The Activation of Iron Catalyst for Ammonia Synthesis

The activation of ammonia catalysts is essentially a reduction of non-porous magnetite particles with hydrogen to yield the internal porous structure of the iron catalyst. The reduction is studied by means of a “core-and-shell” model where the gas-solid reaction proceeds on the interface between the core and shell. Effective diffusion coefficients are calculated from experimental pore size distribution measurements. Different reaction rate expressions were tested on experimental reduction curves for cases with and without water addition, and it is shown that it is necessary to include the adsorption of water in the rate expression. Finally, some limitations in the model are described.