Synthesis and Characterization of Cobalt/Manganese Bimetallic Nanocatalyst Prepared via Reverse Microemulsion Method

The bimetallic cobalt-manganese nanocatalyst was synthesized via reverse
microemulsion method. The reverse microemulsion was used as an alternative route
to prepare the nanocatalyst rather than common catalyst preparation route,
impregnation method as the later have reported problem with the metal dispersion. In
this project, the main objective is to synthesize well-dispersed bimetallic
nanocatalyst consisting of cobalt-manganese in different composition on silica
support via reverse microemulsion method, to study the properties of catalyst by
applying several characterization methods and to study the catalytic performance in a
Fischer-Tropsch (FT) reaction. The following compositions were prepared which are
pure cobalt, pure manganese, 95Co5Mn/SiO2, 88Co12Mn/SiO2 and
76Co24Mn/SiO2. The nanocatalyst was analyzed by using Transmission Electron
Microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM) and
Temperature Programmed Reduction (TPR). The performance of the nanocatalyst
for FT reaction was studied in a stainless steel fixed bed micro reactor. The average
particle size of the nanocatalyst was 2-5 nm. TEM image show nanocatalyst
88Co12Mn/SiO2 was better dispersed compared to other formulations. The TPR
result of the 100Co/SiO2 and 95Co5Mn/SiO2 showed that these nanocatalysts were
reduced at the temperatures of 690 oC and 645 oC, respectively. The reducibility was
improved when 12 wt% Mn was added to Co-based nanocatalyst for
88Co12Mn/SiO2 since the high temperature peak was shifted to lower temperature
(536 oC). However, further increase in Mn content (24 wt%) had shifted the high
temperature peak to higher temperature (600 oC). This indicates that the optimum
Mn content (12 wt%) enhanced the reducibility of the Co-based nanocatalyst. The
catalytic activity in the FT reaction varied with the content of Mn in the Co-based
nanocatalyst. In conclusion, the highest CO conversion (20.5%) and C5+ selectivity
(12.6%) were obtained using 88Co12Mn/SiO2 nanocatalyst.