Chemistry coursework help?

I'm basing my coursework upon the rates of reaction of the "Iodine clock" experiment reacting Pottasium Iodide with SodiumThiosulphate and Potassium Peroxodisulphate. The Peroxidisulphate ions oxidise the iodide ions to form iodine in aqueous soln. while the thiosulphate ions turn the iodine back into iodide ions, once all the thiosulphate ions are used up, the reaction soln. turns black/blue almost instantaneously as the iodine reacts with the starch (also in the soln. but playing no active part in the reaction). I am still at the planning stage, and no matter how much I research I can't find a suitable catalyst(s) to test and compare, my teacher hinted towards transition metals but I wouldn't know how they act as catalysts or whether I would use a transitional metal by itself as a heterogenous catalyst or perhaps as a complex of some sort in soln. as a homogenous catalyst.
I'm probably missing something really obvious here, and if so I apologise. But any help at all would be much appreciated!