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Synthesis of Carbon Nanofibers by CO Disproportionation on Ultra-Fine Fe3O4 Powder

Carbon nanofibers (CNF), a novel mesoporous carbon material and an excellent catalyst support for liquid phase hydrogenation [1] , were synthesized by catalytic CO diproportionation on ultra-fine Fe3O4 powder under different H2 concentrations and temperatures. The structure and texture of as-synthesized CNF, which have evidently influences on the CNF-supported catalyst activity, were characterized by TEM, XRD, and BET. The changes of CNF yield with synthesis conditions were also studied. The as-synthesized CNF has fishbone-like structure and the graphitization degrees of the CNF varies at different H2 concentration and temperature. The BET surface area of as-synthesized CNF decrease from 219.6 to 95.7 m 2 /g when the growth temperature changes from 560 to 640 o C, while it increases from 131.6 to 180.4 m 2 /g when H2 concentration changes from 15% to 25%. These results show that the structure and texture can be controlled by changing the H2 concentration and temperature. The CNF yield as a function of H2 concentration at 560 o C, 600 o C and 640 o C is shown Fig.1. At high temperatures, the agglomeration of catalyst particles will decrease the CO diproportionation rate [2] , thus decreasing the CNF yield. H2 helps to clean the catalyst surface and maintain the catalyst activity. However, it will react with amorphous carbon by gasification. This explains why the CNF yield first increases then decreases with H2 concentration. At 560 o C and with 20% H2, the CNF yield is 162 g/g-cat, which is the highest for the investigated synthesis conditions.