Size-controlled nanocrystals reveal spatial dependence and severity of nanoparticle coalescence and Ostwald ripening in sintering phenomena

Goodman, Emmett D.; Carlson, Evan; Dietze, Elisabeth M.; Tahsini, Nadia; Johnson, Arun; Aitbekova, Aisulu; Taylor, Temy Nguyen; Pleßow, Philipp N.; Cargnello, Matteo

doi:10.1039/d0nr07960j

Cited by 31 publications

(30 citation statements)

References 44 publications

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“…Recent work by Cargnello et al demonstrated that whole particle migration and coalescence could exist as the dominant restructuring mechanism in Pd/SiO2 catalysts during 800°C aging. 37 In the core@shell system, however, we observe the coexistence of Pd cores alongside dispersed halo sites after the first cycle of aging. This suggests that total particle migration and coalescence is not the dominant restructuring mechanism in core@shell architectures.…”

Section: Metastability Of Halo Sites In Pd@sio2mentioning

confidence: 77%

“…This is consistent with other works which have shown that the initial placement of active metal readily implicates thermal stability. 36,37 Pd and CeO2 continued to agglomerate with successive aging cycles. By the end of the fourth 800°C aging cycle, the Pd dispersion dropped over five times to 5.9%.…”

Section: Adverse Restructuring In Conventionally Prepared Pd/ceo2mentioning

confidence: 99%

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Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@shell Nanoparticles for Improved Catalyst Activity and Durability

Hill

Bhat

Berquist

et al. 2021

Preprint

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Stabilizing high dispersions of catalytically active metals is integral to improving the lifetime, activity, and material utilization of catalysts that are periodically exposed to high temperatures during operation or maintenance. We have found that annealing palladium-based core@shell catalysts in air at elevated temperature (800°C) promotes the redispersion of active metal into highly dispersed sites, which we refer to as halo sites. Here, we examine the restructuring of Pd@SiO2 and Pd@CeO2 core@shell catalysts over successive 800°C aging cycles to understand the formation, activity, nanoscale structure and stability of these palladium halo sites. While encapsulation generally improves metal utilization by providing a physical barrier that promotes redispersion over agglomeration, our cycled aging experiments demonstrate that halo sites are not stable in all catalysts. Halo sites continue to migrate in Pd@SiO2 due to poor metal-support bonding, which leads to palladium agglomeration. In contrast, halo sites formed in Pd@CeO2 remain stable. The dispersed palladium also synergistically stabilizes the ceria from agglomerating. We attribute this stability, in addition to an observed improvement in catalytic activity, to the coordination between palladium and reducible ceria that arises during the formation of halo sites. We probe the importance of ceria oxidation state on the stability of halo sites by aging Pd@CeO2 after it has been reduced. While some halo sites agglomerate, we find that returning to air aging mitigates the loss of these sites and catalytic activity. Our findings illustrate how nanoscale catalyst structures can be designed to promote the formation of highly stable and dispersed metal sites.

show abstract

Section: Metastability Of Halo Sites In Pd@sio2mentioning

confidence: 77%

Section: Adverse Restructuring In Conventionally Prepared Pd/ceo2mentioning

confidence: 99%

Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@shell Nanoparticles for Improved Catalyst Activity and Durability

Hill

Bhat

Berquist

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…As a result, nanomaterials are metastable, which is quite sensitive to ambient temperature. To decrease the free energy of the system, atoms on the surface of nanoparticles will experience structural rearrangement and relaxation as the environmental temperature increases [ 25 , 26 , 27 ]. Figure 5 shows the DSC analysis of Cu NPs utilized in the experiment.…”

Section: Resultsmentioning

confidence: 99%

Sintering Bonding of SiC Particulate Reinforced Aluminum Metal Matrix Composites by Using Cu Nanoparticles and Liquid Ga in Air

et al. 2021

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SiC particulate reinforced aluminum metal matrix composites (SiCp/Al MMCs) are characterized by controllable thermal expansion, high thermal conductivity and lightness. These properties, in fact, define the new promotional material in areas and industries such as the aerospace, automotive and electrocommunication industries. However, the poor weldability of this material becomes its key problem for large-scale applications. Sintering bonding technology was developed to join SiCp/Al MMCs. Cu nanoparticles and liquid Ga were employed as self-fluxing filler metal in air under joining temperatures ranging from 400 °C to 500 °C, with soaking time of 2 h and pressure of 3 MPa. The mechanical properties, microstructure and gas tightness of the joint were investigated. The microstructure analysis demonstrated that the joint was achieved by metallurgical bonding at contact interface, and the sintered layer was composed of polycrystals. The distribution of Ga was quite homogenous in both of sintered layer and joint area. The maximum level of joint shear strength of 56.2 MPa has been obtained at bonding temperature of 450 °C. The specimens sintering bonded in temperature range of 440 °C to 460 °C had qualified gas tightness during the service, which can remain 10−10 Pa·m3/s.

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“…This is consistent with other studies, which have shown that the initial placement of active metals readily implicates thermal stability. 36,37 Pd and CeO 2 continued to agglomerate with successive aging cycles. By the end of the fourth 800 °C aging cycle, the Pd dispersion dropped over 5 times to 5.9%.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@Shell Nanoparticles for Improved Catalyst Activity and Durability

Hill

Bhat

Berquist

et al. 2021

ACS Appl. Nano Mater.

View full text Add to dashboard Cite

Stabilizing high dispersions of catalytically active metals is integral to improving the lifetime, activity, and material utilization of catalysts that are periodically exposed to high temperatures during operation or maintenance. We have found that annealing palladium-based core@shell catalysts in air at elevated temperatures (800 °C) promotes the redispersion of active metals into highly dispersed sites, which we refer to as halo sites. Here, we examine the restructuring of Pd@SiO 2 and Pd@ CeO 2 core@shell catalysts over successive 800 °C aging cycles to understand the formation, activity, nanoscale structure, and stability of these palladium halo sites. While encapsulation generally improves metal utilization by providing a physical barrier that promotes redispersion over agglomeration, our cycled aging experiments demonstrate that halo sites are not stable in all catalysts. Halo sites continue to migrate in Pd@SiO 2 due to poor metal− support bonding, which leads to palladium agglomeration. In contrast, halo sites formed in Pd@CeO 2 remain stable. The dispersed palladium also synergistically stabilizes the ceria from agglomerating. We attribute this stability, in addition to an observed improvement in catalytic activity, to the coordination between palladium and reducible ceria that arises during the formation of halo sites. We probe the importance of ceria oxidation state on the stability of halo sites by aging Pd@CeO 2 after it has been reduced. While some halo sites agglomerate, we find that returning to air aging mitigates the loss of these sites and catalytic activity. Our findings illustrate how nanoscale catalyst structures can be designed to promote the formation of highly stable and dispersed metal sites.

show abstract

Size-controlled nanocrystals reveal spatial dependence and severity of nanoparticle coalescence and Ostwald ripening in sintering phenomena

Abstract: Colloidal nanocrystals allow investigating sintering phenomena in supported catalysts.

Cited by 31 publications

References 44 publications

Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@shell Nanoparticles for Improved Catalyst Activity and Durability

Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@shell Nanoparticles for Improved Catalyst Activity and Durability

Sintering Bonding of SiC Particulate Reinforced Aluminum Metal Matrix Composites by Using Cu Nanoparticles and Liquid Ga in Air

Stabilizing Highly Dispersed Halo Sites in Thermally Restructured Palladium Core@Shell Nanoparticles for Improved Catalyst Activity and Durability

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