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首页> 外文期刊>Catalysis science & technology >Deactivation behavior of an iron-molybdate catalyst during selective oxidation of methanol to formaldehyde
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Deactivation behavior of an iron-molybdate catalyst during selective oxidation of methanol to formaldehyde

机译：iron-molybdate的失活行为在甲醇的选择性氧化催化剂对甲醛

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An iron molybdate/molybdenum oxide catalyst (Mo/Fe = 2) was synthesized by a hydrothermal method and the catalyst's performance and compositional changes were followed during selective oxidation of methanol to formaldehyde for up to 600 h. The activity was continuously measured for a series of experiments performed in a laboratory fixed-bed reactor with 10, 100, 250 and 600 h on stream under reaction conditions (5% MeOH, 10% O-2 in N-2, Temp. = 384-416 degrees C, W/F = 1.2 g(cat) h mol(MeOH)(-1)). The structural and compositional changes of the catalyst were investigated by a number of techniques including: XRD, Raman spectroscopy, XPS, SEM-EDS and STEM-EDS. Methanol forms volatile species with molybdenum at reaction conditions, leading to depletion of Mo from the catalyst. Excess MoO3 was shown to volatilize and leave the catalyst during the first 10 h on stream, leading to an initial loss in activity of 50%. From 10 to 600 h on stream leaching of molybdenum from the remaining iron molybdate phase (Fe-2(MoO4)(3), Mo/Fe = 1.5) leads to iron rich phases (FeMoO4 and Fe2O3, Me/Fe 1.5) and simultaneously an increase in activity to approximately 1.5 times the initial activity. Even at high degrees of molybdenum loss (Mo/Fe = 0.49) the formaldehyde selectivity remained above 92%, and the combined CO/CO2 selectivity was below 4%. This is likely due to a surface layer of MoOx on the catalyst at all times due to segregation and a surface in equilibrium with the gaseous molybdenum compounds. After 600 h on stream formation of -MoO3 was observed, indicating that this molybdenum oxide phase is stable to some extent under reaction conditions.
机译：钼酸铁(Mo / Fe /氧化钼催化剂= 2)是由水热合成方法催化剂的性能和组成变化是在选择性氧化甲醇的甲醛h。600活动是一系列连续测量在实验室进行的实验床反应器与10,100、250和600 h流在反应条件下(5%甲醇、10%在n - 0 2, Temp = 384 - 416摄氏度,W / F = 1.2g (cat) h摩尔(甲醇)(1))。成分变化的催化剂调查的技术包括:x射线衍射、拉曼光谱、XPS能谱STEM-EDS。钼在反应条件,导致损耗的钼催化剂。被证明挥发和离开的催化剂在第一个10 h流,导致一个最初的损失50%的活动。流的钼浸出剩余的钼酸铁阶段(Fe-2 (MoO4) (3),Mo / Fe = 1.5)会导致铁(FeMoO4发达阶段、Fe2O3我/ Fe & 活动大约增加1.5倍最初的活动。钼损失(Mo / Fe = 0.49)甲醛选择性仍高于92%,加起来还要多CO / CO2选择性低于4%。由于表层MoOx的催化剂由于种族隔离和表面平衡与气态钼化合物。-MoO3观察,表明这一点氧化钼阶段在某种程度上是稳定的在反应条件下。

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