Cat urine, carpet and a very rusty floor

cat urine is acidic, baking soda is basic so it would neutralize acid to a salt. I would liberally sprinkle a box on the affected spot and let it sit, maybe agitate with a brush and then shop vac up. If it is surface rust on the pan, dump some play sand in there and rub it around and then vac that out. you want it dry and neutral before you paint it with a primer. Ozium and fabreze work great on urine odor.