Iron in faujasite lattice

The crystalline faujasite Y zeolites containing iron have been prepared. Evidence for the presence of Fe in the lattice framework is obtained using XRD solid state MASNMR <29Si,27Al and 13C> ESR both framework and hydroxyl IR spectroscopies and OTA. Lattice Fe leads to increase in the XRD unit... 

The relative crystalline stability of these materials was evaluated by DTA/TG (Fig.2). It is seen that the exothermic peak (indicating the collapse of the faujasite lattice) around 1133 K in NaY( Sample A) progressively shifts to lower temperataures with increasing iron content in the zeolite reaching 1033 K for Sample E indicating that the presence of iron reduces the thermal stability of the lattice... 

Fe with the template ion. DTA studies indicate that Fe-faujasites have lower thermal stability than their A1-analogs. The vibration frequency shifts from 3540 and 3630 to 3570 and 3643 cm-1 respectively on isomorphous substitution of A1 by Fe. Relative changes in the intensity of the ESR peak at g = 4.3 at low temperatures also support the conclusion that iron can be inserted in the faujasite lattice positions. 

Source of Activity in other Siliceous Catalysts.—Although various oxides can be combined with silica to give amorphous, acidic catalysts, the replacement of aluminium in zeolites (specially non-faujasitic zeolites) has proved to be very difficult with any element other than gallium. Materials of ZSM-5 structure with iron or boron in place of aluminium have been claimed recently, but it is not yet certain that either iron or boron is part of the zeolite lattice or that the catalytic activity observed is not due to residual lattice aluminium. 

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