From spinel site occupation to active phase construction: Reconstructing MgAl synergistic doping Co3O4 into metallic co core-shell structure for efficient ammonia decomposition

Ammonia has emerged as a promising hydrogen carrier due to its high hydrogen density and ease of storage and transport. However, the widespread application of ammonia decomposition is hindered by the rapid deactivation and limited intrinsic activity of conventional transition metal catalysts. In this work, a well-defined Mg Al co-doped cobalt-based spinel oxide (Mg 0.18 Al 0.12 Co 2.7 O 4 ) is developed that undergoes in-situ self-assembly under reaction conditions to form a core-shell structure (Co@MgAlO x ). This unique structure features metallic Co nanoparticles as the active core, encapsulated by a dispersed Mg Al oxide shell. The resulting catalyst achieves a hydrogen production rate of 33.5 mmol∙g cat −1 ∙min −1 at 600 °C in ammonia decomposition. Comprehensive characterization reveals that the Mg Al oxide shell not only physically confines the Co nanoparticles against sintering but also induces an electron-deficient state in Co via strong metal-support interactions, leading to a long-term stability about 350 h and cycle stability for six times. Combined with theoretical calculation results, the doping of Al promotes the initial adsorption and dissociation of NH x , while Mg and Al co-doping alleviate lowering the energy barrier of the nitrogen desorption, which is the rate-determining step. This study underscores the importance of synergistic Mg Al co-doping in guiding a stable and active structure, providing an in-situ self-assembly strategy for the rational design of heterogeneous catalysts.