Mossbauer spectroscopic study of iron containing hydrotalcite catalysts for the reduction of aromatic nitro compounds

Carbonated layered double magnesium hydroxides containing Fe with hydrotalc ite structure which are active and selective catalysts for the reduction of aromatic nitro compounds by hydrazine hydrate have been prepared and chara cterized by X-ray diffraction and Mossbauer spectroscopy. Using these techn iques we have shown that when the Fe/(Fe + Mg) ratio was greater than 0.2, which corresponds to the natural phase composition. ferrihydrite Fe5HO8.4H( 2)O was formed, This last phase, characterized at room temperature by a sup erparamagnetic doublet, leads after activation under nitrogen at 723 K to s mall particles of ferric oxide, An in-situ study of the activated catalysts allowed us to show that only iron cations present in this phase could unde rgo an oxidoreduction under the conditions of catalysis and that the cataly tic properties must be related to this last phase.