Controlled Preparation of Co3O4@porous-SiO2 Nanocomposites for Fischer–Tropsch Synthesis

Fischer–Tropsch (F–T) synthesis has attracted much research attention nowadays because of the severe oil crisis and the tight fuel specifications [ 1 , 2 ]. One of the goals of modern F–T synthesis research is to design a catalyst capable of highest selectivity to the desired product without sacrificing activity and lifetime [ 3 ]. Cobalt F–T synthesis catalysts are preferred due to their low activity for the water–gas shift reaction, slow deactivation rates and highly selective to linear paraffin than iron catalysts [ 4 ]. Since cobalt is ~1,000 times more expensive than iron, therefore optimal design of a cobalt catalyst is essential for its utilization. Decreasing the Co particle size to increase the exposed surface areas per unit mass of the Co [ 5 ] and hindering Co particles from agglomerating during reaction would be reasonable pathway to achieve this goal. Although up to now, many methods were designed to prepare cobalt-based catalysts with different Co particle size, and morphologies as well. It had been difficult to translate these advances into successful application in F–T synthesis as to be the drawback of easily agglomeration and sintering of the Co particles under harsh catalytic reaction conditions. In order to prevent Co particles from agglomerating and decrease the deactivation rates of the cobalt catalysts, a novel cobalt catalyst with core@shell 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 thus hindering Co cores from agglomerating. This confined structure enabled cobalt catalyst showing special catalytic performances and product distribution in F–T synthesis. For example, Tsubaki co workers [ 6 – 9 ] had prepared core@shell cobalt catalysts by coating H-ZSM-5 zeolite membranes on the Co/SiO 2 catalysts, which showed an excellent selectivity to the C 5 –C 11 isoparaffins (gasoline distillates) benefiting from the confined reaction conditions constructed by H-ZSM-5 membranes. Moreover, the article of Trépanier et al. [ 10 ] has also showed that carbon nanotubes, when used as a cobalt catalyst support, allowed a better Co dispersion and minimized the Co metal phase interaction with the support. The Co particles located inside the tubes were more active than the ones on the outer surface of the CNT owing to confined effect. Thus, how to synthesize cobalt catalysts with confined structure via a facile method became a big challenge.