Thermally modified active carbon as a support for catalysts for NH3 synthesis

The effect of thermal treatment of a typical active carbon at 1300 degrees C and 1900 degrees C on its structural properties was investigated. It has been found that only a high-temperature heating (1900 degrees C) produced substantial changes in the structure of the carbon used: a disappearance of a considerable part of open micropores and formation of a turbostratic structure. The prepared materials were used as a support in catalysts for NH3 synthesis. The precursor of the active phase was Fe(NO3)(3) . 9H(2)O. The iron nitrate deposited on the raw amorphous carbon decomposes to finely dispersed, hardly reducible iron oxides on heating to 470 degrees C in a H-2+N-2 mixture. Even if reduced to more than 33%, iron is inactive in NH3 synthesis (400-470 degrees C, p=10 MPa). When deposited on the turbostratic, low-surface area carbon, iron forms, however, well developed crystallites (similar to 60 nm), and is active in ammonia synthesis. Potassium activates strongly the surface of Fe, and, in the case of the amorphous support, it stimulates the reduction of iron oxides.