There are more than onel Pemex stations in PV, but I am guessing you are talking about the one up on route 200 next door to the canopy tour office.
If so, yes it can be walked from the Trop, about 20 to 30 minutes depending on how fast you walk or wheather you stop to see the sights (which there are quite a few interestint restaurants, bars and shops you should check out along this walk).
Or if you are in a hurry, a taxi should be about 30 to 35 pesos.