generation of acidity by dehydration
Ammonai reacts with the acid site because of the strong basicity
water reacts with the base site because the basicity of the site is stronger than ammonia
formed OH- replaces the ammonia because the basicity is stronger than ammonia
the water vapor treatment discriminates between the "acid on material which acts as base" and "simple acid"
the latter corresponds to the catalytic ACTIVITY FOR ACID CATALYZED REaction