1. Catalytic Reaction Kinetics
We define a catalyst as a substance that increases the rate of reaction without being substantially consumed in the process
note that the equilibrium condition is governed by thermodynamics, and a catalyst does not alter the equilibrium state, but the rate at reactions proceed
note also that catalysis can bring the system to a condition that is not lowest in free energy, as predicted by thermodynamics.
An initiator generates a species that supports a reaction, which may participate in a large number of substrate transformations but always has a limited lifetime.
CHEE 323

2. Catalytic Activity
The addition of molecular hydrogen to an olefin such as ethylene is a highly favourable reaction from a thermodynamic standpoint.
DGfo (kJ/mole)
C2H
C2H H
DGoreaction
Keq= exp(-DGo/RT)
= exp(101,000J / (8.314J/molK * 298K))
= 5.1*1017
In spite of this thermodynamic driving force, the direct reaction of ethylene and hydrogen does not occur at appreciable rates.
CHEE 323

3. Catalytic Activity LUMO HOMO
An examination of the molecular orbitals of ethylene and hydrogen demonstrates the reason for a low kinetic rate of hydrogenation, in spite of the large thermodynamic driving force.
LUMO
HOMO
CHEE 323

4. Catalytic Activity LUMO HOMO
In addition to s bonds from sp2 orbital overlap, combination of p-orbitals leads to p-molecular orbitals, both bonding and anti-bonding.
LUMO
HOMO
CHEE 323

5. Catalytic Activity LUMO of olefin HOMO of H2
In-phase orbital overlap results in
a lowering of the ground state
energy of the system, and
hence, leads to bonding.
The approach of asymmetric
orbitals (+ve, -ve) leads to no
net positive overlap, and the
reaction is symmetry
forbidden.
Direct addition of H2 to ethylene through a four-centre transition state is symmetry forbidden, as the bonding s orbital of hydrogen (HOMO) and the antibonding p* orbital of the olefin (LUMO) cannot overlap effectively.
Consequently, the rate of hydrogenation by this mechanism is extremely small, and a catalyst is required.
LUMO
of olefin
HOMO
of H2
CHEE 323

6. Catalytic Activity
While direct addition of H2 to an olefin is symmetry forbidden, the reaction can be facilitated
by a transition metal
complex such as RhCl(PPh3)3
1. Oxidative addition of H2 to
the metal centre,
2. Coordination of the olefin
3. Migratory insertion of the
olefin into the M-H bond,
4. Reductive elimination of the
alkane.
CHEE 323

7. Catalytic Selectivity
While olefin hydrogenation by RhCl(PPh3)3 has remarkable activity, catalytic processes are also developed for unique selectivity.
A leading example is the synthesis of Levodopa, an optically active drug generated from non-chiral starting materials for the treatment of Parkinson’s disease.
Phosphine ligand of
rhodium catalyst precursor
CHEE 323

8. CHEE 323 - Objectives On completing CHEE 323, students will have:
surveyed a wide range of catalytic reactions that are relevant to industrial practice,
integrated fundamental chemistry with principles of reaction kinetics, transport phenomena and thermodynamics,
applied this knowledge to solve “open-ended” design problems.
The resources available to help students meet these objectives are:
Lectures: serve as a guide to the course material, introduce the subject matter and highlight difficult elements of the course
Problem Sets: illustrate the course material and allow students to exercise their knowledge
“Open-ended” Design Problems: challenge students to pose their own questions and find original solutions.
CHEE 323

9. CHEE 323 - Course Outline 1. Catalytic Reaction Kinetics
Relationships between kinetics and thermodynamics
Elementary reactions and the reaction coordinate
Formulating complex kinetic rate expressions
Estimating rate parameters from experimental data
2. Free-radical and Carbocationic Chain Reactions
Process dynamics and the kinetic chain length
Design of polymerization, oxidation, alkylation, and isomerization processes
3. Enzyme Catalyzed Reactions
Structure and reactivity of catalytic proteins
Dynamics of closed-sequence, catalytic processes
Enzyme immoblization and mass transfer effects
Coping with catalyst deactivation
CHEE 323

10. CHEE Course Outline
4. Homogeneous Catalysis by Organometallic Complexes
Structure and reactivity of organotransition metal complexes
Dynamics of olefin transformations
Interfacial mass transfer in gas-liquid reactions
Heat transfer in polymerization processes
5. Heterogeneous Catalysis
Synthesis and characterization of heterogeneous catalysts
Heterogeneous reaction dynamics
Mass and heat transfer in heterogeneous processes
Catalytic combustion – automotive applications
6. Acid-Catalyzed Reactions
Hydrocarbon conversion chemistry for fuel applications
Oil refinery unit operations – design of reaction processes
Highly-Ordered Solid Catalysts - Zeolites and Clays
CHEE 323

11. Open-Ended Design Problems
These exercises allow students to engage in more design-oriented activity. Using instructors only for reference as opposed to direct guidance, groups will attempt to solve two process development problems.
A problem will be presented in the first design tutorial session, and groups will prepare a list of questions for each of three areas:
Catalytic chemistry requirements
Overall process flowsheet
Catalytic reactor design
Where possible, information relating to these questions will be provided.
Each group will submit a report (no longer than 9 pages) that details their design concept and calculations.
CHEE 323

12. Food for Thought…
Write a two paragraph article that supports one of the following statements:
The world changed from black & white to colour in 1935.
The hum that is heard upon picking up a phone receiver is the operator saying “ooooooo”
The windmills on farms are used to keep the cows cool.
The blind can read speed bumps like braille, thereby allowing them to drive.
CHEE 323