高导热SiO_(2)@Al载体的制备及其在费托合成中的应用

Preparation of high thermal conductivity SiO_(2)@Al support and its application in Fischer-Tropsch synthesis

通过在弱碱性条件下水解正硅酸乙酯(TEOS),以十六烷基三甲基溴化铵(CTAB)为模板剂成功制备了SiO_(2)@Al核壳结构高导热载体,并采用过量浸渍法负载15%(质量分数)钴物种,进行了费托合成反应性能考察。结果表明,制备得到的核壳结构载体既保留了高金属铝含量,又具有高比表面积壳层,孔径较为均一,为2.6−2.8 nm。通过改变正硅酸乙酯的添加量可以调节载体中二氧化硅的含量,进而控制壳层厚度。随着二氧化硅壳层厚度的增加,载体的比表面积逐渐增大,催化剂还原度降低。二氧化硅壳层增强了金属钴的分散,避免金属钴在铝颗粒上的团聚失活。在相近转化率条件下,壳层厚度较薄的15Co/5-SiO_(2)@Al催化剂显示出最好的费托反应性能,这主要归因于较薄的二氧化硅壳层和金属钴颗粒之间具有适中的金属-载体相互作用,在起到锚定分散钴物种作用的同时提高了钴物种的还原度。

High thermal conductivity supports,core-shell structure SiO_(2)@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-SiO_(2)@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.