UNUSUAL STRUCTURE AND STABILITY OF IRON-OXYGEN NANO-CLUSTERS IN FE-ZSM-5 CATALYSTS

Feng and Hall have recently reported that over-exchanged Fe-ZSM-5 mate rials prepared by a special route show high stability in the selective reduction of 2-methylpropane (isobutane) by NOx. We report that iron- oxygen clusters in ZSM-5 catalysts prepared by a conventional route sh ow unexpected structural features, with significant iron-iron co-ordin ation and a rather short Fe-Fe interatomic distance of 2.53 +/- 0.02 A ngstrom. Iron in these clusters is readily interconvertible between th e (II) and (III) oxidation states, but the clusters are stable against reduction to Fe(0) even at 1250 K in hydrogen. We suggest that the cl usters adopt structures similar to that of ferredoxin II, Fe3S4.