A series of Co–Fe bimetallic catalysts was prepared, characterized, and studied for the hydrogenation of carbon dioxide. The catalyst precursors were prepared via an oxalate coprecipitation method. Monometallic (Co or Fe) and bimetallic (Co–Fe) oxalate precursors were decomposed under a N2 flow at 400 °C and further pretreated under a CO flow at 250 °C. The catalysts (before decomposition of the oxalates or after activation) were characterized by BET, TGA-MS, X-ray diffraction, CO-TPR, SEM, HR-TEM, and Mössbauer spectroscopy techniques. The hydrogenation reaction of CO2 was performed using Co–Fe bimetallic catalysts pretreated in situ in a fixed-bed catalytic microreactor operating in the temperature range of 200–270 °C and a pressure of 0.92 MPa. With increasing Fe fraction, the selectivity to C2–C4 for Co–Fe catalyst increased under all operating conditions. The alcohol selectivity was found to increase with increasing iron content of the Co–Fe catalyst up to 50%, but then it dropped with further addition of iron. Among the three different activation conditions, the CO pretreated Co–Fe (50Co50Fe) catalyst exhibited a much lower selectivity for methane. Addition of 1 wt % Na or 1.7 wt % K to 50Co50Fe catalyst increases its olefinic (C2–C4) and oxygenate selectivities.

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The effect of ammonia in syngas on the Fischer-Tropsch Synthesis (FTS) reaction over 100 Fe/5.1 Si/2.0 Cu/3.0 K catalyst was studied at 220-270 o C and 1.3 MPa using a 1-L slurry phase reactor. The ammonia added in syngas originated from adding ammonia gas, ammonium hydroxide solution or ammonium nitrate (AN) solution. A wide range of ammonia concentrations (i.e., 0.1-400 ppm) was examined for several hundred hours. The Fe catalysts withdrawn at different times (i.e., after activation by carburization in CO, before and after cofeeding contaminants, and at the end of run) were characterized by ICP-OES, XRD, Mössbauer spectroscopy, and synchrotron methods (e.g., XANES, EXAFS) in order to explore possible changes in the chemical structure and phases of the Fe catalyst with time; in this way, the deactivation mechanism of the Fe catalyst by poisoning could be assessed. Adding up to 200 ppmw (wt. NH 3 /av. Wt. feed) ammonia in syngas did not significantly deactivate the Fe catalyst or alter selectivities toward CH 4 , C 5+ , CO 2 , C 4-olefin and 1-C 4 olefin, but increasing the ammonia level (in the AN form) to 400 ppm rapidly deactivated the Fe catalyst and simultaneously changed the product selectivities. The results of ICP-OES, XRD and Mössbauer spectroscopy did not display any evidence for the retention of a nitrogen-containing compound