An investigation of the interaction of water and of saturated hydrocarbons with the (110) surface of iridium

by Wittrig, Thomas Stephen

Abstract (Summary)
The interactions of the reconstructed Ir(110)-(1x2) surface with water and with saturated hydrocarbons have been studied in an ultrahigh vacuum environment. The techniques of thermal desorption mass spectrometry (TDMS), ultrahigh photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy, contact potential difference measurements and low-energy electron diffraction (LEED) were utilized. Chapter 2 describes a refinement in the technique for modelling the kinetics of desorption of adsorbed species by an Arrhenius construction. The functional dependence of the energy of desorption and the rate coefficient on the surface coverage are accounted for. An explicit example is provided. The interaction of water with the Ir(110)-(1x2) surface is discussed in Chapter 3. It is shown that at most, 6% of the adsorbed water dissociates upon adsorption at a temperature of 130 K. Water does dissociate to OH groups when adsorbed on an Ir(110)-(1x2) surface with preadsorbed oxygen. Water exhibits a constant probability of adsorption for all submonolayer coverages. There exist four distinct thermal desorption states of water on the clean Ir(110)-(1x2) surface. A qualitative model is put forth to rationalize the complex thermal desorption behavior. The remaining chapters describe investigations of the adsorption and reaction of saturated hydrocarbons on Ir(110)-(1x2). Chapter 4 presents the results of a study of the interaction of cyclopropane and Ir(110). Chapter 5 considers the coadsorption of hydrogen and cyclopropane on Ir(110). Finally, Chapter 6 presents the results of a study of the adsorption and reaction of ethane, propane, isobutane and neopentane on Ir(110). These saturated hydrocarbons dissociated on the surface at some temperature below 130 K. In each case, this dissociation reaction is poisoned by the presence of adsorbed hydrogen on the surface. This leads to the identification of an active site for hydrocarbon dissociation on the surface. As the surface is heated, the carbon remains adsorbed on the surface and the hydrogen desorbs as H2. For ethane, one thermal desorption peak of H2 is observed that corresponds to hydrogen adsorbed in [beta]2 hydrogen adsites on the metal surface. This thermal desorption peak is observed for the remaining hydrocarbons, as well as two other thermal desorption states associated with hydrogen that exists in partially dehydrogenated hydrocarbon fragments present on the surface. No hydrocarbon species other than the one initially adsorbed were observed to desorb from the surface under any of the conditions reported in this work.
Bibliographical Information:

Advisor:Henry Weinberg

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis

Keywords:chemical engineering


Date of Publication:10/12/1981

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