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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

Reaction data.(a) Light-off curves of CH4 combustion against the increasing temperature and (b) catalytic stability at 420 °C under conditions: 0.1 g catalyst, 6.7% CH4, O2/CH4=2.5, helium balance, space velocity 18 l gcat−1 h−1. Dependencies of reaction rate (r, mmol g−1 h−1) on partial pressures of (c) CH4 (pCH4) and (d) O2 (pO2) at 260 °C, under conditions: 5 mg catalyst, 1.6–5.0 kPa CH4, 5.3–8.4 kPa O2, helium balance, space velocity 800 l gcat−1 h−1. (e) Arrhenius-type plot for CH4 combustion under conditions: 5 mg catalyst, 3.0 kPa CH4, 7.6 kPa O2, helium balance, 220–260 °C, space velocity 800 l gcat−1 h−1. T, Kelvin temperature. HRTEM images of the used catalysts after the reaction at temperatures of (f) 225, (g) 250 and (h) 400 °C. Scale bars, 5 nm (f–h).
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f2: Reaction data.(a) Light-off curves of CH4 combustion against the increasing temperature and (b) catalytic stability at 420 °C under conditions: 0.1 g catalyst, 6.7% CH4, O2/CH4=2.5, helium balance, space velocity 18 l gcat−1 h−1. Dependencies of reaction rate (r, mmol g−1 h−1) on partial pressures of (c) CH4 (pCH4) and (d) O2 (pO2) at 260 °C, under conditions: 5 mg catalyst, 1.6–5.0 kPa CH4, 5.3–8.4 kPa O2, helium balance, space velocity 800 l gcat−1 h−1. (e) Arrhenius-type plot for CH4 combustion under conditions: 5 mg catalyst, 3.0 kPa CH4, 7.6 kPa O2, helium balance, 220–260 °C, space velocity 800 l gcat−1 h−1. T, Kelvin temperature. HRTEM images of the used catalysts after the reaction at temperatures of (f) 225, (g) 250 and (h) 400 °C. Scale bars, 5 nm (f–h).

Mentions: Catalytic combustion of CH4 (CH4+2O2→CO2+2H2O) was used as a probe reaction to evaluate the catalytic properties. The reaction was conducted at 25–700 °C in an oxygen-rich environment with an O2 to CH4 ratio of 2.5. For each test, the product mixture with CO2, CO and residual CH4 gives an almost close carbon balance of 100±3%. In a blank experiment without catalyst, the conversion of CH4 was negligible even at the temperature as high as 700 °C. Temperature dependency of CH4 conversion in the combustion reaction over the catalyst is presented in Fig. 2a, showing that the light-off temperature in the conversion curve was ∼220 °C with 100% selectivity to CO2. The temperature at a conversion of 50% (T50), an important indicator to the activity of a combustion catalyst, is 376 °C, reporting a considerable reaction rate at T50, that is, 26.8 mmol g−1 h−1. Such an activity at a low temperature is superior to the transition metal oxides but close to or even higher than the supported Pd catalysts (Supplementary Fig. 3). The time on stream experiment reveals a satisfactory durability at 420 °C. Although a slight decrease in conversion was observed over the initial several hours, the activity had stabilized and remained at above 60% for ∼20 h. During the whole period, the selectivity to CO2 did not change and kept at almost 100% (Fig. 2b). The catalyst is also capable to efficiently combust propane, aromatics (benzene, toluene, xylenes, ethylbenzene and styrene) and carbon monoxide17 at relatively low temperatures (Supplementary Fig. 4).


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)

Reaction data.(a) Light-off curves of CH4 combustion against the increasing temperature and (b) catalytic stability at 420 °C under conditions: 0.1 g catalyst, 6.7% CH4, O2/CH4=2.5, helium balance, space velocity 18 l gcat−1 h−1. Dependencies of reaction rate (r, mmol g−1 h−1) on partial pressures of (c) CH4 (pCH4) and (d) O2 (pO2) at 260 °C, under conditions: 5 mg catalyst, 1.6–5.0 kPa CH4, 5.3–8.4 kPa O2, helium balance, space velocity 800 l gcat−1 h−1. (e) Arrhenius-type plot for CH4 combustion under conditions: 5 mg catalyst, 3.0 kPa CH4, 7.6 kPa O2, helium balance, 220–260 °C, space velocity 800 l gcat−1 h−1. T, Kelvin temperature. HRTEM images of the used catalysts after the reaction at temperatures of (f) 225, (g) 250 and (h) 400 °C. Scale bars, 5 nm (f–h).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Reaction data.(a) Light-off curves of CH4 combustion against the increasing temperature and (b) catalytic stability at 420 °C under conditions: 0.1 g catalyst, 6.7% CH4, O2/CH4=2.5, helium balance, space velocity 18 l gcat−1 h−1. Dependencies of reaction rate (r, mmol g−1 h−1) on partial pressures of (c) CH4 (pCH4) and (d) O2 (pO2) at 260 °C, under conditions: 5 mg catalyst, 1.6–5.0 kPa CH4, 5.3–8.4 kPa O2, helium balance, space velocity 800 l gcat−1 h−1. (e) Arrhenius-type plot for CH4 combustion under conditions: 5 mg catalyst, 3.0 kPa CH4, 7.6 kPa O2, helium balance, 220–260 °C, space velocity 800 l gcat−1 h−1. T, Kelvin temperature. HRTEM images of the used catalysts after the reaction at temperatures of (f) 225, (g) 250 and (h) 400 °C. Scale bars, 5 nm (f–h).
Mentions: Catalytic combustion of CH4 (CH4+2O2→CO2+2H2O) was used as a probe reaction to evaluate the catalytic properties. The reaction was conducted at 25–700 °C in an oxygen-rich environment with an O2 to CH4 ratio of 2.5. For each test, the product mixture with CO2, CO and residual CH4 gives an almost close carbon balance of 100±3%. In a blank experiment without catalyst, the conversion of CH4 was negligible even at the temperature as high as 700 °C. Temperature dependency of CH4 conversion in the combustion reaction over the catalyst is presented in Fig. 2a, showing that the light-off temperature in the conversion curve was ∼220 °C with 100% selectivity to CO2. The temperature at a conversion of 50% (T50), an important indicator to the activity of a combustion catalyst, is 376 °C, reporting a considerable reaction rate at T50, that is, 26.8 mmol g−1 h−1. Such an activity at a low temperature is superior to the transition metal oxides but close to or even higher than the supported Pd catalysts (Supplementary Fig. 3). The time on stream experiment reveals a satisfactory durability at 420 °C. Although a slight decrease in conversion was observed over the initial several hours, the activity had stabilized and remained at above 60% for ∼20 h. During the whole period, the selectivity to CO2 did not change and kept at almost 100% (Fig. 2b). The catalyst is also capable to efficiently combust propane, aromatics (benzene, toluene, xylenes, ethylbenzene and styrene) and carbon monoxide17 at relatively low temperatures (Supplementary Fig. 4).

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