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This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel phosphide catalysts. This work is the subject of a publication

This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel phosphide catalysts. This work is the subject of a publication of which I am a co-author, as cited below.

Project 1 Abstract: Ethylene Oxychlorination
The current two-step process for the industrial process of vinyl chloride production involves CuCl2 catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. To date, no industrial application of a one-step process is available. To close this gap, this work evaluates a wide range of self-prepared supported CeO2 and EuOCl catalysts for one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623 773 K and 1 bar using feed ratios of C2H4:HCl:O2:Ar:He = 3:3 6:1.5 6:3:82 89.5. Among all studied systems, CeO2/ZrO2 and CeO2/Zeolite MS show the highest activity but suffer from severe combustion of ethylene, forming COx, while 20 wt.% EuOCl/γ-Al2O3 leads to the best vinyl chloride selectivity of 87% at 15.6% C2H4 conversion with complete suppression of CO2 formation and only 4% selectivity to CO conversion for over 100 h on stream. Characterization by XRD and EDX mapping reveals that much of the Eu is present in non-active phases such as Al2Eu or EuAl4, indicating that alternative synthesis methods could be employed to better utilize the metal. A linear relationship between conversion and metal loading is found for this catalyst, indicating that always part of the used Eu is available as EuOCl, while the rest forms inactive europium aluminate species. Zeolite-supported EuOCl slightly outperforms EuOCl/γ Al2O3 in terms of total yield, but is prone to significant coking and is unstable. Even though a lot of Eu seems locked in inactive species on EuOCl/γ Al2O3, these results indicate possible savings of nearly 16,000 USD per kg of catalyst compared to a bulk EuOCl catalyst. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of supported EuOCl catalysts in industrially-relevant reactions.

Project 2 Abstract: Alkyne Semihydrogenation
Despite strongly suffering from poor noble metal utilization and a highly toxic selectivity modifier (Pb), the archetypal catalyst applied for the three-phase alkyne semihydrogenation, the Pb-doped Pd/CaCO3 (Lindlar catalyst), is still being utilized at industrial level. Inspired by the very recent strategies involving the modification of Pd with p-block elements (i.e., S), this work extrapolates the concept by preparing crystalline metal phosphides with controlled stoichiometry. To develop an affordable and environmentally-friendly alternative to traditional hydrogenation catalysts, nickel, a metal belonging to the same group as Pd and capable of splitting molecular hydrogen has been selected. Herein, a simple two-step synthesis procedure involving nontoxic precursors was used to synthesize bulk nickel phosphides with different stoichiometries (Ni2P, Ni5P4, and Ni12P5) by controlling the P:Ni ratios. To uncover structural and surface features, this catalyst family is characterized with an array of methods including X-ray diffraction (XRD), 31P magic-angle nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bulk-sensitive techniques prove the successful preparation of pure phases while XPS analysis unravels the facile passivation occurring at the NixPy surface that persists even after reductive treatment. To assess the characteristic surface fingerprints of these materials, Ar sputtering was carried out at different penetration depths, reveling the presence of Ni+ and P-species. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds display that the oxidized layer covering the surface is reduced under reaction conditions, as evidenced by the induction period before reaching the steady state performance. To assess the impact of the phosphidation treatment on catalytic performance, the catalysts were benchmarked against a commercial Ni/SiO2-Al2O3 sample. While Ni/SiO2-Al2O3 presents very low selectivity to the alkene (the selectivity is about 10% at full conversion) attributed to the well-known tendency of naked nickel nanoparticles to form hydrides, the performance of nickel phosphides is highly selective and independent of P:Ni ratio. In line with previous findings on PdxS, kinetic tests indicate the occurrence of a dual-site mechanism where the alkyne and hydrogen do not compete for the same site.

This work is the subject of a publication of which I am a co-author, as cited below.

