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It wouldn't keep the at alive in terms of the cat being destroyed. . .it keeps the cat active.
I think I made a note of this, but maybe it was on another thread. To get by EPA you can't have any arguments like "well the car is really not producing any HCs in this mode so it doesn't need a cat during this. . ."
They slap you with a fail and send you packing. So Honda had to ensure that the cat stays up at operating temps. During LB EGTs are higher but the cat is going to be acting like a huge exhaust radiator. Its a big metal box with lots of wind exposure and no HCs are getting burnt inside so its surviving in the operating range only by the higher EGTs. To ensure to the EPA's satisfaction that the cat stays hot enough to burn the one in a million HC that slips through the engine unburnt it has to kick out of lean burn to reheat the cat.
It won't damage the cat to run at low temperature(assuming there are no HCs in the exhaust flow, otherwise its going to get covered in soot).
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