Synthetic Manipulation on the Microstructure of Co Species-Containing Mesoporous Silica Matrices: Impact on the Efficiency for Fischer-Tropsch and Water Oxidation Reactions

Abstract

Mesoporous silica containing Co species is effective in a wide variety of catalytic processes. Nevertheless, the catalytic efficiency of such materials strongly depends on their preparation. Two model compounds made of SBA-15 type ordered mesoporous silica monoliths containing Co(II) nitrate salt or CoCo Prussian Blue Analog are thermally treated under oxidizing and reducing atmospheres. A detailed quantitative description of the microstructure of the nanocomposites is obtained by combining X-ray diffraction, electron microscopy, UV-visible and X-ray absorption spectroscopies, and magnetic measurements. The complementarity of these techniques, which are able to identify isolated molecular species as well as amorphous or crystalline condensed species and intra- or inter-particle interactions, allows a deep and unprecedented knowledge of the microstructure of such nanocomposites. The impact that this improved description of the microstructure can have in the field of catalysis is then illustrated i) by revisiting the literature on Fischer-Tropsch catalysts in the light of the improved microstructural description, opening up new perspectives for improving the efficiency of these catalysts and ii) by comparing the catalytic activity of two catalysts with very different microstructures but containing the same amount of Co species for the water photooxidation reaction.