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NASA NTRS2003

Analysis of Surface and Bulk Behavior in Ni-Pd Alloys

The most salient features of the surface structure and bulk behavior of Ni-Pd alloys have been studied using the BFS method for alloys. Large-scale atomistic simulations were performed to investigate surface segregation profiles as a function of temperature, crystal face, and composition. Pd enrichment of the first layer was observed in (111) and (100) surfaces, and enrichment of the top two layers occurred for (110) surfaces. In all cases, the segregation profile shows alternate planes enriched and depleted in Pd. In addition, the phase structure of bulk Ni-Pd alloys as a function of temperature and composition was studied. A weak ordering tendency was observed at low temperatures, which helps explain the compositional oscillations in the segregation profiles. Finally, based on atom-by-atom static energy calculations, a comprehensive explanation for the observed surface and bulk features will be presented in terms of competing chemical and strain energy effects.

Bozzolo, Guillermo↗

NASA NTRS2002

Surface Composition of NiPd Alloys

Surface segregation in Ni-Pd alloys has been studied using the BFS method for alloys. Not only does the method predict an oscillatory segregation profile but it also indicates that the number of Pd-enriched surface planes can vary as a function of orientation. The segregation profiles were computed as a function of temperature, crystal face, and composition. Pd enrichment of the first layer is observed in (111) and (100) surfaces, and enrichment of the top two layers occurs for (110) surfaces. In all cases, the segregation profile shows oscillations that are actually related to weak ordering tendencies in the bulk. An atom-by-atom analysis was performed to identify the competing mechanisms leading to the observed surface behaviors. Large-scale atomistic simulations were also performed to investigate the temperature dependence of the segregation profiles as well as for analysis of the bulk structures. Finally, the observed surface behaviors are discussed in relation to the bulk phase structure of Ni-Pd alloys, which exhibit a tendency to weakly order.

Noebe, Ronald D.↗

DOE OSTI2022

Methane Catalytic Pyrolysis by Microwave and Thermal Heating over Carbon Nanotube-Supported Catalysts: Productivity, Kinetics, and Energy Efficiency

Methane catalytic pyrolysis, which is the reaction to produce hydrogen and carbon without emitting CO 2 , represents an approach for decarbonization using natural gas as an energy resource. In this work, the endothermic pyrolysis reaction was carried out under two heating scenarios: convective thermal heating and microwave-driven irradiative heating. The pyrolysis reaction was conducted at 550-600 °C over carbon nanotube-supported Ni-Pd and Ni-Cu catalysts. On both catalysts, an enhanced methane conversion rate was observed under microwave irradiation. The enhanced catalytic activity was hypothetically caused by the presence of free electrons in the carbon atoms within CNT that enabled the CNT support to absorb microwave energy effectively and to be heated efficiently by microwave. The microwave catalytic pyrolysis has shown improvement in kinetics, where the apparent activation energy dropped from 45.5 kJ/mol under conventional convective heating to 24.8 kJ/mol under microwave irradiation. When the methane conversion rate is increased by 37 %, the microwave power consumption only changed by 10.8 %. The research demonstrated the potential of transforming natural gas to clean hydrogen and value-added carbon in a more energy-efficient way. Process simulation and techno-economic analysis showed that potentially hydrogen minimum selling price of about $1 /kg H 2 could be achieved.

03 NATURAL GAS↗

NASA NTRS1971

The structure of nickel-palladium solid solutions

Ni-Pd alloys atomic arrangements and displacements by single crystal X ray diffuse scattering, using computer simulated model

