Elizabeth Wait

Student

Elizabeth Wait

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Cohort

2016-2017

Biography

Elizabeth Wait is native to South Florida. She is currently a junior in the Burnett Honors College at the University of Central Florida pursuing a B. S. in Biotechnology. She plans on earning a Ph.D. in Computational Neuroscience. Elizabeth has been in Dr. Artëm Masunov's computational chemistry lab since the Fall of 2015 studying the effects of supercritical carbon dioxide on important combustion reactions. She is currently published in the Journal of Physical Chemistry A, but she plans on using these molecular modelling skills in understanding and treating degenerative diseases of the nervous system.

Faculty Mentor

Artëm E. Masunov, Ph.D.

Undergraduate Major

Biotechnology

Future Plans

Computational Neuroscience Ph.D.

Research

Chemical Reaction CO+OH • →CO 2 +H • is Autocatalyzed by Carbon Dioxide: Quantum Chemical Study of the Potential Energy Surfaces

Dr. Artëm E. Masunov, University of Central Florida

The supercritical carbon dioxide medium, used to increase efficiency in oxy combustion fossil energy technology, may drastically alter both rates and mechanisms of chemical reactions. Here we investigate potential energy surface of the second most important combustion reaction with quantum chemistry methods. Two types of effects are reported: formation of the covalent intermediates, and formation of van der Waals complexes by spectator CO2 molecule. While spectator molecule alter the activation barrier only slightly, the covalent bonding opens a new reaction pathway. The mechanism includes sequential covalent binding of CO2 to OH radical and CO molecule, hydrogen transfer from oxygen to carbon atoms and CH bond dissociation. This reduces activation barrier by 11 kcal/mol at the rate-determining step, and is expected to accelerate the reaction rate. The finding of predicted catalytic effect is expected to play an important role not only in combustion, but also in broad array of chemical processes taking place in supercritical CO2 medium. It may open a new venue for controlling reaction rates for chemical manufacturing.

Quantum Chemical Study of Supercritical Carbon Dioxide Effects on Combustion Kinetics

Dr. Artëm E. Masunov, University of Central Florida

In oxy-fuel combustion, the pure oxygen (O2), diluted with CO2 is used as oxidant instead air. Hence, the combustion products (CO2 and H2O) are free from pollution by nitrogen oxides. Moreover, high pressures result in the near-liquid density of CO2 at supercritical state (sCO2). Unfortunately, the effects of sCO2 on the combustion kinetics are far from being understood. To assist in this understanding, in this work we are using quantum chemistry methods. Here we investigate potential energy surfaces of important combustion reactions in the presence of the carbon dioxide molecule. All transition states and reactant and product complexes are reported for three reactions: H2CO + HO2 → HCO + H2O2 (R1), 2HO2 → H2O2 + O2 (R2), and CO + OH → CO2 + H (R3). In reaction R3, covalent binding of CO2 to the OH radical and then the CO molecule opens a new pathway, including hydrogen transfer from oxygen to carbon atoms followed by CH bond dissociation. Compared to the bimolecular OH + CO mechanism, this pathway reduces the activation barrier by 5 kcal/mol and is expected to accelerate the reaction. In the case of hydroperoxyl self-reaction 2HO2 → H2O2 + O2 the intermediates, containing covalent bonds to CO2 are found not to be competitive. However, the spectator CO2 molecule can stabilize the cyclic transition state and lower the barrier by 3 kcal/mol. Formation of covalent intermediates is also discovered in the H2CO + HO2 → HCO + H2O2 reaction, but these species lead to substantially higher activation barriers, which makes them unlikely to play a role in hydrogen transfer kinetics. The van der Waals complexation with carbon dioxide also stabilizes the transition state and reduces the reaction barrier. These results indicate that the CO2 environment is likely to have a catalytic effect on combustion reactions, which needs to be included in kinetic combustion mechanisms in supercritical CO2.

Quantum Chemical Study of CH 3 + O 2 Combustion Reaction System: Catalytic Effects of Additional CO 2 Molecule

Dr. Artëm E. Masunov, University of Central Florida

The supercritical carbon dioxide diluent is used to control the temperature and to increase the efficiency in oxycombustion fossil fuel energy technology. It may affect the rates of combustion by altering mechanisms of chemical reactions, compared to the ones at low CO2 concentrations. Here, we investigate potential energy surfaces of the four elementary reactions in the CH3 + O2 reactive system in the presence of one CO2 molecule. In the case of reaction CH3 + O2 → CH2O + OH (R1 channel), van der Waals (vdW) complex formation stabilizes the transition state and reduces the activation barrier by ∼2.2 kcal/mol. Alternatively, covalently bonded CO2 may form a six-membered ring transition state and reduce the activation barrier by ∼0.6 kcal/mol. In case of reaction CH3 + O2 → CH3O + O (R2 channel), covalent participation of CO2 lowers the barrier for the rate limiting step by 3.9 kcal/mol. This is expected to accelerate the R2 process, important for the branching step of the radical chain reaction mechanism. For the reaction CH3 + O2 → CHO + H2O (R3 channel) with covalent participation of CO2, the activation barrier is lowered by 0.5 kcal/mol. The reaction CH2O + OH → CHO + H2O (R4 channel) involves hydrogen abstraction from formaldehyde by OH radical. Its barrier is reduced from 7.1 to 0.8 kcal/mol by formation of vdW complex with spectator CO2. These new findings are expected to improve the kinetic reaction mechanism describing combustion processes in supercritical CO2 medium.

Disciplines

Biotechnology | Chemicals and Drugs | Chemistry | Computer Sciences | Life Sciences | Medicine and Health Sciences | Neuroscience and Neurobiology

Elizabeth Wait

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