SCR? What is the Catalyst they use in the

I’ve has a handful of trucks having SCR codes intermittently. When they are acting up they do strange things. I’m a bit aggravated with them!!
I set out on a mission with google today to see just exactly what is the catalyst in the SCR, and how’s chemical reaction take place? What are the attributes of the matierial?

I found there are lots of catalysts that will help NOX and Ammonia do there thing, many dating back to the 80’s, and not one article about which the engine companies settle on using?? So now I’m a lot aggravated!!

Does anyone here know? I can’t read another partial scientific article!!!. I say partial because most of them require college credentials to access the whole paper. And it’s been a few years since I would have had those...