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Greatly Enhancing Catalytic Activity of Graphene by Doping the Underlying Metal Substrate.

Guo N, Xi Y, Liu S, Zhang C - Sci Rep (2015)

Bottom Line: When a Zn atom is doped into the substrate, the catalytic activity of the supported graphene is greatly enhanced, and the reaction barrier of the catalyzed CO oxidation is reduced to less than 0.5 eV.Intriguing reaction mechanism of catalyzed CO oxidation is revealed.These studies suggest a new class of graphene-based catalysts and pave the way for future applications of graphene in solid-state catalysis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Graphene Research Centre, National University of Singapore, Singapore 117542.

ABSTRACT
Graphene-based solid-state catalysis represents a new direction in applications of graphene and has attracted a lot of interests recently. However, the difficulty in fine control and large-scale production of previously proposed graphene catalysts greatly limits their industrial applications. Here we present a novel way to enhance the catalytic activity of graphene, which is highly efficient yet easy to fabricate and control. By first-principles calculations, we show that when the underlying metal substrate is doped with impurities, the catalytic activity of the supported graphene can be drastically enhanced. Graphene supported on a Fe/Ni(111) surface is chosen as a model catalyst, and the chemical reaction of CO oxidation is used to probe the catalytic activity of graphene. When the underlying Fe/Ni(111) substrate is impurity free, the graphene is catalytically inactive. When a Zn atom is doped into the substrate, the catalytic activity of the supported graphene is greatly enhanced, and the reaction barrier of the catalyzed CO oxidation is reduced to less than 0.5 eV. Intriguing reaction mechanism of catalyzed CO oxidation is revealed. These studies suggest a new class of graphene-based catalysts and pave the way for future applications of graphene in solid-state catalysis.

No MeSH data available.


Variations of bond lengths (in Å) as functions of MD steps.The MD simulations were done for O2 adsorbed on graphene-Zn@Fe/Ni (111). O1, O2, C1, C2 are atoms as shown in Fig. 3b. The temperature is set to 300 K. NVT ensemble is used in simulations. The MD step is set to 1 fs.
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f4: Variations of bond lengths (in Å) as functions of MD steps.The MD simulations were done for O2 adsorbed on graphene-Zn@Fe/Ni (111). O1, O2, C1, C2 are atoms as shown in Fig. 3b. The temperature is set to 300 K. NVT ensemble is used in simulations. The MD step is set to 1 fs.

Mentions: We would like to point out here that since the system under study is big, the numerical error in total energy calculations could be big also so that the calculation of the adsorption energy of O2 may not be accurate. To confirm the stability of the O2 adsorption, we conducted ab initio molecular dynamics (MD) simulation of the system with adsorbed O2 (Fig. 3a) at room temperature 300 K. The variations of bond lengths (the difference between the current length of the bond and its equilibrium value) of O-O (O2) and two C-O bonds (between graphene of O2) as functions of MD steps are shown in Fig. 4. The variation of O-O bond length at room temperature is always less than 0.1 Å, and the bond lengths of two C-O bonds oscillate between ±0.1 Å after 2000 MD steps, indicating that the adsorption of O2 on graphene after the impurity doping is stable at room temperature. To understand the interaction between the supported graphene and the O2 molecule, we plot the isosurface of charge redistribution caused by O2 adsorption in Fig. 3a. The side views of the charge redistribution are shown in Fig. 3b,c. It can be seen that electrons transferred to 2π* orbital of O2, causing the O-O bond elongated. The adsorption induced change of O2 electronic structures is further illustrated in Fig. 3d where the projected density of states (PDOS) of O2 molecule before and after adsorption is plotted. Before adsorption, the O2 molecule is magnetic and the 2π* orbital of spin-down channel is unoccupied. After adsorption on graphene, three are electrons transferred to the originally empty 2π*, pulling the orbital below the Fermi energy and eliminating the magnetic moment of the molecule. This picture is consistent with the Bader charge analysis that nearly one electron is transferred to O2 after adsorption.


