Presented at the Dennis Dowden commemoration meeting in Durham, 3rd April, 2013

1. Surface Science &
catalysis Cardiff Catalysis Institute
A nanoscale perspective on the effect of acid
washing of carbon catalyst supports
Emir Bouleghlimat, Philip R. Davies,
Robert J. Davies, Jiri Kulahvy, David J. Morgan
Cardiff Catalysis Institute, School of Chemistry, Cardiff
University
Dennis Dowden Commemoration 3rd April 2013 1

2. Surface Science &
catalysis Cardiff Catalysis Institute
Selection of papers by Dowden
Title Journal Year
Catalysis and the electronic-structure of solids Abstracts of American chemical society 1985
Ammonia-synthesis and related reactions over iron-cobalt and iron-
Applied catalysis 1982
nickel alloy catalysts .1. Catalysts reduced at 853-K
Hydrogen spillover on alumina-supported Pt-Re catalysts JCS Chem Comm 1977
Design of heterogeneous catalysts Chimica & lndustria 1973
Crystal and ligand field models of solid catalysts Catalysis reviews 1971
Principles for selection of catalyst carriers Chemie ingenieur technik 1968
Anales de la real sociedad espanola de
Surface valencies chemisorption and catalysis fisica y quimica seria b-quimica
1965
New ideas in catalysis Chemistry & industry 1962
The selective hydrogenation of acetylene Transactions of the Faraday society 1958
The significance of patterns of activity in chemisorption and catalysis Angewandte chemie 1958
Hydrogen-deuterium exchange on the oxides of transition metals Advances in catalysis 1957
The testing of heterogeneous catalysts Advances in catalysis 1957
Heterogeneous catalysis .1. Theoretical basis Chemistry & industry 1949
The heat of adsorption of gases on chromium sesquioxide at low
J. Chem. Soc 1939
pressures and room temperatures
Heats of adsorption of gases on chromic oxide at low temperatures JACS 1938
Dennis Dowden Commemoration 3rd April 2013 2

3. Surface Science &
catalysis Cardiff Catalysis Institute
Carbon as a Catalyst Support for Gold
Hydrochlorination of ethyne
Au/C
C2H2 + HCl C2H3Cl
Vinyl chloride PVC
“Aqua regia …… prepare the most efficient catalysts for the hydrochorination of acetylene by
impregnation of HAuCl4 on carbon …….. due to a combination of the oxidising effect of HNO3
on the carbon support and gold, as well as a nucleation effect of HCl …. the two acids ….. act
synergistically.”
“Aqua Regia Activated Au/C Catalysts for the Hydrochlorination of Acetylene.”
Marco Conte, Peter Johnston, Graham J. Hutchings et al.
Journal of Catalysis 297 (2013) 128
Dennis Dowden Commemoration 3rd April 2013 3

4. Surface Science &
catalysis Cardiff Catalysis Institute
Preparation of Carbon Supported Metals
1. Washing:
• HCl, HNO3, Aqua Regia (HCl & HNO3)
2. Impregnation
• HAuCl4, H2PdCl4 and H2PtCl4
• H2O, HCl, HNO3, Aqua Regia
3. Drying
• 290 oC - 200 oC
4. Regeneration
• H2O, HCl, HNO3, Aqua Regia
Dennis Dowden Commemoration 3rd April 2013 4

5. Surface Science &
catalysis Cardiff Catalysis Institute
Direct synthesis of H2O2
“Switching Off Hydrogen Peroxide Hydrogenation
in the Direct Synthesis Process.”
Edwards, Hutchings et al.
Science 323 (2009) 1037
Fig. 2. STEM-XEDS particle size distributions
acid-pretreated and non treated catalysts.
Table 2. Activity and selectivity of pretreated and untreated
carbon-supported catalysts
Dennis Dowden Commemoration 3rd April 2013 5

6. Surface Science &
catalysis Cardiff Catalysis Institute
Carbon supports
Dennis Dowden Commemoration 3rd April 2013 6

7. Surface Science &
catalysis Cardiff Catalysis Institute
Nanoscale investigation:
can we connect UHV and catalysis?
HOPG
“Bench top” surface science HOPG
• Graphite crystal
Catalyst • Preparation in air
Surface Science
• Carbon powder • Deposition from solution
• Graphite crystal
• Preparation in air • Surface science tools
• UHV
• Deposition from solution
• Vapour deposition
• Surface science tools
Dennis Dowden Commemoration 3rd April 2013 7

8. Surface Science &
catalysis Cardiff Catalysis Institute
Experimental methods:
Sample preparation:
1. Graphite peeled with sticky tape
2. Solutions added by dropper – 1 drop ~ 0.2ml
3. Allowed to stand in air 30 seconds
4. Dried in clean helium stream
Spectroscopic & Microscopic methods
Atomic Force X-ray photoelectron Scanning Tunnelling
Microscopy spectroscopy Microscopy
Dennis Dowden Commemoration 3rd April 2013 8

9. Surface Science &
catalysis Cardiff Catalysis Institute
Control experiments
Clean HOPG surface
Deionised water
Ultra pure water
Dennis Dowden Commemoration 3rd April 2013 9

10. Surface Science &
catalysis Cardiff Catalysis Institute
The effect of acid treatment on HOPG
Clean HOPG surface
0.2 M HCl, 30 min
Dennis Dowden Commemoration 3rd April 2013 10

