Role of ZrO2 in Promoting the Activity and Selectivity of Co-Based Fischer–Tropsch Synthesis Catalysts

Abstract

The effects of Zr promotion on the structure and performance of Co-based Fischer–Tropsch synthesis (FTS) catalysts were investigated. Inclusion of Zr in the catalysts was found to increase the FTS turnover frequency and the selectivity to C5+ hydrocarbons and to decrease the selectivity to methane under most operating conditions. These improvements to the catalytic performance are a function of Zr loading up to an atomic ratio of Zr/Co = 1.0, above which the product selectivity is insensitive to higher concentrations of the promoter. Characterization of the Co nanoparticles by different methods demonstrated that the optimal Zr loading corresponds to half monolayer coverage of the Co surface by the promoter. Measurements of the rate of FTS at different pressures and temperatures established that the kinetics data for both the Zr-promoted and unpromoted catalysts are described by a two-parameter Langmuir–Hinshelwood expression. The parameters used to fit this rate law to the experimental data indicate that ...