catalytic oxidations: finding the optimum composition of aupd … rossi.pdf · 2012. 11. 7. ·...

• 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

• [email protected]

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+


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+


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


•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


Green Chemistry, 2010, 12, 144.


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, 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, 2009, 11,

1366.

Supported Au NP catalysts

Supported AuPd NP catalysts


Oxidation of benzyl alcohol


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.


•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.


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.



•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)

catalytic oxidations: finding the optimum composition of aupd … rossi.pdf · 2012. 11. 7. ·...

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