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I'm certain there were engines fitted with this kind of SCR, now referred to as HC-SCR (hydrocarbon selective catalyst reduction). The idea is the same as with urea injection, except fuel is used as the reduction agent instead of urea.
I just wasn't sure if urea injection systems still used at least some fuel for reduction.
From what I understand, this is basically what led to the VW diesel scandal. The NOx trap needed fuel to be sprayed into the exhaust to reduce NOx without the need for urea injection. Of course spraying fuel into the exhaust made the vehicles get worse fuel mileage too. So the emissions cheat was to only spray the fuel into the exhaust during testing but didn't do it while driving.
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