Catalytic activity of Ru supported on SmCeOx for ammonia decomposition: The effect of Sm doping
SmCeO x composite oxide with Sm 3+ occupying Ce 4+ site in CeO 2 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 Ce 4+ by Sm 3+ 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 Sm 2 O 3 , CeO 2 , and a physical mixture of Sm 2 O 3 and CeO 2 . 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 CeO 2 is replaced by Sm 0.4 Ce 0.6 O 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 H 2 -TPR suggest that the partial substitution of Ce 4+ with Sm 3+ 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 .
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