D. Albani; K. Karajovic; B. Tata; Q. Li; S. Mitchell; N. López; J. Pérez-Ramírez. Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi-Hydrogenation. ChemCatChem 2019. doi.org/10.1002/cctc.201801430
ContributorsTata, Bharath (Author) / Deng, Shuguang (Thesis director) / Muhich, Christopher (Committee member) / Chemical Engineering Program (Contributor, Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
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Description
Past experiments have revealed several unusual properties about interstitial hydrogen atoms in niobium. Absorption isotherms showed that niobium absorbs a large amount of hydrogen without changing its crystal structure. These isotherms also revealed that the interactions between hydrogen atoms in niobium are a combination of long-range attraction and short-range repulsion

Past experiments have revealed several unusual properties about interstitial hydrogen atoms in niobium. Absorption isotherms showed that niobium absorbs a large amount of hydrogen without changing its crystal structure. These isotherms also revealed that the interactions between hydrogen atoms in niobium are a combination of long-range attraction and short-range repulsion and exhibit many-body characteristics. Other experiments reported the facile thermal diffusion of hydrogen and deuterium in niobium. Contrary to the classical theory of diffusion, these experiments revealed a break in the activation energy of hydrogen diffusion at low temperatures, but no such break was reported for deuterium. Finally, experiments report a phenomenon called electromigration, where hydrogen atoms inside niobium respond to weak electric fields as if they had a positive effective charge. These experimental results date back to when tools like density functional theory (DFT) and modern high-performance computing abilities did not exist. Therefore, the current understanding of these properties is primarily based on inferences from experimental results. Understanding these properties at a deeper level, besides being scientifically important, can profoundly affect various applications involving hydrogen separation and transport. The high-level goal of this work is to use first-principles methods to explain the discussed properties of interstitial hydrogen in niobium. DFT calculations were used to study hydrogen atoms' site preference in niobium and its effect on the cell shape and volume of the host cell. The nature and origin of the interactions between hydrogen atoms were studied through interaction energy, structural, partial charge, and electronic densities of state analysis. A phenomenological model with fewer parameters than traditional models was developed and fit to the experimental absorption data. Thermodynamic quantities such as the enthalpy and entropy of hydrogen dissolution in niobium were derived from this model. The enthalpy of hydrogen dissolution in niobium was also calculated using DFT by sampling different geometric configurations and performing an ensemble-based averaging. Further work is required to explain the observed isotope effects for hydrogen diffusion in niobium and the electromigration phenomena. Applications of the niobium-hydrogen system require studying hydrogen's behavior on niobium's surface.
ContributorsRamcahandran, Arvind (Author) / Lackner, Klaus S. (Thesis advisor) / Zhuang, Houlong (Thesis advisor) / Muhich, Christopher (Committee member) / Singh, Arunima (Committee member) / Arizona State University (Publisher)
Created2021
Description
With renewable energy on the rise, researchers have turned their funding and their focus towards new solar cell technologies, and perovskites are a major source of interest. This class of materials is particularly interesting due to their quick, simple synthesis as well as their physical and electrical superiority when compared

With renewable energy on the rise, researchers have turned their funding and their focus towards new solar cell technologies, and perovskites are a major source of interest. This class of materials is particularly interesting due to their quick, simple synthesis as well as their physical and electrical superiority when compared to current silicon-based solar cells. Through this thesis, we will explore the synthesis of various types of perovskites and their subsequent characterization, which includes optical microscopy, photoluminescence spectroscopy, Raman microscopy, and X-ray diffraction. Analyzing two different perovskites both before and after a two-week period of storage revealed that while synthesis is indeed experiment-friendly, these materials have a concerning lack of stability even in ideal conditions.
ContributorsBuzas, Benjamin Joseph (Author) / Tongay, Sefaattin (Thesis director) / Muhich, Christopher (Committee member) / Materials Science and Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
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Description
This research seeks to answer the question if there is a singular relationship between stishovite nucleation and the atomistic structure of the preshocked amorphous SiO$_2$. To do this a stishovite manufacturing method is developed in which 1,152 samples were produced. The majority of these samples did crystallize. The method was

