(560b) Metal/Support Interaction Effects in Fischer-Tropsch Synthesis: Significance of Catalyst Preparation

Recently there has been significantly increased interest in the technology for Gas-to-liquid (GTL) and biomass-to-liquid (BTL) processes based upon Fischer-Tropsch synthesis (FTS) of synthesis gas. Supported cobalt catalysts are often used because of their higher activity and selectivity. SiO2 is often used as a support material. Since the physical and chemical properties of the support influence the catalyst performance, the objective of this paper is to investigate methods for mitigating the adverse effects of such metal-support interaction in the FTS using cobalt catalysts.

In prior work at USF [1], we established the role of cobalt silicate formation on the activity of SiO2 supported cobalt catalysts. Once formed, the silicates cannot be reduced back to recover the active metal catalyst particles. It is suspected that the cobalt silicates are formed by reaction between aqueous cobalt complexes and surface silanol groups. Ernst et al attributed the cobalt silicate formation to the reaction between CoO and SiO2 whereas Puskas et al suspected a two step process in which CoO first reacts with water to form cobalt hydroxide which in turn reacts with SiO(OH)2 to form cobalt silicate.

Therefore, there is reason to expect that by avoiding aqueous solutions during the catalyst preparation stage one can reduce the formation of silicates ( complete elimination of water contact is not possible since water is a byproduct of the FTS reaction). In this paper we will present our studies on catalysts preparation techniques that avoid water.

Engineered egg-shell Co/SiO2 Fischer-Tropsch catalysts were synthesized using various preparation precursors and impregnation techniques. The supported catalysts were analyzed by FTIR, XRD, BET, SEM and XPS methods at intermediate stages of their preparation in order to study metal support interaction. The catalyst performance was studied using a fixed bed reactor. The effects of dispersion techniques, precursors, calcination temperature, drying time and support structure on the performance of the catalyst will be presented.

References:

1. Kababji A.H., Joseph B., Wolan J.T. (2009) Catal Lett (Published online first)

2. Iglesia E. (1997) Appl Catal A 161:59

3. Iglesia E., Soled S.L., Fiato R.A. (1992) J Catal 137:212