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Heterogeneous Catalysis& Solid State Physics

Dohyung Kim

May 2, 2013Physics 141

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Catalysis

Catalysis : Increase in the rate of reaction due to a catalyst

!y"es o# Catalysts

1) Homogeneous : Catalyst and Reactant in the same phase

2) Heterogeneous : Catalyst and Reactant in different phases

http://www.chemguide.co.uk/http://www.chemguide.co.uk/

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Catalysis

!y"es o# Catalysts1) Homogeneous : Catalyst and Reactant in the same phase

e.g.) Organometallic Compounds

2) Heterogeneous : Catalyst and Reactant in different phases

e.g.) etal !urface

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Heterogeneous Catalysis

$lementary ste"s in heterogeneous catalysis

dsor"tion o# reactants

%eaction o# adsored intermediates

Desor"tion o# "roducts

dsor"ti'e "ro"erty o# a catalyst ( Catalytic acti'ity

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D)and Model*Chemisor"tion+

$lectronic structure o# transition metal

nteraction et-een energy le'els

0dsor$ate 0dsor$ate

road $and arro3 $and

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D)and Model*Chemisor"tion+

.ormation o# a chemical ond

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D)and Model*Chemisor"tion+

ariation in adsor"tion energies1) 7ifferent etal catalysts

8&4e')

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D)and Model*Chemisor"tion+

ariation in adsor"tion energies2) 7ifferent 9acets

e) 9CC

/and idth*+ s5rt*6+

Decreasing tomic Density

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D)and Model*Chemisor"tion+

ariation in adsor"tion energies() 0lloying

Control o# reacti'ty through catalyst de"osition

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olcano Cur'e

#lot of reaction rate "s property of a catalyst

4e.g. Heat of adsorption)

olcano Sha"e

!a$atier #rinciple : =he interaction $et3een the

catalyst and the su$strate should $e ?ust right@

A Case of decomposition of formic acid on transition metals

cti'ity related to 'arious "ro"erties o# a catalyst, mostly ul "ro"erties7

!he most #undamental "arameter 8

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/ronsted)$'ans)Polanyi*/$P+ relation

inear relationship $et3een the acti"ation energyand dissociati"e chemisorption energy

&a4D&ts) D a8& E $

02E 2 A F 2 0A

02E 2 A

2 0A

&a

8&

Dissociati'e chemisor"tion energy determines the catalytic acti'ity 9

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Sim"le Kinetic Models

7issociati"e adsorption as R7! 3ithout strongly adsor$ed 02

7issociati"e adsorption as R7! 3ith strongly adsor$ed 02

7issociati"e adsorption as R7! follo3ed $y rn 3ith strongly adsor$ed

A R7! : Rate/determining step

2: 2/ ; 2/

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Sim"le Kinetic Models

Dissociati'e adsor"tion as %DS -ithout strongly adsored 2

0ssumption : Co"erage of 02and on the surface is negligi$le

&> 0mmonia synthesis

Ste" 1 ) 2: 2< ; 2