This research seeks to answer the question if there is a singular relationship between stishovite nucleation and the atomistic structure of the preshocked amorphous SiO$_2$. To do this a stishovite manufacturing method is developed in which 1,152 samples were produced. The majority of these samples did crystallize. The method was produced through two rounds of experiments and fine-tuning with the pressure damp, temperature damp, shock pressure using an NPHug fix, and sample origin. A new random atomic insertion method was used to generate a new and different SiO$_2$ amorphous structure not before seen within the research literature. The optimal values for shock were found to be 60~GPa for randomly atom insertion samples and 55~GPa for quartz origin samples. Temperature damp appeared to have a slight effect optimizing at 0.05~ps and the pressure damp had no visible effect, testing was done with temperature damp from 0.05 to 0.5~ps and pressure damp from 0.1 to 10.0~ps. There appeared to be significant randomness in crystallization behavior. The preshocked and postnucleated samples were transformed into Gaussian fields of crystal, mass, and charge. These fields were divided and classified using a cut-off method taking the number of crystals produced in portions of each simulation and classifying each potion as nucleated or non-nucleated. Data in which some nucleation but not a critical amount was present was removed constituting 2.6\% to 20.3\% of data in all tests. A max method was also used which takes only the maximum portions of each simulation to classify as nucleating. There are three other variables tested within this work, a sample size of 18,000 or 72,728~atoms, Gaussian variance of 1 or 4~\AA, and Convolutional neural network (CNN) architecture of a garden verity or all convolution along with the portioning classification method, sample origination, and Gaussian field type. In total 64 tests were performed to try every combination of variable. No significant classifications were made by the CNNs to nucleation or non-nucleation portions. The results clearly confirmed that the data was not abstracting to atomistic structure and was random by all classifications of the CNNs. The all convolution CNN testing did show smoother outcomes in training with less fluctuations. 59\% of all validation accuracy was held at 0.5 for a random state and 84\% was within $\pm0.02$ of 0.5. It is conclusive that prenucleation structure is not the sole predictor of nucleation behavior. It is not conclusive if prenucleation structure is a partial or non-factor within nucleation of stishovite from amorphous SiO$_2$.
ContributorsChristen, Jonathan Scorr (Author) / Oswald, Jay (Thesis advisor) / Muhich, Christopher (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2021
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Description
Two-dimensional quantum materials have garnered increasing interest in a wide

variety of applications due to their promising optical and electronic properties. These

quantum materials are highly anticipated to make transformative quantum sensors and

biosensors. Biosensors are currently considered among one of the most promising

solutions to a wide variety of biomedical and environmental problems

Two-dimensional quantum materials have garnered increasing interest in a wide

variety of applications due to their promising optical and electronic properties. These

quantum materials are highly anticipated to make transformative quantum sensors and

biosensors. Biosensors are currently considered among one of the most promising

solutions to a wide variety of biomedical and environmental problems including highly

sensitive and selective detection of difficult pathogens, toxins, and biomolecules.

However, scientists face enormous challenges in achieving these goals with current

technologies. Quantum biosensors can have detection with extraordinary sensitivity and

selectivity through manipulation of their quantum states, offering extraordinary properties

that cannot be attained with traditional materials. These quantum materials are anticipated

to make significant impact in the detection, diagnosis, and treatment of many diseases.

