Abstract Iron molybdate/molybdenum oxide catalysts with varying content of Mo (Mo/Fe = 1.6 and 2.0) were synthesized by a mild hydrothermal method and structurally characterized by XRD, XPS, Raman spectroscopy, SEM–EDX, BET and ICP-OES. The stability of the prepared catalysts in selective oxidation of methanol to formaldehyde was investigated by catalytic activity measurements for up to 100 h on stream in a laboratory fixed-bed reactor (5% MeOH, 10% O 2 in N 2 , temp. = 380–407 °C). Excess MoO 3 present in the catalyst volatilized under reaction conditions, which lead to an initial loss of activity. Interestingly, the structure of the excess MoO 3 significantly affected the stability of the catalyst. By using low temperature hydrothermal synthesis, catalysts with the thermodynamically metastable hexagonal h-MoO 3 phase was synthesized, which yielded relatively large crystals (2–10 µm), with correspondingly low surface area to volume ratio. The rate of volatilization of MoO 3 from these crystals was comparatively low, which stabilized the catalysts. It was furthermore shown that heat-treatment of a spent catalyst, subject to significant depletion of MoO 3 , reactivated the catalyst, likely due to migration of Mo from the bulk of the iron molybdate crystals to the surface region. Graphical Abstract Fe 2 (MoO 4 ) 3 /MoO 3 catalysts for selective oxidation of methanol were synthesized by hydrothermal synthesis forming large hexagonal-MoO 3 crystals. Significantly lower rate of catalyst deactivation due to volatilization of MoO 3 under reaction conditions was observed for the large h-MoO 3 compared to smaller crystals of thermodynamically stable α-MoO 3 .

中文翻译：

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用于甲醇选择性氧化成甲醛的钼酸铁催化剂的稳定性：制备方法的影响

摘要 通过温和的水热法合成了具有不同 Mo 含量（Mo/Fe = 1.6 和 2.0）的钼酸铁/氧化钼催化剂，并通过 XRD、XPS、拉曼光谱、SEM-EDX、BET 和 ICP-OES 对其进行了结构表征。通过在实验室固定床反应器（5% MeOH，10% O 2 in N 2，温度 = 380）中进行长达 100 小时的催化活性测量，研究了制备的催化剂在甲醇选择性氧化成甲醛中的稳定性–407 °C）。存在于催化剂中的过量 MoO 3 在反应条件下挥发，导致初始活性损失。有趣的是，过量MoO 3 的结构显着影响了催化剂的稳定性。通过低温水热合成，合成了具有热力学亚稳态六方 h-MoO 3 相的催化剂，这产生了相对较大的晶体 (2-10 µm)，相应的表面积与体积比较低。MoO 3 从这些晶体中挥发的速率相对较低，这稳定了催化剂。进一步表明，对经历过MoO 3 显着消耗的废催化剂进行热处理，可能是由于Mo从钼酸铁晶体的主体迁移到表面区域而使催化剂重新活化。图形摘要 Fe 2 (MoO 4 ) 3 /MoO 3 甲醇选择性氧化催化剂通过水热合成法合成，形成大六方-MoO 3 晶体。与热力学稳定的α-MoO 3 的较小晶体相比，对于大的h-MoO 3 观察到由于MoO 3 在反应条件下挥发而导致的催化剂失活率显着降低。