UV light pre-treatment was examined as a means of enriching the catalytic activation of oxygen by bimetallic AuPt deposits loaded on TiO2. The rate of catalytic oxygen activation was assessed by monitoring the rate of formic acid oxidation in an aqueous system. A catalytic synergy was observed to exist for the bimetallic AuPt on TiO2 and was governed by the Au–Pt structure and ratio. The extent of the synergy was further enhanced upon UV light pre-treatment. Exceptional improvements in bimetallic catalysts are often simply attributed to a synergy effect, which is not necessarily well-understood. The Au–Pt bimetallic synergy and UV light pre-illumination phenomena were probed using high-end characterisation tools in conjunction with first principle calculations with the effects attributed to a combined influence of work-function difference and lattice mismatch between Au and Pt. Understanding the origin of bimetallic synergism is a critical step toward developing advanced catalysts.

1. Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D
Key Contact
Particles and Catalysis Research Group,
School of Chemical Engineering,
The University of New South Wales,
Sydney, NSW 2052, Australia.
E-mail: r.amal@unsw.edu.au
jason.scott@unsw.edu.au
e-
UV pre-illumination-enhanced bimetallic
synergy work-function-driven electron
transfer pathway.
Au
Pt
Oxygen
Electron

2. Introduction
Oxidation
CO2
Volatile organic compound
Carbon monoxide
+ O2
Pollutant removal
http://butane.chem.uiuc.edu/pshapley
/GenChem2/C10/index.html
Energy generation
Fuel + O2 CO2 + H2O
+ Energy
Oxygen reduction
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

3. Introduction
High activity
J. Phys. Chem. B, 2004, 108, 17886–17892.
CO deactivation
CO resistance
Room temperature reaction
Volcano Plot for ORR
UV pre-illumination enhancement
UV pre-illumination enhancement
ACS Catal., 2017, 7 (5), pp 3644–3653
Catal. Sci. Technol., 2016, 6, 8188-8199
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

4. EDS
Au
86.3 %
Pt
13.7 %
Au
69.2 %
Pt
30.8 %
5.0 nm
Au
25.7 %
Pt
74.3 %
(a) (b) (c)
5.0 nm 5.0 nm
Sizedistribution
(d) (e) (f)
95 counts 215 counts 343 counts
Fig. 1 Deposits with Au0.5Pt0.5 (b) and Au0.8Pt0.2 (gold-rich, (g)) compositions exhibit a
homogeneous AuPt distribution while Pt-rich deposits (i) formed segregated clusters
where the Au/Pt boundary is highlighted by a black dotted line. (d–f) Show the particle
size distributions of Au0.8Pt0.2, Au0.5Pt0.5, and Au0.2Pt0.8, respectively, with the red
column indicating percentage of bimetallic particles as determined from STEM-EDS.
Au0.2Pt0.8Au0.5Pt0.5Au0.8Pt0.2
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

5. (a) (b)
Fig. 2 (a) Rate at which 50% of the initial formic acid added is oxidised (R50) for individual Au (pink), Pt (grey),
and bimetallic AuPt (blue) deposits loaded on TiO2 without UV light pre-treatment as well as the effect of UV
light pre-treatment on the R50 values of AuPt/TiO2 catalysts (purple). The x-axis labels for each cluster of
columns indicate the amounts of each metal (individual) and the bimetallic ratio for the catalyst. (b) The
synergism (in the form of an enhancement factor) achieved by coupling the Au and Pt in the bimetallic
deposits, both without (blue) and with (purple) UV light pre-treatment. The enhancement factor was
determined by dividing the R50 of the bimetallic catalyst by the sum of the corresponding R50 values for the
individual Au/TiO2 and Pt/TiO2 catalysts. An enhancement factor = 1.0 corresponds to no enhancement. UV
light pre-treatment time: 30 min; formic acid loading: 1000 μmol.
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

