Surfactant selection as a strategy for tailoring the structure and properties of UCT manganese oxides

Abstract

Mesoporous manganese oxides were synthesized using the UCT inverse micelle templating method with four different Pluronic surfactants to investigate the effects on the morphology, microstructure and desulfurization behavior of these materials. All of the as-synthesized samples exhibited similar hierarchical microstructures, but the size and shape of the primary nanoparticles for each sample was different. The primary nanoparticle sizes for these samples vary between 2.3 and 7.0 nm. Most of the samples are crystalline and are composed of a mixture of Mn3O4 and Mn5O8 phases. The adsorption behavior of these samples was tested using a fixed bed reactor at a temperature of 200 °C. Microstructural analysis of the samples after the desulfurization tests revealed a transformation of the mesoporous manganese oxide to a dense manganese sulfide phase; this involves a volumetric expansion of the crystal, leading to densification and a rapid decay in the sorption capacity after the breakthrough point. The variation in the structure and properties of these materials is related to ratio of the PEO and PPO chain segment lengths in the Pluronic surfactants used. This indicates that the ratio must dictate the volume, shape and assembly of the inverse micelles in the UCT synthesis.