regions of the surface covered by chemisorbed oxygen atoms and describes the CO chemisorption probability as a decreasing function of the atomic oxygen coverage in the chemisorbed phase. The model also takes into account the migration of oxygen atoms from oxide domains to domains with chemisorbed oxygen atoms. According to the model, the reaction rate initially increases with the CO exposure because the rate of CO chemisorption is enhanced as the coverage of chemisorbed oxygen atoms decreases during reaction. Longer rate delays are predicted for the partially oxidized surface because oxygen migration from the oxide phase maintains high oxygen coverages in the coexisting chemisorbed oxygen phase that hinder CO chemisorption. It is shown that the time evolution of the CO oxidation rate is determined by the relative rates of CO chemisorption and oxygen migration, R(ad) and R(m), respectively, with an increase in the relative rate of oxygen migration acting to inhibit the reaction. We find that the time lag in the reaction rate increases nearly exponentially with the initial oxygen coverage [O](i) (tot) when [O](i) (tot) exceeds a critical value, which is defined as the coverage above which R(ad)R(m) is less than unity at fixed CO incident flux and surface temperature. These results demonstrate that the kinetics for CO oxidation on oxidized Pt(111) is governed by the sensitivity of CO binding and chemisorption on the atomic oxygen coverage and the distribution of surface oxygen phases.