<p>In recent years, first principles periodic Density Functional Theory (DFT) calculation</p><p>has been used to investigate heterogeneous catalytic reactions and examine catalyst</p><p>structures as well as adsorption properties in a variety of systems. The increasing</p><p>contribution to give detailed understanding of elementary reaction mechanism is critical to</p><p>provide fundamental insights into the catalyst design. It is a link to the fundamental</p><p>knowledge and a bridge to the practical application. DFT calculations is also a powerful</p><p>tool to predict and yield promising catalysts which is time- and cost-saving in the practical</p><p>end.</p><p>Because of the recent boom in natural shale gas deposit, there is an increasing interest</p><p>in developing more efficient ways to transform light alkanes into desired and high-value</p><p>chemicals, such as propylene. Propylene is a valuable raw material in the petrochemical</p><p>application to make value-added commodities, such as plastics, paints, and fibers, etc. The</p><p>conventional cracking, steam cracking (SC) and fluid catalytic cracking (FCC), could not</p><p>meet the growing demand of propylene. Thus, it has motivated extensive research of</p><p>production technologies. On the other hand, the abundance of light alkanes extracted from</p><p>the shale gas makes on-purpose production an appealing method which is economically</p><p>competitive. Non-oxidative dehydrogenation of propane (PDH) is a one of ways to make</p><p>up the supply and solve the issue.</p><p>xiii</p><p>According to the current research and industrial work, platinum (Pt) shows promising</p><p>performance for the PDH. However, it suffered from some major drawbacks, such as</p><p>thermodynamic limitation, rapid deactivation leading to poor catalytic performance and</p><p>frequent regeneration. In addition, it is a relatively high cost noble metal. Consequently,</p><p>many efforts have been devoted to the enhancement of the catalytic performance. It was</p><p>found that the stability and the selectivity of Pt-based catalysts can be improved via</p><p>modifying its properties with transition metals as promoters.</p><p>In this thesis, DFT calculations were performed for propane dehydrogenation over</p><p>two different catalyst systems, bimetallic platinum-zinc alloy and monometallic platinum</p><p>catalysts. The work provides insights into the catalyst crystal structures, the adsorption</p><p>characteristics of diverse adsorbates as well as the energy profiles regarding to the</p><p>selectivity of the propane dehydrogenation. Bulk calculation signifies a stable tetragonal</p><p>configuration of the PtZn catalyst which is in accordance with the experimental result. The</p><p>thermodynamic stability regarding to the stability of bulk and surface alloys are studied</p><p>with the consideration of physical constrains. We have identified the thermodynamic</p><p>stability of several PtZn low-index surface facets, (101), (110), (001), (100) flat surfaces</p><p>and stepped surface (111), at certain chemical potential environmental conditions through</p><p>the surface energy phase diagram. Stoichiometric and symmetric (101) slab is</p><p>thermodynamically stable under the region of high Pt chemical potential, and the offstoichiometric</p><p>and symmetric (100 Zn-rich) slab under the low Pt chemical potential.</p><p>In this work, PtZn(101) is used as a model surface to demonstrate the effect on the</p><p>catalytic performance with zinc promotion of platinum. In comparison with Pt(111) surface,</p><p>an elimination of 3-fold Pt hollow site on PtZn(101) is of important and it leads to the</p><p>xiv</p><p>change of binding site preferences. The divalent groups (1-propenyl, 2-propenyl) change</p><p>from Pt top site on PtZn(101) to 3-fold site on Pt(111), which is because of the lack of Pt</p><p>3-fold site on alloyed surface. As for propylene, it changes from di-σ site on PtZn to 𝜋 site</p><p>on Pt. The surface reaction intermediates are found to bond more weakly on PtZn(101)</p><p>than on the Pt surface. Especially, the binding energy of propylene reduces from -1.09 to -</p><p>0.16 eV. The weaker binding strength facilitates the activity of propylene on alloyed</p><p>surfaces.</p><p>Through a complete and classic reaction network analysis, the introduction of Zn</p><p>shows an increase in the endothermicity and the energy barrier of each elementary reaction</p><p>on the alloy surface. With the consideration of entropy for kinetic under real experimental</p><p>condition, the alloying of Zn is found to lower the energy barrier for the propylene product</p><p>desorption and increases that for propylene dehydrogenation. Meanwhile, the competition</p><p>between desired C-H and undesired C-C cleavages is investigated. It is found that the</p><p>cleavage of C-H is energetically favorable than that of C-C. These positive factors</p><p>potentially lead to a high selectivity toward propylene production on PtZn(101).</p><p>Subsequently, Microkinetic modeling is performed to estimate kinetic parameters</p><p>including the reaction order, rate-determining step to build a possible reaction mechanism.</p><p>Finally, conclusions brought out about the comparison between bimetallic and</p><p>monometallic catalyst, and suggestions for future work are presented.</p>

