Identification and switchover of reaction sites in CO oxidation on Pt(113) and (112)

Matsushima, Toshiyasu; Akiyama, Hirokuni; Lesar, Antonija; Sugimura, H.; Torre, Gonzalo E.D.; Yamanaka, Toshiro; Ohno, Yuichi

doi:10.1016/s0039-6028(97)00317-8

Cited by 11 publications

(8 citation statements)

References 25 publications

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“…The oxidation of CO on surfaces with defect sites has been the focus of several UHV studies. 24,25,[27][28][29][30][31][32][33][34][35][36][37] The active site for CO 2 formation on stepped surfaces depends on the surface coverages of CO and oxygen. 28,35 CO adsorbed on terraces is more easily oxidized than CO adsorbed at steps, and preferential formation of CO 2 at terrace sites has been observed on stepped platinum surfaces.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10^-5 Torr

et al. 2005

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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.

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Section: Introductionmentioning

confidence: 99%

Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10^-5 Torr

et al. 2005

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“…This is because, in the latter case, CO 2 desorption peaked simply along the bulk surface normal. 2,22 The distributions in the former azimuth were fairly different in the two regions. Typical angular distributions are shown in Figure 3.…”

Section: Resultsmentioning

confidence: 91%

“…AR-TDS has been applied to both site identification and switching in the CO oxidation on stepped surfaces, Pt(112), (113), (335), and (557). ,− ,− The resultant CO 2 spatial distribution shows that the product is desorbed from narrow terraces or steps. On Pt(113), CO 2 is predominantly formed on the (111) site at high CO(a) coverage, while at high O(a) coverage, the contribution from the (001) site is enhanced and the site preference is reversed.…”

Section: Introductionmentioning

confidence: 99%

“…Two kinds of oxygen adsorption sites, suitable for CO oxidation, were proposed on Pt(113) in AR-TDS work, , i.e., the 3-fold hollow sites on (111) facets and the 4-fold hollow sites on (001) steps. The former declines 29.5°, whereas the latter inclines 25.2° in the opposite direction.…”

Section: Introductionmentioning

confidence: 99%

“…On Pt(113), CO 2 is predominantly formed on the (111) site at high CO(a) coverage, while at high O(a) coverage, the contribution from the (001) site is enhanced and the site preference is reversed. The site preference at low temperatures is not merely controlled by the reactivity of oxygen because of the limited surface mobility of CO. 2 Two kinds of oxygen adsorption sites, suitable for CO oxidation, were proposed on Pt(113) in AR-TDS work, 2,22 i.e., the 3-fold hollow sites on (111) facets and the 4-fold hollow sites on (001) steps. The former declines 29.5°, whereas the latter inclines 25.2°in the opposite direction.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics on Individual Reaction Sites in Steady-State Carbon Monoxide Oxidation on Stepped Platinum(113)

et al. 1999

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The reaction kinetics and dynamics of carbon monoxide oxidation on a stepped Pt(113) = (s)2(111) × (001) surface were studied by angle-resolved kinetic and velocity measurements at the steady state. CO2 desorption sharply collimated nearly along either the (111) site normal or the (001) site normal. Only two reaction sites, the (111) and (001) sites, were operative. The translational energy of CO2 was characteristic of each site throughout a site switching. At surface temperatures above 520 K in the active region, where the reaction was first order in CO, the preference of the (111) site was suppressed with increasing CO pressure. Below 520 K, on the other hand, site switching slowly took place under limited conditions, in which both sites considerably contributed to the reaction and a meta-stable adsorbed phase seemed to be formed. The preference for the (111) site over the (001) site was caused by the former's higher reactivity of oxygen.

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Angle-resolved measurements of product desorption and reaction dynamics on individual sites

Matsushima

2003

Surface Science Reports

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Identification and switchover of reaction sites in CO oxidation on Pt(113) and (112)

Cited by 11 publications

References 25 publications

Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10^-5 Torr

Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10^-5 Torr

Dynamics on Individual Reaction Sites in Steady-State Carbon Monoxide Oxidation on Stepped Platinum(113)

Angle-resolved measurements of product desorption and reaction dynamics on individual sites

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Identification and switchover of reaction sites in CO oxidation on Pt(113) and (112)

Cited by 11 publications

References 25 publications

Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10-5 Torr

Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10-5 Torr

Dynamics on Individual Reaction Sites in Steady-State Carbon Monoxide Oxidation on Stepped Platinum(113)

Angle-resolved measurements of product desorption and reaction dynamics on individual sites

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Product

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Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10^-5 Torr

Enhanced Low-Temperature CO Oxidation on a Stepped Platinum Surface for Oxygen Pressures above 10^-5 Torr