Layered double hydroxides derived Ni_x(Mg_yAl_zO_n) catalysts: Enhanced ammonia decomposition by hydrogen spillover effect

The NiMgAl-layered double hydroxides, with the stoichiometric ratios of Mg/Ni and Mg/Al being 0–9 and 0–3, respectively, were synthesized and employed as the Ni catalyst precursors for NH₃ decomposition. The resulting catalyst of the certain Ni, Mg, and Al contents showed high catalytic efficiency and outstanding durability for the target reaction. The features of cost effective (with only Mg and Al elements besides Ni), easy fabrication, and thermally durable are attractive for large-scale operation. The characterizations revealed the related changes in structure and property, such as the Ni particle size and distribution, the reduction of Ni²⁺ species, the Ni-oxide matrix interaction, the surface basicity as well as the adsorption/desorption behavior of hydrogen, in line with the stoichiometry of Ni, Mg, and Al in the samples. The superior catalytic activity and stability are thought to be associated with the structurally isolated active Ni species by the oxide matrix and the synergism between Ni-Mg sites. Particularly, the “spillover effect” of surface hydrogen accounts for a higher turnover frequency.