CONTENTS

Front Matter

Title Page, Preface and Acknowledgements
About the Author
Status, History, Issues and Updates
Complementary Textbooks
Teaching Notes and Resources
A Note about Numerical Solutions

Course Units

I. Chemical Reactions
1. Stoichiometry and Reaction Progress
2. Reaction Thermochemistry
3. Reaction Equilibrium
II. Chemical Reaction Kinetics
A. Rate Expressions
4. Reaction Rates and Temperature Effects
5. Empirical and Theoretical Rate Expressions
6. Reaction Mechanisms
7. The Steady State Approximation
8. Rate-Determining Step
9. Homogeneous and Enzymatic Catalysis
10. Heterogeneous Catalysis
B. Kinetics Experiments
11. Laboratory Reactors
12. Performing Kinetics Experiments
C. Analysis of Kinetics Data
13. CSTR Data Analysis
14. Differential Data Analysis
15. Integral Data Analysis
16. Numerical Data Analysis
III. Chemical Reaction Engineering
A. Ideal Reactors
17. Reactor Models and Reaction Types
B. Perfectly Mixed Batch Reactors
18. Reaction Engineering of Batch Reactors
19. Analysis of Batch Reactors
20. Optimization of Batch Reactor Processes
C. Continuous Flow Stirred Tank Reactors
21. Reaction Engineering of CSTRs
22. Analysis of Steady State CSTRs
23. Analysis of Transient CSTRs
24. Multiple Steady States in CSTRs
D. Plug Flow Reactors
25. Reaction Engineering of PFRs
26. Analysis of Steady State PFRs
27. Analysis of Transient PFRs
E. Matching Reactors to Reactions
28. Choosing a Reactor Type
29. Multiple Reactor Networks
30. Thermal Back-Mixing in a PFR
31. Back-Mixing in a PFR via Recycle
32. Ideal Semi-Batch Reactors
IV. Non-Ideal Reactions and Reactors
A. Alternatives to the Ideal Reactor Models
33. Axial Dispersion Model
34. 2-D and 3-D Tubular Reactor Models
35. Zoned Reactor Models
36. Segregated Flow Models
37. Overview of Multi-Phase Reactors
B. Coupled Chemical and Physical Kinetics
38. Heterogeneous Catalytic Reactions
39. Gas-Liquid Reactions
40. Gas-Solid Reactions

Supplemental Units

S1. Identifying Independent Reactions
S2. Solving Non-differential Equations
S3. Fitting Linear Models to Data
S4. Numerically Fitting Models to Data
S5. Solving Initial Value Differential Equations
S6. Solving Boundary Value Differential Equations

Unit 10. Heterogeneous Catalysis

This website provides learning and teaching tools for a first course on kinetics and reaction engineering. The course is divided into four parts (I through IV). Here, in Part II of the course, the focus is on chemical reaction kinetics, and more specifically, on rate expressions, which are mathematical models of reaction rates. As you progress through Part II, you will learn how rate expressions are generated from experimental kinetics data.

This first section of Part II of the course focuses upon the selection of an equation to be tested as a rate expression. The equation to be tested can be chosen simply for its mathematical convenience. Alternatively, theory can be used to select the mathematical form of the equation to be tested. For some reactions, theory can be applied directly. In other cases the reaction must be described in terms of a group of reactions that comprise what is known as a reaction mechanism. In the latter case theory can be applied to the reactions in the mechanism which are then combined to get the mathematical form of the equation to be tested.

The most common type of heterogeneous catalysis involves gas phase reactants and products and a solid catalyst. The mechanistic steps in such a reaction typically take place on the surface of the catalyst. This unit shows how the rates of these reactions can be modeled using the fractional coverage of the surface by the various species in place of surface concentrations. Similarly, the conservation of catalyst can be expressed in terms of fractional coverages instead of concentrations. With these modifications, the methods considered in previous units for generating a rate expression from a mechanism can be applied to heterogeneous catalytic reaction mechanisms. The unit also shows that if the most of the catalyst surface is covered by one species, then the mechanistic rate expression can be simplified considerably. The unit also offers a comparison of Michaelis-Menten rate expressions for enzymatic reactions to Langmuir-Hinshelwood rate expressions for heterogeneous catalytic reactions.

Learning Resources

Teaching Resources

Practice Problems

1. Suppose that the gas phase conversion of A to B is heterogeneously catalyzed and the mechanism is given by reactions (1a) through (1c). In addition, suppose that gas phase species Z adsorbs reversibly on the catalyst as given in equation (1d). Derive an acceptable expression for the rate of generation of B taking place in the presence of Z. Your rate expression should not include any surface coverages.

  A + ⁕ ↔ A-⁕ (1a)  
  A-⁕ ↔ B-⁕ (1b)  
  B-⁕ ↔ B + ⁕ (1c)  
  Z + ⁕ ↔ Z-⁕ (1d)  

(Problem Statement as .pdf file)

2.* Assume that methane partial oxidation, equation (2), takes place on a metal catalyst according to the simplified mechanistic scheme given in equations (2a) through (2d). Step (2c) may be assumed to be the rate-limiting step. Develop a rate expression for the overall reaction in terms of only the concentrations of the gas phase species (methane, oxygen, and methanol) and the equilibrium and rate constants. If it is assumed that the surface of the catalyst is almost completely covered with adsorbed O (which is the most abundant surface intermediate), how does this simplify the rate expression? Comment upon the result.

  2 CH4 + O2 → 2 CH3OH (2)  
  CH4 + ⁕ ↔ CH4-⁕ (2a)  
  O2 + 2 ⁕ ↔ 2 O-⁕ (2b)  
  CH4-⁕ + O-⁕ → CH3OH-⁕ (2c)  
  CH3OH-⁕ ↔ CH3OH + ⁕ (2d)  

(Problem Statement as .pdf file)

* This problem introduces something new that wasn't encountered in the informational or illustrational readings and videos.