It is possible that the O2 sensors and the CAT are both bad, just highly unlikely without any engine codes. I have heard that the front O2 sensor can get slow with age and covered in soot, replacing it cures all ills.

First, I would have a mechanic look for a vacuum leak. Unmetered air entering the intake manifold causes the engine to run rich, which fouls the O2 sensor.

If there are no vacuum leaks, then replace the front O2 sensor. The rear O2 sensor usually lasts much longer than the front.

Because the CAT is expensive, save that for a last resort.

Klaus
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Always willing to listen, just not able to take direction.