Cobalt
catalysts supported on activated carbon and on carbon nanotubes
(CNTs) with different porosities were prepared by an incipient wetness
impregnation method and characterized by a series of methods. The
samples were reduced and then evaluated in a fixed-bed reactor for
Fischer–Tropsch (FT) synthesis. The porosity of the carbon
support greatly influenced the microstructure, the reducibility, the
dispersion, and the FT performance of the cobalt catalysts. The carbon
structure and the cobalt dispersion determined CO conversion. CNTs
with larger pore sizes were more stable at high temperature in a H2 atmosphere. The cobalt particle size impacted the CO turnover
frequency (TOF) and the C5+ selectivity. Larger cobalt
particles (up to 7 nm) resulted in higher TOF and C5+ selectivity;
for cobalt particles larger than 7 nm, no such increase in these parameters
was seen. The carbon support influenced the C5+ selectivity
and the C5+ hydrocarbon distribution. Interestingly, the
olefin/paraffin ratio of C2 was lower than that of C3 or C4 and a positive relationship existed between
the C2–C4 olefin/paraffin ratio and the
C5+ selectivity.
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