Hydrogenation of Carbon Dioxide over Co-Fe Bimetallic Catalysts

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.