No, they are secondary cats. I'm not really sure why they are necessary, but they are there. Normally, a secondary cat is suppose to clean whatever is remaining after the main cats, but the function of the main cats is to clean up small amounts left after combustion. If the other emission controls are functioning properly and the engine is maintained there should not be much even hitting the primary cats so really the secondaries shouldn't be doing anything at all.

What i'm still unsure of is how much workload the secondary cats can take. If their normal duty is to clean up remains then what happens if they are the first line of defense? Can they handle that?