The catalytic converter helps to manage this in a gasoline engine. Cats are more difficult for diesel, which led to the ammonia fluids that current diesels use to minimize NOx emissions.
I don't understand why not simply cool the exhaust gasses down with a big heat exchanger enough to condense the water vapour. That water would then react with the NOx to form dilute nitric acid, dilute enough to just drip onto the road with little environmental harm.
The same condensation process would also trap all the carbon particulates.
The same condensation process would also trap all the carbon particulates.