Density Functional Theory Simulations of MOFs Encapsulated-Catalyzed Systems

The research is mainly on Computational Design of Highly Selective Transition Metal Catalysts Encapsulated by Metal-­‐Organic Frameworks for Butane Oxidation to 1-­‐Butanol. Metal Organic Framework (MOF) grown over a heterogeneous catalyst. Pores of framework allow only certain molecules of correct size, orientation, or chemical properties to access catalyst. The framework will force molecule into desired orientation where only the terminal atoms will “see” the catalyst. In our simulation we would like to use the helium ring to simulate the MOFs pores, since He is inert and exhibits the no chemical reactivity. The reaction we are looking into is butane oxidation to 1-­‐butanol. The specific catalyst surface, which we are working on, is Ag3Pd. However, we found that there is problem existing on the very first oxygen dissociation step which the activation energy and reaction energy is positive and pretty large. As a result, we are taking consideration into other Alloy surface such as Cu3Pd and PdZn , which bind the O2 more strongly and may facilitate the O2 dissociation. What’s more, the metal oxide is another material we will look into in the future

Tuning oxo formation energies using spectator ligands in the MIL-100 metal organic framework

https://tigerprints.clemson.edu/csrp/1008/thumbnail.jp

Simultaneous X-ray and radio observations of Young Stellar Objects in NGC 1333 and IC 348

Young Stellar Objects (YSOs) and in particular protostars are known to show a variety of high-energy processes. Observations in the X-ray and centimetric radio wavelength ranges are thought to constrain some of these processes, e.g., coronal-type magnetic activity. There is a well-known empirical correlation of radio and X-ray luminosities in active stars, the so-called Guedel-Benz relation. Previous evidence whether YSOs are compatible with this relation remains inconclusive for the earliest evolutionary stages. The main difficulty is that due to the extreme variability of these sources, simultaneous observations are essential. Until now, only few YSOs and only a handful of protostars have been observed simultaneously in the X-ray and radio range. To expand the sample, we have obtained such observations of two young clusters rich in protostars, NGC 1333 and IC 348. While the absolute sensitivity is lower for these regions than for more nearby clusters like CrA, we find that even in deep continuum observations carried out with the NRAO Very Large Array, the radio detection fraction for protostars in these clusters is much lower than the X-ray detection fraction. Very few YSOs are detected in both bands, and we find the radio and X-ray populations among YSOs to be largely distinct. We combine these new results with previous simultaneous Chandra and VLA observations of star-forming regions and find that YSOs with detections in both bands appear to be offset toward higher radio luminosities for given X-ray luminosities when compared to the Guedel-Benz relation, although even in this sensitive dataset most sources are too weak for the radio detections to provide information on the emission processes. The considerably improved sensitivity of the Expanded Very Large Array will provide a better census of the YSO radio population as well as better constraints on the emission mechanisms.Comment: Accepted for publication in Ap

Multiwavelength Signatures of Magnetic Activity from Young Stellar Objects in the LkH\alpha101 Cluster

[abridged] We describe the results of our multi-wavelength observing campaign on the young stellar objects in the LkH$\alpha$101 cluster. Our simultaneous X-ray and multi-frequency radio observations are unique in providing simultaneous constraints on short-timescale variability at both wavelengths as well as constraints on the thermal or nonthermal nature of radio emission from young stars. Focussing in on radio-emitting objects and the multi-wavelength data obtained for them, we find that multi-frequency radio data indicate nonthermal emission even in objects with infrared evidence for disks. We find radio variability on timescales of decades, days and hours. About half of the objects with X-ray and radio detections were variable at X-ray wavelengths, despite lacking large-scale flares or large variations. Variability appears to be a bigger factor affecting radio emission than X-ray emission. A star with infrared evidence for a disk, [BW88]~3, was observed in the decay phase of a radio flare. In this object and another ([BW88]~1), we find an inverse correlation between radio flux and spectral index which contrasts with behavior seen in the Sun and active stars. We interpret this behavior as the repopulation of the hardest energy electrons due to particle acceleration. A radio and X-ray source lacking an infrared counterpart, [BW88]~1, may be near the substellar limit; its radio properties are similar to other cluster members, but its much higher radio to X-ray luminosity ratio is reminiscent of behavior in nearby very low mass stars/brown dwarfs. We find no correspondence between signatures of particle acceleration and those of plasma heating, both time-averaged and time-variable. The lack of correlated temporal variability in multi-wavelength behavior, the breakdown of multi-wavelength correlations of...Comment: accepted for publication in Ap

Machine Learning (ML) For Tracking the Geo-Temporality of a Trend: Documenting the Frequency of the Baseball-Trucker Hat on Social Media and the Runway

