Adrianna Brush

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• Mullen, G., Evans, E., Siegert, B., Miller, N., Rosselet, B., Sabzevari, I., Brush, A., Duan, Z., & Buddie Mullins, C. (2018). The interplay between ceria particle size, reducibility, and ethanol oxidation activity of ceria-supported gold catalysts. Reaction Chemistry and Engineering, 3(1). doi:10.1039/c7re00175d
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  The structure of a support material can have profound impacts on the behavior of a catalyst, altering the activity and selectivity of chemical reactions. In this article, we investigate the influence of the support material's structure on the activity of Au/CeO2 catalysts for selective oxidation of ethanol in a fixed-bed flow reactor. By doping the ceria support with Al, La, and Zr during synthesis and by altering the temperature of pretreatment in air after synthesis, ceria particles varying in size between 3 nm and 22 nm were prepared. The smaller ceria particles exhibited higher oxygen storage capacities as determined by temperature programmed reduction testing and resulted in more active catalysts for ethanol oxidation. We note a linear correlation between oxygen storage capacity and catalytic activity for ethanol oxidation.
• Brush, A., McDonald, S., Kota, S., Mullen, G., Buddie Mullins, C., & Dupré, R. (2017). Apparatus for efficient utilization of isotopically-labeled gases in pulse transient studies of heterogeneously catalyzed gas phase reactions. Reaction Chemistry and Engineering, 2(4). doi:10.1039/c7re00038c
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  Transient techniques, such as Steady state isotopic transient kinetic analysis (SSITKA), are powerful methods for determining various mechanistic and kinetic insights into heterogeneously catalyzed gas-phase reactions. However, the reactor systems commonly used in these techniques underutilize the costly isotopically labeled reactants crucial to these experiments. In this manuscript, we describe a novel apparatus that allows more efficient utilization of isotopically labeled reactants. This pulse injection apparatus is relatively easy and inexpensive to install on new or existing reaction systems. Sample data and analysis of SSITKA experiments performed on this system are also included.
• Brush, A., Evans, E., Mullen, G., Jarvis, K., & Mullins, C. (2016). Tunable Syn-gas ratio via bireforming over coke-resistant Ni/Mo2C catalyst. Fuel Processing Technology, 153(Issue). doi:10.1016/j.fuproc.2016.07.012
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  This study demonstrates the ability of Ni/Mo2C to catalyze the Methane Bireforming Reaction (combined Dry Methane Reforming Reaction, CH4 + CO2 ➔ 2H2 + 2CO, and Steam Methane Reforming Reaction, CH4 + H2O ➔ 3H2 + CO). By varying the ratio of CO2:H2O, the resulting H2:CO ratio could be tuned from 0.91 to 3.0, covering a wide range of Syn-gas (H2 + CO) ratios relevant to various hydrocarbon syntheses. We also document the unusual deactivation behavior of Ni/Mo2C in this system. The catalytic activity would change from very high (> 50% conversion) to very low (< 10% conversion) within 10 min. Despite running under conditions typically favorable for coking with a Ni catalyst (high temperature, 950 °C, and excess methane), XRD, TGA, TEM, SEM, and EDX results clearly show no evidence of coking during the reaction or after deactivation. In addition, the changes to the Ni/Mo2C catalyst seen after deactivation (oxidation of Mo2C to MoO2, Ni-phase changes, and catalyst morphology changes) could not be seen in the catalyst subjected to reaction conditions that were halted before deactivation could occur. This suggests a sudden, rapid deactivation “event” occurs in this catalytic system as opposed to gradual catalyst deactivation, a behavior more typically seen with catalysts.
