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

Highlights: • Composite oxide SmCeOx was prepared by citric acid complexation. • SmCeOx offers plenty of single-electron oxygen vacancies. • Oxygen vacancies have a strong interaction with Ru. • Ru/SmCeO_x has a high ammonia decomposition activity. SmCeO_x 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 SmCeO_x 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/g_cat·h when CeO₂ is replaced by Sm_0.4Ce_0.6O_1.8. TEM and CO chemisorption investigations reveal that the excellent performance of Ru/SmCeO_x 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 SmCeO_x, 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.