Despite the exciting promise of these cutting-edge technologies, it is largely

unknown what the inherent toxicity and biocompatibility of two-dimensional (2D)

materials are. Studies are greatly needed to lay the foundation for understanding the

interactions between quantum materials and biosystems. This work introduces a new

method to continuously monitor the cell proliferation and toxicity behavior of 2D

materials. The cell viability and toxicity measurements coupled with Live/Dead

fluorescence imaging suggest the biocompatibility of crystalline MoS2 and MoSSe

monolayers and the significantly-reduced cellular growth of defected MoTe2 thin films

and exfoliated MoS2 nanosheets. Results show the exciting potential of incorporating

kinetic cell viability data of 2D materials with other assay tools to further fundamental

understanding of 2D material biocompatibility.
ContributorsTran, Michael, Ph.D (Author) / Tongay, Sefaattin (Thesis advisor) / Green, Matthew (Thesis advisor) / Muhich, Christopher (Committee member) / Arizona State University (Publisher)
Created2019
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Description
Transition metal di- and tri-halides (TMH) have recently gathered research attention owing to their intrinsic magnetism all the way down to their two-dimensional limit. 2D magnets, despite being a crucial component for realizing van der Waals heterostructures and devices with various functionalities, were not experimentally proven until very recently in

Transition metal di- and tri-halides (TMH) have recently gathered research attention owing to their intrinsic magnetism all the way down to their two-dimensional limit. 2D magnets, despite being a crucial component for realizing van der Waals heterostructures and devices with various functionalities, were not experimentally proven until very recently in 2017. The findings opened up enormous possibilities for studying new quantum states of matter that can enable potential to design spintronic, magnetic memory, data storage, sensing, and topological devices. However, practical applications in modern technologies demand materials with various physical and chemical properties such as electronic, optical, structural, catalytic, magnetic etc., which cannot be found within single material systems. Considering that compositional modifications in 2D systems lead to significant changes in properties due to the high anisotropy inherent to their crystallographic structure, this work focuses on alloying of TMH compounds to explore the potentials for tuning their properties. In this thesis, the ternary cation alloys of Co(1-x)Ni(x)Cl(2) and Mo(1-x)Cr(x)Cl(3) were synthesized via chemical vapor transport at a various stoichiometry. Their compositional, structural, and magnetic properties were studied using Energy Dispersive Spectroscopy, Raman Spectroscopy, X-Ray Diffraction, and Vibrating Sample Magnetometry. It was found that completely miscible ternary alloys of Co(1-x)Ni(x)Cl(2) show an increasing Néel temperature with nickel concentration. The Mo(1-x)Cr(x)Cl(3) alloy shows potential magnetic phase changes induced by the incorporation of molybdenum species within the host CrCl3 lattice. Magnetic measurements give insight into potential antiferromagnetic to ferromagnetic transition with molybdenum incorporation, accompanied by a shift in the magnetic easy-axis from parallel to perpendicular. Phase separation was found in the Fe(1-x)Cr(x)Cl(3) ternary alloy indicating that crystallographic structure compatibility plays an essential role in determining the miscibility of two parent compounds. Alloying across two similar (TMH) compounds appears to yield predictable results in properties as in the case of Co(1-x)Ni(x)Cl(2), while more exotic transitions, as in the case of Mo(1-x)Cr(x)Cl(3), can emerge by alloying dissimilar compounds. When dissimilarity reaches a certain limit, as with Fe(1-x)Cr(x)Cl(3), phase separation becomes more favorable. Future studies focusing on magnetic and structural phase transitions will reveal more insight into the effect of alloying in these TMH systems.
ContributorsKolari, Pranvera (Author) / Tongay, Sefaattin (Thesis advisor) / Jiao, Yang (Committee member) / Muhich, Christopher (Committee member) / Arizona State University (Publisher)
Created2020
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Description
Losses in commercial microwave dielectrics arise from spin excitations in paramagnetic transition metal dopants, at least at reduced temperatures. The magnitude of the loss tangent can be altered by orders of magnitude through the application of an external magnetic field. The goal of this thesis is to produce “smart” dielectrics

Losses in commercial microwave dielectrics arise from spin excitations in paramagnetic transition metal dopants, at least at reduced temperatures. The magnitude of the loss tangent can be altered by orders of magnitude through the application of an external magnetic field. The goal of this thesis is to produce “smart” dielectrics that can be switched “on” or “off” at small magnetic fields while investigating the influence of transition metal dopants on the dielectric, magnetic, and structural properties.

