Dissertation
Surface Reconstruction and Lateral Adsorbate Interactions on Cobalt-Based Catalysts: An Investigation Using Lattice Gas Models and Density Functional Theory
Washington State University
Doctor of Philosophy (PhD), Washington State University
12/2019
DOI:
https://doi.org/10.7273/000005572
Abstract
This dissertation deals with the problem of computationally determining the structure and catalytically active phase of cobalt-based Fischer-Tropsch (FT) catalysts driven toward oxygenates. Cobalt-copper based catalysts are examined first using density functional theory calculations. The interactions of carbon monoxide (CO) with cobalt-copper nanoparticle surfaces are analyzed for CO's possible role in restructuring these nanoparticles and subsequent creation of the catalytically active phase. It is shown that cobalt-copper catalysts preferentially form Co Cu core-shell nanoparticles, and that CO can induce up to half of step edge and one quarter of terrace copper atoms to be substituted with cobalt atoms from the core. Cobalt enrichment is limited due to the formation of cobalt subcarbonyl complexes. These complexes are shown to be capable of rupturing and diffusing across the surface, providing the ingredients needed for nanoisland formation and facet reconstruction. This work points to new models that are likely important to cobalt-copper catalyzed FT. New lattice gas (LG) cluster expansion (CE) tools are also developed in this dissertation via the development of the ab initio Mean-field Augmented Lattice Gas Modeling (AMALGM) code. A new theoretical reformulation of the CE formalism, which is more appropriate for the LG paradigm, is detailed. AMALGM is designed to use a newly developed convergent version of the leave-multiple-out cross-validation (LMO-CV) score as the objective function for optimization of LG CEs. A new method for quantifying the errors of the effective cluster interactions of CEs is also developed. This error quantification is shown to capture the uncertainty in CEs due to geometric relaxations in DFT data. AMALGM and these new methods are then utilized to investigate the differences in CO adsorption energetics on the face centered cubic (fcc) and hexagonal close packed (hcp) phases of cobalt relevant to FT. It is shown that the first nearest neighbor (1NN) dominates and is very repulsive in both but significantly more repulsive for fcc cobalt. At high chemical potentials, 1NN CO pairings may be allowed on hcp cobalt where they are still energetically prohibited on fcc cobalt, suggesting a potential source for the reduced activity observed on hcp cobalt catalysts.
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Details
- Title
- Surface Reconstruction and Lateral Adsorbate Interactions on Cobalt-Based Catalysts
- Creators
- Gregory Brandon Collinge
- Contributors
- Jean-Sabin McEwen (Chair)NORBERT KRUSE (Committee Member)Cornelius F Ivory (Committee Member) - Washington State University, Chemical Engineering and Bioengineering, School ofKirk Arnold Peterson (Committee Member) - Washington State University, Chemistry, Department of
- Awarding Institution
- Washington State University
- Academic Unit
- Chemical Engineering and Bioengineering, School of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 350
- Identifiers
- 99901054232201842
- Language
- English
- Resource Type
- Dissertation