Graphene based catalyst

Contents
1. INTRODUCTION
2. Structure
3. History of graphene
4. PROPERTIES OF GRAPHENE
5. GRAPHENE: Synthesis
6. Graphene for catalysis
 Catalyst for Organic Reactions
 Fuel cell catalyst
 Boron-Doped Graphene
7. Conclusion
8. References

Introduction
Graphene can be described as a one- atom thick layer of
graphite.
It is a flat monolayer of carbon atoms tightly packed into a
2-D honeycomb structure.
It is the basic structural element of other allotropes,
including graphite, charcoal, carbon nanotubes and fullerenes.
Graphene is the strongest, thinnest material known to exist.
It a Semi metal of future.

Structure
It is the one-atom thick planar sheet of sp2 hybridised carbon atoms (graphite), which makes it
the thinnest material ever discovered.
2-dimentional crystalline allotrope of carbon.
C-C Bond length is 0.142 nm.
Graphite (layered material) formed by stacks of graphene sheets separated by 0.3 nm and held
together by weak vanderWaals forces.

History of graphene
GRAPHENE existed in theory in 1962, when
chemist Hanns-Peter Boehm described it in a
paper published in the Journal of Inorganic and
General Chemistry.
But in 2004 Andre Gelm and Kostya
Novoselov at the University of Manchester
extracted single atom thick crystallites from
bulk graphite.
For this work,Gelm and Novoselov received
the Nobel Prize in Physics in 2010.
ANDRE GELM KOSTYA NOVOSELOV

They were examing how efficient graphite as a transistor.
Andre and Kostya pulled graphene layers from graphite and transferred them
onto thin SiO2 on a silicon wafer in a process called Micromechanical Cleavage
or the Scotch tape technique. This left them with graphene.

PROPERTIES OF GRAPHENE
it has incredibly stretching property.
It is stiff. It is the hardest material known even harder than
diamond.
Able to retain its initial size after strain i.e. Elasticity.
It carries electricity more efficiently than any other known
material.

GRAPHENE: Synthesis
Two basic techniques used are :
To cleave multi layer graphite into single
layers. (EXFOLIATION)
By depositing one layer of Carbon onto
another material (EPITAXY)

EXFOLIATION:
DRAWING METHOD
The basic ‘recipe’ for making
graphene using “scotch tape”
technique requires using 300nm
of SiO2-coated silicon wafer.
Following this one patiently peels
graphite by sandwiching it
between scotch tape repeatedly
till the tape is translucent.
Graphene layer formed using
Scotch tape.

EPITAXY
Epitaxy refers to the deposition of a
crystalline overlayer on a crystalline substrate
and the graphene substrate interaction can be
further passivated
In some cases epitaxial graphene layers are
coupled to surfaces weakly enough.(by van
der waals forces)
SILICON CARBIDE EPITAXY
Heating silicon carbide (SiC) to high
temperatures (>1100 °C) under low pressures
(~10−6 torr) reduces it to graphene.

Graphene for cataysis
Catalysis plays a major role in today’s society, impacting an estimated 90% of all
commercially produced chemical products.
Graphene, as a form of carbon with a high electron mobility and specific surface area,
arises as a natural candidate as a catalytic support.
In its purest form graphene is chemically inert surface, because there are no free
chemical bonds.
Therefore Chemically Modified Graphenes(CMGs) are promising catalyst & also
attractive components for developing new catalyst.
CMGs such as graphene oxide(GO), reduced graphene oxide(rGO) have been widely
explored as catatyst for chemical, or as carbonaceous support for loading catalyst for
metals, oxides or carbon nanomaterials.

Front. Chem. Sci. Eng.
https://doi.org/10.1007/s11705-018-1722-y
Structure diagram of (a) GO and (b) rGO

Catalyst for Organic Reactions
Perfect graphene is a material with zero band gap and few
functional groups. Thus, it has weak catalytic activity.
In contrast, CMGs such as GO and rGO are used, since
they are potential catalyst for various organic reactions.
 GO catalyst not only showed high catalytic activities for
various chemical reactions, but can also be conveniently
removed or reused by filtering it from the reaction systems.

GO was tested to be capable of catalyzing the oxidation reaction from benzyl
alcohol to benzaldehyde with a high yield (>92%) and good selectivity.

GO is also able to catalyze the oxidation of cis-stilbene and hydration of various alkynes.

Fuel cell catalyst(N-doped graphene:a
next generation catalyst)
Research at Georgia Tech are working on the ways to bring down the cost of fuel cell
technology.
Pt act as a catalyst in fuel cells but its high cost has hindered its commercial viability.
Proton exchange membrane fuel cells(PEMFCs) are expected to play a dominant role in future
energy solutions. A major impediment to the commercialization of PEMFCs is its high cost &
stability of Pt-based electrocatalyst.
Researchers at Canada have discovered a new metal free catalyst, N-doped graphene that could
make fuel cells more cost effective & stable.
N – graphene has been synthesized on large scale using ammonia and the heat treatment of
graphene.

