Carbon supported Gold Catalysts for Catalytic

Applications

By : S.DHIVYA 9908118001 17th May 2010

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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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