Curious as to any other drivablility concerns? A very common cause of o2 sensor (lamda) and catalytic converter curruption can be a rich running condition. This can be caused by things like faulty fuel injectors,etc. Having a shop perform an injector balance test, may be a good place to start. Ignition coils (especially Coil On Plug) style are known to fail causing a rich condition as well............just a couple of thoughts.