Liquid-feed flame spray pyrolysis (LF-FSP) 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.

Richard Laine

J.A. Azurdia, J.C. Marchal, P. Shea, H. Sun, X. Q Pan, and R.M. Laine (2006)

Chem. Mater., 18:731-9.

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 xNi(O2CCH2CH3)2/yAl(OCH2CH2)3N EtOH solutions at selected x:y ratios provides mixed-metal oxide nanopowders with compositions covering much of the Al2O3−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 m2/g), all product powders offer SSAs ≥ 45 m2/g (average particle sizes ≤ 30 nm) without microporosity. At NiO/Al2O3 ratios near 1:1, the LF-FSP nanopowders are single phase, bright blue NiAl2O4 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 Ni2+ in the alumina lattice or formation of traces of NiAl2O4. Compositions near 20:80 mol NiO/Al2O3 generate an inverse spinel structure, per XRD with peaks shifted ≈4° 2θ to higher values from those of pure NiAl2O4. This contrasts with the published phase diagram, which suggests a mixture of NiAl2O4 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−Al2O3 phase space with potential value as a new catalyst.

nanopowders, spinel, catalyst