Preparation of high thermal conductivity SiO₂@Al support and its application in Fischer-Tropsch synthesis

High thermal conductivity supports, core-shell structure SiO₂@Al, was successfully prepared by hydrolyzing tetraethyl orthosilicate (TEOS) under weak alkaline condition and using hexadecyl trimethyl ammonium bromide (CTAB) as the template. 15% (mass fraction) of cobalt was loaded on these supports by excessive impregnation method for Fischer-Tropsch synthesis reaction. The prepared catalysts have high metal aluminum content, high specific surface shell layer and relatively uniform pore size of 2.6−2.8 nm. By changing the added amount of TEOS, the content of silica in the supports and the thickness of the shell layer can be adjusted. As the thickness of the silica shell layer increases, the specific surface area of the supports gradually increases, the interaction between cobalt and the supports increases, and at the same time, the reduction degree of the catalysts decreases. The silica shell enhances the dispersion of metallic cobalt and avoids deactivation caused by agglomeration of metallic cobalt on aluminum particles. Under the condition of similar conversion rate, the catalyst 15Co/5-SiO₂@Al with a thinner shell layer has the best performance in Fischer-Tropsch synthesis which is mainly due to the moderate metal-support interaction between the thin silica shell layer and metal cobalt particles. The thinner silica shell layer can anchor and disperse cobalt species to increase the reduction degree of cobalt species.