I have just written a practice research paper on gold nano particle catalysis which was an interesting topic. The catalysts are easy enough to prepare in a lab but If you at school I'm not sure what sort of characterisation you would be able to do on them.
When I was at school I had to do an essay on the reaction between calcium carbonate and hydrochloric acid. When you put the carbonate into the acid CO2 is released, the amount per unit time of which you can measure. You can then change certain factors and see how the rate of reaction is effected. I think the usual thing to change is the conc of the acid and the size of the carbonate, powdered carbonate will react faster than big lumps of if. That would be a good one to do; I don't know if it will be a bit easy though.