If it is a three way cat (TWC), then yes, I would think it would matter. Because a TWC performs reduction (controls NOx) first and any left over O2 is stored in the substate material and released during Oxidation (controls HC and CO). I would suspect that if it performed oxidation first, the byproducts (H2O and CO2) may split and under temperature will attach to the nitogen atom. But I don't know for sure.
