© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Ammonia is a potential carrier of hydrogen as a zero-emission fuel. Herein, the effects of calcination and reduction temperatures on the ammonia-synthesis activity of Ru/La0.5Ce0.5O1.75 are investigated under mild synthesis conditions (≤400 °C, ≤3 MPa), which are the preferred conditions for the storage of hydrogen as an energy source. The highest catalytic activity is obtained after calcination of the support at 700 °C and reduction of the catalyst at 650 °C. Calcination using a higher temperature than that used for reduction results in the induction of a strong metal–support interaction (SMSI) effect. This high-temperature calcination also provides heat resistance to the support, which prevents sintering of the primary support particles during reduction. Thus, calcination and reduction at temperatures higher than those normally used for the preparation of Ru catalysts provide a novel approach for obtaining supported highly dispersed Ru catalysts exhibiting the SMSI effect and high catalytic activities.