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
Résumé
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.
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