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In the past ten years the study of the mechanisms of chemical transformations on metal surfaces has advanced appreciably. Today complex reaction networks can be unraveled by combining several spectroscopies, derived principally from the practice of ultrahigh-vacuum surface physics. Of paramount importance in this field is the combination of mass spectrometric methods for the identification of reaction products with spectroscopies which help identify surface-bound reactive intermediates. This quasi-monograph highlights the progress in this field with studies which clearly exemplify such research and at the same time provide more general understanding of chemical reactivity at surfaces. This book was constructed to be a resource to all scientists interested in the chemical reactivity of metals, including those whose primary interest may lie in fields outside surface reactivity. The book is'intended to be an advanced case­ study text, not a "review" in the standard sense. Each chapter develops principles and illustrates the use of experimental methods. Consequently, more attention is given to experimentation than normally found in journal articles or review articles. My intent in organizing these chapters was to make this field accessible to professionals and graduate students in the fields of chemistry, material science, and physics. Even so, we hope that experts in the field of surface reactivity will also find these chapters informative. After the introduction (Chap. 1) the book consists of chapters on the mechanism of selective oxidation by silver (Chap. 2 by R.1. Madix and J.T.



1. Introduction

In 1956 in a classic experiment Ehrlich and Hickmott determined the evolution of the pressure of N2 evolved from a tungsten filament with time, measured by an ionization gauge, revealing the presence of several kinetic routes for desorption with different energetics [1.1]. Shortly thereafter Redhead extended this method to a continuously pumped volume, yielding pressure bursts which were the derivatives of the pressure buildup curves of the method of Ehrlich and Hickmott and from which activation energies and preexponential factors could be easily estimated [1.2].
R. J. Madix

2. The Problem of Heterogeneously Catalyzed Partial Oxidation: Model Studies on Single Crystal Surfaces

The oxidation of organic molecules mediated by metal surfaces is a subject of immense importance. Either complete oxidation to water and carbon dioxide or partial and selective oxidation to valuable chemical intermediates may be desired. These two extremes are obviously mutually exclusive, and identification of the surface-bound intermediates involved and their rates of reaction is needed to intelligently design reaction systems favoring partial or complete oxidation. The current understanding of metal mediated oxidation processes is the subject of this chapter.
R. J. Madix, J. T. Roberts

3. Desulfurization Reactions Induced by Transition Metal Surfaces

Catalytic desulfurization reactions are of extreme industrial importance due to the need for upgrading fossil fuel feedstocks with a high sulfur content. Sulfur must be removed from fuel because SO x combustion products contribute to acid rain and sulfur renders “catalytic converters” in automobile engines ineffective. Fundamental studies of desulfurization reactions induced on single-crystal metal surfaces under ultrahigh vacuum conditions are the focus of this chapter. There have been many excellent studies of desulfurization reactions under well-defined conditions which we use here to establish several general features of this class of surface reactions. While we have attempted to include all of these studies, some fine work has most certainly been overlooked and we apologize in advance for our oversight.
C. M. Friend

4. Tricyclisation and Heterocyclisation Reactions of Ethyne over Well-Defined Palladium Surfaces

The unusual cyclisation reactions of ethyne on Pd surfaces are described and discussed with reference to analogies with the chemistry of transition metal clusters. Detailed spectroscopic and kinetic characterisation of the adsorbed reactant, intermediate and product species permits the molecular pathway to be constructed in considerable detail. A C4H4 tilted metallopentacycle is found to be the crucial surface intermediate for benzene formation and for the formation of heterocycles. Single-crystal data enable useful predictions to be made about the behaviour of practically supported metal catalysts and in regard to new areas of catalytic chemistry. These ideas are borne out in practice, and the effects on cyclisation chemistry of modifying the metal surface by promoters, poisons and alloying are described and discussed.
R. M. Lambert, R. M. Ormerod

5. Model Organic Rearrangements on Aluminum Surfaces

To what extent are the reactivity patterns of discrete organometallic complexes predictive of reaction pathways on surfaces? This question is a central focus of much current research, and the general understanding which is beginning to emerge suggests that a close similarity may often exist. The best established correlations in these so-called cluster-surface analogies, are ones which are structural in nature [5.1]. Considerable advances have been made in recent years and it is now clear that the bonding patterns of hydrocarbon moieties on surfaces find many analogies in corresponding discrete transition and main group organometallic complexes. This progress notwithstanding, structural determinations of these often transient surface species remain far from routine, require the application of multiple techniques, and frequently are beset by controversy.
L. H. Dubois, B. E. Bent, R. G. Nuzzo

6. The Adsorption of Hydrogen at Copper Surfaces: A Model System for the Study of Activated Adsorption

One of the most exciting challenges of present-day surface science is the task of developing a detailed microscopic picture of surface chemical reactions. This task involves understanding the intra- and inter-molecular motions of species, as they undergo chemical change at a surface, and understanding the related issues of the energy requirements, energy flow, and energy disposal for these microscopic interactions. Studies directed at describing atomic and molecular motion and the interplay between molecular motion and energy throughout a surface process, such as chemisorption, physisorption, or scattering, define the field of surface chemical dynamics. The descriptions acquired from studies of surface dynamics can range from simple conceptual models, which yield insight into qualitative aspects of molecular interactions, to detailed theories, which provide quantitative information about dynamical processes.
H. A. Michelsen, C. T. Rettner, D. J. Auerbach

7. Kinetics and Dynamics of Alkane Activation on Transition Metal Surfaces

The initial reaction with and subsequent chemical rearrangements of saturated hydrocarbons on transition metal surfaces are vitally important to industrial catalysis [7.1] and other processes. Indeed, much applied and fundamental research [7.2–9] has been conducted on these chemical systems which has provided a significant increase in our understanding of these complex phenomena. However, an accurate predictive capability, the ultimate level of understanding, is far out of reach and will remain so, for the near term.
C. B. Mullins, W. H. Weinberg


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