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Journal ArticleDOI

A molecular beam investigation of the catalytic oxidation of CO on Pd (111)

01 Aug 1978-Journal of Chemical Physics (AIP Publishing)-Vol. 69, Iss: 3, pp 1267-1281
TL;DR: In this paper, a detailed investigation of the steady-state and nonsteady-state reaction CO+1/2O2→CO2 on Pd (111) has been carried out with the molecular beam technique.
Abstract: A detailed investigation of the steady‐state and nonsteady‐state reaction CO+1/2O2→CO2 on Pd (111) has been carried out with the molecular beam technique. It could be shown conclusively that the reaction proceeds between two adsorbed species (Langmuir–Hinshelwood mechanism) throughout the temperature and pressure range investigated. For low CO coverages, the activation energy of the reaction was determined to be 25 kcal/mole, whereas at moderate CO coverages, a rearrangement of the oxygen adlayer takes place resulting in a reduction of the activation energy to 14 kcal/mole. It is not possible to formulate a simple kinetic expression for the reaction rate which is valid over the entire range of temperatures and pressures due to changes in the adsorption rate for O2, coadsorption of CO and O2, to diffusion in the adlayer, and to changes in the geometrical arrangement within the adlayer with varying coverage.
Citations
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Journal ArticleDOI
TL;DR: This Review concludes that CO oxidation, although seemingly a simple chemical reaction, provides us with a panacea that reveals the richness and beauty of heterogeneous catalysis.
Abstract: CO oxidation, although seemingly a simple chemical reaction, provides us with a panacea that reveals the richness and beauty of heterogeneous catalysis. The Fritz Haber Institute is a place where a multidisciplinary approach to study the course of such a heterogeneous reaction can be generated in house. Research at the institute is primarily curiosity driven, which is reflected in the five sections comprising this Review. We use an approach based on microscopic concepts to study the interaction of simple molecules with well-defined materials, such as clusters in the gas phase or solid surfaces. This approach often asks for the development of new methods, tools, and materials to prove them, and it is exactly this aspect, both, with respect to experiment and theory, that is a trade mark of our institute.

573 citations

Journal ArticleDOI
TL;DR: In this paper, the authors studied the reaction of carbon monoxide catalyzed by Pt(111) using reactive molecular beam-surface scattering and showed that at low coverage, the reaction proceeds with an activation energy E*LH =24.1 kcal/mole and a pre-exponential υ4 =0.11 cm2 particles−1
Abstract: The oxidation of carbon monoxide catalyzed by Pt(111) was studied in ultrahigh vacuum using reactive molecular beam–surface scattering. Under all conditions studied, the reaction follows a Langmuir–Hinshelwood mechanism: the combination of a chemisorbed CO molecule and an oxygen adatom. When both reactants are at low coverage, the reaction proceeds with an activation energy E*LH =24.1 kcal/mole and a pre‐exponential υ4 =0.11 cm2 particles−1 sec−1. At very high oxygen coverage, E*LH decreases to about 11.7 kcal/mole and υ4 to about 2×10−6 cm2 particles−1 sec−1. This is largely attributed to the corresponding increase in the energy of the adsorbed reactants. When a CO molecule incident from the gas phase strikes the surface presaturated with oxygen, it enters a weakly held precursor state to chemisorption. Desorption from this state causes a decrease in chemisorption probability with temperature. Once chemisorbed, the CO molecule then has almost unit probability of reacting to produce CO2 below 540 K. The CO2 product angular distribution varies from cosγ to cos4γ depending sensitively upon the adsorbed reactant concentrations.

522 citations

Book ChapterDOI
TL;DR: In this article, the authors investigated the influence of surface structure on the catalytic activity of a single crystal whose surface was curved in such a way that not only the plane but also vicinals with varying step density of two different crystallographic directions were present.
Abstract: Publisher Summary Catalytic oxidation of carbon monoxide over catalysts from the platinum group metals has been investigated. Apart from its enormous practical importance, this reaction is considered to proceed through a relatively simple mechanism because only diatomic molecules are involved and product formation occurs presumably only over a very few steps. This chapter discusses the adsorptive properties of the reactants, their mutual interaction, and the mechanism and kinetics of product formation as well as the investigations with well defined single-crystal surfaces. The activity of a catalyst for a particular reaction is strongly dependent on the surface structure. Directive investigation of the influence of the surface structure on the catalytic activity was performed by using a platinum single crystal whose surface was curved in such a way that not only the plane but also vicinals with varying step density of two different crystallographic directions were present.

493 citations

Journal ArticleDOI
TL;DR: The data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size.
Abstract: Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption−desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1−20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O2 pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O2 activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C16O−18O2−16O2 reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of r...

428 citations

Journal ArticleDOI
J.A. Barker1, Daniel J. Auerbach1
TL;DR: In this article, a review of recent advances in the use of thermal energy atomic and molecular beam methods to explore the dynamics of physical and chemical processes occuring at surfaces is presented.

408 citations

References
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Journal ArticleDOI
TL;DR: In this article, the adsorption and desorption of H2 on the (100, (110), and stepped (310) crystal faces of copper was studied. And the energy and incident angle of the H2 beam were measured by a rotatable mass spectrometer.

372 citations

Journal ArticleDOI
TL;DR: The adsorption of oxygen on the ruthenium (001) surface has been studied using a combination of techniques: LEED/Auger, Kelvin probe contact potential changes, and flash desorption mass spectrometry as mentioned in this paper.

356 citations

Journal ArticleDOI
TL;DR: The surface region of Pd(111) is characterized by three different types of oxygen atoms, which may be distinguished by their thermal, chemical, structural and electronic properties as discussed by the authors.

280 citations

Journal ArticleDOI
TL;DR: In this paper, the angular distribution of desorbeded H2 molecules has been studied and the measured angular distributions are strongly peaked forward, indicating that they are not uniformly distributed.

200 citations

Journal ArticleDOI
TL;DR: In this article, the adsorption and catalytic reaction of oxygen and carbon monoxide on a Pd(110) surface has been studied by means of low energy electron diffraction (LEED) and mass spectrometric techniques.

200 citations