Calorimetric Measurements of Heats of Adsorption on Single Crystal Surfaces
Kyser, Dale Anthony
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https://hdl.handle.net/2142/69785
Description
Title
Calorimetric Measurements of Heats of Adsorption on Single Crystal Surfaces
Author(s)
Kyser, Dale Anthony
Issue Date
1987
Doctoral Committee Chair(s)
Masel, R.I.
Department of Study
Chemical Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Abstract
The first calorimeter capable of measuring heats of adsorption of reactive gases on low area single crystal surfaces has been developed in our laboratory. The calorimeter utilizes a bead thermistor to measure the energy released when gas adsorbs on a single-crystal sample. The apparatus is capable of measuring energy releases on the sample as small as 15 to 20 microcalories. This new apparatus has been utilized to measure the heat of adsorption of carbon monoxide and ethylene on clean and adsorbate covered Pt(111).
Our measurements indicate that the integral heat of adsorption of carbon monoxide on clean Pt(111) is about 33.27 kcal/mole at moderate coverages and decreases with increasing CO coverage, while the integral heat of adsorption of ethylene was found to be 35.5 kcal/mole at high coverages. Both of these results agree reasonably well with the available estimates of the heats of adsorption from various experimental and theoretical studies.
The effect of preadsorbing oxygen, sulfur, and calcium on the binding energy of CO was also investigated with this technique. Oxygen appeared to slightly increase the heat of adsorption of CO, while substantially reducing the amount of CO that will adsorb on the sample. Calcium had the opposite effect. The presence of calcium on a Pt(111) single crystal reduced the heat of adsorption of CO to about 25 kcal/mole while increasing the saturation coverage of CO by a factor of two. This behavior is very unusual and can't be easily explained. The sulfur experiments in this work proved to be inconclusive as to the effect of sulfur on the binding energy of CO. This work describes in detail both the development of the technique as well as the experimental results.
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