Iron nitride catalysts precipitated

Studies of the Fischer-Tropsch synthesis on nitrided catalysts at the Bureau of Mines have been described (4,5,23). These experiments were made in laboratory-scale, fixed-bed testing units (24). In reference 5, the catalyst activity was expressed as cubic centimeters of synthesis gas converted per gram of iron per hour at 240°C. and at a constant conversion of 65%. Actually, the experiments were not conducted at 240°C., but the activity was corrected to this temperature by the use of an empirical rate equation (25). Conditions of catalyst pretreatment for one precipitated and two fused catalysts are given in Table IV. 

Shultz, Seligman, Shaw, and Anderson (5) attempted to prepare nitrides by treating raw (oxide) iron catalysts directly with ammonia. An analogous reaction, the formation of iron carbides by treatment of raw precipitated catalysts with carbon monoxide or synthesis gas, can be carried out at temperatures between 200° and 325°C. However, ammonia treatment of a precipitated catalyst (Fe203-Cu0-K2C03, Bureau of Mines number P3003.24) at 300°, 350°, and 400°C. resulted... 

Nitrided iron catalysts are remarkably stable toward oxidation and deposition of elemental carbon in the synthesis at both 7.8 and 21.4 atm. Shultz, Seligman, Lecky, and Anderson (23) described composition changes in nitrided fused, sintered, and precipitated catalysts in the synthesis. In a test (X218) with 1H2 + ICO synthesis gas at 7.8 atm., the catalyst was sampled frequently for analysis. X-ray diffraction patterns showed only the e-nitride or carbonitride phase, except for weak... 

Comparative tests at the Piltsbur i Energy Technology Center with a Fe-Cu - K catalyst revealed a better stability for the nitrided iron catalyst [63]. The precipitated nitrided iron catalyst gave a higher percentage of oxygenates than did nitrided fused iron. 

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