Surface Reconstruction and Lateral Adsorbate Interactions on Cobalt-Based Catalysts An Investigation Using Lattice Gas Models and Density Functional Theory

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

Review of Essential Catholic Social Thought

Bernard V. Brady titles his textbook Essential Catholic Social Thought to indicate that his focus extends beyond documents of the Church’s magisterium, usually designated “Catholic social teaching” (CST), but his emphasis is on those documents nonetheless. I will comment on this book from my perspective as a teacher for twenty years of a course called “Catholic Social Teaching.” My course is addressed to upper-level undergraduates in a Catholic university and specifically to those majoring in international studies (though it is open to others), but I hope these comments will be helpful to anyone who is considering Brady’s book for teaching or learning Catholic social thought. Currently I use the full texts or excerpts from the texts of the official documents reprinted in O’Brien and Shannon’s Catholic Social Thought (2016), supplemented by chapters from Daniel Groody’s Globalization, Spirituality, and Justice (2015)

Using Narrow Band Photometry to Detect Young Brown Dwarfs in IC348

We report the discovery of a population of young brown dwarf candidates in the open star cluster IC348 and the development of a new spectroscopic classification technique using narrow band photometry. Observations were made using FLITECAM, the First Light Camera for SOFIA, at the 3-m Shane Telescope at Lick Observatory. FLITECAM is a new 1-5 micron camera with an 8 arcmin field of view. Custom narrow band filters were developed to detect absorption features of water vapor (at 1.495 microns) and methane (at 1.66 microns) characteristic of brown dwarfs. These filters enable spectral classification of stars and brown dwarfs without spectroscopy. FLITECAM's narrow and broadband photometry was verified by examining the color-color and color-magnitude characteristics of stars whose spectral type and reddening was known from previous surveys. Using our narrow band filter photometry method, it was possible to identify an object measured with a signal-to-noise ratio of 20 or better to within +/-3 spectral class subtypes for late-type stars. With this technique, very deep images of the central region of IC348 (H ~ 20.0) have identified 18 sources as possible L or T dwarf candidates. Out of these 18, we expect that between 3 - 6 of these objects are statistically likely to be background stars, with the remainder being true low-mass members of the cluster. If confirmed as cluster members then these are very low-mass objects (~5 Mjupiter). We also describe how two additional narrow band filters can improve the contrast between M, L, and T dwarfs as well as provide a means to determine the reddening of an individual object.Comment: 43 pages, 17 figures. Accepted for publication in the Astrophysical Journal 27 June 200