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Results for “Co-Pt”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Structural and Valence State Modification of Cobalt in CoPt Nanocatalysts in Redox Conditions

Platinum is the primary catalyst for many chemical reactions in the field of heterogeneous catalysis. However, platinum is both expensive and rare. Therefore, it is advantageous to combine Pt with another metal to reduce cost while also enhancing stability. To that end, Pt is often combined with Co to form Co-Pt nanocrystals. However, dynamical restructuring effects that occur during reaction in Co-Pt ensembles can impact catalytic properties. In this study, model Co 2 Pt 3 nanoparticles supported on carbon were characterized during a redox cycle with two in situ approaches, namely X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM) using a multimodal microreactor. The sample was exposed to temperatures up to 500 °C under H 2 , and then to O 2 at 300 °C. Irreversible segregation of Co in the Co-Pt particles was seen during redox cycling and substantial changes of the oxidation state of Co were observed. After the H 2 treatment, a fraction of Co could not be fully reduced and incorporated into a mixed Co-Pt phase. Re-oxidation of the sample increased Co segregation, and the segregated material had a different valence state than in the fresh, oxidized sample. Furthermore, this in situ study describes dynamical restructuring effects in CoPt nano-catalysts at the atomic scale that are crucial to understand to improve the design of catalysts used in major chemical processes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Catalytic Oxidation of CO on a Curved Pt(111) Surface: Simultaneous Ignition at All Facets through a Transient CO-O Complex

The light-off of the CO oxidation is simultaneous on all Pt crystal surfaces vicinal to the (111) plane, regardless of the reaction conditions, and in contrast with the structural dependence of Pd. In this work, using ambient-pressure XPS we find that, immediately prior to ignition, atomic oxygen incorporates to the subsurface plane, leading to buckling of the topmost CO-Pt layer, and effectively equaling the CO desorption temperature at terraces and steps.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Configuration Space Integration for Adsorbate Partition Functions: The Effect of Anharmonicity on the Thermophysical Properties of CO–Pt(111) and CH 3 OH–Cu(111)

A method for computing anharmonic thermophysical properties for adsorbates on metal surfaces has been extended to include libration, or frustrated rotation. Classical phase space integration is used with Monte Carlo sampling of the configuration space to obtain the partition function of CO on Pt(111) and CH 3 OH on Cu(111). A minima-preserving neural network potential energy surrogate is used within the integration routines. Direct state counting using discrete variable representation is used to benchmark the results. We find that the phase space integration approach is in excellent agreement with the direct state counting results. Comparison with standard models such as the harmonic oscillator indicates that anharmonicity contributes significantly to the thermodynamic properties of CH 3 OH on Cu(111). We find that there is also a considerable difference between the harmonic oscillator and phase space integration for CO on Pt(111), although the discrepancy can largely be attributed to the presence of multiple binding sites within the unit cell. We demonstrate that a multisite harmonic oscillator model might be sufficient for CO-Pt(111). A more thorough description of the potential energy surface, which can be achieved with phase space integration, is necessary for weakly bound adsorbates such as CH 3 OH. In conclusion, the thermophysical properties were used to calculate free energies of adsorption on the respective metals, and subsequently the equilibrium constants and Langmuir isotherms in relevant temperature ranges. The results show that the choice of model to obtain partition functions greatly affects the resulting surface coverages in kinetic models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Materials Data on Co3Pt by Materials Project

Co3Pt is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are three inequivalent Co sites. In the first Co site, Co is bonded to eight Co and four equivalent Pt atoms to form distorted CoCo8Pt4 cuboctahedra that share corners with four equivalent PtCo12 cuboctahedra, corners with fourteen CoCo8Pt4 cuboctahedra, edges with six equivalent PtCo12 cuboctahedra, edges with twelve CoCo8Pt4 cuboctahedra, faces with four equivalent PtCo12 cuboctahedra, and faces with sixteen CoCo8Pt4 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.47–2.74 Å. All Co–Pt bond lengths are 2.61 Å. In the second Co site, Co is bonded to eight Co and four equivalent Pt atoms to form distorted CoCo8Pt4 cuboctahedra that share corners with four equivalent PtCo12 cuboctahedra, corners with fourteen CoCo8Pt4 cuboctahedra, edges with six equivalent PtCo12 cuboctahedra, edges with twelve CoCo8Pt4 cuboctahedra, faces with four equivalent PtCo12 cuboctahedra, and faces with sixteen CoCo8Pt4 cuboctahedra. All Co–Co bond lengths are 2.52 Å. All Co–Pt bond lengths are 2.61 Å. In the third Co site, Co is bonded to eight Co and four equivalent Pt atoms to form distorted CoCo8Pt4 cuboctahedra that share corners with four equivalent PtCo12 cuboctahedra, corners with fourteen CoCo8Pt4 cuboctahedra, edges with six equivalent PtCo12 cuboctahedra, edges with twelve CoCo8Pt4 cuboctahedra, faces with four equivalent PtCo12 cuboctahedra, and faces with sixteen CoCo8Pt4 cuboctahedra. There are a spread of Co–Co bond distances ranging from 2.47–2.74 Å. All Co–Pt bond lengths are 2.61 Å. Pt is bonded to twelve Co atoms to form PtCo12 cuboctahedra that share corners with six equivalent PtCo12 cuboctahedra, corners with twelve CoCo8Pt4 cuboctahedra, edges with eighteen CoCo8Pt4 cuboctahedra, faces with eight equivalent PtCo12 cuboctahedra, and faces with twelve CoCo8Pt4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CoPt2 by Materials Project

Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

36 MATERIALS SCIENCE↗