Briefly define a homogenous catalyst? Help please!?
A homogenous catalyst is in the same phase as the rxn it is catalyzing. Most people think of catalysts as heterogenous: either sold (cat) liquid (rxn) (Raney Ni hydrogenation) or solid (cat) gas phase rxn) (catalytic convertors, NH3 production, SO2 oxidation, nitric acid production) polyethylene synthesis with Ziegler Natta catalysts. (Wikipedia). However starting probably with the Wilkinson hydrogenation catalyst Rh(PPh3)3Cl in 1966 a whole field of homogeneous catalysis has develope where the catayst is in soln. It proved to be a Renaissance for Inorg chem. These catalysts have several advantages over heterogenous catalysts: take place under mild conditions (green chem); the mechanisms are usually understood and can therefore be modified to be extremely specific for a substrate. There have been several Nobel Prizes in this area in the last decade because of their importance in organic synthesis: 2010, 2005, 2001. The one type of homolytic gas phase catalysis rxn I can think of are those that involve a radical chain mechanism: destruction of O3 by Cl? and chlorination (bromination) of alkanes.
