In situ Fe K-edge XANES experiments point to a distinct difference in reducibility of iron in Fe-silicalite (without aluminum) and FeZSM-5 (with aluminum) upon dehydration. Whereas a noticeable part of Fe3+ is reduced to ferrous ions in the iron-containing aluminosilicalite, the ferric species in the ferrosilicalite maintain their oxidation state. The ability to selectively oxidize benzene to phenol with nitrous oxide in ferroaluminosilicalite relates to these Fe2+ centers. It is proposed that the large difference in reactivity between ferroaluminosilicalite and ferrosilicalite is due to the chemical difference of iron in FeOAl and FeOFe adducts. A new preparation method is introduced which leads to more selective and stable catalysts.