A proof of principle demonstration of a resonator that can switch from a high-Q “on state” to a low-Q “off state” at reduced temperatures is demonstrated in (Al1-xFex)2O3 and La(Al1-xFex)O3. The Fe3+ ions are in a high spin state (S=5/2) and undergo electron paramagnetic resonance absorption transitions that increase the microwave loss of the system. Transitions occur between mJ states with a corresponding change in the angular momentum, J, by ±ħ (i.e., ΔmJ=±1) at small magnetic fields. The paramagnetic ions also have an influence on the dielectric and magnetic properties, which I explore in these systems along with another low loss complex perovskite material, Ca[(Al1-xFex)1/2Nb1/2]O3. I describe what constitutes an optimal microwave loss switchable material induced from EPR transitions and the mechanisms associated with the key properties.

As a first step to modeling the properties of high-performance microwave host lattices and ultimately their performance at microwave frequencies, a first-principles approach is used to determine the structural phase stability of various complex perovskites with a range of tolerance factors at 0 K and finite temperatures. By understanding the correct structural phases of these complex perovskites, the temperature coefficient of resonant frequency can be better predicted.

A strong understanding of these parameters is expected to open the possibility to produce new types of high-performance switchable filters, time domain MIMO’s, multiplexers, and demultiplexers.
ContributorsGonzales, Justin Michael (Author) / Newman, Nathan (Thesis advisor) / Muhich, Christopher (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2020
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Description
Interfacial interactions between materials in complex heterostructures can dominate the material's response in manymodern-day energy-related devices and processes. Considerable research has been dedicated towards addressing the profound effects of interfaces. Here, first-principles-based quantum mechanical simulations are discussed to characterize the interfacial materials properties of two systems. First, density-functional theory (DFT) calculations were performed

Interfacial interactions between materials in complex heterostructures can dominate the material's response in manymodern-day energy-related devices and processes. Considerable research has been dedicated towards addressing the profound effects of interfaces. Here, first-principles-based quantum mechanical simulations are discussed to characterize the interfacial materials properties of two systems. First, density-functional theory (DFT) calculations were performed for ceramic oxide grain boundaries in undoped and doped CeO2. Second, the development, theoretical framework, and utilization of high-throughput, workflow-based, DFT calculations are presented to model the synthesis of two-dimensional (2D) heterostructured materials. Utilizing this workflow, predictive machine learning models were created to elucidate key interface-property relationships in 2D heterostructured materials. The DFT simulations reveal that the Σ3(111)/[101] grain boundary was energetically more stable than theΣ3(121)/[101]grain boundary due to the larger atomic coherency in the Σ3(111)/[101] grain boundary plane. The alkaline-earth metal-doped grain boundary energies demonstrate a parabolic dependence on the size of the solutes, interfacial strain, and packing density of the grain boundary. The grain boundary energies were stabilized upon Ca, Sr, and Ba doping whereas Be and Mg render them energetically unstable. The electronic density of states reveals that no defect states were present in/above the band gap. The thermodynamic trapping of oxygen vacancies in the near grain boundary region was not significantly impacted by the presence of Ca-solute ions. However, the migration energy barriers within the grain boundary core were dramatically reduced with high local Ca-solute concentrations, around 0.3 eV-0.5 eV. Chapter 5 and Chapter 6 discusses the development of the open-source, high-throughput computational "synthesis"based workflow package Hetero2d and the application of Hetero2d using 52 Janus 2D materials and 19 metallic, cubic phase, elemental substrates. The 438 Janus 2D-substrate pairs were analyzed by identifying substrate surfaces that stabilize metastable Janus 2D materials, characterizing their effects on the post-adsorbed 2D materials, and identifying the bonding between the 2D material and substrate. Machine learning models were applied to predict the binding energy, z-separation, and charge transfer of the Janus 2D-substrate pairs providing insight into the critical properties which factor into these properties.
ContributorsBoland, Tara Maria (Author) / Crozier, Peter A (Thesis advisor) / Singh, Arunima K (Thesis advisor) / Rez, Peter (Committee member) / Muhich, Christopher (Committee member) / Dholabhai, Pratik (Committee member) / Arizona State University (Publisher)
Created2022
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Description
Siloxane, a common contaminant present in biogas, is known for adverse effects on cogeneration prime movers. In this work, the solid oxide fuel cell (SOFC) nickel-yttria stabilized zirconia (Ni-YSZ) anode degradation due to poisoning by siloxane was investigated. For this purpose, experiments with different fuels, different deposition substrate materials, different

