CHEE 323 - Objectives

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. 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. 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. 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. • DGfo (kJ/mole) • C2H6 -32.9 • C2H4 68.1 • H2 0 • DGoreaction -101.0 • 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. 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 J.S. Parent

6. Catalytic Activity • 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 J.S. Parent

7. Catalytic Activity • 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 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. 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 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 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 production • 2. Catalytic converter design for a lawn mower J.S. Parent