<p>The recent surge in shale gas production led to increases in alkane resources across the United States. One promising approach to convert the alkanes to higher value products is through dehydrogenation and oligomerization processes. This conversion to alkenes, if done in small modular units near the shale wells further aids in the ease of transportation and distribution of the final products. However, having highly selective processes is a major hindrance to improve the economic feasibility of the modular processes. Theoretical studies are of great significance to analyze detailed reaction mechanisms and identify the reaction pathways that leads to unselective product formations. These studies further enable the search for selective catalysts for any given chemistry based on descriptor analysis. Therefore, in this work Density Function Theory and Ab-initio Molecular Dynamics methods are used in conjunction with microkinetic modeling analyses to investigate the complex reaction networks involved in the shale gas conversion. Specifically, the work focuses on propane dehydrogenation (PDH) on alloy surfaces along with ethylene oligomerization on zeolite catalysts.</p><p> A major part of thesis is focused on finding selective and stable alloy catalysts for PDH chemistry. The initial work focused on understanding the selectivity, activity, and stability differences between 1:1 intermetallic alloys (PdIn) and the pure metal surfaces. This combined experimental and computational study shed light on the important role of step surfaces in understanding the activity trends across alloys. Through a detailed microkinetic analysis and simplified rate expression analysis, a novel selectivity descriptor in terms of effective barriers for propane C-H bond breaking and propyne C-C bond breaking was derived for propylene formation. This newly proposed descriptor showed greater fidelity for predicting the trends in experimental selectivities for a small set of Pd alloys than the previously proposed selectivity descriptors. Building upon these insights, a high throughput screening framework using graph-theory algorithms and python-based databasing has been developed to identify trends across a larger set of alloy combinations. The framework helped us identify a novel set of alloys that have not been explored until now for this chemistry. These alloy combinations were then experimentally tested and shown to have high selectivities for propylene formation and along with stabilities close to benchmark Pt-Sn catalysts. Detailed transition state analysis on terraces shows that the undesired C-C bond breaking pathways involves larger surface atom ensembles (4-5 atoms) while the C-H bond breaking involves smaller surface atom ensembles (1-2 atoms). This led to the conclusion that the site-isolation of active metal atoms is important to increase the selectivities for propylene formation. More importantly the combination of detailed mechanistic and screening studies using graph-theory methods shows a generalized framework towards finding new catalysts spaces for complex chemistries.</p><p>The work on ethylene oligomerization on the other hand is focused on understanding the role of mobility of active Ni species in the zeolites towards isomerization and deactivation reaction mechanisms. For this specific project, we have used state-of-the-art AIMD methods, including potential of mean force calculations, for accurate estimation of free energies for the reaction intermediates and transition states. The thermodynamic and kinetic analyses show that the reaction pathways involving mobile intermediates have the highest rates towards butene formations even under pressures lower than 1 bar. Further the isomerization step is found to be feasible on Ni-ethyl complex in agreement with experiments. Finally, the mobile complexes were shown to dimerize through alkyl bridged complexes and the generated complex has higher barriers for C-C bond formation than the isolated complex indicating that these are likely pathways for catalyst deactivation. This mechanistic understanding paves the way for fine-tuning the reaction conditions as well as ways in which the active site can be speciated inside the zeolitic frameworks to increase the selectivity towards 1-butene and reduce deactivation.</p>