Flame aerosol synthesis of WO3/CeO2 from aqueous solution: Two distinct pathways and structure design

Flame aerosol synthesis is a continuous one-step method to obtain metal oxides. However, production of uniform particle is considered an inherent challenge for flame aerosol synthesis from aqueous solution. It is necessary to fully understand the synthesis route and the essential governing factors to break through the barrier. A series of flames with different temperatures were employed to synthesize WO 3 , CeO 2 and the WO 3 /CeO 2 composite powders. Flame temperature and precursor concentration were investigated to determine the synthesis pathways from aqueous droplet to particle. Size distribution of the powders indicated that they were homogeneous (unimodal) micron particles at low temperature flame process, nanopowders at high temperature, and inhomogeneous (bimodal) particles in between. Two distinct pathways (droplet-particle and droplet-vapor-particle) were generalized from experiments and verified by size statistics. It was the competition between the temperature of flame and the vapor pressure of precursor solute that played an important role on selection of pathways. Based on the different response to temperature, the nanosized WO 3 /CeO 2 mixture and nanoparticle-decorated WO 3 @CeO 2 were designed. Furthermore, this generalized method was applicable for other tungsten oxide nanostructured catalysts, e.g. WO 3 @Al 2 O 3 , WO 3 @ZrO 2 .