Angle-Resolved Thermal Desorption Spectroscopy as a Surface Probe
Horton, Dorothy Roy
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/69727
Description
Title
Angle-Resolved Thermal Desorption Spectroscopy as a Surface Probe
Author(s)
Horton, Dorothy Roy
Issue Date
1982
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
In the past fifteen years it has become apparent that the desorption process is not as well understood as it appeared when Knudsen formulated his cosine law of desorption in the early 1900's. Directed desorption, where the flux is focused along the surface normal, has been observed in several systems, notably hydrogen desorbing from nickel. This has been explained by invoking a flat barrier to adsorption that selects particles with some minimum normal component of kinetic energy to adsorb. However, all of the previous work has been done without directly measuring the activation barrier to adsorption. By using angle-resolved thermal desorption spectroscopy one can observe directed desorption under conditions where the activation barrier to adsorption can be measured independently. For hydrogen on polycrystalline nickel, the desorption distribution observed is approximately cos ('5)(theta), which is similar to distributions observed at much higher temperatures. The activation barrier to adsorption is found to be negligible. A model is proposed in which the desorption flux distribution is intimately related to the desorption site structure. Data for carbon monoxide on the (100) face of tungsten are also presented. Progressive reconstruction of the tungsten surface with CO desorption is indicated. Adsorption and desorption have long been regarded as reverse processes even under nonequilibrium conditions. The present results call this assumption into question. The work here demonstrates that angle-resolved thermal desorption spectroscopy can be used to provide a probe which is sensitive only to desorption site structure, and not to the host of other sites present, making it a useful tool to study active sites on catalysts.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
