The effect of silanol groups on the metal-support interactions in silica-supported cobalt Fischer-Tropsch catalysts. A temperature programmed surface reaction

Abstract

The effect of H bonded and isolated silanol groups on the metal support interactions of SiO2-supported Co catalysts in Fischer-Tropsch (FT) synthesis are reported. SiO2 supports were pre-treated in order to improve the concentration of isolated SiOH on the surface of the SiO2. Isolated SiOH groups act as an aid to achieving relatively good metal dispersions by creating metal anchoring sites, and enhances smaller metal crystallites deposition on the surface of the SiO2. SiO2 supports were pre-treated in two different ways: (a) pre-treatment by thermal method (HT); (b) pre-treatment by ethylene glycol (EG). The incipient wetness impregnation technique was adopted for the preparation of the catalysts, each catalyst loaded with approximately 10 wt% Co on each of the three supports designated as Co/SiO2 – UT, Co/SiO2 – HT, and Co/SiO2 – EG. Co/SiO2 – UT was used as a reference for this study. A number of characterization methods were applied to study the chemical and physical properties of the supports and the catalysts namely BET, XRD, ICP-OES, FTIR, H2 chemisorption, TEM, TPR, and TPSR. The results from H2 chemisorption, TEM and XRD indicated that the Co/SiO2 – EG showed relatively smaller metal crystallites and a better cobalt crystallite dispersion while TPR, CO TPD, and TPSR studies indicated that Co/SiO2 – EG catalyst exhibited stronger metal-support interaction, unlike the other two catalysts. Catalyst evaluation experiments showed that Co/SiO2-HT catalysts showed better FT activity while the Co/SiO2 – EG catalyst favored light olefins. FT catalyst evaluation results were in agreement with the TPSR studies.