Supported Au nanoparticles as Heterogeneous …...SJNANO 2013 Supported Au nanoparticles as...
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SJNANO 2013
Supported Au nanoparticles as Heterogeneous Catalyst for Organic
Reactions
Hermenegildo García and Avelino Corma Instituto de Tecnología Química, Technical University of Valencia
Spain
Outline: Au NPs and Nanoscience Au NPs as catalyst
For aerobic oxidations For carbamoylation For tandem reactions
Role of impurities Isolation of Au intermediates Conclusions and Acknowledgements
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Catalytic activity of noble metals
Why not gold?
As the only exception in noble metals up to the 80s Au was catalytically inactive
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Gold nanoparticles as catalyst
C + H2O CO + H2
syngas
H2O
CO2 + H2
water gas shift
Hydrogen technology
Low temperature, selective CO combustion: the smaller the particle size, the higher the activity
M Haruta, N Yamada, T Kobayashi, S Iijima: J. Cat. 115 (1989) 301-09.
CO + O2
AuCO2
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Au NPs
They can be easily obtained.
“Bare” small Au NPs (1-2 nm) tend to grow
The key issue is to stabilize small Au NPs
“Stabilized” nanoparticles are surrounded by a ligand shell or supported on a solid
Typically, for bulk materials, surface atoms form a negligible part of the total number of atoms 20 nm
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Stabilizing Gold Nanoparticles
HAuCl4
PTC PPh3 NaBH4
1.4 nm Gold
Particles
Use of ligands (Brust method)
Supporting on a solid: Deposition-Precipitation method
HAuCl4
NH4OH CH3OH
Au nanoparticles
Au(OH)3
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Organic reaction types
H2
Pd/C
Hydrogenations N
OH
N
OHH2SO4
(oleum)
Brönsted acids
O
CH3(CH3CO)2O
AlCl3
Lewis acids
CH3 CH3
O
CH3
O CH3
CH3
NaOH
Br
BOHHO
Pd
Bases
Oxidations Transition metal catalysts
CH3 CH3
H OH
CH3 CH3
OK2CrO4
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Au NPs supported on nanoparticulated ceria
CeO2 nanoparticles
•Increasing CeIII population
•Creation of oxygen vacancies
•From insulator to semiconductor
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150
20
40
Cou
nts
Diameter (nm)
Interplanar distance of Au Particle size distribution
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Solventless, aerobic (1 atm) oxidation of alcohols by Au/CeO2
Substrate
Time
[h]
Conversion[a]
[%]
Product Selectivity[%]
1b
3-octanol 2.5 97 3-octanone 96
2b
sec-phenylethanol 2.5 92 acetophenone 97
3b
2,6-dimethylcyclohexanol 2.5 78 2,6-dimethylcyclohexanone 94
4b
1-octen-3-ol 3.5 80 1-octen-3-ona >99
5b cinnamylalcohol 7 66 cinnamaldehyde 73
6b 3,4-dimethoxybenzyl alcohol 7 73 3,4-dimethoxybenzaldehyde 83
7b 3-phenyl-1-propanol 6 70 3-phenylpropyl- 3-phenylpropanoate 98
8c vanillin alcohol 2 96 vanillin 98
9c
2-hydroxybenzyl alcohol 2 >99 2-hydroxybenzaldehyde 87
10c
3,4-dimethoxybenzyl alcohol 2 >99 3,4-dimethoxybenzylic acid >99
11c
cinnamyl alcohol 3 >99 cinnamylic acid 98
12d
n-hexanol 10 >99 hexanoic acid >99
13e
n-hexanol 10 >99 hexanoic acid >99
14c
sec-phenylethanol 5 >99 acetophenone 51
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Solventless aerobic alcohol oxidation and the green chemistry principles
1. Avoid wastes (minimise E factor). 2. Use tolerable reagents and produce non-toxic
products. 3. Use environmental friendly processes. 4. Use renewable feedstocks. 5. Develop more active and selective catalysts. 6. Avoid derivatisation, protecting groups and isolations. 7. Maximise the atomic economy. 8. Use environmentally friendly solvents. 9. Minimise energy consumption 10. Use self- or bio- degradable products 11. Real time analyses 12. Minimise hazards
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Replacement of toxic phosgene: Catalytic carbamoylation of aromatic diamines
phosgene
isocyanate
polyurethanespolyol
(Best selling industrial polymers)
• Problem: development of a catalyst
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Carbamoylation of 2,4-diaminotoluene
0
25
50
75
100
0 1 2 3 4 5 6 7
t(ht)
Pro
du
ct
sele
cti
vit
y (
%)
Final yield > 90%
Au NPs on other supports give rise to N-methylation products:
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Tandem reaction
CH3
NH2
NH2CH3
OC
OH3C
O CH3
HN
HN
C
O
OCH3
C
O
OCH3
CH3
NO2
NO2 H2
Two steps, two processes:
or two-steps one process:
CH3
NO2
NO2
CH3 HN
HN
O
O
O
O
DMC
H2 (5 bar)
T=150ºCt=12 hours
Conversion = 95.2
Selectivity = 98.3
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Role of Pd impurities in Au catalysis
•Pd is a very efficient catalyst •Au contains 5-10 ppm of Pd
• Has Au intrinsic activity?
High purity Au is also active for Sonogashira coupling
•Au complexes of a single atom is not able to promote Sonogashira •Au NPs are active
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Isolation of Au intermediates
Au catalyst
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Conclusions and Acknowledgements
Financial Support:
•Japanish-Spanish Cooperative program
Prof. Avelino Corma Dr. Alberto Abad Dr. Raquel Juárez Dr. Abdessamad Grirrane
Supported small sized Au NPs are highly active catalysts