  The effect of silica-promotion on the reduction of iron oxides in hydrogen
was investigated using in situ X-ray diffraction and aberration-corrected
transmission electron microscopy to understand the mechanism of reduction and
the identity of the iron(II) silicate phase that has historically been
designated as the cause of the iron-silica interaction in such materials. In
the absence of a silica promoter the reduction of hematite to {\alpha}-Fe
proceeds via magnetite. Silica promoted amorphous iron oxide is reduced to
{\alpha}-Fe via stable magnetite and w\"ustite phases. During reduction of
silica-promoted iron oxide, Fe0 diffuses out of the amorphous silica-promoted
iron oxide matrix upon reduction from Fe2+ and coexists with an amorphous
Fe-O-Si matrix. Certain portions of w\"ustite remain difficult to reduce to
{\alpha}-Fe owing to the formation of a protective silica-containing layer
covering the remaining iron oxide regions. Given sufficient energy, this
amorphous Fe-O-Si material forms ordered, crystalline fayalite.
