Structural and chemical characterization of novel Ni_xZn_1−xGa₂O₄ nanocatalysts at atomic resolution

Ni_xZn_1−xGa₂O₄ has already been demonstrated as a noteworthy example of potentially useful catalytic properties such as NO_x reduction. In our previous work, it was interesting to find out that the operating temperature of NiGa₂O₄ catalyst in NO_x reduction can be tuned by simple chemical substitution of Ni²⁺ by Zn²⁺. It is believed that the mechanism behind such stoichiometry-dependence on operating temperature should be strongly correlated with microstructure, surface morphology as well as the local composition of the nanocatalysts. In the present investigation, Ni_xZn_1−xGa₂O₄ solid solution was synthesized via a hydrothermal ion-exchange reaction, using NaGaO₂ and the corresponding acetic salts as the starting materials. By means of a state-of-the-art aberration corrected STEM and high resolution TEM, the structural and chemical characterization at the atomic scale on the Ni_xZn_1−xGa₂O₄ nanocatalyst was carried out, including the crystal structure, size, morphology, surface structure and local composition. It is found that the catalyst was solid solution and most possible exposed facets may be (1 1 1).