Liquid-Feed Flame Spray Pyrolysis as a Method of Producing Mixed-Metal Oxide Nanopowders of Potential Interest as Catalytic Materials. Nanopowders along the NiO−Al₂O₃ Tie Line Including (NiO)_0.22(Al₂O₃)_0.78, a New Inverse Spinel Composition

Liquid-feed flame spray pyrolysis (LF-FSP) is a general aerosol combustion route to unagglomerated and often single crystal mixed-metal oxide nanopowders with exact control of composition. LF-FSP of x Ni(O 2 CCH 2 CH 3 ) 2 / y Al(OCH 2 CH 2 ) 3 N EtOH solutions at selected x: y ratios provides mixed-metal oxide nanopowders with compositions covering much of the Al 2 O 3 −NiO phase space. All powders were characterized by XRD, BET, FTIR, SEM, TEM, and TGA-DTA. With the exception of pure NiO (specific surface area, SSA, ∼7 m 2 /g), all product powders offer SSAs ≥ 45 m 2 /g (average particle sizes ≤ 30 nm) without microporosity. At NiO/Al 2 O 3 ratios near 1:1, the LF-FSP nanopowders are single phase, bright blue NiAl 2 O 4 inverse spinel. The blue color of these materials is typical of Ni spinels. At higher NiO contents, NiO is the dominant phase with some δ-alumina and intermediate spinels. At low NiO contents, blue powders form but the δ-alumina phase predominates, suggesting incorporation of Ni 2+ in the alumina lattice or formation of traces of NiAl 2 O 4 . Compositions near 20:80 mol NiO/Al 2 O 3 generate an inverse spinel structure, per XRD with peaks shifted ≈4° 2θ to higher values from those of pure NiAl 2 O 4 . This contrasts with the published phase diagram, which suggests a mixture of NiAl 2 O 4 spinel, and corundum should form at this composition. This material resists transformation to the expected phases on heating to 1400 °C, indicating a single stable phase which contrasts with the known phase diagram and, therefore, is a new material in NiO−Al 2 O 3 phase space with potential value as a new catalyst.