Homogeneous Catalysis HMC Dr. K.R.Krishnamurthy National Centre for Catalysis Research Indian Institute of Technology, Madras Chennai Homogeneous Catalysis- 1 Basics Homogeneous Catalysis- General features Metal complex chemistry- Metals & Ligands bonding & reactivity Reaction cycles Reaction types/ Elementary reaction steps Kinetics & Mechanism Catalysis 1850 Berzelius 1895 Ostwald: A catalyst is a substance that changes the rate of a chemical reaction without itself appearing into the products Definition: a catalyst is a substance that increases the rate at which a chemical reaction approaches equilibrium without becoming itself permanently involved. Catalysis is a kinetic phenomenon. Obeys laws of thermodynamics Catalysis Types Heterogeneous Homogeneous Enzymatic/Bio Photo/Electro/Photo-electro Phase transfer Homogeneous Catalysis Reactions wherein the Catalyst components and substrates of the reaction are in the same phase, most often the liquid phase Mostly soluble organometallic complexes are used as catalysts Characterized by high TON & TOF Operate under milder process conditions Amenable to complete spectroscopic characterization Homogeneous processes without a heterogeneous counterpart: Pd-catalyzed oxidation of ethylene to acetaldehyde (Wacker process) Ni-catalyzed hydrocyanation of 1,3-butadiene to adiponitrile (DuPont) Rh- and Ru-catalyzed reductive coupling of CO to ethylene glycol Enantioselective hydrogenation, isomerization, and oxidation reactions. Catalysis- Heterogeneous Vs Homogeneous AspectHeterogeneousHomogeneous Activity Reproducibility Comparable Difficulty in reproducibility Comparable Reproducible results SelectivityHeterogeneous sites. Difficult to control selectivity Relatively higher selectivity, easy to optimize, various types of selectivity Reaction conditionsHigher temp. & pressure, better thermal stability Lower temp. (