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Abstract

Green hydrogen can be used as the backbone of a novel energy system and as a feedstock for renewable chemistry. H₂ storage and transport are challenging, but ammonia as a hydrogen carrier could potentially solve these inefficiencies. Many studies focus on high catalytic activities, but the long-term stability is often insufficiently investigated. This work reports on the stability of a nickel-based reference catalyst and a coprecipitated Ni/Al₂O₃ catalyst over 800 h time on stream (TOS) in 98% NH₃ at atmospheric pressure. An automated temperature control is necessary to adjust the temperature of the heat source to compensate for the changing heat demand resulting from catalyst activation or deactivation. Under reaction conditions the reference catalyst first undergo an activation phase before reaching its maximum conversion of 91.9% after 250 h TOS followed by a minor decrease in conversion. In comparison, the Ni/Al₂O₃ catalyst shows lower activity and undergo a continuous deactivation due to sintering. Overall, the activity loss at 534 °C amounted to only 1.5% for the reference catalyst and to 13.5% for the Ni/Al₂O₃ catalyst compared with the maximum conversion level. Thus, the Ni-based reference catalyst proves to be very stable under industrially relevant NH₃ decomposition conditions.