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采用原位穆斯堡尔谱、XRD、XPS、IR和UVDRS等对Fe/Mo=0.67的Fe_2(MoO_4)_3和Fe/Mo=0.29的Fe_2(MoO_4)_3-4MoO_3样品进行了研究。实验结果表明,在甲苯氧化反应条件下,样品中一部分Fe_2(MoO_4)_3相还原为β-FeMoO_4。在反应温度(450℃)下通空气氧化,生成的β-FeMoO_4又氧化为Fe_2(MoO_4)_3。在甲苯选择性氧化中,易还原为β-FeMoO_4的样品,其甲苯选择性氧化活性较高。样品中的Fe~(3+)起着稳定Mo~(6+)的作用而Fe~(3+)还原为Fe~(2+)。在氧的作用下,Fe~(2+)再氧化为Fe~(3+),并使表面上吸附的氧转化为晶格氧。Fe_2(MoO_4)_3中的Mo~(6+)吸附甲苯分子,反应时,钼酸铁的表面晶格氧和甲苯反应使之生成苯甲醛和水。
The samples of Fe_2 (MoO_4) _3 with Fe / Mo = 0.67 and Fe_2 (MoO_4) _3 ~ 4MoO_3 with Fe / Mo = 0.29 were investigated by in-situ Mossbauer spectroscopy, XRD, XPS, IR and UVDRS. The experimental results show that a part of Fe_2 (MoO_4) _3 phase in the sample is reduced to β-FeMoO_4 under toluene oxidation conditions. At the reaction temperature (450 ℃) through the air oxidation, the generated β-FeMoO_4 and then oxidized to Fe_2 (MoO_4) _3. In selective oxidation of toluene, the sample that is easy to be reduced to β-FeMoO_4 has higher toluene selective oxidation activity. Fe 3+ in the sample plays a role of stable Mo 6+ and Fe 3+ reduced to Fe 2+. Under the action of oxygen, Fe ~ (2+) reoxidizes to Fe ~ (3+) and converts the oxygen adsorbed on the surface into lattice oxygen. Mo 6+ in Fe 2 (MoO 4) 3 adsorbs toluene molecules. During the reaction, the lattice oxygen of the molybdenum molybdate reacts with toluene to form benzaldehyde and water.