Greatly Enhancing Catalytic Activity of Graphene by Doping the Underlying Metal Substrate.

Guo N, Xi Y, Liu S, Zhang C - Sci Rep (2015)

Variations of bond lengths (in Å) as functions of MD steps.The MD simulations were done for O2 adsorbed on graphene-Zn@Fe/Ni (111). O1, O2, C1, C2 are atoms as shown in Fig. 3b. The temperature is set to 300 K. NVT ensemble is used in simulations. The MD step is set to 1 fs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496776&req=5

f4: Variations of bond lengths (in Å) as functions of MD steps.The MD simulations were done for O2 adsorbed on graphene-Zn@Fe/Ni (111). O1, O2, C1, C2 are atoms as shown in Fig. 3b. The temperature is set to 300 K. NVT ensemble is used in simulations. The MD step is set to 1 fs.
Mentions: We would like to point out here that since the system under study is big, the numerical error in total energy calculations could be big also so that the calculation of the adsorption energy of O2 may not be accurate. To confirm the stability of the O2 adsorption, we conducted ab initio molecular dynamics (MD) simulation of the system with adsorbed O2 (Fig. 3a) at room temperature 300 K. The variations of bond lengths (the difference between the current length of the bond and its equilibrium value) of O-O (O2) and two C-O bonds (between graphene of O2) as functions of MD steps are shown in Fig. 4. The variation of O-O bond length at room temperature is always less than 0.1 Å, and the bond lengths of two C-O bonds oscillate between ±0.1 Å after 2000 MD steps, indicating that the adsorption of O2 on graphene after the impurity doping is stable at room temperature. To understand the interaction between the supported graphene and the O2 molecule, we plot the isosurface of charge redistribution caused by O2 adsorption in Fig. 3a. The side views of the charge redistribution are shown in Fig. 3b,c. It can be seen that electrons transferred to 2π* orbital of O2, causing the O-O bond elongated. The adsorption induced change of O2 electronic structures is further illustrated in Fig. 3d where the projected density of states (PDOS) of O2 molecule before and after adsorption is plotted. Before adsorption, the O2 molecule is magnetic and the 2π* orbital of spin-down channel is unoccupied. After adsorption on graphene, three are electrons transferred to the originally empty 2π*, pulling the orbital below the Fermi energy and eliminating the magnetic moment of the molecule. This picture is consistent with the Bader charge analysis that nearly one electron is transferred to O2 after adsorption.

Bottom Line: When a Zn atom is doped into the substrate, the catalytic activity of the supported graphene is greatly enhanced, and the reaction barrier of the catalyzed CO oxidation is reduced to less than 0.5 eV.Intriguing reaction mechanism of catalyzed CO oxidation is revealed.These studies suggest a new class of graphene-based catalysts and pave the way for future applications of graphene in solid-state catalysis.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Graphene Research Centre, National University of Singapore, Singapore 117542.

ABSTRACT
Graphene-based solid-state catalysis represents a new direction in applications of graphene and has attracted a lot of interests recently. However, the difficulty in fine control and large-scale production of previously proposed graphene catalysts greatly limits their industrial applications. Here we present a novel way to enhance the catalytic activity of graphene, which is highly efficient yet easy to fabricate and control. By first-principles calculations, we show that when the underlying metal substrate is doped with impurities, the catalytic activity of the supported graphene can be drastically enhanced. Graphene supported on a Fe/Ni(111) surface is chosen as a model catalyst, and the chemical reaction of CO oxidation is used to probe the catalytic activity of graphene. When the underlying Fe/Ni(111) substrate is impurity free, the graphene is catalytically inactive. When a Zn atom is doped into the substrate, the catalytic activity of the supported graphene is greatly enhanced, and the reaction barrier of the catalyzed CO oxidation is reduced to less than 0.5 eV. Intriguing reaction mechanism of catalyzed CO oxidation is revealed. These studies suggest a new class of graphene-based catalysts and pave the way for future applications of graphene in solid-state catalysis.

No MeSH data available.