FISCHER-TROPSCH SYNTHESIS: INVESTIGATION OF THE IMPACT OF Pt AND Ag PROMOTOR LOADING ON THE LOCAL ATOMIC STRUCTURE OF Co/ALUMINA CATALYSTS USING AN IN-SITU XAS

摘要

Cobalt/alumina is an effective Fischer-Tropsch synthesis catalyst for gas-to-liquids (GTL) production with high H2/CO ratio (～2:1). There is general agreement that reduced Co metal surface sites are active sites for Fischer-Tropsch synthesis over this catalyst. Following calcination, cobalt oxide particles on alumina surface are normally very small due to the strong interaction of alumina with cobalt oxide. Accordingly, it is rather difficult to generate a high degree of reduced Co metal by activation in H2. The addition of noble metal promoter (e.g., Pt) enhances the reducibility of cobalt oxide species, perhaps by a H2 dissociation and spillover mechanism (1) or chemical promotion. Although platinum is an excellent promoter, one drawback is that it is very expensive. Although proposed previously, Ag metal as an alternative was further investigated in this work. Silver can successfully promote the reduction of Co/alumina catalyst and, particularly, its price is very low ($24/Troy oz.) compared to that of Pt ($1690/Troy oz.). In this study, a comparison of the local atomic structure between Pt-promoted Co/alumina and Ag-promoted Co/alumina catalyst was thoroughly studied using X-ray absorption techniques.