Abstract: The catalytically active components of a series of Fe2O3-Sb2O4 mixed oxide catalysts with different Sb/Fe ratios, calcined at elevated temperature, with or without support, have been investigated by X-ray diffraction, Mossbauer spectroscopy and XPS in order to elucidate their catalytic behavior in ammoxidation of propylene. X-ray diffraction measurement showed that FeSbO4 is present in all samples, and that the appearence of α-Fe2O3 or Sb2O4 depends upon the Sb/Fe ratio. All the Mossbauer spectra showed a doublet caused by paramagnetic Fe3+ in FeSbO4; only at Sb/Fe<1, an additional sextet appeared typically for α-Fe2O3. All catalysts with Sb/Fe>1 and calcined at 800℃ showed a superposed second doublet undoubtely arising from Fe2+ of a new active component, perhaps of FeSb2O6. Surface analysis by XPS confirmed this result through the appearence of a shoulder at BE = 709.3 eV for Sb-rich catalysts. The rate of conversion of propylene was shown to vary with the ratio of Fe3+/Fe2+. This fact shows that, the catalytic behavior of catalyst could not be attributed to one component only. Correlations of acrylonitrile yield with concentrations of Fe2+ and Fe3+ respectively showed that, FeSbO4 seems to be the basic active component of catalyst, upon which the formation of a new phase containing Fe2+ may be responsible for good selective oxidation.

摘要： 为了阐明Fe_2O_3-Sb_2O_4复合氧化物催化剂在丙烯氨氧化中的催化性能,我们采用X线衍射、穆斯堡尔谱和XPS对有、无载体的不同锑铁比和焙烧温度的一系列催化剂进行了研究.X线衍射测定表明,这些样品中都有FeSbO_4,并且a-Fe_2O_3或Sb_2O_4的出现与Sb/Fe有关.催化剂的穆斯堡尔谱都有一对由FeSbO_4中顺磁Fe~(3+)引起的双峰;只有在Sb/Fe<1时,才有a-Fe_2O_3的典型六线谱出现.经800℃焙烧的Sb/Fe>1催化剂还都展现出由FeSb_2O_6中Fe~(2+)引起的另一对双峰.根据对富锑催化剂的XPS分析,结合能为709.3电子伏特的肩峰的出现,又进一步证明这种含Fe~(2+)的新活性组分FeSb_2O_6的存在.丙烯转化速度与Fe~(3+)/Fe~(2+)的关系表明,催化剂的催化性能不只取决于一种活性组分.以丙烯腈的生成速度与Fe~(3+)和Fe~(2+)的浓度关系可以得出结沦:FeSbO_4是基本活性组分,而在其上生成含Fe~(2+)新相则可能是使催化剂具有选择氧化作用的原因.