Post on 14-Feb-2017
1 11Nanoscience and Catalysis 111
The Impact of Nanoscience inHeterogeneous Catalysis
R. Schlögl
Fritz Haber Institut der MPG
www.fhi-berlin.mpg.de
Sharifah Bee Abd Hamid,
Combicat Centre, University of Malaya
combicat@um.edu.my
A EuropeanPerspective?
2 22Nanoscience and Catalysis 222
Self-organisation: Nanomagnets: Co/Au(111)
Size too small: no remanence at 300 K!
Increase active volume by height increase
Result: nanostructured data storage system
Magnetfeld (T)
J. Kirschner et al.
MPI Mikrostrukturphysik, Halle
300x300nm
Au(111) Co-Nanomagneta
7nm13nm
3 33Nanoscience and Catalysis 333
Nano-CatalysisCatalysis is a multi-
functional phenomenon:It is multi-scale and hence
ever since“nanocatalysis”
A pleonasmus?Or:
What`s new in thenanoera?
4 44Nanoscience and Catalysis 444
Polymer-Metal Interface: Multiscale Approach
Simulation of coarse-grainedBPA-PC liquids (T = 570K)next to metal surface
Specific surface interactionsinvestigated via ab initio calculations (CPMD,…)
Molecular structure coarse-grainedonto bead-spring chain
Delle Site, Abrams, Kremer, MPI Polymer Science
5 55Nanoscience and Catalysis 555
Literature
10
100
1000
10000
1989 1994 1999 2004
[a]
[n]
At every hour every daya paper on nanoscience
is published.
Two reviews per dayoccur on the subject
6 66Nanoscience and Catalysis 666
The EU view
• ERA in nanotechnology
• “nanotechnology is an all-embracing term forvarious aspects of science and technologyinvolved in the study, manipulation and control ofindividual atoms and molecules”…”nanotechnology is predicted to underpin thenext industrial revolution”.
• Integration and integrated teaching as long-term structural targets.
7 77Nanoscience and Catalysis 777
The ERA Nanotechnology
• Nanoelectronics, molecular electronics quantumcomputing
• Nanobiotechnology, drug delivery systems,biocompatible implants, single cell analysis andmanipulation
• Nanomaterials: nanomaterials for structuraltasks (polymers, ceramics, metals)
“The potential for nanotechnology applied tocatalysis and to local reactions (lab on a chip)
offers further fields of developments.
8 88Nanoscience and Catalysis 888
Dispersion
Why Nano
5 nm 10 nm
Autoreduction
After Catal. Ar 673 K
Ru clusters in zeolite Y:
Synthesis ex ion-exchanged Ru-red.
Thermal activation up to673 K.
Use in ammonia synthesisfor 400 h.
9 99Nanoscience and Catalysis 999
Why Nano ?
Catalytic sites operatebest (selective) whenthey are isolated fromeach other to limitexchange of electronsand adsorbates:
by defaultnanostructuredfunctional materials
2 nm
Site Isolation
10 1010Nanoscience and Catalysis 101010
Size Effects in Catalysis
0
2
4
6
8
10 100 1000 10000
Number of Atoms
Siz
e [n
m]
0
0,05
0,1
0,15
0,2
10 100 1000
Number of valence electronsE
nerg
y ga
p (e
V)
0102030405060708090
100
3 5 7 9
Size [nm]
Con
vers
ion
[%]
C Au/OxideC Au/C
Selective oxidation of glycol to glyoxalwith air (Haruta et al.)
It is not the ground state electronic structurethat matters
Sizeparameter:
37,5
11 1111Nanoscience and Catalysis 111111
Nanocatalysis10 nm
2 nmWorking hypothesis:
The “nanoeffect” is the kinetic stabilisation ofmetastable materials containing or representingthe active sites. The extent of stabilisation issize-dependent (surface free energy vs.cohesion energy).
It is not size that matters but a local metastablestructure the existence of which under reactionconditions is linked to “size”.
12 1212Nanoscience and Catalysis 121212
Cs - HPAActive state - HPA
Hydrated - HPA
Dehydrated - HPA
HPA: A metastable phase
13 1313Nanoscience and Catalysis 131313
0.01 0.02 0.03
0 1 2 3 4 5
FT
(c(k
)*k3 )
R, (Å)
T, (K)
773 773
700
600
500
400
Cs3[PMo12O40]*xH2O
0.01 0.02 0.03 0.04
0 1 2 3 4 5 F
T(c
(k)*
k3 ) R, (Å)
T, (K)
773 773
700
600
500
400
Cs2H[PMo12O40] *xH2O
„Migration“ of Mo from the Keggin-Anion – in situ XAS
10% propene /10% oxygen
14 1414Nanoscience and Catalysis 141414
In-situ functional analysis: Transformation essential
O + H2O + O2
MOx Cs2H[PMo12O40]
1.98
2.00
3.42
3.44
3.46
3.74
3.76
0.0
373 473 573 673 773
Dis
tanc
e R
, (Å
)
Temperature, (K)
MS
signal Acrolein (m/e = 56)
Mo – O
Mo – Moc
Mo – Moe
1.0
15 1515Nanoscience and Catalysis 151515
The Combicat M Approach• Replace post-synthetic
defectation by planfulsynthesis of structurallycomplex but chemicallysimple materials.
