PO420 and PO430 CEL errors after failed alternator

Hi,
My 08 4Runner SR5-V8 recently died on the side of the road, right before it died the instrument panel light up all the error lights and then everything stopped. I replaced the battery so I could get it home, (battery was almost 6 yrs old anyway) and then took it to a shop to replace the alternator. I did confirm it was a faulty alternator, because it wasn't charging the new battery either. Now the alternator has been replaced and everything runs great again except now I have PO420 and PO430 codes and the CEL is on. I tried catcleaner, I also replaced the two downstream O2 sensors, and cleared the errors, but CEL comes back on in a few hours or a day later. I bought a code reader so now I can see the live data, but nothing is jumping out at me. My concern is why did these codes pop up after the alternator died? Do I really new new cats to fix this, or is there some other issue that I'm not thinking about? If any of code reader data would be useful, I can post that as well. I don't really understand what all the numbers mean yet so I could be missing something obvious as well. Thanks in advance for your help!

 

So this happened after the new alternator? I’ve seen goofy shit happen when it’s not an oem alternator. I absolutely would consider that angle before cats.

 

Just throwing out thoughts.
There is the new alternator but there is also the "dead car" event. Either way this was electrical stuff and cats are not electrical in their operation so it seems unlikely any of this could have effected/damaged them. OP, you mentioned replacing the downstream O2 sensors but not upstream. I would look at checking out electrical items involved with that system.