Chen, liang
(2006)
Molecular simulation study of adsorption, diffusion and dissociation.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
There are two main objectives in my research work. The first objective is toinvestigate the adsorption behavior of various gases on single walled carbon nanotubes. This is accomplishedby using the classical molecular simulation methods. Our simulation work has providedmolecular level interpretation of some interesting phenomena observed experimentally by our collaborators.The second objective is to study the catalytic properties of metal/metal carbide surfaces and interfacialphenomena by using ab initio density functional theory.We have studied the adsorption of various gases on carbon nanotubes byusing classical molecular simulation and optimization techniques. We specifically haveinvestigated the displacement of adsorption on different adsorption sites.The systems investigated includeCO2 on SWNT, Xe/CF4 on SWNT and CO2/Xe on SWNT. Our simulations indicate that CO2 is easily replaced fromthe endohedral and interstitial sites of SWNT bundles by Xe,while the groove/external surface sites loose much less CO2. These calculations agreevery well with the experimental observations.We have also observed unique one dimensional behavior of gases adsorbed on carbon nanotubes by using optimization andparallel tempering Monte Carlo. The results show that CO2 molecules adsorbed in thegroove sites of single walled carbon nanotubes display behavior thatis quasi-1-dimensional. At finite coverages of CO2 in groovesclusters containing only odd numbers of molecules are formed at lowtemperatures. Even numbers of molecules form two clusters, eachcontaining an odd number of molecules.We have carried out density functional theory studies on the catalyticproperties of metal surfaces. We investigated adsorption of CO on the Ag(110)surface and CO adsorption, diffusion and dissociation on the W(111) surface.The CO molecule isfound to non-dissociatively adsorb in end-on configurations (alphastates) and dissociatively absorb in inclined configurations (betastates). The dissociation of beta state CO is found to have anactivation energy of about 0.8 eV, which is lower than the energyrequired to desorb CO molecularly from the surface.We have also studied the tungsten difussion mechanisms in cobalt. Our calculationsindicate that the diffusion is vacancy mediated. Therefore, we proposed the triangleand quadrangle mechanims, and examined the full diffusion pathways.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
27 September 2006 |
| Date Type: |
Completion |
| Defense Date: |
25 January 2006 |
| Approval Date: |
27 September 2006 |
| Submission Date: |
7 April 2006 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Chemical Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
; ab initio; adsorption; diffusion; dissociation; Molecular simulation |
| Other ID: |
http://etd.library.pitt.edu/ETD/available/etd-04072006-170554/, etd-04072006-170554 |
| Date Deposited: |
10 Nov 2011 19:34 |
| Last Modified: |
15 Nov 2016 13:38 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/6849 |
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