© 2022 Hydrogen Energy Publications LLCIn this study, the ammonia decomposition reaction to produce COx-free hydrogen is investigated in a microwave reactor system using nickel-based catalysts supported by different materials. Unlike the activated carbon supported catalyst (Ni@AC), the alumina supported catalyst (Ni@Alumina) is mixed with carbon in a 1:1 ratio to reach the necessary reaction temperature in the microwave reactor. Ni@Alumina gives an overall hydrogen production rate of 73 mmol/min.gcat with 99% conversion at 400 °C under pure ammonia flow (60 ml/min). Ni@Alumina outperforms Ni@AC under microwave reactor conditions, but underperforms Ni@AC under the conventional testing, which is done for comparison. It is suggested that selective heating of nickel species in Ni@Alumina enables better performance in the microwave reactor in comparison to Ni@AC. On the other hand, high surface area and small nickel particles present in the Ni@AC structure in comparison to the Ni@Alumina structure, causes higher activity in the conventional reactor at temperatures over 550 °C. Between 400 and 550 °C, both Ni@Alumina and Ni@AC have substantially lower activity under conventional heating than microwave heating when compared at the same temperatures. Hot spot formation and microwave selective catalytic effect are considered as possible reasons for the improved performance of microwave reactor system.