The study applied fine-grained Machine Learning (ML) to document the frequency of baseball-trucker hats on social media with images populated from the Matzen et al. (2017) StreetStyle-27k Instagram dataset (2013-2016) and as produced in runway shows for the luxury market with images populated from the Vogue Runway database (2000-2018). The results show a low frequency of baseball-trucker hats on social media from 2013-2016 with little annual fluctuation. The Vogue Runway plots showed that baseball-hats appeared on the runway before 2008 with a slow but steady annual increase from 2008 through 2018 with a spike in 2016 to 2017. The trend is discussed within the context of social, cultural, and economic factors. Although ML requires refinement, its use as a tool to document and analyze increasingly complex trends is promising for scholars. The study shows one implementation of high-level concept recognition to map the geo-temporality of a fashion trend

The Significant Differences in Solvation Thermodynamics of C1-C3 Oxygenates in Hydrophilic versus Hydrophobic Pores of a Hydrophilic Ti-FAU Zeolite Model

The rates of catalytic reactions have been observed to be dramatically different in zeolites, depending on if they are hydrophobic or hydrophilic. Hypotheses aimed at explaining this behavior have pointed to various solvent molecule and zeolite properties as having influence on entropy. Herein, the influence of various solvent and adsorbate properties on the solvation energies, entropies, and free energies of eleven C1-C3 oxygenates in hydrophobic and hydrophilic pores within a hydrophilic model of Ti-FAU zeolite are tested. The results indicate significant variation in the calculated solvation thermodynamics depending on the adsorbate type, as well as if it is bound within a hydrophobic or hydrophilic pore. Further, while solvation energies are related to solvent-adsorbate interactions, solvation entropies have multiple contributions, and these differ depending on if the adsorbate is in a hydrophobic or hydrophilic pore. Specifically, solvation entropies in hydrophobic pores are related to solvent structural properties, whereas solvation entropies in hydrophilic pores are related to adsorbate polarity. The large range of results obtained from two different pores within one zeolite model with minimal unique adsorption sites suggests that solvation behavior in zeolites is complicated and that the phenomena that control observed performance depend on the zeolite, reaction, and solvent

Effect of Water On Deep Eutectic Solvents: Structural Properties and Interactions with CO2

One of the biggest research challenges of the current time is developing technologies for removing CO2 from air. Deep eutectic solvents (DESs), specifically comprised of ionic liquids along with hydrogen bond donors, are promising for direct air capture (DAC) due to their low volatilities, high thermal stabilities, tuneable properties, and high sustainabilities. As water is inevitable in DAC, DESs designed for DAC must be able to function in the presence of water. Addition of water to DESs is believed to have a strong impact on DES properties, including hydrogen bond networks, molecular transport, and interactions with CO2. This study employs classical molecular dynamics (MD) simulations to explore the impact of water addition on the structural and intermolecular properties of DESs composed of 1-ethyl-3-methylimidazolium cations ([EMIM]) and 2-cyanopyrrolide anions ([2CNPyr]) along with three different hydrogen bond donors - ethylene glycol (EG), propylene glycol (PG), and monoethanolamide (MEA). Results show significant structural changes in the DESs due to addition of water, including enhanced interactions between CO2 and [EMIM], [2CNpyr], and MEA

Reaction Pathways and Microkinetic Modeling of <i>n</i>‑Butane Oxidation to 1‑Butanol on Cu, Cu₃Pd, Pd, Ag₃Pd, and PdZn (111) Surfaces

Density functional theory (DFT) calculations and microkinetic modeling are used to model reactions in the oxidation of <i>n</i>-butane to 1-butanol, 1-butanal, and 1-butene over pure metal and metal alloy (111) surfaces. Specifically, catalytic thermodynamic and kinetic energies are calculated with DFT, and linear scaling relationships are developed that link these values to simpler “descriptors” of catalytic activity. The scaling relationships are used in microkinetic modeling to identify the optimal descriptor values, which maximize the rate and selectivity to 1-butanol. Degree of rate control (DRC) analysis is performed to reveal the catalytic intermediates and transition states that have the greatest influence on the rate. The Cu₃Pd­(111) and Ag₃Pd­(111) surfaces are found to be the most active for <i>n</i>-butane oxidation to 1-butanol, with Cu₃Pd additionally exhibiting high selectivity for 1-butanol. Achieving high activity and selectivity toward 1-butanol is found to require a precise balance of the catalyst affinity for OH* and O*, with catalysts that bind these species too strongly garnering large coverages of O*, which block active sites and inhibit the rate of <i>n</i>-butane conversion, and catalysts that bind these species too weakly promoting dehydrogenation of C₄ species, as this process supplies H atoms that can convert OH* and O* to the more-stable H₂O*. Catalytic affinity for C* is also found to have a significant impact on selectivity toward 1-butanol, since the formation energy of C* on catalyst surfaces is found to correlate to catalytic ability to break C–H bonds, with catalysts that bind C* too strongly tending to overdehydrogenate C₄ species. The reaction C₄H₉* + O* ↔ C₄H₉O* + * is found to be rate-controlling on those catalysts that are most active for 1-butanol production