Abstract:
Mössbauer spectroscopy, X-ray spectroscopy, SEM, EDX, heat capacity and SQUID measurement were carried out in conjunction with a catalytic study on mixed Fe-Mo oxides, some of which have been used in selective oxidation of certain hydrocarbons. With the specific activity being sensitive to the catalytic particle size and morphology, an aerogel process was employed to prepare seven samples covering Fe/Mo ratios from 1/2 to 2/1and some of the samples were annealed at 300oC and 500oC . Mössbauer data have been analyzed, with each set well fitted to reflect one Fe3+ and two or more non-equivalent Fe2+ sites. There isomer shift, quadruple splitting and molar fraction are analyzed in terms of temperature and Fe/Mo-ratio dependence. The Fe-rich samples exhibit magnetic ordering at low temperatures, revealing multiple sextets corresponding to different magnetic hyperfine fields. Two samples with the Fe:Mo ratio 1:1 and 2:3 were study in more detail their X-ray diffraction pattern reveal that they crystallize with the β-FeMoO4 structure. SEM gives unusual morphology and the material form into hallow sphere with 2um in diameter. EDS confirms that the metal ion is fairly uniformly distributed and close to the nominal values. Finally heat capacity and SQUID measurements confirm the antiferromagnetic phase transition near 13K for the heat treated samples.
