51.    HALL, W. K., TARN, W. H., AND ANDERSON, R. B.  Studies of the Fischer-Tropsch Synthesis, VIII.  Surface-Area and Pore-Volume Studies of Iron Catalysts.  Jour. Am. Chem. Soc., vol. 72, 1950, pp. 5436-5443.

              Changes are reported in surface area and pore volume during the reduction of 2 widely different Fe catalysts, a precipitated Fe₂O₃-CuO-K₂CO₃ catalyst and a fused Fe₃O₄-MgO-K₂O catalyst.  Information is presented as to the nature of Fe catalysts at the start of the Fischer-Tropsch synthesis, as well as data pertinent to the mechanism of reduction.  The surface areas of raw precipitated Fe gel catalysts are high, and their pore diameters are small; conversely unreduced Fe-synthetic NH₃-type catalysts have essentially no surface area and no pore volume.  After reduction at 300° and 450°-550°, respectively, both types have moderate surface areas of about 8 m.² per gm. and reasonably large pore diameters of 350-900 Å.  Thermal sintering of precipitated Fe gels causes drastic changes in structure, but removal of O₂ by reduction produces an even greater effect.  The surface area and pore volume of an Fe-synthetic NH₃-type catalyst increased in a linear manner with extent of reduction, whereas the average pore diameter remained constant.  It is shown that only surface-area measurements and complete chemical analysis of the raw catalyst are necessary to establish the pore structure of an Fe-synthetic NH₃-type catalyst as a function of the extent of reduction.  Increasing the reduction temperature of an Fe-synthetic NH₃-type catalyst from 450° to 650° produced an 8-fold increase in the pore diameter.