Could it be the Catalytic Converter?

Hello, What are the diagnostic trouble codes (DTC's) you are seeing? When a DTC pops up, it does not say what to change, it says what has gone wrong. DTC's are clues, not maps, so replacing whatever part is most closely related will just cost money and time. If you have an emissions error, replacing all the O2 sensors will only help if all of the O2 sensors are bad, but there are a host of other issues that can cause the engine to run inefficiently. This would result in the O2 sensors saying "hey, we have a problem". Let me know what codes you have, and avoid throwing parts at the problem without a diagnosis.