Synthesis of mixed metal oxides for use as selective oxidation catalysts

Motshweni, Jim Sipho (Stellenbosch : University of Stellenbosch, 2007-03)


The synthesis of mixed metal oxides, specifically the need and ability to successfully and accurately control the particle size, their stability and the reactivity of these nanoparticles is required, so as to allow the attachment of catalyst nanoparticle to the surface of a substrate or to other particles without leading to coalescence of the catalyst particle and hence to loss of their size induced properties. However, the synthesis of mixed metal oxides is a complex problem. Though various methods of preparing these types of oxides have been reported and applied, such methods they rarely produced pure forms and have often been recorded as having been contaminated with other phases. Often the particle sizes are too large in the micrometer range, and the size distribution is overly wide. Moreover, even if particles of nanometer size are formed, they tend to aggregate or agglomerate. In the current research, microemulsions were used to synthesize the nanoparticles. Such microemulsion consists of water droplets encapsulated by surfactant molecules in a pool of oil, comprising: water in oil (w/o) or reverse micelles. Reverse micelles in the nanometer size range are thermodynamically stable and optically transparent in the solution. They are believed to be highly dynamic structures whose components rearrange themselves over time and space through interaction or collision, coalescing and redispersing. However, the advantage of this method over using the standard method is that the particle size can largely be controlled, and a narrow size distribution obtained. The aim of the research was to investigate the feasibility of using the reverse micelle technique for the synthesis of mixed metal oxides - specifically α-bismuth molybdate (α- Bi2Mo3O12) with a controlled and desirable particle size and a narrow size distribution...

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