1 research outputs found
Effects of Sodium on the Catalytic Performance of CoMn Catalysts for Fischer–Tropsch to Olefin Reactions
The
effects of a sodium (Na) promoter on the catalytic performance
of cobalt-manganese (CoMn) catalysts for Fischer–Tropsch to
olefin (FTO) reactions were investigated. For the sample without Na,
Co<sup>0</sup> was found to be the active phase for the traditional
Co-based Fischer–Tropsch reaction with low CO<sub>2</sub> selectivity.
The olefin/paraffin (O/P) ratio was found to be low with a C<sub>2–4</sub><sup>=</sup> selectivity of only 15.4 C%. However, with the addition
of Na, cobalt carbide (Co<sub>2</sub>C) quadrangular nanoprisms with
the (101) and (020) facets exposed were formed. The Co<sub>2</sub>C nanoprisms displayed a high C<sub>2–4</sub><sup>=</sup> selectivity
(54.2 C%) as well as a low methane selectivity (5.9 C%) under mild
reaction conditions. The O/P ratio for C<sub>2–4</sub> reached
23.9, and the product distribution deviated greatly from the classical
Anderson–Schulz–Flory (ASF) distribution. Co<sub>2</sub>C nanoprisms were considered to be an effective FTO active phase
with strong facet effects. The Na promoter played a key role in the
evolution of the FTO catalysts. The addition of Na, which acted as
an electronic donor to cobalt, resulted in stronger CO adsorption
and enhanced CO dissociation, which also benefited the formation of
the Co<sub>2</sub>C phase, leading to highly stable and active catalysts.
The effects of other alkali promoters were also studied, and only
the K promoter had an effect similar to that of Na on the CoMn catalysts
for promoting the FTO reaction