The adsorption energy of the methoxybenzene molecule on Cu(111) was calculated as ads = methoxy+C... more The adsorption energy of the methoxybenzene molecule on Cu(111) was calculated as ads = methoxy+Cu(111) − Cu(111) − methoxy Where methoxy+Cu(111) , Cu(111) , and methoxy denote the total energy for the methoxybenzene adsorbed on Cu(111) surface, the Cu(111) slab and the gas phase methoxybenzene molecule, respectively. Adsorption of the methoxybenzene was calculated on all possible sites available on the Cu(111) surface, the bridge, fcc, hcp and top sites. Due to the symmetry of the surface, the molecule can be oriented either in the 0 o or at 30 o relative to the Cu atom rows. This resulted in eight different adsorption sites. To determine the appropriate supercell size which induces minimal lateral interactions between adjacent periodic methoxybenzene molecules, the adsorption site scan was conducted on (4 × 4) and (5 × 5) Cu(111) supercells, as shown in Figure S1.
Despite its high thermodynamic stability, the presence of a negative electric field is known to f... more Despite its high thermodynamic stability, the presence of a negative electric field is known to facilitate the activation of CO2 through electrostatic effects. To utilize electric fields for a reverse water gas shift reaction, it is critical to elucidate the role of an electric field on a catalyst surface toward activating a CO2 molecule. We conduct a first-principles study to gain an atomic and electronic description of adsorbed CO2 on YSZ (111) surfaces when external electric fields of +1 V/Å, 0 V/Å, and −1 V/Å are applied. We find that the application of an external electric field generally destabilizes oxide bonds, where the direction of the field affects the location of the most favorable oxygen vacancy. The direction of the field also drastically impacts how CO2 adsorbs on the surface. CO2 is bound by physisorption when a +1 V/Å field is applied, a similar interaction as to how it is adsorbed in the absence of a field. This interaction changes to chemisorption when the surface...
When a loss of primary containment of liquefied natural gas (LNG) occurs on the ground, a pool, t... more When a loss of primary containment of liquefied natural gas (LNG) occurs on the ground, a pool, that simultaneously spreads and vaporizes, is formed posing cryogenic, asphyxiating, and flammable hazards to its surrounding. Determining the pool size and vapour generation upon release play key roles in the accuracy of dispersion and consequence models. This work focuses on LNG source term model validation through the evaluation of an existing model with a newly generated data.
Water plays pivotal roles in tailoring reaction pathways in many important reactions, including c... more Water plays pivotal roles in tailoring reaction pathways in many important reactions, including cascade C−C bond formation and oxygen elimination. Herein, a kinetic study combined with complementary analyses (DRIFTS, isotopic study, 1 H solid-state magic angle spinning nuclear magnetic resonance) and density functional theory (DFT) calculations are performed to elucidate the roles of water in cascade acetone-to-isobutene reactions on a Zn x Zr y O z mixed metal oxide with balanced Lewis acid−base pairs. Our results reveal that the reaction follows the acetone−diacetone alcohol−isobutene pathway. Isobutene is produced through an intramolecular rearrangement of the eight-membered ring intermediate formed via the adsorption of diacetone alcohol on the Lewis acid−base pairs in the presence of cofed water. OH adspecies, formed by the dissociative adsorption of water on the catalyst surface, were found to distort diacetone alcohol's hydroxyl functional group toward its carbonyl functional group and facilitate the intramolecular rearrangement of diacetone alcohol to form isobutene. In the absence of water, diacetone alcohol binds strongly to the Lewis acid site, e.g., at a Zr 4+ site, via its carbonyl functional group, leading to its dramatic structural distortion and further dehydration reaction to form mesityl oxide as well as subsequent polymerization reactions and the formation of coke. The present results provide insights into the cooperative roles of water and Lewis acid−base pairs in catalytic upgrading of biomass to fuels and chemicals.
We report a comprehensive study combining surface science, Density Functional Theory (DFT) calcul... more We report a comprehensive study combining surface science, Density Functional Theory (DFT) calculations, and catalyst synthesis, characterization, and testing to investigate the preferential oxidation of CO in the presence of H 2 over single-site Pt 1 /Cu x O catalysts. Surface science studies show that while Pt 1 /Cu x O model surfaces enable low-temperature CO oxidation via a Mars-van Krevelen mechanism, there was no evidence for H 2 activation or oxidation. DFT-based calculations explain these results and demonstrate that the H 2 oxidation barrier is high as compared to H 2 desorption from Pt 1 /Cu x O. Inspired by these model catalyst studies, nanoporous Pt 1 /Cu x O catalysts were synthesized and demonstrated to be active and highly selective for the preferential oxidation of CO. This work highlights the potential of combined surface science, theory, and catalyst studies for identifying new catalytic materials, which in this case led to the development of a promising single-site Pt 1 /Cu x O catalyst for the preferential oxidation of CO.
The adsorption energy of the methoxybenzene molecule on Cu(111) was calculated as ads = methoxy+C... more The adsorption energy of the methoxybenzene molecule on Cu(111) was calculated as ads = methoxy+Cu(111) − Cu(111) − methoxy Where methoxy+Cu(111) , Cu(111) , and methoxy denote the total energy for the methoxybenzene adsorbed on Cu(111) surface, the Cu(111) slab and the gas phase methoxybenzene molecule, respectively. Adsorption of the methoxybenzene was calculated on all possible sites available on the Cu(111) surface, the bridge, fcc, hcp and top sites. Due to the symmetry of the surface, the molecule can be oriented either in the 0 o or at 30 o relative to the Cu atom rows. This resulted in eight different adsorption sites. To determine the appropriate supercell size which induces minimal lateral interactions between adjacent periodic methoxybenzene molecules, the adsorption site scan was conducted on (4 × 4) and (5 × 5) Cu(111) supercells, as shown in Figure S1.
Engineering Leaders Conference 2014 on Engineering Education, 2015
An independent 7-week module on imaging systems is being offered in spring 2002 to introduce fres... more An independent 7-week module on imaging systems is being offered in spring 2002 to introduce freshmen engineering students to basic methods of problem solving, image analysis tools, and design. It offers several top-down, high-level methodologies for building solutions to interesting challenges, motivating the students to consider engineering as a problem solving discipline, rather than an assemblage of many low-level facts and skills. Preliminary assessment results will be given at the presentation of this paper. The module begins with the presentation of basic digital imaging methods and issues, using PC hardware and web cameras available in the department electronics lab. As student proficiency grows, they advance in teams to the High Tech Tools and Toys Laboratory, which supports five dedicated imaging stations. At each station, the students face a particular imaging problem, which they solve using a variety of hardware and software tools. Solutions are structured to make sure the students can be reasonably successful with their novice level of understanding. The 'Tools and Toys' include different cameras, frame grabbers and digital channels, and imaging software ranging from MATLAB to LabVIEW and Vision Foundry. Problem solving is emphasized, as is the engineer's choice of appropriate and varied tools. The advanced stations present problems in gauging, pattern recognition, coin counting, tracking, and acoustic imaging. Several also incorporate data interfaces, so that the system can change the environment based on image analysis. The software tools illustrate a range of user control and programming, including menu-driven systems, LabVIEW, MATLAB and C++.
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Papers by Nisa Ulumuddin