Siloxane, a common contaminant present in biogas, is known for adverse effects on cogeneration prime movers. In this work, the solid oxide fuel cell (SOFC) nickel-yttria stabilized zirconia (Ni-YSZ) anode degradation due to poisoning by siloxane was investigated. For this purpose, experiments with different fuels, different deposition substrate materials, different structure of contamination siloxane (cyclic and linear) and entire failure process are conducted in this study. The electrochemical and material characterization methods, such as Electrochemical Impedance Spectroscopy (EIS), Scanning Electron Microscope- Wavelength Dispersive Spectrometers (SEM-WDS), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and Raman spectroscopy, were applied to investigate the anode degradation behavior. The electrochemical characterization results show that the SOFCs performance degradation caused by siloxane contamination is irreversible under bio-syngas condition. An equivalent circuit model (ECM) is developed based on electrochemical characterization results. Based on the Distribution of Relaxation Time (DRT) method, the detailed microstructure parameter changes are evaluated corresponding to the ECM results. The results contradict the previously proposed siloxane degradation mechanism as the experimental results show that water can inhibit anode deactivation. For anode materials, Ni is considered a major factor in siloxane deposition reactions in Ni-YSZ anode. Based on the results of XPS, XRD and WDS analysis, an initial layer of carbon deposition develops and is considered a critical process for the siloxane deposition reaction. Based on the experimental results in this study and previous studies about siloxane deposition on metal oxides, the proposed siloxane deposition process occurs in stages consisting of the siloxane adsorption, initial carbon deposition, siloxane polymerization and amorphous silicon dioxide deposition.
ContributorsTian, Jiashen (Author) / Milcarek, Ryan J. (Thesis advisor) / Muhich, Christopher (Committee member) / Wang, Liping (Committee member) / Phelan, Patrick (Committee member) / Nian, Qiong (Committee member) / Arizona State University (Publisher)
Created2022
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Description
This study presents an evaluation of the predicted flow behavior and the minimum outlet diameter in a computationally simulated hopper. The flow pattern in hoppers was simulated to test three size fractions, three moisture levels of microcrystalline cellulose (MCC), and two hopper wall angles in Multiphase Flow with Interphase eXchanges

This study presents an evaluation of the predicted flow behavior and the minimum outlet diameter in a computationally simulated hopper. The flow pattern in hoppers was simulated to test three size fractions, three moisture levels of microcrystalline cellulose (MCC), and two hopper wall angles in Multiphase Flow with Interphase eXchanges (MFiX). Predictions from MFiX were then compared to current literature. As expected, the smaller size fractions with lower water content were closer to ideal funnel flow than their larger counterparts. The predicted minimum outlet diameter in simulations showed good agreement with close to ideal flowability. These findings illustrate the connection between lab flowability experiments and computational simulations. Lastly, three fluidized bed simulations were also created in MFiX with zeolite 13X to analyze the pressure and velocity within the bed. The application of flowability simulations can improve the transport of solids in processing equipment used during the production of powders.
ContributorsBuchanan, Lidija (Author) / Emady, Heather (Thesis advisor) / Muhich, Christopher (Committee member) / Deng, Shuguang (Committee member) / Arizona State University (Publisher)
Created2023