CHEE 323 J.S. Parent 1

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, and had quite enough of Dr. Parent’s ramblings.

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 J.S. Parent 2

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 be asked to 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 J.S. Parent 3

Catalytic Reaction Kinetics

We define a catalyst as a substance that increases the rate of approach to equilibrium of a 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 which this state is reached.

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 J.S. Parent 4

Catalytic Activity

The addition of molecular hydrogen to an olefin such as ethylene is a highly favourable reaction from a thermodynamic standpoint.

Gfo (kJ/mole)

C2H6 -32.9 C2H4 68.1 H2 0

Goreaction -101.0

Keq= exp(-Go/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.

33222 CHCHHCHCH

CHEE 323 J.S. Parent 5

Catalytic Activity

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 J.S. Parent 6

Catalytic Activity

In addition to bonds from sp2 orbital overlap, combination of p-orbitals leads to -molecular orbitals, both bonding and anti-bonding. LUMO

HOMO

CHEE 323 J.S. Parent 7

Catalytic Activity

In-phase orbital overlap results in a lowering of the ground stateenergy of the system, andhence, leads to bonding.

The approach of asymmetricorbitals (+ve, -ve) leads to nonet positive overlap, and thereaction is symmetry forbidden.

Direct addition of H2 to ethylene through a four-centre transition state is symmetry forbidden, as the bonding orbital of hydrogen (HOMO) and the antibonding * orbital of the olefin (LUMO) cannot overlap effectively.

Consequently, the rate of hydrogenation by this mechanism is extremely small, and a catalyst is required.

LUMOof olefin

HOMOof H2

CHEE 323 J.S. Parent 8

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 J.S. Parent 9

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 J.S. Parent 10

CHEE 311 - Course Outline

1. Catalytic Reaction Kinetics Restrictions imposed by thermodynamics Collision and transition state theory for elementary reactions Formulating kinetic rate expressions from reaction

mechanisms

2. Homogeneous Catalysis by Organometallic Complexes Structure and reactivity of organotransition metal complexes Olefin hydrogenation, hydroformylation, polymerization and

metathesis; -C-H bond activation

3. Surface Catalysis Structure of heterogeneous catalysts Catalytic reactions of functionalized surfaces Catalysis on metal surfaces and supported metals Metal oxide catalyzed reactions

CHEE 323 J.S. Parent 11

CHEE 311 - Course Outline

5. Acid-Base Catalyzed Reactions General and specific acid and base catalysis Hydrocarbon conversion Highly-Ordered Solid Catalysts - Zeolites and Clays Steric and transport effects

6. Enzyme Catalyzed Reactions Nature of the catalytic site of enzymes Enzyme encapsulation Mass transfer effects in encapsulated systems

Design Project Topics:1. Olefin hydroformylation for soap production2. Catalytic converter design for a lawn mower