1. Lecture 24
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.

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

3. Last Lecture Catalytic Reforming Reaction (Gasoline)
Normal Pentane Octane Number=62
Iso-Pentane Octane Number=90
Normal Pentane  Iso-Pentane

5. Steps in a Catalytic Reaction

6. Ethylidyne as chemisorbed on platinum (Adapted from G. A
Ethylidyne as chemisorbed on platinum (Adapted from G.A.Somorjai, Introduction to Surface Chemistry and Catalysis, Wiley, New York, 1994)

7. Steps in a Catalytic Reaction
Adsorption on Surface
Surface Reaction
Single Site
Dual Site
Desorption from Surface

8. Platinum on alumina (Figure from R. I
Platinum on alumina (Figure from R.I. Masel, Chemical Kinetics and Catalysis, Wiley , New York, 2001, p 700)

9. n-pentane i-pentane
0.75 wt% Pt
Al2O3
n-pentane n-pentene
-H2 Pt
Al2O3
i-pentene
+H2
i-pentane
n-pentene i-pentene
Al2O3
N I

11. 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.

12. 2. Assume a rate-limiting step
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

13. 3. Find the expression for concentration of the adsorbed species CI. S
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

14. 4. Write a Site Balance.
5. Derive the rate law. Combine steps 2, 3 and 4 to arrive at the rate law:

18. Automotive Catalytic Converters
Placed inline with exhaust system (~$500)
NOx plays big role in smog formation

19. Automotive Catalytic Converters
1) Propose a mechanism

20. Automotive Catalytic Converters
(from graph data, we see CO2 is not on the surface and that the surface reaction is irreversible)

21. Automotive Catalytic Converters

22. Automotive Catalytic Converters
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

23. Automotive Catalytic Converters
optimum

25. End of Lecture 24