N – graphene has exhibited comparable or better activity & stability than commercial Pt/C
towards oxygen-reduction reaction.
N – graphene was also reported to exhibit high quality & selectivity for the oxidation of
arylalkanes in aq. Phase, reduction of nitro compounds, peroxides & oxidation of glucose &
benzyl alcohols.
(A) Schematic of a membrane-free single-chamber air-cathode MFC
reproduced with permission from ref. 214 ª 2011 American Chemical
Society.

Synthesis of N-doped graphene
A solvothermal process has been developed for synthesis of N-doped graphene.
Example- the reaction of Lithuim Nitride & tetrachloro methane was carried out at 250 0 C for
5-10 hours in a stainless steel autoclave in nitrogen. After washing, 18% HCl aq. Solution , water
& ethanol added N-doped graphene was obtained.

Schematic diagram of N-Doped graphene derivatives

Boron-Doped Graphene
for Electrocatalytic N2 Reduction
Ammonia (NH3) is an essential chemical that is widely used in agriculture and industry
Applications. Ammonia is predominently synthesized via the Haber-Bosch process with Fe-based
catalyst.
Boron-doped graphene with different boron structures was rationally synthesized to enhance the
adsorption of N2, thus enabling an efficient metal-free electrocatalyst for electrochemical N2 reduction in
aqueous solution at ambient conditions.
https://doi.org/10.1016/j.joule.2018.06.007

The electrocatalytic N2 reduction reaction (NRR), ideally under ambient
conditions and using water as the hydrogen source, has been proposed as a
sustainable alternative for nitrogen fixation and ammonia production, while its
efficiency has generally been extremely low.
The mechanism of NRR can be generally considered as the adsorption of N2 on
catalyst surfaces, followed by successive cleavage of N–N and formation of N–H
bonds with consecutive proton additions.
The two-dimensional (2D), boron-doped graphene (BG) features as an ideal
NRR electrocatalyst that can promote adsorption of N2.
The graphene framework doped with Boron atoms can retain its original sp2
hybridization & conjugated planar structure.

Boron is an important doping element that induces electron deficiency in
Graphene, leading to a much improved electrocatalytic activity.
The positively charged boron atoms are beneficial for adsorbing N2, thus
providing excellent catalytic centers for the B–N bond formation and the
subsequent production of NH3.
 the catalytic activities of different boron-doped carbon structures, in which the
BC3 structure enables the lowest energy barrier for N2 electroreduction to NH3.
At a doping level of 6.2%, the boron-doped graphene achieves a
NH3 production rate of 9.8 μg·hr−1·cm−2 and one of the highest reported faradic
efficiencies of 10.8% at −0.5 V versus reversible hydrogen electrode in aqueous
solutions at ambient conditions.

Synthesis of Boron-doped Graphene
H3BO3 and graphene oxide with different mass ratios were dispersed
in deionized (DI) water under sonication for 1 hr to obtain a uniform
mixture.
The mixture was frozen overnight, dried, and then heated to 900 0C
under a H2-Ar atmosphere for 3 hr at a heating rate of 5 0 C.min-1.
Afterward, the sample was cooled to room temperature naturally.
The product was washed in DI water four times to remove the
residue of B2O3 and dried under a vacuum at 40 0C.

https://doi.org/10.1016/j.jphotochem.2018.06.002
Structural transformation of GO to BR-GO.

Conclusion
 Graphene materials can be applied to fabricating various unique catalysts.
Doping of graphene with nitrogen or boron creates a band gap & makes it a n-type or p-type
material. Such chemically doped materials have useful properties.
The superior properties of graphene based catalysts are mainly ascribed to the atom-thick 2D
structure, functional groups, high specific surface area and electrical conductivity of graphene
sheets.
A variety of methods such as in situ growth, mixing, CVD(chemical vapour deposition) and
hydrothermal or solvothermal reactions have been developed for preparing graphene based
catalysts.
Graphene based catalysts are attractive because of their potential in replacing conventional
catalysts.

References
Kong X K, Chen C L, Chen Q W. Doped graphene for metal-free catalysis. Chemical Society
Reviews, 2014, 43(8): 2841–2857
 Indrawirawan S, Sun H, Duan X, Wang S. Low temperature combustion synthesis of nitrogen-
doped graphene for metal-free catalytic oxidation. Journal of Materials Chemistry. A, Materials
for Energy and Sustainability, 2015, 3(7): 3432–3440
Graphene based catalysts Cancan Huang, Chun Li and Gaoquan Shi*Received 15th May 2012,
Accepted 20th August 2012 DOI: 10.1039/c2ee22238h
Recent advances on metal-free graphene-based catalysts for the production of industrial
chemicals:Zhiyong Wang, Yuan Pu, Dan Wang, Jie-Xin Wang, Jian-Feng Chen.
Front. Chem. Sci. Eng. https://doi.org/10.1007/s11705-018-1722-y.
Kong X K, Chen C L, Chen Q W. Doped graphene for metal-free catalysis. Chemical Society
Reviews, 2014, 43(8): 2841–2857

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