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Modern Alchemy: Catalysis by Gold Nano-particles: Part 2
Masatake HarutaTokyo Metropolitan
University
PIRE-ECCI/ICMRSummer ConferenceSanta Barbara17 August, 2006
1. Carbon and Gold in Nanotechnology2. Applications of Gold Catalysts
Air Quality ControlPropylene EpoxidationLiquid Phase Aerobic Oxidation
3. Clusters
Nano-Science & Technology
1 nm = 1 x 10-3 μm= 1 x 10ー6 mm= 1 x 10-9 m
1 mm = 1 x 10-9 x 1000 kmping pong ball the Earth
What elements are the major players in Nanotechnology?
• It is a must for commercial applications that a material should be stable under ambient atmosphere.
Carbon:2- and 3- dimensional structure sp2 → graphite,C60, nanotube, activated C sp3 → diamond
Gold : Thermodynamically the most stable,Dramatic size effect, Recyclable.
Sp2 hybrid orbital:graphite,fullerrene,nanotube
Single and Multi Wall Carbon Nanotube
Buckminster fullerene : C60
Presumed by Prof. Osawa(Kyoto Univ.)
Discovered in 1985F, Curl Jr.,
H. W. KrotoR. E. Smalley
Diameter 1nm1x108 rotation/sec.
Gold Nano-wire:“7” is the magic number.
High Resolution Transmission Electron Microscopy by Prof. Kunio Takayanagi,Tokyo Inst. Tech.
Gibbs Energy of Reaction
Δr G = Δr H - TΔr S
+ : not naturally occurring
Gibbs Energy Enthalpy EntropyAbsoluteTemp.
heat of reaction under constant pressure
regularity inmolecular array
+ : endothermic + : disordered
- : naturally occurring
- : exothermic - : ordered
0 : equilibrium
Gibbs Energies for metal oxide formation : Yes or No ?
ΔfGo(298K), kJ/molO24/3Au + O2 → 2/3Au2O3 +53.3 No
4Ag + O2 → 2Ag2O -22.4 Yes
Pt + O2 → PtO2 - 168 Yes
2Fe + O2 → 2FeO - 493 Yes
Where are Gold Catalysts used?
Air Purification: CO, HCHO, Odor
Propylene Epoxidation
H2 Production: H2O shift, CO oxid.
Direct H2O2 Synthesis
Aerobic Oxidation: alcohols, alkenes
1
10
100
1000
104
0 15 30 45 60
CO濃
度 / p
pm
反応時間 / min
Au/TiO2
1
10
100
1000
104
0 15 30 45 60
CO濃度 / ppm
反応時間 / min
Pt/TiO2
・ 0.1 g catalyst is used for 12L room air at room temp..・ Gold catalyst covers a wide range of CO concentration.
CO removal from Ambient Air
Regeneration of Au/TiO2 Catalyst by
Photo Irradiation
Activity decreases due to theaccumulation of contaminants.
Regeneration by photoirradiation?
• New Catalysts:Au-Ir/CeO2Au/CeO2-ZrO2
Conventional Cat.:Au/Fe2O3 (AIST)Pt/CeO2(Toyota
Central Lab.)
20 40 60 80 100 1200
20
40
60
80
100
Conv
ers
ion,
%
Reaction Temperature, ℃
Au/Ce0.5
Zr0.5
O2
Au/CeO2-ZrO
2(3:7)
Au/CeO2-ZrO
2(5:5)
Au/CeO2-ZrO
2(7:3)
Au-Ir/CeO2
Pt-Ir/CeO2
Fixed bed Flow reactor, SV=40,000ml/h・g- cat., 50ppm HCHO in air, Cat. :100mg
Oxidative Decomposition of HCHO
0
2 0
4 0
6 0
8 0
1 0 0
5 0 1 0 0 1 5 0 2 0 0 2 5 0
A u / N i F e 2 O 4
P d / A l 2 O 3
金 触 媒
パ ラ ジ ウ ム触 媒
( P d 1 w t % )
( A u 1 w t % )
反 応 温 度 / ℃
トリメチル
アミン
除去
率/
%
(CH3)3N CO2, N2, H2Oトリメチルアミン
(100ppm) 触媒
空気中O2
(SV=20,000h-1ml/g-触媒)
Gold Catalyst as an Odor Eater1992, “Beauty Toilet”, Matsushita Housing Products Co., Ltd.
E factors for Chemical Products
RefineryRefinery
Bulk chemiclas
Medicine,Pepticide
E factor = Product weightByproduct weight
World Annual Production, 103 ton
R.A.Sheldon(1992)
0.1
1
10
100E>25~100
E=5~50
E<1~5
E=ca. 0.1
10 102 103 104 105 106
E f
acto
r
Fine chemicals
Gold catalysts may become a major player in
• Simple reactions consuming minimum process energies (gas phase)
• Reactions without using solvents or using water as a solvent
• New reactions with high atom efficiency
Green Sustainable Chemistry!
Propylene Oxide
• World Annual Production = 6 million tons
→ Polyurethane (60-60%) Propylene glycol (20-25%)
• Annual Market Growth = above 5%
• Market Share = Dow Chem. 30%, Lyondell 18%
Synthesis of Propylene Oxide
Current Industrial Process Dow Chemical Co.