6. Fig. 3 Au4f and Pt4f binding energy (B.E.)
shifts in AuPt/TiO2 at various Au : Pt ratios.
Binding energy shifts are determined
relative to the binding energies of the
corresponding species in the monometallic
catalysts of the same metal loading; for
example, the Au binding energy shift for
Au0.8Pt0.2/TiO2 is relative to 0.8 at%
Au/TiO2. Note that, although PtO2 was
detected in Au0.5Pt0.5/TiO2, the binding
energy shift for PtO2 is not presented as it
is not present in 0.5 at% Pt/TiO2, so it is
not possible to calculate the shift due to
the lack of a reference value.
Au
TiO2
Pt
2
1
3 5.6 eV
5.1 eV
4.9 eV
Scheme 1 Work-function-driven electron transfer pathways.
[1] Represents the direct electron transfer pathway from the
TiO2 into the Pt. [2] and [3] Represent the indirect electron
transfer pathway from the TiO2 into the Au and from the Au to
the Pt, respectively.
Fig. 4 PL spectra showing
the effect of bimetallic
Au:Pt ratio on electron–
hole recombination in the
TiO2 support. The PL
signal decreases with
increasing Pt ratio in the
bimetallic deposit,
indicating that an Au-rich
alloy gives a higher
electron–hole
recombination rate.
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

7. Pt4f
Pt0
PtOads
PtO
(b)
Pt4f
Pt0
PtOads
PtO
(c)
PtO2
*
Au4f Pt4f
Pt0
PtOads
PtO
As-prepared
Pre-0
Pre-30
Post
reaction
(c)(e)
Au0.2Pt0.8
Pt0
(a)
Pt0
(b)
Fig. 5 Extent of Pt speciation for Au0.8Pt0.2/TiO2 (a), Au0.5Pt0.5/TiO2 (b), and Au0.2Pt0.8/TiO2 (c) at various
stages of the UV light pre-treatment process and formic acid oxidation reaction. XPS measurements were
performed on the as-prepared dry catalyst powder (as-prepared), the catalyst recovered from the reaction
medium before light pre-treatment (Pre-0), the catalyst after 30 min light pre-treatment (Pre-30), and the
recovered catalyst after formic acid oxidation (post reaction). The * in (b) indicates the unquantifiable
amount of Pt0 after 30 min light pre-treatment. Pt speciation are normalised to the total amount of Pt. Pre-
illumination time: 30 min; formic acid loading: 1000 μmol.
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

8. DFT calculations show improved O2 adsorption on the bimetallic clusters.
Light pre-treatment improves charge transfer to the adsorbed oxygen and weakens the
metal-oxygen bond (longer bond length).
O-O: 1.375 Å
Pt-O: 2.03 Å
Pt-O: 2.18 Å
DFT model AuPt/TiO2 showing Pt-O and O-O
bond lengths.
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

9. (a) (b)
0.8 at% Au/TiO2
Au0.8Pt0.2/TiO2
Au0.5Pt0.5/TiO2
Au0.2Pt0.8/TiO2
Pt-O
0.2 at% Pt/TiO2
Au0.8Pt0.2/TiO2
Au0.5Pt0.5/TiO2
Au0.2Pt0.8/TiO2
(a) (b)
Fig. 6 (a) Au L3 XANES and (b) Pt L3
XANES of various bimetallic AuPt/TiO2
samples before and after UV light pre-
treatment, with their respective metal foil
standards and monometallic samples as
references. Insets: Au L3 and Pt L3
absorption edge shifts.
Fig. 7 Fourier transform of EXAFS spectra
for (a) Au L3 and (b) Pt L3 of various
bimetallic AuPt/TiO2 samples before and
after UV light pretreatment, with their
respective metal foil standards and
monometallic samples as references.
Dotted lines represent EXAFS spectra of
the respective sample after 30 min UV light
pre-treatment. Analysis on Au0.5Pt0.5/TiO2
after UV light pre-treatment was not
performed. The peaks at R < 2.0 Å in (a)
could not be identified and will require
further investigations.
Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D

10. Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D
(b)(a)
Fig. 8 (a) XPS valence band spectra of AuPt/TiO2 with various Au:Pt metal ratios compared to
0.8 at% Au/TiO2 and 0.2 at% Pt/TiO2. Inset: Shift in valence band edges. Arrow indicates the
emerging hybrid states; (b) Au0.8Pt0.2/TiO2 before and after UV light pre-treatment compared to
its corresponding monometallic counterparts. Arrows indicate selected Pt valence band
features adopted by Au0.8Pt0.2/TiO2 following UV light pretreatment.

11. Catalysis Science & Technology
Volume 7, Number 20, pages 4792-4805, 25 September 2017, DOI: 10.1039/C7CY01326D
Conclusion
• Au-Pt synergy is a combined
effect of:
(i) work function difference
(ii) lattice mismatch
• Light pre-illumination is able to promote oxygen activation on
Au/TiO2 and bimetallic AuPt/TiO2 at room temperature and
atmospheric pressure
• Au-Pt synergy and pre-
illumination enhancement can be
controlled with Au:Pt ratio
Au Pt
e-