[null and void]

Pt is around $980 a troy oz.

A trillion bucks is roughly a billion oz.

There are ≈8 million oz of Pt bullion on the entire planet.

This singular coin would sop up ≈125 times the entire world's available Pt.

No more Pt for catalytic converters, therefore no more gasoline powered vehicles.

[stylin19a]

does that mean we’d need a new coin to cover the shortfall?

[lepton]

This singular coin would sop up ≈125 times the entire world’s available Pt.

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Only if the value is the metal value. They could make it dime-sized if they weren’t afraid of losing the thing on someone’s shoe.