The impact of nitrogen mobility on the activity of zirconium oxynitride catalysts for ammonia decomposition

A zirconium oxynitride catalyst was used for the decomposition of ammonia to hydrogen and nitrogen. The onset of catalytic activity at ∼550 °C coincided with the onset of nitrogen ion mobility in the material and a phase change from the initial image phase (∼Zr7O11N2) to the nitrogen-rich image ZrON phase (∼Zr7O9,5N3). No hydrazine formation during an extended time on stream was detectable. Moreover, the onset of activity was also correlated to a rapid change in the electronic structure of the surface accompanying formation of the more active image ZrON phase. The results presented here show for the first time a direct correlation among the onset of ion conductivity as a bulk property, a modified electronic structure of the surface, and the catalytic performance of a heterogeneous catalyst.