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In situ oxidation of carbon-encapsulated cobalt nanocapsules creates highly active cobalt oxide catalysts for hydrocarbon combustion.

Wang H, Chen C, Zhang Y, Peng L, Ma S, Yang T, Guo H, Zhang Z, Su DS, Zhang J - Nat Commun (2015)

Bottom Line: Combustion catalysts have been extensively explored to reduce the emission of hydrocarbons that are capable of triggering photochemical smog and greenhouse effect.Palladium as the most active material is widely applied in exhaust catalytic converter and combustion units, but its high capital cost stimulates the tremendous research on non-noble metal candidates.For methane combustion, the catalyst displays a unique activity being comparable or even superior to the palladium ones.

View Article: PubMed Central - PubMed

Affiliation: Shenyang National Laboratory for Material Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China.

ABSTRACT
Combustion catalysts have been extensively explored to reduce the emission of hydrocarbons that are capable of triggering photochemical smog and greenhouse effect. Palladium as the most active material is widely applied in exhaust catalytic converter and combustion units, but its high capital cost stimulates the tremendous research on non-noble metal candidates. Here we fabricate highly defective cobalt oxide nanocrystals via a controllable oxidation of carbon-encapsulated cobalt nanoparticles. Strain gradients induced in the nanoconfined carbon shell result in the formation of a large number of active sites featuring a considerable catalytic activity for the combustion of a variety of hydrocarbons (methane, propane and substituted benzenes). For methane combustion, the catalyst displays a unique activity being comparable or even superior to the palladium ones.

No MeSH data available.


Related in: MedlinePlus

Morphology of catalysts after reaction at 700 °C.TEM images during tilting the sample holder from 0.11° to 13.84°. Scale bars, 200 (a), 10 (b) and 5 nm (c–i).
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f3: Morphology of catalysts after reaction at 700 °C.TEM images during tilting the sample holder from 0.11° to 13.84°. Scale bars, 200 (a), 10 (b) and 5 nm (c–i).

Mentions: It is worth mentioning that the obtained Co3O4 nanoparticles displayed an unexpected thermal stability against severe sintering at a high temperature. We detailed the microstructure of the catalyst after the reaction at 700 °C (Fig. 3) by tilting the sample holder inside the TEM chamber. The images clearly reveal the existence of concavities or cracks on the surface and an interconnecting characteristic at a specific angle. The diameter of pores or channels is estimated to be 2–4 nm, being higher than mean free path of reactants and products to allow the efficient mass transport. The nanoscale and devious channels are expected to possess a large number of surface atomic steps on the interior wall that often acted as the catalytically active sites in molecular dissociation and consequential reaction. Although the phase transition at the elevated temperatures led to particle aggregation, the defective carbon shell still plays a pivotal role to prevent serious sintering at the initial stage. The temperature-programmed oxidation test shows that the carbon shells totally disappeared at ∼550 °C (Supplementary Fig. 5). As the metallic Co atoms reacted with O2, the oxidation of metallic subsurface at the defective sites was much faster than that in the regions capsulated by well-defined graphitic layers due to the diffusion of oxygen. The atomic diffusion of residual metallic Co into the oxygen-rich phase being driven by the Kirkendall effect finally resulted in a number of disordered voids or channels inside the enlarged particles9. Note that the residual carbon shells can also block the approach of reactant molecules to active sites, which would certainly reduce the overall catalytic activity to some extent.


In situ oxidation of carbon-encapsulated cobalt nanocapsules creates highly active cobalt oxide catalysts for hydrocarbon combustion.

Wang H, Chen C, Zhang Y, Peng L, Ma S, Yang T, Guo H, Zhang Z, Su DS, Zhang J - Nat Commun (2015)

Morphology of catalysts after reaction at 700 °C.TEM images during tilting the sample holder from 0.11° to 13.84°. Scale bars, 200 (a), 10 (b) and 5 nm (c–i).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490405&req=5

f3: Morphology of catalysts after reaction at 700 °C.TEM images during tilting the sample holder from 0.11° to 13.84°. Scale bars, 200 (a), 10 (b) and 5 nm (c–i).
Mentions: It is worth mentioning that the obtained Co3O4 nanoparticles displayed an unexpected thermal stability against severe sintering at a high temperature. We detailed the microstructure of the catalyst after the reaction at 700 °C (Fig. 3) by tilting the sample holder inside the TEM chamber. The images clearly reveal the existence of concavities or cracks on the surface and an interconnecting characteristic at a specific angle. The diameter of pores or channels is estimated to be 2–4 nm, being higher than mean free path of reactants and products to allow the efficient mass transport. The nanoscale and devious channels are expected to possess a large number of surface atomic steps on the interior wall that often acted as the catalytically active sites in molecular dissociation and consequential reaction. Although the phase transition at the elevated temperatures led to particle aggregation, the defective carbon shell still plays a pivotal role to prevent serious sintering at the initial stage. The temperature-programmed oxidation test shows that the carbon shells totally disappeared at ∼550 °C (Supplementary Fig. 5). As the metallic Co atoms reacted with O2, the oxidation of metallic subsurface at the defective sites was much faster than that in the regions capsulated by well-defined graphitic layers due to the diffusion of oxygen. The atomic diffusion of residual metallic Co into the oxygen-rich phase being driven by the Kirkendall effect finally resulted in a number of disordered voids or channels inside the enlarged particles9. Note that the residual carbon shells can also block the approach of reactant molecules to active sites, which would certainly reduce the overall catalytic activity to some extent.

Bottom Line: Combustion catalysts have been extensively explored to reduce the emission of hydrocarbons that are capable of triggering photochemical smog and greenhouse effect.Palladium as the most active material is widely applied in exhaust catalytic converter and combustion units, but its high capital cost stimulates the tremendous research on non-noble metal candidates.For methane combustion, the catalyst displays a unique activity being comparable or even superior to the palladium ones.

View Article: PubMed Central - PubMed

Affiliation: Shenyang National Laboratory for Material Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China.

ABSTRACT
Combustion catalysts have been extensively explored to reduce the emission of hydrocarbons that are capable of triggering photochemical smog and greenhouse effect. Palladium as the most active material is widely applied in exhaust catalytic converter and combustion units, but its high capital cost stimulates the tremendous research on non-noble metal candidates. Here we fabricate highly defective cobalt oxide nanocrystals via a controllable oxidation of carbon-encapsulated cobalt nanoparticles. Strain gradients induced in the nanoconfined carbon shell result in the formation of a large number of active sites featuring a considerable catalytic activity for the combustion of a variety of hydrocarbons (methane, propane and substituted benzenes). For methane combustion, the catalyst displays a unique activity being comparable or even superior to the palladium ones.

No MeSH data available.


Related in: MedlinePlus