burned up after cat oxygen sensor and burned out catalytic convertor

1996 geo 1.0 engine,pulled oxygen sensor after cat and found both the sensor burned in half and catalytic convertor empty replaced both and went four cyclinder size catlytic convertor..still wondering what happened...help thanks

Oh, BOTH sensors were burnt up. Sounds to me like you have some leaky valves shooting flames down the exhaust! heh. Exhaust gas temperatures won't melt an o2 sensor like that. Not even a turbocharger. They were either intentionally burnt off, and the cat removed, or you have some really bad valve leakage, and gasoline is still burning as it's leaving the engine.

only the oxygen sensor after the catalytic was burned about a quarter of inch gone and the inside of the cat itself burned out thanks

I did some research on this, and here's what I came up with.
People use octane booster to get a little extra power. Knowing most metros are pretty gutless, i'm sure the previous owner put plenty in. Or, if he's an old-schooler, he could have put moth balls in the tank. Some moth balls contain a hydrocarbon called naphthalene. If you drop these moth balls into your gas tank, it may give you a boost. I don't know personally. The only octane boosting I use is Turbo Blue 110 straight from the pump. The naphthalene itself won't harm your car at all. It will burn straight through, just like the gasoline. He may have just heard that moth balls give you octane, and started throwing dichlorobenzene moth balls in. If you burn dichlorobenze, you add chlroine to the mix. And when you oxidize(burn) chlorine, and hydrocarbons, you get our good friend, HCl(Hydrochloric acid). Now, as we all know, HCl will eat just about anything except glass. The cat, and the o2 sensors are both very sensitive to HCl, because they are made with precious metals which react very easily to acids. This may explain why your cat is empty, and your o2 sensors are apparently burnt away.