Oil choice helpful for Cat preservation?

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Hi Everyone, I posted a few weeks ago about a bad cat code in my college son's 2010 Mazda 6 with 90ish thousand miles on it. O2 sensors are working properly and garage said we need to replace the cat eventually. He's been using grocery store gas because he's a poor college student, so I told him to run a couple tanks of Top Tier gas (now and always) and some fuel system cleaner to see if it helped at all. The car has been very well maintained since new and drives normally. One tank with Techron and a subsequent tank with Redline SL-1, and the code went away without having to clear it.

It's almost time for an oil change anyway, so I told him to change it early since he just ran 2 tanks of fuel system cleaner. He normally uses Pennzoil Platinum or Castrol Edge EP, and changes at 8K miles or 1 year, whichever comes first. So here's my question, would there be any benefit of using M1 ESP or the new Castrol Edge high mileage which says "Castrol EDGE High Mileage is liquid engineered with Phosphorous Replacement Technology to reduce harmful phosphorus to protect the catalytic converter and preserve the life of your emission system."? He graduates in May and ideally wants to drive the car for 1-2 more years before he sells it to get something a bit newer and more his style.

I appreciate your constructive and informed opinions. Thank you, and Happy New Year!
 
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I’d run that Castrol. I’ve had extremely good luck with Castrol in my vehicles it cleaned the cat up nicely in my dads Camry and made it last a little while longer until we could afford to replace it. However I would not go that much on an oil change interval go 5,000 at the most that’s probably the main issue there is it’s probably getting dirty and not being able to clean it as good when it gets to that point.
 
The only fluid that will preserve your Cat correctly is likely formaldehyde.

The oil that will preserve your catalytic converter the best is any oil that met the manufacturer's specifications for your year and model.
 
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