Some unique aspects of CO oxidation on supported Pt
TL;DR: In this paper, a supported Pt catalyzed oxidation of CO was studied as a function of sintering severity and sustained isothermal oscillations were observed, which can be rationalized by viewing the oxidation process as one consisting of an Eley-Rideal mechanism involving gaseous CO reacting with adsorbed O 2 at low CO concentrations, and chemisorption of O 2 upon a surface partially covered with CO at higher CO concentrations.
About: This article is published in Journal of Catalysis.The article was published on 1975-07-01. It has received 167 citations till now. The article focuses on the topics: Chemisorption.
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TL;DR: It is suggested that the catalytic activity for CO adlayer oxidation is predominantly influenced by the ability of the surface to dissociate water and to form OH(ad) on defect sites rather than by CO energetics.
Abstract: Using high-resolution transmission electron microscopy (TEM), infrared reflection−absorption spectroscopy (IRAS), and electrochemical (EC) measurements, platinum nanoparticles ranging in size from 1 to 30 nm are characterized and their catalytic activity for CO electrooxidation is evaluated TEM analysis reveals that Pt crystallites are not perfect cubooctahedrons, and that large particles have “rougher” surfaces than small particles, which have some fairly smooth (111) facets The importance of “defect” sites for the catalytic properties of nanoparticles is probed in IRAS experiments by monitoring how the vibrational frequencies of atop CO (νCO) as well as the concomitant development of dissolved CO2 are affected by the number of defects on the Pt nanoparticles It is found that defects play a significant role in CO “clustering” on nanoparticles, causing CO to decrease/increase in local coverage, which yields to anomalous redshift/blueshift νCO frequency deviations from the normal Stark-tuning behavior
526 citations
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
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
TL;DR: In this paper, the kinetics of the CO-O2 and CO-NO reactions over single crystal Rh(111) and over alumina-supported Rh catalysts have been compared at realistic reactant pressures.
444 citations
TL;DR: In this article, the authors address the question of below which particle size the metallic properties are lost and the practical ways of producing metals with particle sizes around the critical value calculated above.
Abstract: Publisher Summary Metals constitute a wide class of catalysts, and because catalysis occurs on the surface, there is an economic incentive, especially for precious metals, to obtain catalysts in the form of small metal particles. This, however, raises two main problems. One is fundamental in nature and addresses the question as to below which particle size the metallic properties are lost. The other is more practical and concerns the preparation and characterization of very small particles and their catalytic activity. The other problem concerns the practical ways of producing metals with particle sizes around the critical value calculated above. The easiest and most practical way to achieve this goal is to deposit the metal in low concentration on a high-surface-area support. The main purpose of using a carrier is, of course, to achieve a high dispersion of the metal and to stabilize it against sintering. In a number of reactions, however, the metal support is not inert and the overall process is actually a combination of two functions: that of the metal and that of the catalytically active support.
371 citations
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411 citations
TL;DR: In this article, the surface interactions of single-component and multi-component adsystems were examined by means of ultrahigh vacuum techniques, including thermal flash desorption and residual gas analysis.
116 citations
87 citations
TL;DR: In this paper, the Einzelkorn-Instabilitat in Festbettreaktoren spielt bezuglich thermischer or kinetisch bedingt sein kann.
Abstract: Bei stationaren Reaktionszustanden offener Systeme in grosem Abstand vom chemischen Gleichgewicht konnen sprunghafte und oszillatorische Instabilitaten auftreten. Fur sprunghafte Instabilitaten im Sinne von Zund/Losch-Erscheinungen genugt bereits die Wechselwirkung eines Transportprozesses mit einer chemischen Reaktion von nichtlinearem Verhalten, das entweder thermisch oder kinetisch bedingt sein kann. In Festbettreaktoren spielt bezuglich thermischer Instabilitat auser der Einzelkorn-Instabilitat die Ruckkopplung durch axialen Warmetransport eine wesentliche Rolle. Sie bestimmt auch das Verhalten von „wandernden Reaktionszonen”.—Oszillatorisches Verhalten (Grenzzyklen) setzt voraus, das das Reaktionssystem mindestens zwei Speicher fur Stoffe bzw. Warme enthalt, die in nichtlinearer Weise miteinander gekoppelt sind. Die Ergebnisse der Untersuchungen am Einzelkorn lassen erkennen, das der Chemisorption, deren Einflus bisher unbeachtet geblieben ist, eine zentrale Bedeutung zukommt, da sie einerseits als Transportprozes wirksam werden, andererseits nichtlineares Reaktionsverhalten verursachen und schlieslich bei Oszillationen auch als Speicherkapazitat auftreten kann.
29 citations