A New Route Au/Ti-SiO2 Hayashi & Haruta, 1994
Three Major Factors Controlling
the Activity and Selectivity
Strong Contact with the Supports
Size of Gold Particles
Type of the Supports
Effect of Contact Structure in PO Synthesis
Prod
uct Y
ield
(%)
Catalyst Temperature (K)
T.Hayashi et al.,J.Catal. 178(1998)566.
Support Effect in PO Synthesis
M. Haruta et al., Res. Chem. Intermed. 24(1998)329.
Au Size Effect in PO Synthesis
Prod
uct Y
ield
(%)
Au Mean Diameter (nm)
T.Hayashi et al.,J.Catal. 178(1998)566.
Product Selectivity Changes with Metals
–
–1.72.4
DAu(nm)
1
10.05
1
Load.(wt%)
>990–3.1353
9208712298Pt
9809857298Pd
0>99–0.63353Au
C3H8POH2C3H6(K)Selec. (%)Conv. (%)Temp.Metal
on TiO2
Step Density of Hemispherical Au
Mavrikakis, Stoltze and Nørskov, Catal. Lett., 64 (2000) 101.
NAu
edge
/NA
utot
al
Au Cluster Size (nm)
STM & LBH Images of Model Au/TiO2
Large
Small
LBH
STM Local Barrier HeightY. Maeda et al., Appl. Surf. Sci. 222(2003)409.
-1.2
-0.8
-0.4
0.0
0.4
0.8
0 0.2 0.4 0.6 0.8 1Height(nm)
ΔΦ (e
V)
0.0
1.0
2.0
3.0
4.0
Eg (e
V)
Work Function and Energy Gap vs Thickness
Au Cluster Height (nm)
Ener
gy G
ap (e
V)
metallicnonmetallic
Y. Maeda et al., Appl. Surf. Sci. 222(2003)409.
Liquid Phase Aerobic Oxidation
• Activated carbons
• Fine polymer particles
• Nanocrystalline CeO2• MgAl2O3
• Al2O3-SiO2
Supports for Au
353K,TBHP
+ ½ O2Au/a. c.
O
cis-cyclooctene
G.T. Hutchings et al., Nature 437, 1132(2005)
Conv. 7.9%(24h)Sel. 81%
Liquid alkene epoxidation with O2in the absence of a solvent
Liquid Phase Selective Oxidation
Glucose to Gluconic Acid in Water
M. Rossi et al., Angew. Chem. Int. Ed.43(2004)5812.
Au / Activated Carbon
303K,React. period: 100 s,
glucose 0.38M / H2O glucose : Au =12 000
Conversion vs 1/DAu in Glucose Oxidation
Aerobic oxidation of 3-octanol: Support effect
A. Corma et al., Angew. Chem. Int. Ed., 44, 4066(2005)
5 nm CeO2
Aerobic alcohol oxidation over Au/CeO2
A. Corma et al., Tetrahedron,2006, in press.
Bioethanol : CH3CH2OH +O2 → CH3COOH + H2O453K, 3Mpa
0
50
100
Pd/ Pt/
Yie
ld (
%)
Au/MgAl2O3C. H. Christensen et al., Angew. Chem. Int. Ed. 45, 4648(2006)
HOCH2 - CH2OH + CH3OH + O2
HOCH2 - COCH3 + 2H2OO
Pilot plant for the synthesis of methyl ester glycolate
T. Hayashi, Nippon Shokubai Co.
1~2x104 t/year( 3 years later)
cleaner for semiconductors and liquid crystals, raw materials for cosmetics and biodegradable polymers
Au / Al-SiO2
Reactivities of Au clusters dramatically change with size and
structure.
2nm
<Au Clusters> <Au Nanoparticles>
Number of Atoms 300
Non-metallicQuantum Size Effect3D Structure
No Surface PlasmonAbsorption
MetallicEdges & Corners
Contact Interfaces
Surface PlasmonAbsorption
T. Tsukuda et al., J. Amer. Chem. Soc.127, 9374(2005).
Gold clusters are more active!
XPS of Au after Exposure to Oxygen Atom
Boyen et al., Science, 297 (2002) 1533
Inte
nsity
(Arb
.Uni
t)
Binding Energy (eV)
Taken after radio frequency oxygen plasma
Au55 is nobler than bulk gold!
Au3+ Au3+Au0 Au0
Au13 Clusters Supported on Mg(OH)2 by DP
4–6%100%CO OxidationEfficiency (200K)
7:9358 : 42NIcosa. : NCubo-Octa.
Icosahedron Cubo-Octahedron
D.H.A.Cunninghamet al., J.Catal.177(1998)1.
Summary
Gold catalysts are useful for air purificationowing to high oxidation activity at room temperature and to the activity enhancement by moisture.
Thermodynamic stability and dramatic size effect of gold clusters smaller than 2nm is opening an exciting field of science.
Gold catalysts have great potentials and capabilities in developing Green Sustainable Chemistry.
Thank you!