Postdoctoral Scholar, California Institute of Technology
Develop and apply catalysts to transform carbon-containing molecules into high-value products
New catalysts (a type of nano-material) enabled the creation of many important technologies in the 20th century. For example, industrial processes used to make products such as fertilizer, gasoline, and plastics, as well as technologies used to reduce emissions from automobiles all have made very large, positive impacts on society and all were made possible by catalysts. Effective use of catalysts in the future for key areas such as energy, consumer goods, and infrastructure requires better design of catalysts and development of new methods to produce high-value chemicals and fuels from carbon-containing resources, such as shale gas. The objective of this research is to design, develop, and apply new catalysts with tailored properties to efficiently transform carbon-containing molecules into a diverse range of valuable chemicals with reduced environmental impact.
Abstract: Supported metal nanoparticles are vital as heterogeneous catalysts in the chemical transformation of hydrocarbon resources. The catalytic properties of these materials are governed by the surface electronic structure and valence orbitals at the active metal site and can be selectively tuned with promoters or by alloying. Through an integrated approach using density functional theory (DFT), kinetics, and in situ X-ray spectroscopies, we demonstrate how Zn addition to Pt/SiO2 forms high symmetry Pt1Zn1 nanoparticle alloys with isolated Pt surface sites that enable near 100% C2H4 selectivity during ethane dehydrogenation (EDH) with a 6-fold higher turnover rate (TOR) per mole of surface Pt at 600 °C compared to monometallic Pt/SiO2. Furthermore, we show how DFT calculations accurately reproduce the resonant inelastic X-ray spectroscopic (RIXS) signatures of Pt 5d valence orbitals in the Pt/SiO2 and PtZn/SiO2 catalysts that correlate with their kinetic performance during EDH. This technique reveals that Zn modifies the energy of the Pt 5d electrons in PtZn, which directly relates to TOR promotion, while ensemble effects from the incorporation of Zn into the catalyst surface lead to enhanced product selectivity.
Pub.: 11 May '17, Pinned: 29 Jun '17
Abstract: Zeolite and zeolite-like molecular sieves are being used in a large number of applications such as adsorption and catalysis. Achievement of the long-standing goal of creating a chiral, polycrystalline molecular sieve with bulk enantioenrichment would enable these materials to perform enantioselective functions. Here, we report the synthesis of enantiomerically enriched samples of a molecular sieve. Enantiopure organic structure directing agents are designed with the assistance of computational methods and used to synthesize enantioenriched, polycrystalline molecular sieve samples of either enantiomer. Computational results correctly predicted which enantiomer is obtained, and enantiomeric enrichment is proven by high-resolution transmission electron microscopy. The enantioenriched and racemic samples of the molecular sieves are tested as adsorbents and heterogeneous catalysts. The enantioenriched molecular sieves show enantioselectivity for the ring opening reaction of epoxides and enantioselective adsorption of 2-butanol (the R enantiomer of the molecular sieve shows opposite and approximately equal enantioselectivity compared with the S enantiomer of the molecular sieve, whereas the racemic sample of the molecular sieve shows no enantioselectivity).
Pub.: 01 May '17, Pinned: 29 Jun '17
Abstract: The formose reaction (FR) has been long the focus of intensive investigations as a simple method for synthesis of complex biologically important monosaccharides and other sugar-like molecules from the simplest organic substrate-formaldehyde. The fundamental importance of the FR is predominantly connected with the ascertainment of plausible scenarios of chemical evolution which could have occurred on the prebiotic Earth to produce the very first molecules of carbohydrates, amino- and nucleic acids, as well as other vitally important substances. The practical importance of studies on the FR is the elaboration of catalytic methods for the synthesis of rare and non-natural monosaccharides and polyols. This Minireview considers the FR from the point of view of chemists working in the field of catalysis with emphasis on the mechanisms of numerous parallel and consequent catalytic transformations that take place during the FR. Based on its kinetics, the FR may be considered as a non-radical chain process with degenerate branching. The Minireview also considers different approaches to the control of selectivity of carbohydrate synthesis from formaldehyde and lower monosaccharides.
Pub.: 17 Jun '14, Pinned: 29 Jun '17
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