Nanopartículas de cobalto encapsuladas como catalisador na síntese de Fischer-Tropsch

Abstract

Silica-encapsulated cobalt oxide core-shell particles were prepared by a solvothermal treatment and by the Stöber method. Carbon-encapsulated cobalt oxide yolk-shell particles were also prepared with resorcinol and formaldehyde, using the silica-encapsulated particles as template. In addition, silica-encapsulated cobalt nanoparticles were evaluated as a catalyst for Fischer-Tropsch synthesis at 210 °C and 2 MPa under two different reaction protocols. The samples were characterized by thermogravimetric analysis, inductively coupled plasma optical emission spectroscopy, N2 physisorption at - 196 °C, X-ray diffraction, temperature programmed reduction and electron microscopy. The methods used during the preparation of the silicaencapsulated particles were efficient to obtain uniform particles without agglomeration, while the carbon-encapsulated particles exhibited the coagulation of the shell or nonencapsulated template particles. The silica-encapsulated cobalt nanoparticles were more active in the Fischer-Tropsch synthesis compared to a silica-supported cobalt catalyst. Moreover, the encapsulation of the active phase generated a narrower product distribution and avoided deactivation by sintering. Increasing the silica shell thickness elevated the selectivity towards methane and light hydrocarbons, indicating that the silica pores exerted a confinement effect over the hydrocarbon chain growth or caused diffusional limitations. Furthermore, the use of a protocol that allowed the addition of the feed gas under milder conditions proved the good stability of the encapsulated catalysts within 47 h.