Sorry I don't have the answer. I had similar issue showing up, I took it to the dealer. I was pissed of, he told me that there was nothing wrong with the catalyst nor anything. It was just some erronoeus codes and that If I wanted them to go away, I have to pay $70 on the top of $95 he charged for diagnosis. I told him to get lost!
I'm not sure if it is the same pb, the problem started showing up after I lent my car to a friend for a drive and he let the gas level go low. I usually never let it go below mid level cause I know , the junk at the bottom of the tank is hurtful for the engine/pump/filter.
Anyways, now it goes and come back regularly :-(