Mixed metal oxides derived from Ni-doped Mg-Al layered double hydroxides based solid solution series: Optimizing nickel composition toward improving the isopropanol catalytic decomposition and enhancing the electrical and dielectric performances

Abstract

Ni-doped Mg-Al mixed metal oxides (MMOs) were synthesized from (Mg_1-yNi_y)₄-Al layered double hydroxides (LDHs) intercalated with carbonate ions (y = 0, 0.1, 0.5 and 1) by calcining the LDHs at 500 °C. The LDHs were synthesized using the co-precipitation at a constant pH method, and characterized by XRD, TGA/DTA and FTIR spectroscopy. The obtained LDHs based solid solution series was confirmed by XRD through the evolution of the cell parameter (a) as a function of nickel content (y) according to Vegard's law. All phases of the MMOs adopted the NaCl-type structure, and exhibited a decreased cell parameter (a) and an increased crystallite size as the nickel content increased. The 50 % Ni-doped Mg-Al MMO exhibited the highest surface area and total conversion among the catalysts. Furthermore, pure acetone production was achieved using the 100 % Ni-doped Mg-Al MMO. Regarding the electrical response of the MMOs, an electrical equivalent circuit model was constructed to describe two contributions related to the grains and grain boundaries, which occur at high and low frequencies, respectively. Additionally, nickel has been shown to enhance electrical conductivity, and increase both the dielectric constant and the dielectric loss tangent. Thus, by optimizing the nickel composition, this study investigated the potential of fully nickel-doped Mg-Al MMO for producing acetone through the catalytic decomposition of isopropanol and for use as an electrolyte solid material. Undoped Mg-Al MMO was also found to be suitable for dielectric energy storage due to its low dielectric energy dissipation.