Heterogeneous Catalysis Thoughts and Insights Robert Schlögl.
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Transcript of Heterogeneous Catalysis Thoughts and Insights Robert Schlögl.
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Heterogeneous CatalysisThoughts and Insights
Robert Schlögl
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Dept. AC, Fritz-Haber-Institut(MPG), Berlin
Study of catalysis is key to the ability to manufacture structural and functional materails
Catalysis and Industry
Automotive Industry
Chemical Industry
Life science
Power generation
Chemical Engineering
Catalysis
Catalyst manufactur
e
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Where do you find catalysts
• Selten im Alltag direkt:– Autoabgaskatalysator– Backofenreiniger (Plastiktüte)
• Manchmal indirekt mit Produkten der chemischen Industrie– Dünger– Styropor– Treibstoffe
• Meist überhaupt nicht, da die Produkte der chemischen Industrie die Ausgangsmaterialien aller anderen Industrien sind.
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Catalysis and Technology
• Mit (heterogener) Katalyse werden über 90% aller Chemikalien hergestellt
• Ohne Chemikalien gibt es keine– Computer, elektronische Produkte– Speichermedien (CD, MC, HDD)– Medikamente– Kunststoffe (und Folgeprodukte)– Farben und Lacke– Life sciences
• Ohne Katalyse gibt es keine Mobilität (Treibstoffe)
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Catalysis and Economy
Wirtschaftlich fundamental wichtig:• 16 %deutschen BSP (100 G€): chemische
Industrie (90% Katalyse) (excl. Petrochemie)• Weltmarkt Katalysatoren: 10 G€ (D etwa 10%)• Weltmarkt der damit erzeugten Produkte: 500 G€• „Strategische“ Technologie, etwa 15 Hersteller
weltweit, einige nur „in-house“
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Catalysis and Chemical Feedstocks
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Catalysis: a mature science?
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Dept. AC, Fritz-Haber-Institut(MPG), Berlin
Catalysis and Science
Interdiciplinarity
Materials science
Physical Chemsitry
Surface science
EngineeringSynthetic Chemistry
Inorganic
Catalysis
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History of Concept
Berzelius 1920
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History of Concept
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The active site
Catalysts are:
defective
non-equilibrium states
under kinetic control (dynamic)
They are not:
well-ordered
static
uniform or homogeneous
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Microstructure of Carbon Nanotubes
Before After
Temperature 550°C
LHSV 0.5 h-1
Excess of O2 2 times
Time 20 h
EB- ODH Reaction
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Surface Science and Catalysis
• The single crystal approach:
• well-defined geometrical
• controlled or absent dynamics
• but poorly reactive in complex reactions (not studied in surface science)
• The MODEL systems
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Eisenoxid-Modellkatalysatorsysteme
FeO(111) KFe O (111)a-Fe O (0001)Fe O (111)
Christian Kuhrs, Modellkatalyse, Abt. AC, Fritz-Haber-Institut (MPG), Berlin
3 4 2 3 x y
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Model of a reacting Cu surface:Relevant and Spectating Components
3 oxygen-containing sites in addition to bare Cu metal were identified
Sub-surface atomic oxygen is further present
CO +H O2 2
CH O+H2 2O
O+ O
CH OH3
CH OH3
CH OH3
CO+H2
CH O+H2 2
O2
Cu 0
Oxsurf
Ox
bulk
Subox
Ovol
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Supported Systems
The special properties of metal particles in cataylsis become now transparent due to the „rigorous particle“ approach
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Catalysis: Complexity
multi-dimensional space-time problem
knowldege of all domains simultaneously required for understanding or even „design“ of a cataylst
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A cartoon: How works a catalyst?
Ein Katalysator enthält eine geringe Anzahl von Aktiven Zentren „active sites“, welche eine Reaktion herbeiführen können.
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The Homogeneous Reaction
Consider the reaction
2 AB A2 + B2
(e.g. NO decomposition)Inert
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The Heterogeneous Reaction
Consider the reaction
2 AB A2 + B2
(e.g. NO decomposition)
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The Catalytic Cycle
Intermediates and transition states (not shown) are usually not known
Active site
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Elementary Processes• Transport von Stoffen und Energie• Adsorption der Edukte auf der Oberfläche• Transport zum aktiven Zentrum• (Dissoziative) Aktivierung der Eduktmoleküle• Zusammentreffen der nötigen Fragmente • Elektronentausch, Bildung der Produkte• Desorption der Produkte• Rückbildung des aktiven Zentrums• Transport von Stoffen und Energie
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The active site
Atoms A, B interact differently with the catalyst.
Local perturbation of the catalyst from bonding of substrate
Range and character will depend on nature of substrate
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Catalysis: large numbers
Wir glauben, daß sich beobachtbare Mengen von chemischen Individuen alle gleich verhalten. Denken Sie an derartige Mengen menschlicher Individuen !?– 1 ml Gas enthält etwa 1x1020 Individuen– 1 cm2 Oberfläche enthält etwa 1x1015 Atome– Die Weltbevölkerung beträgt etwa 6x109
Individuen
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The active site
The chemical complexity of interactions between atoms and elemental substrates can be substantial and essential for the desired function
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The archetype MvK idea
J. Haber, 1991
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The site isolation concept
A series of ordered defects in MoO3 create site isolation by „shear defects“ (Mo18O52)
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Complexity
Die rote Untereinheit enthält als aktives Zentrum ein Metallatom, der komplexe Rest dient der räumlichen und chemischen Fixierung des Enzyms und der Adsorption des Eduktes.
Trypsin, an enzyme
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Even simple reactions may be „complex“
NO + CO
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Structure-Function Relations
Å
Å
The atomic structure of model systems transform ireversibly upon subjecting the model to the desired function
no extrapolations from ideal to real states
no methods to investigate dynamics
no basic understanding of underlying chemistry
“complexity”