Synthesis of highly dispersed MnOx–CeO2 nanospheres by surfactant-assisted supercritical anti-solvent (SAS) technique: The important role of the surfactant

Abstract

In this work, highly dispersed mesoporous MnOx–CeO2 hollow nanospheres have been prepared using a surfactant-assisted supercritical anti-solvent (SAS) technique. The phase equilibria of methanol–CO2, precursor-methanol–CO2 and surfactant, precursor-methanol–CO2 systems were measured to preliminarily screen suitable surfactants. The MnOx–CeO2 particles were characterized using N2 adsorption/desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). Polyvinylpyrrolidone (PVP) and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) both efficiently reduced the interconnectivity and agglomeration of MnOx–CeO2 particles and led to the formation of highly dispersed particles with higher specific surface areas, more uniform pores and larger pore volumes. The effects of the SAS process parameters including the surfactant to precursor mass ratio, the temperature and the pressure, on the morphology, particle size, particle size distribution, specific surface area and pore volume of the particles were also investigated. In addition, the catalytic activities of the synthesized hollow nanospheres for the low temperature denitrification (deNOx) in the presence of NH3 were evaluated. Over the entire experimental temperature range (100–220°C), NO conversions of the MnOx–CeO2 particles prepared by introducing PVP or P123 during SAS were much higher than those for MnOx–CeO2 particles prepared without surfactants.