10.37 Chemical and Biological Reaction Engineering, Spring 2007
Prof. William H. Green
Lecture 16: Catalysis
This lecture covers: Inorganic and enzyme catalysis and their properties; kinetics of
heterogeneous catalytic reactions; adsorption isotherms, derivation of rate laws; and
Langumuir-Hinshelwood kinetics
What initiates the reaction?
A + B → starts upon mixing
B
A
Product
Figure 1. Bi-molecular reaction in a CSTR.
Temperature drastically increases reaction rate.
Hot
C2H6
Rxn occurs
Fire
Figure 2. Schematic of tube reactor.
Catalyst dramatically increases reaction rate.
A
catalyst
Figure 3. Schematic of packed bed reactor.
Catalyst: Accelerates rate of reaction but is not consumed
Cite as: William Green, Jr., course materials for 10.37 Chemical and Biological Reaction Engineering,
Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu), Massachusetts Institute of Technology.
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transition state
E
reactants
~Ea
products
rxn coordinate
Figure 4. Reaction diagram.
rate constant:
k BT
⎡ (G − Greactants ) ⎤
exp ⎢ − ts
⎥
h
RT
⎣
⎦
G = H − TS
k=
e − G / RT = e− H / RT e S / R
no catalyst
E
with catalyst
rxn coordinate
Figure 5. Reaction diagram with and without catalyst.
The reaction forms many intermediates. A catalyst lowers the energy of these
intermediates.
Acid/Base catalysis
ROR + H 2O → 2ROH
k1
ROR + H ⊕
k−1
H
H
ROR
⊕
k2
ROR → ROH + R ⊕
⊕
k3
R ⊕ + H 2O → ROH + H ⊕
10.37 Chemical and Biological Reaction Engineering, Spring 2007
Prof. William H. Green
Lecture 16
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H
ROR , R ⊕
QSSA
⊕
⎡ H ⎤
d ⎢ ROR ⎥
H
⊕
⎦ = k ⎡ H + ⎤ ROR − (k + k ) ⎡ ROR ⎤
O≈ ⎣
[
]
⎢
⎥
−
1⎣
1
2
⎦
dt
⎣ ⊕ ⎦
⎡ H ⎤
k1
⎡⎣ H + ⎤⎦ [ ROR ]
=
⎢ ROR
⎥
⊕
k
k
+
−1
2
⎣
⎦ QSSA
d [ ROH ]
dt
⎡ H ⎤
= 2k2 ⎢ ROR ⎥
⎣ ⊕ ⎦ QSSA
d [ ROH ]
2k1k2
⎡⎣ H + ⎤⎦ [ ROR ] = r
≈
dt
k−1 + k2
rA ∼ [ A]
rA ∼ [ catalyst ]
(where ∼ denotes “proportional to”)
N +
⎡ H ⎤
⎡⎣ H + ⎤⎦ + ⎢ R O R ⎥ + ⎡⎣ R + ⎤⎦ = H added = ⎡⎣ H + ⎤⎦
added
⊕
V
⎣
⎦
⎛ k [ ROR ]
⎞
k1k2 [ ROR ]
⎡⎣ H + ⎦⎤ ⎜1 + 1
= ⎣⎡ H + ⎦⎤
+
⎟
⎜
⎟
added
k1 + k2
k3 (k−1 + k2 ) [ H 2O ] ⎠
⎝
r=
r=
keff [ ROR ] ⎡⎣ H + ⎤⎦
1+ k [ ROR ]
added
k [ catalyst ] [ A]
1+ k A [ A] + k B [ B ] + ...
All the things that the
catalyst binds to
Langmuir-Hinshelwood: all reagents bind to catalyst, bound forms react
Eley-Rideal: one reagent binds, 2nd reagent reacts with bound form
dN A
= VrA
dt
f
([ A] , ⎡⎣ H ⎤⎦ )
+
10.37 Chemical and Biological Reaction Engineering, Spring 2007
Prof. William H. Green
Lecture 16
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moles
dN A
= ( area of
dt
metal
) rA′′
area s
f (θ A )
where
θA =
N A bound
N total sites
on surface
10.37 Chemical and Biological Reaction Engineering, Spring 2007
Prof. William H. Green
Lecture 16
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Cite as: William Green, Jr., course materials for 10.37 Chemical and Biological Reaction Engineering,
Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu), Massachusetts Institute of Technology.
Downloaded on [DD Month YYYY].