Amine and nitroxide based radical-trapping antioxidants (RTAs) have long been known to display remarkable efficacy as inhibitors of hydrocarbon autoxidation. Their unique ability to catalytically trap the chain-carrying peroxyl radicals responsible for oxidative degradation of organic materials has led to their widespread use in petroleum-derived materials. While a great deal of research has been done to understand and expand upon this reactivity, little improvement in the chemistry behind diarylamine and nitroxide RTAs has emerged. In recent years our group has established that heterocyclic analogues of phenolic and diarylaminic RTAs are more stable to one-electron oxidation than the equivalent phenyl derivatives. This has allowed substitution of these RTAs with strong electron donating groups without compromising their stability to oxidation, and has led to the development of some of the most effective RTAs ever reported – compounds which often have reactivities ca. 200-fold greater than the current industrial standards. Herein, we describe the development of novel fluorometric and spectrophotometric methods to measure the reactivities of these RTAs, which replace more traditional approaches that are often laborious and require highly specialised equipment. Co-autoxidations with the highly absorbent probes PBD-BODIPY and STY-BODIPY allow for rapid and convenient measurement of RTA activity under a wide variety of conditions by UV/Vis spectrophotometry. Similarly, the high temperature activity of these RTAs can be measured in heavy hydrocarbon autoxidations, where hydroperoxide formation is monitored through the use of a pro-fluorescent phosphine. The key step in Korcek’s proposed diarylamine catalytic cycle has been studied and found to proceed through different mechanisms depending on the structure of the intermediate N,N-diarylalkoxyamine. While unactivated alkoxyamines widely react through N-O homolysis/disproportionation to regenerate the diarylamine RTA, activation of either the aryl or alkyl fragments allows regeneration through a more efficient, pericyclic retro-carbonyl-ene (RCE) reaction. Additionally, the mechanism behind the high temperature RTA activity of dialkylnitroxides – key intermediates in the activity of hindered amine light stabilizers (HALS) – has been evaluated and found to be dependent on in situ formation of carboxylic acids. Upon protonation by these acids, dialkylnitroxides become potent RTAs capable of trapping oxygen-centered radicals. The oxoammonium ions arising from this reaction then oxidize alkyl radicals competitively with O2 addition to regenerate the nitroxide. Lastly, we have extended the strategy used for heterocyclic phenols and diarylamines to the development of highly reactive azaphenoxazine and azaphenothiazine RTAs. While synthesis of these compounds is complicated by the presence of a favorable smiles rearrangement, synthesis of the ‘correct’ isomers yields extremely potent RTAs, capable of trapping peroxyl radicals under diffusion control. Applying these compounds in both ambient and high temperature autoxidations reveals that they may be some of the most effective RTAs ever reported, outperforming even the most reactive of the heterocyclic diarylamines previously studied.

