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(O 2 CCH 2 CH 3 ) 2 /yAl(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 g 45 m 2 /g (average particle sizes e 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.

Spinel compounds are of continuing interest because they exhibit a wide range of novel and manipulable applications of value in electronic, magnetic, catalytic, photonic, and structural properties. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Thus, the crystal structures, phase equilibria and composition ranges of materials that form both normal and inverse spinels have been studied extensively, frequently to optimize specific properties. Properties optimization drives continuing efforts to produce new materials, extend phase fields and improve homogeneity. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] This in turn provides the impetus to develop new synthesis and processing approaches.We recently demonstrated that liquid-feed flame spray pyrolysis, LF-FSP provides access to a new hexagonal phase in nano-Y 3 Al 5 O 12 and a general route to nano-a-Al 2 O 3 (30-90 nm). [19,20] We now find that LF-FSP offers a general route to common phase pure spinel nanopowders, (MO) 1 À x (Al 2 O 3 ) x M ¼ Mg, Ni, Co, Zn, and (MgO) 0.6 (Fe 2 O 3 ) 0.4 , with compositions previously unknown thereby greatly extending their phase fields. [1,2,[13][14][15][16][17][18][19]21] Given their significant academic and commercial import, access to entirely new compositions in spinel phase materials could expand the horizons of spinel materials' properties greatly. In LF-FSP, alcohol solutions of metalloorganics [e.g. Al(OCH 2 CH 2 ) 3 N (alumatrane) and Mg(2,4-pentanedionato) 2 ] are aerosolized with O 2 into a quartz chamber (1.5 m) and combusted [22] at 1500 8-2000 8C. Quenching to %300 8C in 30 ms over %1 m gives dispersible nanopowders often with novel phases as noted above [19,20] and for example a one step synthesis of the difficult to produce Na þ doped b 00 -alumina. [22] In an effort to dope nano-a-Al 2 O 3 with MgO to prevent grain growth during sintering, [23,24] LF-FSP was used to combinatorially produce MgO doped nano-d-Al 2 O 3 as a prelude to a second pass through the LF-FSP system to produce Mg doped a-Al 2 O 3 .[24] Figure 1 shows XRDs for LF-FSP generated (MgO) x (Al 2 O 3 ) 1 À x nanopowders where x ¼ 0-0.20. Exact compositions were confirmed by XRF analyses.[22]As substantiated by numerous studies, [9][10][11][12][13][14][15][25][26][27] . In some instances, as in the nickel system, [28] the materials are mostly the inverse spinel.The reported (NiO) x (Al 2 O 3 ) 1 À x phase diagram shows a spinel phase field in the alumina rich region that extends from x ¼ 0.50 to 0.60 at 1500 8C but broadens to %0.68 at temperatures near 2000 8C.[29] Thus, our observation of a pure spinel phase at x ¼ 0.78 greatly extends this phase field. The resulting spinel is very stable, resisting transformation to the phase diagram composition even on heating for 10 h at 1150 8C, Figure 2. Similar observations are made for the (CoO) x (Al 2 O 3 ) 1 À x system, where at 1500 8C the published phase diagram in the alumina rich region extends to 45 mol % (x ¼ 0.45) but expands to 78 mol % near 1950 8C. [31,32] We observe...

We describe here the use of liquid-feed flame spray pyrolysis (LF-FSP) to produce high surface area, nonporous, mixed-metal oxide nanopowders that were subsequently subjected to high-throughput screening to assess a set of materials for deNO(x) catalysis and hydrocarbon combustion. We were able to easily screen some 40 LF-FSP produced materials. LF-FSP produces nanopowders that very often consist of kinetic rather than thermodynamic phases. Such materials are difficult to access or are completely inaccessible via traditional catalyst preparation methods. Indeed, our studies identified a set of Ce(1-x)Zr(x)O(2) and Al(2)O(3)-Ce(1-x)Zr(x)O(2) nanopowders that offer surprisingly good activities for both NO(x) reduction and propane/propene oxidation both in high-throughput screening and in continuous flow catalytic studies. All of these catalysts offer activities comparable to traditional Pt/Al(2)O(3) catalysts but without Pt. Thus, although Pt-free, they are quite active for several extremely important emission control reactions, especially considering that these are only first generation materials. Indeed, efforts to dope the active catalysts with Pt actually led to lower catalytic activities. Thus the potential exists to completely change the materials used in emission control devices, especially for high-temperature reactions as these materials have already been exposed to 1500 degrees C; however, much research must be done before this potential is verified.

We report here the use of liquid‐feed flame spray pyrolysis (LF‐FSP) to produce a series of nanopowders along the CoOx–Al2O3 tie line. The process is a general aerosol combustion synthesis route to a wide range of lightly agglomerated oxide nanopowders. The materials reported here were produced by aerosolizing ethanol solutions of alumatrane [Al(OCH2CH2)3N] and a cobalt precursor, made by reacting Co(NO3)2·6H2O crystals with propionic acid. The compositions of the as‐produced nanopowders were controlled by selecting the appropriate ratios of the precursors. Nine samples with compositions (CoO)y(Al2O3)1−y, y=0−1 along the CoOx–Al2O3 tie line were prepared and studied. The resulting nanopowders were characterized by X‐ray fluorescence, BET, scanning electron microscopy, high‐resolution transmission electron micrographs, X‐ray diffraction (XRD), thermogravimetric analysis (TGA), and FTIR. The powders typically consist of single‐crystal particles <40 nm diameter and specific surface areas (SSAs) of 20–60 m2/g. XRD studies show a gradual change in powder patterns from δ‐Al2O3 to Co3O4. The cobalt aluminate spinel phase is observed at stoichiometries (21 and 37 mol%) not seen in published phase diagrams, likely because LF‐FSP processing involves a quench of >1000°C in microseconds frequently leading to kinetic rather than thermodynamic products. Likewise, the appearance of Co3O4 rather than CoO as the end member in the tie line is thought to be a consequence of the process conditions. TGA studies combined with diffuse reflectance FTIR spectroscopic studies indicate that both physi‐ and chemi‐sorbed H2O are the principal surface species present in the as‐processed nanopowders. The only sample that differs is Co3O4, which has some carbonate species present that are detected and confirmed by a sharp mass loss event at ∼250°C. The thermal behavior of the high cobalt content samples differs greatly from the low cobalt content samples. The latter behave like most LF‐FSP‐derived nanopowders exhibiting typical 1%–4% mass losses over the 1400°C range due mostly to loss of water and some CO2. The high cobalt content samples exhibit a sharp mass loss event that can be attributed to the decomposition of Co3O4 to CoO.