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Carbon supported Gold Catalysts for Catalytic
Applications
By : S.DHIVYA 9908118001 17th May 2010
04/21/23
2
Introduction
Synthesis of Au/carbon catalyst by sol - immobilization method
Physico – Chemical Characterisation of Au/C catalyst XRD – Composition, Crystallographic phase, Crystallite size ICP analysis of the filtrate – Estimation of Au on carbon support UV Vis analysis – Surface plasmon resonance – approximate idea of particle size TGA – Thermal stability and also the amount of gold loading on carbon BET sorptometry – Specific surface area and pore size distribution SEM analysis - Surface Morphology of Au nano structures on the cabron support TEM analysis – Surface Morphology of Au nano structures
Use of Au/C catalysts for Oxygen Reduction Reaction (ORR)
Work status
Contents
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Why Au ?Why Au ?
Electrochemical potential of gold is lowest of any metal
Gold is the most electronegative of all metals (in the Pauling or absolute scale)
Ability to catalyze (in nano state) the reduction of oxygen
Good resistance to corrosion and dissolution
Hiroko Okatsu et.al., Applied Catalysis A : General 369 (2009) 8-14
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Why Carbon Support ?Why Carbon Support ?
Inert support - only slightly affects the catalytic properties of Au nanoparticles (NPs)
Stable in both acidic and basic environments
Combustible to allow the recovery of catalytic metals
Presence of acidic function group on the carbon surfaces enhances the
deposition and dispersion of Au NPs
Electrically conductive , leading to applications to electrodes for fuel cells,
batteries, and chemical sensors
Hiroko Okatsu .et.al., Applied Catalysis A : General 369 (2009) 8-14
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Catalysis by Gold : Some Glittering Facts
Catalysis by Gold – a ‘rags to riches’ story
It has been overlooked for many years as a key component in catalysis
Two key observations of 1980’s that revolutionized the field:
i. Finding of G. J. Hutchings that gold would be the best catalyst for ethylene hydro chlorination
ii. Finding of Haruta et al. that supported Au nanoparticles possess exceptionally high CO oxidation activity
2.0 nm appears to be a crutial diameter for noble metals (gold) to lose intrinsic metallic nature
Gold clusters with diamters below 2.0 nm or with atoms less than 300 will lead to many interesting and useful scientific discoveries
G. J. Hutchings, J. Catal. 96 (1985) 292M. Haruta, T. Kobayashi, H. Sano, N. Yamada, Chem. Lett. 1987, 405
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Sol immobilization method
Deposition precipitation method
Impregnation method
Solid grinding method
Au/C catalyst - Methods of preparation
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232 mL of H2O + 0.2 M NaOH (7.5 mL)
5mL dil. aq. THPC (1.2 mL,78 wt.% THPC solution made upto 100 mL)Stirring for 2 minutes
0.03 g Au (15 mL, 0.0102 M HAuCl4
Stirring for 1 h
0.97 g Carbon (Carbon support)Stirring for 3 h
Filtering, washing, drying and mortaring
Inert gas, Ar, treatment (3 h/350 °C/ N2)
Reduction (3 h/350 °C/ H2 )
3 wt.% Au/C (1.0 g)Demirel Gulen and Lucas Claus, Catalysis Today, 102-103 (2005) 166-172
Gold-Sol Immobilization Method
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Images of the process of Catalyst preparation
Stirring of 15 mL, 0.0102 M HAuCl4 in the presence of NaOH and THPC solutions (reddish brown colour
solution of Au is seen)
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Filtering of Au - C suspensionThe colour of the filtrate is reddish brown, almost
similar to the colour of the solution before C addition
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Synthesis of Au/Nuchar Activated Carbon
Au sol
solvent rich adsorption layer
Carbon support
Filtration and dryingStirring
AuCarbon support
AuCarbon support
Schematic representation of the catalyst synthesis process
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The filtrate turns purple colour after 2 weeks indicating the agglomeration of gold NPs
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X - ray Diffraction (XRD)
