SURFACE MODIFICATION OF SUPPORTED Ru : Mn/SiO2 FISCHER-TROPSCH SYNTHESIS CATALYSTS

ABSTRACT Co-impregnated ruthenium–manganese bimetallic catalysts supported on high-surface area silica support were exposed to high-temperature reduction–oxidation–reduction (R/O/R) treatment to generate catalytic surfaces having specific geometry. The impact of R/O/R modifications was probed via a model Fischer-Tropsch synthesis (FTS) reaction aided by various characterisation techniques (TEM, XPS, s-SIMS, selective chemisorption). The characterisation results indicated that alternating reduction and oxidation of the catalyst was propitious to the formation of a specific surface landscape enriched in Ru : Mn bimetallic sites as well as in ruthenium and manganese oxides. The increase in metal dispersion and BET surface area following R/O/R exposures of the catalysts was due to re-dispersion of particles in the range of 2–10 nm, to surface modification, and to changes in active sites. The presence of ruthenium oxide, manganese oxide and Ru : Mn was likely to be at the origin of the enhancement in the production of unsaturated hydrocarbons in the FTS reaction.