Nanoscale perspective on the effect of acid washing carbon catalyst supports

Dennis Dowden Commemoration 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


Surface Science &


Title Journal YearCatalysis and the electronic-structure of solids Abstracts of American chemical society 1985

Ammonia-synthesis and related reactions over iron-cobalt and iron-

nickel alloy catalysts .1. Catalysts reduced at 853-KApplied catalysis 1982

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

Surface valencies chemisorption and catalysisAnales de la real sociedad espanola de

fisica y quimica seria b-quimica1965

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

pressures and room temperaturesJ. Chem. Soc 1939

Heats of adsorption of gases on chromic oxide at low temperatures JACS 1938

Selection of papers by Dowden


Surface Science &


Carbon as a Catalyst Support for Gold

Hydrochlorination of ethyne

C2H2 + HCl C2H3ClAu/C

Vinyl chloride PVC

“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

“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.”


Surface Science &


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


Surface Science &


Direct synthesis of H2O2

“Switching Off Hydrogen Peroxide Hydrogenation in the Direct Synthesis Process.”

Edwards, Hutchings et al. Science 323 (2009) 1037

Table 2. Activity and selectivity of pretreated and untreated carbon-supported catalysts

Fig. 2. STEM-XEDS particle size distributions acid-pretreated and non treated catalysts.


Surface Science &


Carbon supports


Surface Science &


Nanoscale investigation:

can we connect UHV and catalysis?

Catalyst• Carbon powder• Preparation in air• Deposition from solution

HOPG

Surface Science• Graphite crystal• UHV• Vapour deposition• Surface science tools

HOPG

“Bench top” surface science• Graphite crystal• Preparation in air• Deposition from solution• Surface science tools


Surface Science &


Experimental methods:

Sample preparation:1. Graphite peeled with sticky tape2. Solutions added by dropper – 1 drop ~ 0.2ml3. Allowed to stand in air 30 seconds4. Dried in clean helium stream

Spectroscopic & Microscopic methods

Atomic ForceMicroscopy

X-ray photoelectronspectroscopy

Scanning TunnellingMicroscopy


Surface Science &


Clean HOPG surface

Deionised water

Control experiments

Ultra pure water


Surface Science &


The effect of acid treatment on HOPG

Clean HOPG surface

0.2 M HCl, 30 min


Surface Science &


Low concentration HCl

0.2 M HCl, 30 min

0.1 M HCl, 30 min

Surface coverage of features ~ 20% surface area


Surface Science &


Comparison of HCl and HNO3:

Effect of acid concentration

0.1 M HCl, 30 min

0.1 M HNO3, 30 min


Surface Science &


Comparison of HCl and HNO3:

Effect of acid concentration II

0.5 M HCl

10 M HCl10 M

0.5 Mx10


Surface Science &


Models to account for the features


Surface Science &


XPS

HNO3

HCl

Clean

HNO3

HCl

Clean


Surface Science &


HNO3

HCl

HNO3

HCl

XPS

• No Ca, K, Na• Maximum O(a) ~ 4% monolayer


Surface Science &


Models to account for the features


Surface Science &


STMClean graphite 0.1 M HCl treated

0.1 M HCl treated 0.1 M HCl treated Conclusion

• The graphite lattice extends over the features

• “Bubbles” not deposits


Surface Science &


Local delamination

HCl


Surface Science &


Gold deposition on acid treated surfaces6.2 x10-5 M HAuCl4

Sample preparation:1. Clean graphite treated with 0.5 M HCl2. 6x10-5 M HAuCl4 solution, 1 drop ~ 0.2ml3. Stand 1 minute, blown dry in clean helium stream

Gold “doughnuts”!


Surface Science &


Gold nucleation on acid treated surfaces0.5M HCl, 6.2 x10-6 M HAuCl4

0.5M HCl HAuCl4

Au nucleation on acid induced defects HCl

Au


Surface Science &


XPS of Gold on Acid Treated Carbons

• Auo dominates

• % Auo/Au+/Au3+ similar

• Au nucleation greater on HCl treated surface


Surface Science &



HNO3

HCl

HNO3

HCl

HNO3

HNO3

HCl

HCl


Surface Science &


Au deposition ona HCl treated

surface


Surface Science &



HNO3

HCl

HNO3

HCl

HNO3

HNO3

HCl

HCl


Surface Science &


Au deposition with an acid

HCl dosed with AuHNO3 dosed with Au

Sample preparation:1. Clean graphite2. 6x10-6 M HAuCl4 solution in 0.5 M HCl or HNO3, 1 drop ~ 0.2ml3. Stand 1 minute, blown dry in clean helium stream

HNO3

HCl


Surface Science &


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


Surface Science &


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


Surface Science &


Funded by EP/I038748/1Cardiff University CUROP awards

Nanoscale perspective on the effect of acid washing carbon catalyst supports

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