I agree with Glacier saying "Your puppy needs to be firmly and consistently told NO when he chases a cat. He should be kept leashed or crated until he learns not to chase."

Smokey & Maggie were always on leash in the house when
they were first introduced to the kitties until they learned this
lesson. It's really best to teach the dog that harassing the cat
is a no no. I wouldn't wait to let them "work it out". It's too
dangerous to do that.