Measurement of the Influence of the Microstructure of Alumina-Supported Cobalt Catalysts on their Activity and Selectivity in Fischer-Tropsch Synthesis by using Steady-State and Transient Kinetics

Abstract : Five alumina-supported Co catalysts with different particle sizes and structures were synthesized. The catalysts showed different activities during long-term Fischer–Tropsch experiments. Steady-state isotopic transient kinetic analysis (SSITKA) 12CO/H2 !13CO/H2 experiments were performed during these long-term runs. The number of active sites for CO adsorption and activation was estimated through the summation of all surface intermediates derived from the SSITKA results. Rather than comparing turnover frequencies, a kinetic analysis was performed. A simple kinetic rate equation based on the in situ number of active sites described the steady-state CO conversion over the five catalysts adequately. Thus the difference in the catalytic performance could not be attributed to a difference in particle size, phase orientation (face-centered cubic or hexagonal close packed), or Pt-promotion effect but instead was only because of the number of reduced Co atoms exposed during the reaction. Similarly, the selectivity depended on the CO conversion level and temperature and not on the catalyst structure.