Abstract
Monodispersible Co3O4 nanoparticles were prepared via a facile solvothermal route using polyvinylpyrrolidone (PVP) as capping agent and the porous silica shell was then coated by means of the Stöber process to fabricate Co3O4@porous-SiO2 (Co3O4@p-SiO2) nanocomposites. The particle size of Co3O4 and porous silica shell thickness of Co3O4@p-SiO2 nanocomposites could be easily controlled through changing the amount of PVP and tetraethoxysilane, respectively. The high resolution transmission electron microscopy results, together with the X-ray diffraction results, indicated that monodispersible Co3O4 nanoparticles were successfully prepared and uniformly encapsulated by porous silica. During the growth of silica shell, the PVP was trapped and dispersed in the silica shell. As a result, the porous silica shell was obtained after burning off the PVP and a positive correlation existed between the Brunauer–Emmett–Teller surface area of the porous silica shell and quantity of PVP in the original Co3O4 nanoparticles. Compared with the Co/SiO2 reference catalyst, CO conversion of the Co@p-SiO2 model catalyst was more stable and higher in a period of 240 h, and hydrocarbon selectivity towards C5–C18 fraction was also higher than that of the Co/SiO2 catalyst. The results of analysis for the Co@p-SiO2 catalyst showed that core@shell structure could maintain high dispersion of Co particles so as to provide higher number of Co active sites, and enhance selectivity towards C5–C18 fraction due to confined structure of porous channel in the silica shell. Schematic diagram of the procedure for synthesizing Co3O4@p-SiO2 nanocomposites.
Highlights
Fischer–Tropsch (F–T) synthesis has attracted much research attention nowadays because of the severe oil crisis and the tight fuel specifications [1, 2]
Monodispersible Co3O4 nanoparticles were prepared via a facile solvothermal route using polyvinylpyrrolidone (PVP) as capping agent and the porous silica shell was coated by means of the Stober process to fabricate Co3O4@porous-SiO2 (Co3O4@p-SiO2) nanocomposites
The porous silica shell was obtained after burning off the PVP and a positive correlation existed between the Brunauer–Emmett–Teller surface area of the porous silica shell and quantity of PVP in the original Co3O4 nanoparticles
Summary
Fischer–Tropsch (F–T) synthesis has attracted much research attention nowadays because of the severe oil crisis and the tight fuel specifications [1, 2]. Controlled Preparation of Co3O4@p-SiO2 structure was preferable to be adopted, where a porous shell played dual roles as: permitting syngas molecules to pass through the channel freely and preventing Co cores from coming into direct contact each other and hindering Co cores from agglomerating. This confined structure enabled cobalt catalyst showing special catalytic performances and product distribution in F–T synthesis. Compared with the conventional Co/SiO2 catalyst prepared via precipitation method, the Co@p-SiO2 catalyst, together with high dispersion of Co particles due to confined structure, could exhibit higher and more stable CO conversion and higher selectivity towards C5–C18 fraction in F–T synthesis
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