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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

Morphological properties of oxidized Co@C nanocapsules.TEM and HRTEM images of (a,e,i) the pristine and samples that were oxidized at (b,f,j) 200, (c,g,k) 225 and (d,h,l) 250 °C, as well as (m–p) the residual carbon shells in the oxidized samples at 225 °C after washing by hydrochloric acid. Scale bars, 50 (a–d), 5 (e–l) and 10 nm (m–p). (q) XRD spectra of oxidized samples.
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f1: Morphological properties of oxidized Co@C nanocapsules.TEM and HRTEM images of (a,e,i) the pristine and samples that were oxidized at (b,f,j) 200, (c,g,k) 225 and (d,h,l) 250 °C, as well as (m–p) the residual carbon shells in the oxidized samples at 225 °C after washing by hydrochloric acid. Scale bars, 50 (a–d), 5 (e–l) and 10 nm (m–p). (q) XRD spectra of oxidized samples.

Mentions: To follow the structural change of the Co@C nanocapsules in a flow of diluted oxygen, we used transmission electron microscope (TEM) to detail the morphological properties of the sample after the oxidation at various temperatures. As shown in Fig. 1a–l, the Co@C nanocapsules present as mostly regular spheres with a diameter ranging from 8 to 50 nm. A typical core–shell structure comprises several atomic layers of graphitic carbon as a shell and metallic Co as a core featuring with d002 spacing of 2.03 Å. After the oxidation at 200 °C, the carbon shell of nanocapsules with a diameter of ∼5 nm was cracked due to the burning by O2, while big nanocapsules with highly graphitic shells still kept unchanged. This difference can be related with the chemical reactivity of the carbon atoms on the surface of small nanocapsules with a high surface-to-volume ratio12. One metallic core was simultaneously oxidized and disintegrated into several Co3O4 nanocrystals with lattice distances of 2.44 and 2.86 Å, being assigned to {311} and {220} planes, respectively. These oxide particles spilled from the rupture while the carbon shells were severely deformed (Fig. 1m–p), indicating that a large strain force was produced during the oxidative destruction of nanocapsules. As the treatment temperature was elevated, the Co3O4 nanocrystals started to aggregate but still kept an irregular shape, while the oxidation of Co nanoparticles without carbon shells is apt to produce oxide particles with a regular shape (Supplementary Fig. 1).


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)

Morphological properties of oxidized Co@C nanocapsules.TEM and HRTEM images of (a,e,i) the pristine and samples that were oxidized at (b,f,j) 200, (c,g,k) 225 and (d,h,l) 250 °C, as well as (m–p) the residual carbon shells in the oxidized samples at 225 °C after washing by hydrochloric acid. Scale bars, 50 (a–d), 5 (e–l) and 10 nm (m–p). (q) XRD spectra of oxidized samples.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Morphological properties of oxidized Co@C nanocapsules.TEM and HRTEM images of (a,e,i) the pristine and samples that were oxidized at (b,f,j) 200, (c,g,k) 225 and (d,h,l) 250 °C, as well as (m–p) the residual carbon shells in the oxidized samples at 225 °C after washing by hydrochloric acid. Scale bars, 50 (a–d), 5 (e–l) and 10 nm (m–p). (q) XRD spectra of oxidized samples.
Mentions: To follow the structural change of the Co@C nanocapsules in a flow of diluted oxygen, we used transmission electron microscope (TEM) to detail the morphological properties of the sample after the oxidation at various temperatures. As shown in Fig. 1a–l, the Co@C nanocapsules present as mostly regular spheres with a diameter ranging from 8 to 50 nm. A typical core–shell structure comprises several atomic layers of graphitic carbon as a shell and metallic Co as a core featuring with d002 spacing of 2.03 Å. After the oxidation at 200 °C, the carbon shell of nanocapsules with a diameter of ∼5 nm was cracked due to the burning by O2, while big nanocapsules with highly graphitic shells still kept unchanged. This difference can be related with the chemical reactivity of the carbon atoms on the surface of small nanocapsules with a high surface-to-volume ratio12. One metallic core was simultaneously oxidized and disintegrated into several Co3O4 nanocrystals with lattice distances of 2.44 and 2.86 Å, being assigned to {311} and {220} planes, respectively. These oxide particles spilled from the rupture while the carbon shells were severely deformed (Fig. 1m–p), indicating that a large strain force was produced during the oxidative destruction of nanocapsules. As the treatment temperature was elevated, the Co3O4 nanocrystals started to aggregate but still kept an irregular shape, while the oxidation of Co nanoparticles without carbon shells is apt to produce oxide particles with a regular shape (Supplementary Fig. 1).

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