Kinetics of steam gasification of both delayed and fluid cokes, byproducts from thermal cracking processes of Athabasca bitumen, have been studied in laboratory-size stirred and fixed bed reactors. The hydrogen sulphide in the product gas was captured in-situ using calcined dolomite and limestones as acceptors. Experiments were carried out at atmospheric pressure and at temperatures between 800°C and 930°C. The coke particle size ranged from 0.1 to 3.5 mm, and the steam partial pressure was varied from 15.15 to 60.6 kPa. The carbon and sulphur conversions were computed from the knowledge of gas compositions and flowrates and the gasification kinetics of both species established. The effects of sorbent type, particle size, calcination conditions, and Ca/S molar ratios on the extent of sulphur capture during gasification were examined in separate series of experiments. Scanning electron microscopy, surface area analysis, and mercury porosimetry were employed to relate physical structure changes in the solids to experimental kinetic data. The rate of gasification for the delayed coke was generally higher than that for the fluid coke, and both cokes were almost unreactive to steam gasification at temperatures below 800°C. Increased reaction temperatures or reduced particle sizes increased both carbon as well as sulphur conversion. The carbon conversion rates were found to go through maxima as the time of reaction and extent of conversion increased. As the reaction proceeded the surface area of the coke increased to a maximum of about five times its initial value and thenfell off sharply. The extent of carbon conversion alone dictated the specific surface area irrespective of temperature, particle size and steam partial pressure. Both calcined dolomite and calcined limestone were found to be effective in removing sulphur from the product gas. Sorbents possessing a larger specific area or smaller grain size had higher capacity to accept sulphur. At a Ca/S molar ratio of 2.0, the overall sulphur removal was approximately 90% for the first 3 hrs and the H₂S concentration in the produced gas was reduced to about 200 ppm from nearly 1250 ppm. The rate of sorbent conversion from CaO to CaS decreased monotonically with time. Three available kinetic models for gasification - the Random Capillary Model, the Random Pore Model and the Modified Volumetric Model, were tested with the experimental gasification data. Although reasonable fits were obtained for Xc-t results, the sharp drop in rate at high conversion could not be adequately modelled. Rate constants were established for the initial stage of reaction only. The Grain model and Continuous reaction models were tested with the experimental sulphidation results. The sulphidation process was controlled by chemical reaction at low sorbent conversion, and subsequently by diffusion through the product layer at higher conversions. The reaction rate constant and the effective diffusivity were accordingly established as functions of temperature. Values compared favourably with results of sulphidation kinetics done without simultaneous gasification reported in the literature. The results suggest that the gasification process and the sulphur capture process, which occur together in gasifiers with sorbent injection, can be treated independently. Indexing terms: Gasification, Carbon Conversion, Sulphur Conversion, Sulphur Removal, Calcine, Limestone, Dolomite, Hydrogen Sulphide, Sulphidation. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

A clear and predictive understanding of the propensity for crystallisation of one polymorph over another is lacking, and in this regard glycine is a model system due to difficulties in crystallisation of the thermodynamically stable gamma polymorph. The preferential crystallisation of gamma-glycine in the presence of micellar CTAB (Cetyltrimethylammonium bromide) as opposed to the alpha form commonly crystallised from pure solution was observed. A rationale for this result was sought through the observation of the nucleation and growth kinetics of the alpha and gamma polymorphs of glycine (and DL-alanine) using in situ microscopy, the measurement of induction times and following the solution mediated phase transformation of alpha-glycine. These observations help explain the dominant crystal form produced in a number of solutions. The nucleation and growth rates of alpha-glycine were shown to be orders of magnitude greater than those of gamma-glycine in pure solution. Also, the addition of a cationic surfactant (such as CTAB) or modification of the solution pH were shown to dramatically accelerate the nucleation and growth of polar gamma-glycine and DL-alanine, a rarely reported phenomenon. In addition, the growing (00-1) faces of gamma-glycine and DL-alanine, at which growth was accelerated, were shown to be macroscopically rough, indicating a growth mechanism dominated by nucleation rather than the growth of layers. The most likely cause of the inhibited kinetics of gamma-glycine and DL-alanine is water bound electrostatically at the negatively charged (00-1) faces, while the growth acceleration inferred by the additives is related to their ability to release water from these surfaces. Other mechanisms which may play a role include the adsorption of adventitious impurities, strong electrostatic repulsion between like-charged carboxylate groups at the (00-1) surface resulting in structural disorder, and the effect of surface energy on the rate of surface nucleation. This research provides an important example of nature’s complexity in selecting crystal form in polymorphic systems, gives further insight into the causes of the asymmetric growth of polar crystal structures, and introduces the possibility that the crystallisation kinetics of ‘difficult’ slow growing compounds may sometimes be modified through the use of additives.