11. Surface Science &
catalysis Cardiff Catalysis Institute
Low concentration HCl
0.2 M HCl, 30 min
0.1 M HCl, 30 min
Surface coverage of features ~ 20% surface area
Dennis Dowden Commemoration 3rd April 2013 11

12. Surface Science &
catalysis Cardiff Catalysis Institute
Comparison of HCl and HNO3:
Effect of acid concentration
0.1 M HCl, 30 min
0.1 M HNO3, 30 min
Dennis Dowden Commemoration 3rd April 2013 12

13. Surface Science &
catalysis Cardiff Catalysis Institute
Comparison of HCl and HNO3:
Effect of acid concentration II
0.5 M HCl
10 M HCl
10 M
0.5 M
x10
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14. Surface Science &
catalysis Cardiff Catalysis Institute
Models to account for the features
Dennis Dowden Commemoration 3rd April 2013 14

15. Surface Science &
catalysis Cardiff Catalysis Institute
XPS
HNO3
HNO3
HCl HCl
Clean Clean
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16. Surface Science &
catalysis Cardiff Catalysis Institute
XPS
HNO3
HNO3
HCl HCl
• No Ca, K, Na
• Maximum O(a) ~ 4% monolayer
Dennis Dowden Commemoration 3rd April 2013 16

17. Surface Science &
catalysis Cardiff Catalysis Institute
Models to account for the features
Dennis Dowden Commemoration 3rd April 2013 17

18. Surface Science &
catalysis Cardiff Catalysis Institute
STM
Clean graphite 0.1 M HCl treated
Conclusion 0.1 M HCl treated 0.1 M HCl treated
• The graphite lattice
extends over the features
• “Bubbles” not deposits
Dennis Dowden Commemoration 3rd April 2013 18

19. Surface Science &
catalysis Cardiff Catalysis Institute
Local delamination
HCl
Dennis Dowden Commemoration 3rd April 2013 19

20. Surface Science &
catalysis Cardiff Catalysis Institute
Gold deposition on acid treated surfaces
6.2 x10-5 M HAuCl4
Sample preparation:
1. Clean graphite treated with 0.5 M HCl
2. 6x10-5 M HAuCl4 solution, 1 drop ~ 0.2ml
3. Stand 1 minute, blown dry in clean helium stream
Gold “doughnuts”!
Dennis Dowden Commemoration 3rd April 2013 20

21. Surface Science &
catalysis Cardiff Catalysis Institute
Gold nucleation on acid treated surfaces
0.5M HCl, 6.2 x10-6 M HAuCl4
Au
0.5M HCl HAuCl4
Au nucleation on acid induced defects HCl
Dennis Dowden Commemoration 3rd April 2013 21

22. Surface Science &
catalysis Cardiff Catalysis Institute
XPS of Gold on Acid Treated Carbons
• Auo dominates
• % Auo/Au+/Au3+ similar
• Au nucleation greater on HCl treated surface
Dennis Dowden Commemoration 3rd April 2013 22

23. Surface Science &
catalysis Cardiff Catalysis Institute
Gold deposition on acid treated surfaces
6.2 x10-6 M HAuCl4
HNO3 HCl
HNO3
HCl
HNO3 HCl
HCl
HNO3
Dennis Dowden Commemoration 3rd April 2013 23

24. Surface Science &
catalysis Cardiff Catalysis Institute
Au deposition on
a HCl treated
surface
Dennis Dowden Commemoration 3rd April 2013 24

25. Surface Science &
catalysis Cardiff Catalysis Institute
Gold deposition on acid treated surfaces
6.2 x10-6 M HAuCl4
HNO3 HCl
HNO3
HCl
HNO3 HCl
HCl
HNO3
Dennis Dowden Commemoration 3rd April 2013 25

26. Surface Science &
catalysis Cardiff Catalysis Institute
Au deposition with an acid
Sample preparation:
1. Clean graphite
2. 6x10-6 M HAuCl4 solution in 0.5 M HCl or HNO3, 1 drop ~ 0.2ml
3. Stand 1 minute, blown dry in clean helium stream
HNO3
HCl
HNO3 dosed with Au HCl dosed with Au
Dennis Dowden Commemoration 3rd April 2013 26

27. Surface Science &
catalysis Cardiff Catalysis Institute
Conclusions
• Mild acid treatment of graphite results in local delamination
• Au nucleation occurs at defect sites
• Pretreatment with acid
 HCl enhances Au nucleation & deposition
 HNO3 generates larger gold nanoparticles
• Au depositon in acid
 HCl enhances nucleation of smaller particles
 HNO3 generates larger particles
Dennis Dowden Commemoration 3rd April 2013 27

28. Surface Science &
catalysis Cardiff Catalysis Institute
Next steps: Aqua Regia
Fig. 3 Conversion () after 5 h and Au3+ () for Au/C catalysts
containing different amounts of Au3+. The catalysts were obtained
from impregnation using solutions containing different HNO3 volume
fraction in the HCl/HNO3 mixture.
“Modifications of the Metal and Support During the Deactivation and Regeneration of Au/C Catalysts
for the Hydrochlorination of Acetylene.”
Marco Conte, Catherine J. Davies, Graham J. Hutchings et al.
Catalysis Science & Technology 3, (2012) 128 Dennis Dowden Commemoration 3rd April 2013 28

29. Surface Science &
catalysis Cardiff Catalysis Institute
Funded by EP/I038748/1
Cardiff University CUROP awards
Dennis Dowden Commemoration 3rd April 2013 29