Ceria-supported Ni, Ru and NiRu catalysts have been tested in the catalytic decomposition of ammonia to yield hydrogen and their performance in long-term tests has been compared to alumina-supported Ni and Ru samples. The catalysts have been characterized by XRD, TPR, NH3-TPD, HAADF-STEM, SEM, BET and XPS. Ceria-based samples are more active in ammonia decomposition with respect to their alumina-based counterparts, which has been ascribed to a particular metal-support interaction, while acidity does not seem to play an important role. Ru-based catalysts are more active than Ni-based samples, but they deactivate rapidly, in particular the Ru/Al2O3 sample. This is ascribed to loss of exposed Ru, as demonstrated by XPS and HAADF-STEM. Considering the high cost and limited availability of Ru, the Ni/CeO2 catalyst appears as a promising system for ammonia decomposition due to its good performance and low cost. In situ XPS experiments reveal that the active sites for the catalytic decomposition of ammonia are metallic Ni and Ru. Bimetallic NiRu catalysts do not outperform their monometallic counterparts, irrespective of the order in which the metals are added.