Heterogeneous catalysis is a powerful chemical technology because it can enhance the conversion of reactants, promote selectivity to a desired product, and lower the reaction temperature requirements. The breaking and forming of chemical bonds in heterogeneous catalysis is facilitated on a solid surface where adsorbed gas-phase species react and form products. This study is concerned with utilizing heterogeneous catalysis in the automobile industry via the generation and utilization of hydrogen to reduce NOx emissions. In spark ignition engines, the three-way-catalyst technology is ineffective at the more efficient, lean-burn conditions. In compression-ignition engines, an ammonia-based technology is implemented but has associated high cost and ammonia slip challenges. This motivates providing an alternative technology, such as hydrogen selective catalytic reduction (H2-SCR). In this study, four catalysts were investigated for the lean-burn selective catalytic reduction of NO using hydrogen. The catalysts were platinum (Pt) and palladium (Pd) noble metals supported on cerium oxide (CeO2) and magnesium oxide (MgO). Additionally, finding a source of hydrogen for H2-SCR on board a vehicle is a challenge due to the issues associated with hydrogen storage. A numerical study was performed to investigate the utilization of the partial oxidation of natural gas on a rhodium surface to synthesis gas, CO and H2. A kinetic understanding of natural gas demands an understanding of its components. While methane and ethane have been extensively studied, propane partial oxidation on rhodium has only been kinetically examined at low temperatures. The aim of the numerical study was to obtain an improved understanding of propane partial oxidation kinetics by extending the surface reactions mechanism to high temperatures and developing a gas phase mechanism to capture the effects of gas-phase reactions. Moreover, the optimal temperature and pressure for H2 generation were determined, and the kinetic simulation results were analyzed by temperature sensitivity, chemical path flux and hydrogen production sensitivity analyses.

Thesis advisor: Jeffery A. Byers / This dissertation discusses the development of an electrochemically switchable system for copolymer synthesis as well as surface modifications. In Chapter one, the usage of electrochemistry to control polymerization reactivities is introduced. In Chapter two, an electrochemically redox switchable polymerization for lactide and cyclohexene oxide will be presented. In Chapter three, a surface modification method based on the electrochemically redox switchable catalysis is discussed. The surface-anchored catalyst responds to applied electrochemical potentials towards two different ring-opening polymerizations to generate binary polymer patterns in one step. The method represents a facile way to generate polymer coatings on surfaces. In Chapter four, a discussion on the detailed kinetic analysis of an iron-catalyzed epoxide polymerization will be presented, the study allows us to unveil the importance of entropy-controlled reactions. In Chapter five, future perspectives on the electrochemically redox switchable catalysis will be discussed. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

The kinetics of the reaction of atomic sulfur with acetylene (S (3P) + C2H2) were investigated experimentally via the flash photolysis resonance fluorescence method, and the theoretical potential energy surface for the reaction CN + SO was modeled via the density functional and configuration interaction computational methods. Sulfur is of interest in modern chemistry due to its relevance in combustion and atmospheric chemistry, in the Claus process, in soot and diamond-film formation and in astrochemistry. Experimental conditions ranged from 295 – 1015 K and 10 – 400 Torr of argon. Pressure-dependence was shown at all experimental temperatures. The room temperature high-pressure limit second order rate constant was (2.10 ± 0.08) × 10-13 cm3 molecule-1 s-1. The Arrhenius plot of the high-pressure limit rate constants gave an Ea of (11.34 ± 0.03) kJ mol-1 and a pre-exponential factor of (2.14 ± 0.19) × 10-11 cm3 molecule-1 s-1. S (3P) + C2H2 is likely an adduct forming reaction due to pressure-dependence (also supported by a statistical mechanics analysis) which involves intersystem crossing. The potential energy surface for CN + SO was calculated at the B3LYP/6-311G(d) level and refined at the QCISD/6-311G(d) level. The PES was compared to that of the analogous reaction CN + O2. Notable energetically favorable products are NCS + O, CO + NS, and CS + NO. The completed PES will ultimately be modeled at the CCSD(T) level (extrapolated to infinite basis set limit) for theoretical reaction rate analysis (RRKM).

Lignin is the most abundant natural aromatic polymer on the earth. In this work, lignin properties were studied in order to explore its use as a low cost carbon precursor for graphene production. Initial studies focused on kinetics of lignin pyrolysis using ‘Kissinger method’ and ‘ASTM E 1641’ using thermogravimetry. The values obtained for kinetic parameters varied for the two methods and activation energy increased with increase in lignin purity. Lignin was solvent fractionated, using three organic solvents to extract the high molecular weight fraction suitable for the production of highly ordered graphene nano platelets. Acetone and Methanol were successful in sequential fractionation. Finally, polycrystalline graphene was produced using Protobind 1000 and lignosulfonate lignins by carbonization. The acid purified graphene had relatively less catalytic material remaining, and nitric acid purification was successful compared to HCl purification. However, HNO3 purification introduced minor structural damages to the sample.

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N/A / Thesis / Master of Engineering (ME)