Catalytic activity of Ru supported on SmCeOx for ammonia decomposition: The effect of Sm doping

SmCeOx composite oxide with Sm3+ occupying Ce4+ site in CeO2 crystal lattice, prepared via citric acid complexation method, was loaded with 2 w% Ru by impregnation method and the as-prepared catalyst was then evaluated for ammonia decomposition. The results show that the partial substitution of Ce4+ by Sm3+ produces a positive effect on the catalyst performance and SmCeOx supported Ru exhibits a much higher low-temperature catalytic activity for ammonia decomposition compared with other supports such as Sm2O3, CeO2, and a physical mixture of Sm2O3 and CeO2. For example, the ammonia conversion is increased from 54.6% to 74.9% at a temperature of 400 ​°C and a space velocity of 3900 ml/gcat·h when CeO2 is replaced by Sm0.4Ce0.6O1.8. TEM and CO chemisorption investigations reveal that the excellent performance of Ru/SmCeOx catalyst is related to its high Ru dispersion. The results of BET, EPR and H2-TPR suggest that the partial substitution of Ce4+ with Sm3+ may induce the formation of oxygen vacancies and the high Ru dispersion can be attributed to the presence of large amount of single-electron trapped oxygen vacancies on the surface of SmCeOx, which have a strong interaction with Ru and thus Ru preferentially occupies the oxygen vacancies. This experimental observation is also supported by the DFT calculation result that Ru species adsorbed on the oxygen vacancy has a low adsorption energy.