The reactive activity and selectivity of platinum single crystal surfaces
Wang, Jianhua
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Permalink
https://hdl.handle.net/2142/21069
Description
Title
The reactive activity and selectivity of platinum single crystal surfaces
Author(s)
Wang, Jianhua
Issue Date
1994
Doctoral Committee Chair(s)
Masel, Richard I.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Physics, Condensed Matter
Language
eng
Abstract
Alcohol, methylamine, acetylene, and ethyl iodide decomposition on platinum single crystal surfaces have been investigated in this thesis work. The objective of this research is to examine factors affecting surface reaction pathways and the rate of the reaction.
Alcohol conversion on transition metals has been studied for many years. The importance of this research is to find new ways to synthesyze fuel and useful byproducts economically. Platinum is considered a good catalyst for alcohol conversion. For a long time, there was a controversy in the literature about alcohol conversion on platinum and palladium. With the same catalysts, J. M. White et al. and B. Madix et al. detected carbon-oxygen bond scission. But L. H. Dubois et al. and B. A. Sexton et al. found no carbon-oxygen bond scission. Through various surface analytical spectroscopies, it is found that surface structure change should also be considered as a reaction variable. By varying the platinum (110) surface from (2x1) to (1x1), the reaction pathway changes from leaving the carbon-oxygen intact to breaking the bond. In the study of the oxidation of methanol on platinum, only carbon monoxide was produced since the oxidation is complete. But when the surface was pre-covered by oxygen atoms, total oxidation could be successively suppressed to get a useful product, formaldehyde.
The surface structure effects are further examined by conducting ethanol, acetylene, methylamine, and ethyl iodide experiments on Pt(110). Ethanol undergoes secondary bond scission at low temperature when adsorbing on the (2x1)Pt(110) to form methanol and methane; acetylene partially reconstructs (2x1) to (1x1) and three types of adsorbing forms are formed during its dissociation on (2x1)Pt(110); methylamine shows the same structure sensitivity on Pt(110) as ethylene and methanol on Pt(110); ethyl iodide decomposes to form ethylene and ethylidyne intermediates.
The effect of the heat of adsorption over reaction pathways is also examined by using Pt(210) as a reaction catalyst. Both Pt(210) and (1x1)Pt(110) have similar sites but the binding energies of hydrogen on these two surfaces are very different. Pt(210) has much higher hydrogen binding energies than Pt(110). Alcohol decomposition on Pt(210) shows that the heat of adsorption plays a major role when the heat of adsorption is greatly changed. Methanol decomposes to form carbon monoxide and hydrogen on Pt(210) without breaking its carbon-oxygen bond.
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