Chemical Reaction Engineering (CRE) is the field that studies the rates and mechanisms of

chemical reactions and the design of the reactors in which they take place.

Lecture 24

Today’s lecture   Normal Pentene Iso-Pentane   Langmuir Adsorption Isotherm   Catalytic Converters for Automobiles

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Last Lecture   Catalytic Reforming Reaction (Gasoline)

 Normal Pentane Octane Number=62   Iso-Pentane Octane Number=90  Normal Pentane Iso-Pentane

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Steps in a Catalytic Reaction

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Steps in a Catalytic Reaction

Adsorption on Surface

Surface Reaction Single Site

Dual Site

Desorption from Surface

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n-pentane i-pentane 0.75 wt% Pt

Al2O3

n-pentene i-pentene Al2O3

N I

n-pentane n-pentene -H2

Pt

Al2O3 i-pentene

+H2

Pt i-pentane

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Isomerization of n-pentene (N) to i-pentene (I) over alumina

N I Al2O3

1. Select a mechanism (Mechanism Dual Site)

Adsorption on Surface:

Surface Reaction:

Desorption:

Treat each reaction step as an elementary reaction when writing rate laws.

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2. Assume a rate-limiting step. Choose the surface reaction first, since more than 75% of all heterogenous reactions that are not diffusion-limited are surface-reaction-limited. The rate law for the surface reaction step is

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3. Find the expression for concentration of the adsorbed species CI.S. Use the other steps that are not limiting to solve for CI.S (e.g., CN.S and CI.S). For this reaction,

From

From

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4. Write a Site Balance.

5. Derive the rate law. Combine steps 2, 3 and 4 to arrive at the rate law:

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Placed inline with exhaust system (~$500)

NOx plays big role in smog formation

Automotive Catalytic Converters

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1) Propose a mechanism

Automotive Catalytic Converters

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(from graph data, we see CO2 is not on the surface and that the surface reaction is irreversible)

Automotive Catalytic Converters

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Automotive Catalytic Converters

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Is this consistent with the given data?

-No CO2 in rate law

-rate law decreases as PN2 increases

The contribution of PN2 is very small and can be neglected

Automotive Catalytic Converters

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optimum

Automotive Catalytic Converters

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End of Lecture 24

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