What is urea? What is AdBlue?

Urea is a chemical substance whose base is natural gas. Urea is used today for fertilizers in agriculture as well as in food and make-up.
AdBlue is a liquid solution that consists of urea and water. The urea concentration is about 32%. AdBlue corresponds to DIN standard 70070.

The chemical process
Adblue: (NH2) 2CO (urea) + H2O (water)

Warm exhaust and water are needed to decompose urea into ammonia and carbon dioxide:
 (NH2) 2CO + H2O => 2NH3 + CO2

Reduction of nitrogen oxide by ammonia in the presence of oxygen:
 NOx+NH3+O2 => (catalytic reaction) => N2 + H2O