In Situ Scanning Transmission Electron Microscopy of Ni Nanoparticle Redispersion via the Reduction of Hollow NiO

TY - JOUR

T1 - In Situ Scanning Transmission Electron Microscopy of Ni Nanoparticle Redispersion via the Reduction of Hollow NiO

AU - LaGrow, Alec

AU - Lloyd, David Carlos

AU - Gai, Pratibha L

AU - Boyes, Edward

N1 - © 2017 American Chemical Society. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details

PY - 2018/1/9

Y1 - 2018/1/9

N2 - Oxidation and reduction cycles are used in the regeneration of nanoparticle catalysts that have deactivated due to sintering or poisoning. Nickel oxidation and reduction cycles for the redispersion of nickel nanoparticles were studied via in situ high angle annular dark field environmental scanning transmission electron microscopy. Cycling the Ni/NiO system through successive redox cycles shows that the particles retain the same general size distributions even though Ostwald ripening and particle migration and coalescence is occurring. The regeneration of the smallest nanoparticle sizes, which disappear due to sintering processes, occur by the ejection of small (2−3 nm) nickel particles during the reduction of the hollow nickel oxide nanostructures. The nickel nanoparticles above ∼3.5 nm in size form hollow polycrystalline nickel oxide nanostructures upon oxidation. Upon reduction, the grains making up the shell of the hollow nickel oxide reduce separately at the grains surface and at the grain boundaries between the polycrystalline grains. The contraction in particle size upon reduction destabilizes the hollow nanostructure and causes the particle to rearrange and collapse. As this process occurs, some parts of the material are ejected from the reducing particle and forms small particles of nickel, which regenerate the smallest parts of the size distribution. Once the particle collapses, the nickel rearranges, reforming solid nickel nanoparticles enclosed by low index facets.

AB - Oxidation and reduction cycles are used in the regeneration of nanoparticle catalysts that have deactivated due to sintering or poisoning. Nickel oxidation and reduction cycles for the redispersion of nickel nanoparticles were studied via in situ high angle annular dark field environmental scanning transmission electron microscopy. Cycling the Ni/NiO system through successive redox cycles shows that the particles retain the same general size distributions even though Ostwald ripening and particle migration and coalescence is occurring. The regeneration of the smallest nanoparticle sizes, which disappear due to sintering processes, occur by the ejection of small (2−3 nm) nickel particles during the reduction of the hollow nickel oxide nanostructures. The nickel nanoparticles above ∼3.5 nm in size form hollow polycrystalline nickel oxide nanostructures upon oxidation. Upon reduction, the grains making up the shell of the hollow nickel oxide reduce separately at the grains surface and at the grain boundaries between the polycrystalline grains. The contraction in particle size upon reduction destabilizes the hollow nanostructure and causes the particle to rearrange and collapse. As this process occurs, some parts of the material are ejected from the reducing particle and forms small particles of nickel, which regenerate the smallest parts of the size distribution. Once the particle collapses, the nickel rearranges, reforming solid nickel nanoparticles enclosed by low index facets.

KW - In situ ESTEM, Nanoparticles redispersion reduction

KW - redispersion

KW - reduction

UR - http://www.scopus.com/inward/record.url?scp=85040348539&partnerID=8YFLogxK

U2 - 10.1021/acs.chemmater.7b04184

DO - 10.1021/acs.chemmater.7b04184

M3 - Article

SN - 0897-4756

VL - 30

SP - 197

EP - 203

JO - Chemistry of Materials

JF - Chemistry of Materials

ER -