• Prof. Dr. Liane M. Rossi • Laboratory of Nanomaterials and Catalysis
• Instituto de Química
• Universidade de São Paulo
• Av. Prof. Lineu Prestes 748
• São Paulo 05508-000, SP – Brasil
• +55 11 30919143
Catalytic oxidations: finding the
optimum composition of AuPd core-
shell nanoparticle catalysts
Brazilian ChemComm Symposium – Chemistry and Sustainable Energy
5th November 2012, São Paulo, Brazil
• hazardous or toxic chemicals
• volatile organic solvents
• large amounts of toxic wastes
Stoichiometric Oxidations
are very far
from being
ideal from the
green
point of view!
Catalytic oxidations are widely used in the manufacture of
bulk petrochemicals, but are not a commonplace in the fine
chemicals and pharmaceutical industry, and at the organic
laboratory level:
Oxidizing reagent Residue
KMnO4 Mn2+/MnO2
K2CrO4 Cr3+
CH3COOOH CH3COOH
t-BuOOH t-BuOH
ClO- Cl-
H2O2 H2O
O2 H2O
Catalytic Oxidations
Control the reactivity of oxygen species to obtain valuable organic oxygenates and avoid overoxidation.
Discriminate functional groups in the same molecule. Oxidations in fine chemicals is generally more difficult, however, owing to the multifunctional nature of the molecules of interest.
Green oxidizing agents, O2 and
H2O2, do not readily react in a
selective way with organic
substrates, unless a catalyst is
present.
R-CH2-OH R-CHO R-COOH CO2 + H2O
Development of metal nanoparticle catalyst
*Gold was discovered as an
active catalyst in the late
80s after the seminal
contribution of Haruta and
Hutching.
• high control on particle size, size distribution and surface chemistry
Soluble NPs
Supported NPs
Future Targets • Control on particle size, size distribution and uniform dispersion of
NPs on solid supports - dial up the active sites • Prevent metal leaching • Improve metal recovery • Understand the role of stabilizers on metal NP catalysis
Metal nanoparticle catalyst
Supported metal NPs
•Immobilization of pre-formed metal NPs
•Metal salt impregnation and reduction method
Catalyst
Support Mx+
Mx+
Mx+
Mx+
Mx+
Mx+ Mx+
•Poor control on metal dispersion
•Particles size and sized distribution
Tune NPs size with uniform dispersion of
NPs on supports
Catalyst
Support
Mx+ Mx+
Mx+
Mx+
Mx+
Mx+
Mx+
= NH2, en, COOH, SH, PR2, ...
Si(OR)3
Supported metal NPs
Ligand-assisted method Nanoscale, 2012, 4, 5826.
None NH2R= NH NH2R=
Inorganic Chemistry, 2009, 48, 4640.
Improve metal
recovery using
magnetic support
Catalyst
Support
Mx+ Mx+
Mx+
Mx+
Mx+
Mx+
Mx+
= NH2, en, COOH, SH, PR2, ...
Si(OR)3
Supported metal NPs
Ligand-assisted method
Applied Catalysis. A, General, 2008, 338, 52.
Nanoscale, 2012, 4, 5826.
Low metal
leaching
Catalyst
Support
Mx+ Mx+
Mx+
Mx+
Mx+
Mx+
Mx+
= NH2, en, COOH, SH, PR2, ...
Si(OR)3
Supported metal NPs
Ligand-assisted method
ChemCatChem, 2012, 4, 698.
Nanoscale, 2012, 4, 5826.
Supported metal NPs
Ligand-assisted method: metal support interaction
Chemistry A European Journal, 2011, 17, 4626.
X-ray absorption fine structure spectroscopy studies
11900 11910 11920 11930 11940 11950
0.0
0.2
0.4
0.6
0.8
1.0
1.2
t
Energy / eV
(a)
(b)(c)
(d)
(e)(a) Au(CH3COO)3
(b) SiO2-Au3+
(c) HAuCl4
(d) SiO2-NH2-Au
(e) Au foil
Si
NH2
OO
OSi
NH2
O
O
O
Si
H2N
OO
OSi
NH2
O
OO
H2N
NH2
NH2
NH2
Au3+
Au3+ Au3+
Au3+
Auσ+
Auσ+
Auσ+
Auσ+
SiO2-NH2 -Au3+
SiO2-Au3+
Supported metal NPs
Ligand-assisted method: metal support interaction
Au L3-edge
Chemistry A European Journal, 2011, 17, 4626.
•Rh NPs •PtNPs
Applied Catalysis. A, General, 2008,
338, 52.
Applied Catalysis. B, Environmental,
2009, 90, 688.
Catalysis Communications,
2009, 10, 1971.
Selected examples of magnetically recoverable catalysts
Applied Catalysis. A, General,
2009, 360, 177.
•Ru NPs •Ir NPs
ChemCatChem, 2012, 4, 698.
•AuNPs
Chemistry A European Journal, 2011, 17, 4626.
Green Chemistry, 2010, 12, 144.
Green Chemistry, 2009, 11, 1366.
Selected examples of magnetically recoverable catalysts
•PdNPs
Inorganic Chemistry. , 2009, 48, 4640.
Appl. Catal. B, Environ., 2010, 100, 42.
Journal of Catalysis, 2010, 276, 382.
•NiNPs
ACS Catalysis, 2012, 2, 925.
•AuNPs
Chemistry A European Journal,
2011, 17, 4626.
Green Chemistry, 2010, 12, 144.
Green Chemistry, 2009, 11,
1366.