• Brush, A., Mullen, G., Kota, S., Buddie Mullins, C., & Dupré, R. (2016). Evidence of methane adsorption over Mo2C involving single C-H bond dissociation instead of facile carbon exchange. Reaction Chemistry and Engineering, 1(6). doi:10.1039/c6re00141f
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  Mo2C catalysts have been widely studied for methane reforming reactions. One of the proposed mechanisms for Mo2C catalysts is a redox type mechanism that includes active participation of the carbide carbon in the reaction. While evidence for this mechanism has been provided by several studies, one of the most surprising results previously reported asserts that a stream of pure methane can undergo significant, facile carbon exchange with the Mo2C catalyst at temperatures above 550 °C. Using pulses of 13CH4, we have found no evidence of carbon exchange between methane and Mo2C, even at 800 °C, in contrast to these previous results. In addition, by using pulses of CD4, we have found evidence of a small degree of dissociative methane adsorption at 800 °C, involving the breaking and reforming of a single methane-hydrogen/deuterium bond. While the present study does not contradict the model of active carbide carbon participation via a redox mechanism in methane reforming reactions, it doesn't support the notion of significant and facile carbon exchange between methane and Mo2C without an oxidant.
• Pan, M., Brush, A., Pozun, Z., Ham, H., Yu, W., Henkelman, G., Hwang, G., & Mullins, C. (2013). Model studies of heterogeneous catalytic hydrogenation reactions with gold. Chemical Society Reviews, 42(12). doi:10.1039/c3cs35523c
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  Supported gold nanoparticles have recently been shown to possess intriguing catalytic activity for hydrogenation reactions, particularly for selective hydrogenation reactions. However, fundamental studies that can provide insight into the reaction mechanisms responsible for this activity have been largely lacking. In this tutorial review, we highlight several recent model experiments and theoretical calculations on a well-structured gold surface that provide some insights. In addition to the behavior of hydrogen on a model gold surface, we review the reactivity of hydrogen on a model gold surface in regards to NO2 reduction, chemoselective C=O bond hydrogenation, ether formation, and O–H bond dissociation in water and alcohols. Those studies indicate that atomic hydrogen has a weak interaction with gold surfaces which likely plays a key role in the unique hydrogenative chemistry of classical gold catalysts. © 2013 The Royal Society of Chemistry.
• Brush, A., Pan, M., & Mullins, C. (2012). Methanol O-H bond dissociation on H-precovered gold originating from a structure with a wide range of surface stability. Journal of Physical Chemistry C, 116(39). doi:10.1021/jp308099y
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  Gold has been shown to exhibit promising catalytic activity, and understanding the fundamental interactions of reactants and hydrogen atoms on a gold surface is key to gaining insight into hydrogenation reaction mechanisms. In this paper, we report that the adsorption of methanol onto a H-precovered Au(111) surface induces an adsorbate structure, or set of structures, on the surface involving both methanol and hydrogen adatoms with a wide range of stability on the surface. Coadsorption of H/MeOD or D/MeOH indicates H/D exchange between the two surface species, providing evidence that the H-precovered gold surface can dissociate the methanol O-H bond at low temperature (
• Pan, M., Brush, A., Dong, G., & Mullins, C. (2012). Tunable ether production via coupling of aldehydes or aldehyde/alcohol over hydrogen-modified gold catalysts at low temperatures. Journal of Physical Chemistry Letters, 3(17). doi:10.1021/jz301105e
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  Ethers are an important group of organic compounds that are primarily prepared via homogeneous catalysis, which can lead to operational and environmental issues. Here we demonstrate the production of ethers via heterogeneous catalysis over H adatom-covered gold at temperatures lower than 250 K. Symmetrical ethers can be formed via a self-coupling reaction of corresponding aldehydes; for example, homocoupling of acetaldehyde and propionaldehyde yields diethyl ether and di-n-propyl ether, respectively. In addition, coupling reactions between alcohols and aldehydes, with different carbon chain lengths, are observed via the production of the corresponding unsymmetrical ethers. A reaction mechanism is proposed, suggesting that an alcohol-like intermediate via partial hydrogenation of aldehydes on the surface plays a key role in these reactions. These surface chemical reactions suggest possible heterogeneous routes to low-temperature production of ethers. © 2012 American Chemical Society.
• Pan, M., Pozun, Z., Brush, A., Henkelman, G., & Mullins, C. (2012). Low-temperature chemoselective gold-surface-mediated hydrogenation of acetone and propionaldehyde. ChemCatChem, 4(9). doi:10.1002/cctc.201200311