Catalan word in- comes from Latin ingratus (Thankless. Ungrateful. Unpleasant, disagreeable.)

Detailed word origin of in-

Dictionary entry	Language	Definition
ingratus	Latin (lat)	Thankless. Ungrateful. Unpleasant, disagreeable.
in-	Catalan (cat)	In- ; un- (reversal of meaning or lack of an attribute).