The Chemical Engineering Division of Argonne National Laboratory in the U.S. has come up with a possible alternative to ammonia and urea. Their process uses Cu-ZSM-5, a zeolite with copper ions attached within its micropore structure, "with an external coating of cerium oxide", according to Christopher Marshall, who helped develop the technology. The technology also does not contain platinum, which is expensive and not compatible with the older diesel fuels which contained high amounts of sulphur.
This catalyst is currently under testing, but is proving to work out well enough that Argonne is expecting to have the product commercially available in as little as two years. I think it sounds pretty promising myself, because while I don't mind using urea at all, I think it is good that the consumer would not be left in charge of being sure that the Adblue tank was not empty.
[Source: Argonne National Laboratory]