Various core-shell structured Ni@SiO2 nanocatalysts were prepared to provide an insight into the intrinsic effects of shell structures on the ammonia decomposition activity. The thickness of silica shell structure can be fine tuned in the range of 5-20 nm. With the increase in shell thickness, it was found that the catalytic activity did not decrease obviously, even though the reducibility determined by H-2-TPR exhibited a noticeable changes. As for the porosity of the shell, the SP-1 sample with a well-developed pore structure showed better catalytic performance than the SP-0 sample with a less-developed pore structure. It can be concluded that diffusion limitations would be greatly influenced by shell porosity nor shell thickness to some extent. Various core-shell structured Ni@SiO2 nanocatalysts were prepared to provide an insight into the intrinsic effects of shell structures on the ammonia decomposition activity. The thickness and porosity of silica shell structure were fine tuned. It was concluded that diffusion limitations would be probably greatly influenced by shell porosity nor shell thickness to some extent. [GRAPHICS]