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A catalyst is a material which speeds up the rate of a specific reaction. A reaction that is of significant importance to the chemical industry is the selective transformations of light alkanes (ethane, propane), which are largely available in shale gas, to olefins. These olefins can then be converted into higher-value chemicals, materials, and fuels. However, there are several undesired reactions that take place alongside the main dehydrogenation reaction, so a catalyst of high selectivity is desired. Apart from the industrially used PtSn catalyst, work by our experimental collaborators has shown that various other Pt and Pd alloys (In, Zn) are also highly selective and active for propane dehydrogenation (PDH). We aim to use Density Functional theory (DFT) to determine the trends in catalytic reactivity and selectivity across a wider space of alloy catalysts. This can be achieved through the development of linear scaling relationships (LSR), which relate the thermodynamic adsorption properties of chemically related species on various alloys. Initial results on the Pd alloys (Pd3Sn, PdIn, PdZn) show that the alloys have lower binding energies as compared to a pure metal. These results can have implications on the higher selectivity observed on the alloys experimentally.

Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3-4 Å/cycle for TMA+O2 ALD (O2 half-cycles at 623 K). No preferential growth of Al2O3 on the steps of Cu(111) was observed. According to STM, Al2O3 grows homogeneously on Cu(111) terraces.

Silicon is a promising alternative to graphite as an anode material for lithium-ion batteries due to its enhanced safety and significantly higher theoretical capacity. Drastic volume changes in silicon during lithiation and delithiation cycles, however, hinder cyclability and capacity retention. Most strategies for improving the cyclability of silicon involve the engineering of interfacial chemistry and nanoscale architectures, and to further these efforts, fundamental insights into lithiation processes at well-defined silicon surfaces are greatly needed. In this discussion, we present an extensive computational study of lithiation of silicon/electrolyte interfaces. Using first principles density functional theory calculations, we investigate the thermodynamics and kinetics of lithiation of Si(111), Si(110), and Si(100) surfaces, and we determine voltage/capacity curves for each of these facets. The curves exhibit a distinct, high-voltage feature for the (110) facet of silicon and thereby provide a compact thermodynamic explanation for the experimentally observed anisotropy in lithiation of Si nanowires and micropillars. The atomistic origins of this thermodynamic driving force are traced to a combination of the intrinsic strain-fracture dynamics of the various Si crystal planes and the local strength of Si–Li bonds. We discuss the effects of surface passivation on these lithiation processes, and we close with a comparison of the lithiation characteristics of Si to those of Ge and selected transition metal oxides, including titania.