Cerium-exchanged sodium-type mordenite (CeNa-MOR) was studied in comparison with a non-redox lanthanide mordenite (LaNa-MOR) and an acid-type mordenite (H-MOR) for nitric oxide reduction with ammonia in the presence of excess oxygen. The activity of CeNa-MOR was found to be high over a wide temperature range of 250-560-degrees-C. LaNa-MOR showed a similar nitric oxide conversion profile versus temperature as H-MOR, becoming substantially active only above 400-degrees-C. Bronsted acid sites are assumed to be responsible for the catalysis by LaNa-MOR, while over CeNa-MOR, two plausible reaction pathways involving the redox couple (Ce(III)/Ce(IV)) are proposed and discussed.