ICP Analysis
UV-Vis Analysis
Scanning Electron Microscopy (SEM)
Transmission Electron Microscopy (TEM)
BET sorptometry
Physico-Chemical Characterization
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Analysis of the filtrate for Au content:
1. To know the amount of Au loaded o the carbon support, 10 mL of the filtrate is diluted to 500 mL and 25 mL of this dilute solution of the filtrate is given for ICP analysis
Presence and state of Au on Carbon support:
The presence as well as the cystallographic structure of Au particles on C support in the Au/C catalyst is be evaluated by XRD analysis
ICP Analysis
XRD Analysis
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Au/Nuclar activated carbon – XRD Analysis
XRD pattern of Au/C (Nuchar)
o The broad and intense diffractionpeak at the 2 value of 24.7is attributed to the (002) plane of Nuchar activated carbon
o The diffraction peaks atthe 2 values of 38.8, 44.8, 64.7and 78.4 were indexed to the (111), (200), (220) and(311) Diffraction planes ofAu metal particles in fcc lattice
o The crystallite size of Au Nano structures on gold wasCalculated by considering (111) peakUsing Debye Scherrer’s equation
o The crystallite size of Au nanoparticles on carbon support is 3.4 nm
Au/Vulcan XC 72 R – XRD Analysis
20 40 60 800
200
400
600
800
(31
1)
(22
0)
(20
0)
(11
1)
Inte
nsi
ty (
cps)
2 (degree)
Au/Vulcan XC 72 R
(00
2)
XRD pattern of Au/C (Vulcan XC 72 R)
Au/Black Pearl 2000 – XRD Analysis
20 40 60 800
500
1000
1500
(311
)
(220
)(200
)
(111
)
Inte
nsity
(cp
s)
2 (degree)
Au/Black Pearl 2000
(002
)
XRD pattern of Au/C (Black Pearl 2000)
Au/CDX 975 – XRD Analysis
20 40 60 800
200
400
600
800
1000
(31
1)
(22
0)
(20
0)(1
11
)
Inte
nsi
ty (
cps)
2 (degree)
Au/CDX 975
(00
2)
XRD pattern of Au/C (CDX 975)
Au/C catalysts – BET sorptometry
Catalyst Specific surface area (m2/g)
Total pore volume (cm3/g)
Au/Nuchar 1078 0.86
Au/Vulcan 191 0.59
Au/Black Pearl 1322 2.8
Au/CDX 975 197 0.48
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Oxygen reduction reaction (ORR) is a four electron process:O2 + 4 H+ + 4 e- → 2 H2O Eo = 1.229 V vs. NHE
Oxygen Reduction Mechanism
Importance of electrochemical reduction of oxygen
Fuel Cells
Metal-Air batteries
Industrial electrolytic processes
H+
H+
H+
H+
H+
Cathode
Water
Air/O2
Electrons
H+
Fuel Cells - Principles and Applications; Viswanathan, B., Aulice Scibioh, M., Eds.; Universities Press (India) Private Limited, 2006.
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Reaction pathways for oxygen reduction reaction
Path A – direct pathway, involves four-electron reduction O2 + 4 H+ + 4 e- 2 H2O ; Eo = 1.229 V
Path B – indirect pathway, involves two-electron reduction followed by further two-electron reduction
O2 + 2 H+ + 2 e- H2O2 ; Eo = 0.695 V
H2O2 + 2 H+ + 2 e- 2 H2O ; Eo = 1.77 VHalina S. Wroblowa, et,al., J. Electroanal. Chem., 69 (1979) 195
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Reversible
Oxygen adsorption capacity
Structural stability during oxygen adsorption and reduction
Stability in electrolyte medium and also in suitable potential window
Ability to decompose H2O2
Good conductivity
Low cost
Essential criteria for choosing an electro catalyst for oxygen reduction
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S.No
Catalyst Metal loading ( Wt %)
ORR activity
1 Au/MWCNT 1 0.057 mA/cm2
2 Au/Vulcan XC-72R & BP
5 2.5 (mA/cm2
3 AuPt/C 4 (Pt:Au=3:2) 793.2 mW/cm2
4AuPt/C
(IE=mA/cm2/mg AuPt) 20
0.5 M KOH 0.5 M H2SO4
-0.1V at 400 C
IE
-0.1v at 500C
IE
0.55V at 400C
IE
0.55V at 500C
IE
Au72Pt28/C 125 180 32 37
Au56Pt44/C 54 54 190 203
Au based catalysts for ORR
Nadezda Alexeyeva.et.al., Journal of Electroanalytical Chemistry (2010)Michael Bron.et.al., Journal of Electroanalytical Chemistry 624 (2008) 64-68 Yuanwei Ma.et.al., catalysis Communications 11 (2010) 434-437Jin Luo.et.al., Electrochemistry Communication 8 (2006) 581-587
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The ORR activity of Au/Vulcan XC 72 is evaluated
The ORR activity of Au/Nuchar, Au/Black Pearl and Au/CDX 975
is being tested
Work in progress
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