Lin, W.↗

DOE OSTI2020

Materials Data on NiPd3 by Materials Project

Pd3Ni is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pd is bonded to eight equivalent Pd and four equivalent Ni atoms to form PdNi4Pd8 cuboctahedra that share corners with four equivalent NiPd12 cuboctahedra, corners with fourteen equivalent PdNi4Pd8 cuboctahedra, edges with six equivalent NiPd12 cuboctahedra, edges with twelve equivalent PdNi4Pd8 cuboctahedra, faces with four equivalent NiPd12 cuboctahedra, and faces with sixteen equivalent PdNi4Pd8 cuboctahedra. There are a spread of Pd–Pd bond distances ranging from 2.65–2.74 Å. There are two shorter (2.69 Å) and two longer (2.70 Å) Pd–Ni bond lengths. Ni is bonded to twelve equivalent Pd atoms to form NiPd12 cuboctahedra that share corners with six equivalent NiPd12 cuboctahedra, corners with twelve equivalent PdNi4Pd8 cuboctahedra, edges with eighteen equivalent PdNi4Pd8 cuboctahedra, faces with eight equivalent NiPd12 cuboctahedra, and faces with twelve equivalent PdNi4Pd8 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on NiPd by Materials Project

PdNi crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Pd sites. In the first Pd site, Pd is bonded to six equivalent Pd and six Ni atoms to form distorted PdNi6Pd6 cuboctahedra that share corners with twelve PdNi6Pd6 cuboctahedra, edges with twelve PdNi6Pd6 cuboctahedra, edges with twelve NiNi6Pd6 cuboctahedra, faces with six equivalent PdNi6Pd6 cuboctahedra, and faces with twelve NiNi6Pd6 cuboctahedra. All Pd–Pd bond lengths are 2.70 Å. All Pd–Ni bond lengths are 2.64 Å. In the second Pd site, Pd is bonded to ten equivalent Pd and six Ni atoms to form distorted PdNi6Pd10 cuboctahedra that share corners with ten NiNi6Pd6 cuboctahedra, corners with twelve PdNi6Pd6 cuboctahedra, edges with eight NiNi6Pd6 cuboctahedra, edges with sixteen PdNi6Pd6 cuboctahedra, faces with sixteen equivalent PdNi6Pd10 cuboctahedra, and faces with eighteen NiNi6Pd6 cuboctahedra. There are a spread of Pd–Pd bond distances ranging from 2.70–5.40 Å. All Pd–Ni bond lengths are 2.64 Å. There are three inequivalent Ni sites. In the first Ni site, Ni is bonded to six equivalent Pd and six equivalent Ni atoms to form distorted NiNi6Pd6 cuboctahedra that share corners with twelve NiNi6Pd6 cuboctahedra, edges with twelve equivalent PdNi6Pd6 cuboctahedra, edges with twelve NiNi6Pd6 cuboctahedra, faces with six equivalent NiNi6Pd6 cuboctahedra, and faces with twelve equivalent PdNi6Pd6 cuboctahedra. All Ni–Ni bond lengths are 2.70 Å. In the second Ni site, Ni is bonded to six Pd and six equivalent Ni atoms to form distorted NiNi6Pd6 cuboctahedra that share corners with five equivalent PdNi6Pd10 cuboctahedra, corners with twelve NiNi6Pd6 cuboctahedra, edges with ten PdNi6Pd6 cuboctahedra, edges with twelve NiNi6Pd6 cuboctahedra, faces with six equivalent NiNi6Pd6 cuboctahedra, and faces with fifteen PdNi6Pd6 cuboctahedra. All Ni–Pd bond lengths are 2.64 Å. All Ni–Ni bond lengths are 2.70 Å. In the third Ni site, Ni is bonded to six Pd and six equivalent Ni atoms to form distorted NiNi6Pd6 cuboctahedra that share corners with five equivalent PdNi6Pd10 cuboctahedra, corners with twelve NiNi6Pd6 cuboctahedra, edges with ten PdNi6Pd6 cuboctahedra, edges with twelve NiNi6Pd6 cuboctahedra, faces with six equivalent NiNi6Pd6 cuboctahedra, and faces with fifteen PdNi6Pd6 cuboctahedra. All Ni–Ni bond lengths are 2.70 Å.

36 MATERIALS SCIENCE↗