Formation of V₂O₅-based mixed oxides in flames

Abstract

V2O5-TiO2 and V2O5-AI2O3 mixed oxide powders were synthesized in a hydrogen-oxygen flame using VOCI3, TiCl 4 , and A1(CH 3 ) 3 as precursors. The particle formation processes were investigated as a function of VOCI3 concentration by laser light-scattering and by collecting particles directly onto transmission electron microscopy grids. In the V2Os-TiO2 system, the oxides condense as an intimate mixture at all three VOCI3 concentrations. Spherical particles, 40 to 70 nm in diameter, are obtained. In the V2O5-AI2O3 system, chain-like particles composed of an intimate mixture of V 2 O 5 and AI2O3 form at the lowest VOCI3 concentration. At high VOCI3 concentrations, the chain-like particles have a core-mantle structure (a core mainly of AI2O3 and a mantle mainly of V 2 O 5 ). The crystalline form and the surface area of these mixed oxides were determined by x-ray diffractometry, FT-IR spectroscopy, and BET analysis by nitrogen desorption. These measurements indicate that amorphous vanadium oxide forms at low VOCI3 concentrations, and V 2 O 5 is obtained at the higher VOC1 3 concentrations. The structure of the amorphous vanadium oxide matches that published for vanadium oxide "supported" catalysts. : Formation of V 2 O5-based mixed oxides in flames oxides 15 17 in flames showed that the flame technique used here allows one to control the shape, size, morphology, and crystalline structure of the powders produced. The results presented here, although preliminary, strongly suggest that a flame process can be used to produce catalysts and to control their formation.

Flame Synthesis of Nanoparticles

“…This catalyst is typically prepared in liquid phase processes. Nevertheless, Katz and co-workers [9,71,72] produced titania nanoparticles in a counterflow diffusion flame with 14, 25, and 50 wt% vanadia from TiCl 4 and VOCl 3 , however, they did not report the activity of their product. Stark et al [18] synthesized spherical titania particles coated homogeneously with amorphous vanadia in a co-flow diffusion flame from titanium tetraisopropoxide and vanadium oxotriisopropoxide.…”

Anatase–rutile transformation in TiO2–V2O5 catalyst coatings for ceramic foams

“…[23][24][25] In the present work, the V 2 O 5 -TiO 2 catalyst mixtures were prepared by drying oxide slurries, which were electrostatically stabilized by varying the suspension pH.…”

Flame Generation of Two New Precursors of Vanadyl Pyrophosphate

“…These lengthy procedures result in long are related to the ability of the (100) plane to accommodate processing times and often generate environmentally troublesome side streams. In earlier papers, we showed that one can produce mixed oxides with well-defined morpholo-gies in a single-step operation by flame synthesis using a nique for producing mixed oxides in a single step process counterflow diffusion flame burner (10)(11)(12). Most recently, has been described in detail elsewhere (10,12,14).…”

“…In earlier papers, we showed that one can produce mixed oxides with well-defined morpholo-gies in a single-step operation by flame synthesis using a nique for producing mixed oxides in a single step process counterflow diffusion flame burner (10)(11)(12). Most recently, has been described in detail elsewhere (10,12,14). Therewe applied this new high-temperature synthesis technique fore, the experimental setup and the procedure used for to produce vanadium-phosphorus mixed oxide catalysts forming and collecting the powders are reviewed here (13).…”