• Compromise betweenstability underapplication andreactivity for controlledfunctionalisation.
Deactivation tobulk ortho-MoO3
MoO4-2
polymolybdates
Homo-polymer Hetero-polymer
Stabilisation by condensation or supporting into nanostructures
Ball - milling Hydrothermal regeneration
16 1616Nanoscience and Catalysis 161616
MoO3 for selective oxidation?
A syntone
17 1717Nanoscience and Catalysis 171717
Control of Solid Formation[Mo]
pH
T
Hx[MopOq]n-x
[Mo7O24]6- [Mo8O26]4-
H2[MoO4]
[Mo2O10]8-[Mo3O14]10-
supramolecular hex
A
B
C
D
E
[Mo36O112]8-[Mo12O40]8-
0 1 2 3 4 5 6-0,02
0,00
0,02
0,04
0,06
0,08
0,10
0,12
0,14
0,16
dpH
/dV
pH
18 1818Nanoscience and Catalysis 181818
5 nm 5 nm
Control of Nanostructure
19 1919Nanoscience and Catalysis 191919
Nano and HTHEReaction Control
Ratio [Mo] : [H2O]Ratio [Mo] : [H3O+]
[] structure-directing cations[] complexing agents for cations
Redox potential of solution
Rate of additionMode of addition
Reactor sizeStirring (speed)
Mode of reaction: decreasing, constant, overflow
Temperature
thermodynamic
Intrinsic parameters
coupling
kinetic
Extrinsic parameters
20 2020Nanoscience and Catalysis 202020
Nano and HTHE
Ageingwashing
DryingCalzination
Cationcomposition
Anioncomposition
Extrinsicvariables
PresentHTHE
21 2121Nanoscience and Catalysis 212121
Nanostructuring by PVDPt(111) substrate
Evapoartion of iron
Pt (111) substrate
43
Repeated evaporation and oxidation
of iron
Fe O (111)Pt(111) substrate
32a
Oxidation in 1 - 10-4 mbar O2 at 970-1100 K
-Fe O (0001)
Pt(111) substrate
Oxidation in 10 -10 mbar O2 at 870-1000 K
FeO(111)Pt(111) substrate
-6 -7
Iron
Oxygen
A
B
C
D
22 2222Nanoscience and Catalysis 222222
Models for UnderstandingTurn over frequencyCatalyst
1.0 x 10-3 molecules/site.s.(2)
- Technical catalyst
5.0 x 10-4 molecules/site.s.(1)
-Polycrystaline iron oxide
6.6 x 10-4 molecules/site.s-Single crystal modelcatalyst
(1) K. Coulter, D. W. Goodman, and R. G. Moore, Catal. Lett. 1995, 31, 1.(2) T. Hirano, Appl. Catal. 1986, 26, 119.
200 400 600 800
O1209201Fe2O3 b rxn
dN/d
E
Energy (eV)
Before
after
Fe
OC
O
Fe
200 400 600 800
dN
/dE
Energy (eV)
0 50 100 150 200
0.0
0.2
0.4
0.6
0.8
1.0
1.2
% C
onve
rsio
n
Time (min)
StyreneFe2O3
23 2323Nanoscience and Catalysis 232323
From Understanding to Mastering
500x450A
0
20
40
60
80
100
0 200 400 600 800 1000Time on stream, min
Eth
ylb
enze
ne
con
vers
ion
s, %
KFe2O3 MWNTs arc d.
24 2424Nanoscience and Catalysis 242424
What about nanocatalysis
• A.T. Bell: …Together with novelapproaches to nanoparticle synthesis thisknowledge (about catalyst function fromin-situ analysis) is contributing to thedesign and development of new catalysts.(Science 2003, 299, 1688)
• G. A. Somorjai: New synthetic methods ofcatalyst preparation are required forprecise control of size, structure,location…… (Appl. Catal. A, 2001, 222, 3)
25 2525Nanoscience and Catalysis 252525
Nanocatalysis: A New Paradigm
Understanding catalysis as a functional systemwith higher complexity than one elementaryreaction (the rds).
Respecting its dynamics given by theinteractions catalyst-reactants and catalyst-reactor (models?).Science of synthesizing (not preparing) and
functionally characterizing a dynamicalsupramolecular material.
26 2626Nanoscience and Catalysis 262626
Nanocatalysis: A Knowledge-basedApproach
Not a “size effect” (nothing new)
But a transition from
Finding a catalyst (by trial and error)
To
Mastering a catalyst (designing)
With (theoretically) pre-determined properties
27 2727Nanoscience and Catalysis 272727
complexity
system descriptor (p,T,[])
„practical“ catalyst
-reactive-
single crystal
-well defined-
additional model systems
choice? pragmatic
In-situ analysis
Functional definition
Structural definition