CoxFe3−xO4 catalytic materials for gaz sensors

Abstract

Nanomaterials based on spinel ferrites have already numerous applications, mainly based on their magnetic properties. Recently, catalytic properties of nickel, copper and cobalt ferrites in the conversion of CO and CH4 were evidenced, opening a new field of applications for these materials [1]. Magnetic properties of nanoparticles, as well as catalytic properties, will depend on their size, but also on their shape and size distribution. These parameters are linked to the elaboration method. The properties of transition metal spinel oxides depend also on the nature of the transition metal and on his site occupation in the structure. The location of the cations in the spinel structure is related to their octahedral or tetrahedral sites preference, but also to the synthesis method. For magnetite Fe3O4, which adopts the inverse spinel structure, the tetrahedral sites are fully occupied by Fe3+ ions, whereas octahedral sites are occupied by Fe3+ and Fe2+. For Co3O4, the octahedral and tetrahedral sites are respectively occupied by Co3+and Co2+ (normal spinel structure). Intermediate situations occur for CoxFe3−xO4,. Thus, three different compositions were prepared CoFe2O4, Co0.6 Fe2.4O4, Co1.4 Fe1.6O4.