Supported Au NP catalysts
Oxidation of benzyl alcohol
K2CO3 = high selectivity and conversion rates, but
low catalyst stability
In the search for a more stable catalysts,
we first chose to adhere to the literature
by adding Pd to our supported gold catalyst
0
20
40
60
80
100
Co
nve
rsio
n (
%)
K2CO
3KOH Et
3N absence
of base
Selectivity =96%
... AuPdNPs
Co
nsi
der
ati
on
s
Bimetallic NPs = metallic domain distributions: alloys (AB) or core-shell (A@B or B@A) NPs
AuPd alloy NPs have received special attention in catalytic applications. However, the surface of an AuPd alloy NP differs from its corresponding bulk concentration
Core-shell NPs can be obtained by the reduction of palladium over pre-formed gold NPs, and vice versa
Op
en
qu
esti
on
How much Pd should be added to activate Au NPs?
•AuNPs
Chemistry A European Journal,
2011, 17, 4626.
Green Chemistry, 2010, 12, 144.
Green Chemistry, 2009, 11,
1366.
Supported Au NP catalysts
Supported AuPd NP catalysts
Chemistry A European Journal, 2011, 17, 4626.
Oxidation of benzyl alcohol
Supported AuPd NP catalysts
Catalytic performance of the Au@Pd catalysts in the oxidation reaction with benzyl alcohol. The amount of Au is fixed (3.4 mol),
while the amount of Pd varies from 0 to 40 mol % (i.e., 0 to 1.4 mol). Reaction conditions: 1 mL (10 mmol) benzyl alcohol, 75 mg
catalyst (3.4 µmolAu), 0 to 1.4 µmol Pd(OAc)2, 6 bar O2, 2.5 h, 100°C.
TEM and HAADF-STEM image of a Au:Pd = 10:1 supported
catalyst particle and the respective Au and Pd maps. The
particle compositional distribution is observed in the line
scans, measured from the regions delimited by the lines
indicated in both maps. The hemispherical shape observed in
the Au line scan contrasts with the flat distribution measured
for Pd, which shows its concentration at the particle shell.
Supported AuPd NP catalysts
•morphologically structured Au-rich core and a Pd-rich shell
Supported AuPd NP catalysts
•morphologically structured Au-rich core and a Pd-rich shell
(a) BF-STEM image of a supported catalyst particle Au:Pd = 5:2 (b) HAADF-STEM image of the supported
catalyst particle and the respective Au and Pd maps. The particle compositional distribution is observed in
the line scans, measured from the regions delimited by the lines indicated in both maps. The
hemispherical shape observed in the Au line scan contrasts with the flat distribution measured for Pd,
which shows its concentration at the particle shell.
Supported AuPd NP catalysts
Catalytic performance of the Au@Pd catalysts in the oxidation reaction with benzyl alcohol. The amount of Au is fixed (3.4 mol),
while the amount of Pd varies from 0 to 40 mol % (i.e., 0 to 1.4 mol). Reaction conditions: 1 mL (10 mmol) benzyl alcohol, 75 mg
catalyst (3.4 µmolAu), 0 to 1.4 µmol Pd(OAc)2, 6 bar O2, 2.5 h, 100°C.
•morphologically structured Au-rich core and a Pd-rich shell
Supported AuPd NP catalysts
•Full-shell cluster model:
... ...
•The most active Au@Pd catalyst, with 89.9% Au and 9.1% Pd, is very close to the nominal composition for the complete coverage of Au cores (12.0 3.2 nm) with one atomic layer of Pd.
0 10 20 30 40
0
20
40
60
80
Ac
tivity
Pd added
Final Remarks
Hypothesis based on
morphological and catalytic
studies: the deposition of one
atomic layer of Pd on Au resulted
in a Au core-Pd-rich shell catalyst
of maximum activity.
Final Remarks
The Au:Pd molar ratio needed to form a monolayer of Pd might
change as a function of Au core size. Consequently, one can
expect the maximum activity to occur at differing AuPd
compositions when using Au core size or size distribution other
than the one we used in our study.
~3 nm AuNP
~45% surface atoms
~40 mol% Pd for
monolayer
~10 nm AuNP
~16% surface atoms
~15 mol% Pd for
monolayer
~20 nm AuNP
~8% surface atoms
~8 mol% Pd for monolayer
Experiments in progress!
Final Remarks
meeting the
increasing demand
for environmentally
friendly chemical
processes
high selectivity
of Au
high activity of
Pd
High activity
and selectivity
•Au core Pd-rich shell: the distribution of metal domains and the
Au:Pd ratio are both important for the synergistic effect observed.
ACKNOWLEDGMENTS Group
Tiago Artur da Silva - PhD
Fernanda Parra da Silva -PhD
Lucas L. R. Vono - PhD
Marco Aurélio S. Garcia - PhD
Natália J. S. Costa – Post Doc
Jean-Claudio Costa – Post Doc
Leonardo Gomes Santos – Undergrad
Bruna Julio - Undergrad
Rafael L. Oliveira
Inna M. Nangoi
Marcos J. Jacinto
Fernando B. Effenberger
Collaboration
Pedro K. Kiyohara (IF/USP)
Renato F. Jardim (IF/USP)
Richard Landers (Unicamp)
Daniela Zanchet (Unicamp)
Érico Teixeira-Neto (IQ-USP)
Elena Goussevskaia (UFMG)
Paulo A. Z. Suarez (UnB)
Joel C. Rubim (UnB)
Karine Philippot (LCC/CNRS, Toulouse, France)
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