Low-temperature activity of Pd/CeO2 catalysts: Mechanism of CO interaction and mathematical modelling of TPR-CO kinetic data

Lashina, Elena A.; Slavinskaya, Elena M.; Boronin, Andrei I.

doi:10.1016/j.ces.2021.116812

Cited by 13 publications

(6 citation statements)

References 39 publications

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“…This is characteristic of dispersed Pd that bonds through an oxygen atom to undercoordinated Ce 3+ , which is typically located at step and edge sites on CeO 2 crystals. ,, As demonstrated in a recent study by Wang et al, these Pd species adopt a coordination-unsaturated, square-planar structure . The formation of coordination-unsaturated Pd–O–Ce bonds perturbs the local electronic environment of CeO 2 , which improves the lattice oxygen mobility and, subsequently, the oxidative activity at low temperatures. ,, XPS measurements in the Pd 3d scan region of Pd@CeO 2 and Pd/CeO 2 in their initial states, and after the first and fourth cycles of 800 °C aging in air, were used to track the abundance of Pd–O–Ce during cycled aging. As shown in Figure , deconvolution of the XPS spectra showed a distribution of metallic Pd 0 , Pd 2+ as PdO, and Pd–O–Ce in the initial Pd/CeO 2 catalyst.…”

Section: Resultsmentioning

confidence: 92%

“…34 The formation of coordination-unsaturated Pd−O−Ce bonds perturbs the local electronic environment of CeO 2 , which improves the lattice oxygen mobility and, subsequently, the oxidative activity at low temperatures. 34,48,49 XPS measurements in the Pd 3d scan region of Pd@CeO 2 and Pd/CeO 2 in their initial states, and after the first and fourth cycles of 800 °C aging in air, were used to track the abundance of Pd−O−Ce during cycled aging. As shown in Figure 5, deconvolution of the XPS spectra showed a distribution of metallic Pd 0 , Pd 2+ as PdO, and Pd− O−Ce in the initial Pd/CeO 2 catalyst.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

See 1 more Smart Citation

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.

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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 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

Section: Resultsmentioning

confidence: 92%

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.

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“…The reduction of CuO samples via H 2 -TPR produces an asymmetric peak, which spans the temperature range of 200 °C–700 °C (Figure A). The reductive peak position indicates the activity of lattice oxygen . The reduction of l -CuO and d -CuO is initiated at 150 °C, which is ∼150 °C lower than that of a -CuO, which indicates a higher reactivity of the lattice oxygen of l -CuO and d -CuO than that of a -CuO.…”

Section: Resultsmentioning

confidence: 97%

“…The reductive peak position indicates the activity of lattice oxygen. 48 The reduction of L-CuO and D-CuO is initiated at 150 °C, which is ∼150 °C lower than that 2− , or O 2− ). 49 L-CuO and D-CuO have a lower O α content than A-CuO (Figure 6C).…”

Section: Chiral Catalysts and Oxygenmentioning

confidence: 98%

Enhanced Replenishment of Active Lattice Oxygen Using Chiral Copper Oxide

Chen,

Li,

Jiang

et al. 2024

ACS Appl. Mater. Interfaces

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Effective catalytic performance of the transition metal oxide is attributed to high specific surface areas, abundant surface oxygen atoms, and balanced valence ratios. Although the chirality of the transition metal has attracted attention, most studies have focused on optical application. A few chiral transition metal oxides were used as electrocatalysts and photocatalysts. The influence of the chiral catalysts on the thermal catalysis process has been less explored. In this study, Mn-loaded chiral (M/l-CuO and M/d-CuO) and achiral CuO (M/a-CuO) were synthesized and compared in the catalytic oxidization of toluene. Spectrally analyzed Mn was well-dispersed on both chiral and achiral CuO. l-CuO and d-CuO showed nanoflower-like chirality. The angles between each (001) plane of CuO were the source of chirality. The toluene turnover frequency (TOF) of the samples was in the order of Mn/d-CuO (5.6 × 10–5 s–1) > Mn/l-CuO (4.4 × 10–5 s–1) > Mn/a-CuO (3.2 × 10–5 s–1) at 240 °C, consistent with the order of the oxygen replenishment rate. The as-prepared catalysts had similar ratios of lattice oxygen/surface adsorbed oxygen, Mn3+/Mn4+, and Cu+/Cu2+. A higher TOF was attributed to chirality, which increased the lattice oxygen replenishment speed from the gaseous phase to the solid surface. Our study indicates gas–solid catalysis from a structure–activity viewpoint.

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“…34 The formation of coordination-undersaturated Pd-O-Ce bonds perturb the local electronic environment of the CeO2, which improves lattice oxygen mobility and, subsequently, oxidative activity at low temperatures. 34,48,49 XPS measurements in the Pd3d scan region of Pd@CeO2 and Pd/CeO2 in their initial state, and after the first and fourth cycles of 800°C aging in air, were used to track the abundance of Pd-O-Ce during cycled aging. As shown in Figure 4, deconvolution of the XPS spectra showed a distribution of metallic Pd 0 , Pd 2+ as PdO and Pd-O-Ce in the initial Pd/CeO2 catalyst.…”

Section: Performance and Stability Of Halo Sites In 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

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

Low-temperature activity of Pd/CeO2 catalysts: Mechanism of CO interaction and mathematical modelling of TPR-CO kinetic data

Cited by 13 publications

References 39 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

Enhanced Replenishment of Active Lattice Oxygen Using Chiral Copper Oxide

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

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