Thermally modified active carbon as a support for catalysts for NH3 synthesis Original Research Article

The effect of thermal treatment of a typical active carbon at 1300 °C and 1900 °C on its structural properties was investigated. It has been found that only a high-temperature heating (1900 °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 · 9H2O. The iron nitrate deposited on the raw amorphous carbon decomposes to finely dispersed, hardly reducible iron oxides on heating to 470 °C in a H2 + N2 mixture. Even if reduced to more than 33%, iron is inactive in NH3 synthesis (400–470 °C, p = 10MPa). When deposited on the turbostratic, low-surface area carbon, iron forms, however, well developed crystallites (~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.