Chemical modification in and on single phase [NiO]_0.5[Al₂O₃]_0.5 nanopowders produces “chocolate chip‐like” Ni_x@[NiO]_0.5‐x[Al₂O₃]_0.5 nanocomposite nanopowders

Abstract

Phase‐pure [NiO]0.5[Al2O3]0.5 spinel nanoparticles (NPs) with limited aggregation were obtained via liquid‐feed flame spray pyrolysis (LF‐FSP) by combusting metalloorganic precursor solutions. Thereafter “chocolate chip‐like” Nix[NiO0.5‐x][Al2O3]0.5 nanoparticles consisting of primary [NiO0.5‐x][Al2O3]0.5 particles with average particle sizes of 40‐60 nm decorated with Ni metal particles (<10 nm in diameter) dispersed on the surface were synthesized by heat treating the spinel NPs at 800°C/7 h in flowing 5% H2:N2 100 mL/min in a fluidized bed reactor. The synthesized materials were characterized using TEM, XRD, FTIR, and TGA/DTA. The Ni depleted areas consist primarily of γ‐Al2O3. The Ni content (800°C) was determined by TGA to be ≈11.3 wt.% based on TGA oxidation behavior. The successful synthesis of such nanocomposites with limited aggregation on a high temperature support provides a facile route to synthesize well‐defined NP catalysts. This work serves as a baseline study for an accompanying paper, wherein thin, flexible, dense films made from these same NPs are used as regenerable catalysts for carbon nanotube syntheses.

Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic

“…Fast exsolution speed. Exsolution of Ni nanoparticles from the current (NiAl)O x solid solution took less than 4 h at 800 °C in H 2 reducing atmosphere, while for exsolution of Ni from spinel, in a prior report, most Ni 2+ remained in the spinel lattice after 7 h at 800 °C 38 . The intrinsic metastability, lattice mismatch between dopant and parent ions, and abundant oxygen vacancies lower the energy barriers to cation diffusion and phase segregation, accelerating the exsolution process 39 .…”