CHARACTERIZATION OF RHFE CLUSTERS IN ZEOLITE NAY BY MOSSBAUER-SPECTROSCOPY, XPS, AND TEMPERATURE-PROGRAMMED REDUCTION

Decomposition of Fe(CO)(5) on prereduced Rh/NaY under flowing 5% H-2/A r has been used to prepare zeolite-encaged RhFex clusters free of Fe2 or Fe3+ ions or Fe oxides. XPS and TPR results indicate the absence o f significant amounts of iron other than Fe-0; some carbon is detected as methane by TPR in flowing H-2. Mossbauer spectroscopy shows a sing let that is assigned to Fe-0 alloyed with Rh but no significant amount s of Fe2+, which is abundant in samples prepared by conventional Fe2ion exchange, followed by reduction. A doublet with an isomer shift of 0.39 mm/s (relative to alpha-Fe) and a quadrupole splitting of 0.90 m m/s strongly contributes to the Mossbauer spectra of both the Fe2+-fre e and the conventional samples. The present results suggest that this signal is caused by some Fe-0 species, not by an irreducible Fe3+ oxid e.