The involvement of water in the selective oxidation of MAL to MAA over a pure Keggin-type H₃PMoO₁₂O₄₀ catalyst was investigated using an in situ DRIFTS reactor coupled with a mass spectrometer for the first time to elucidate the reaction pathway associated with water. Comparing the spectra and activity data using D₂O instead of H₂O during transient switching experiments has allowed us to evaluate the possible active sites where D₂O is activated. It has been found that, during the cycling switches of D₂O in and out of the MAL + O₂ gas feed at 320 °C, the formation of MAA–OD product is increased and decreased when D₂O is added and removed, respectively. This suggests that the deuterium from D₂O is involved in the production of gas phase MAA–OD. In addition, the in situ DRIFTS-MS results obtained from the isotopic switches between D₂O and H₂O reveal changes in the characteristic infrared bands of the Keggin unit between 1200 and 600 cm⁻¹. It is found that the isotopic exchange possibly occurs on the bridging oxygen of Mo–O–Mo unit, where water is activated for the formation of MAA. Based on the in situ DRIFTS-MS analysis from the transient switching experiments, the reaction mechanism associated with the effect of water on the selective oxidation of MAL to MAA over Keggin-type H₃PMoO₁₂O₄₀ catalyst is proposed.

中文翻译：

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阐明了水在甲基异丙烯醛被杂多酸化合物氧化过程中促进甲基丙烯酸形成的作用

首次使用原位DRIFTS反应器和质谱仪研究了水在纯Keggin型H ₃ PMoO ₁₂ O ₄₀催化剂上将MAL选择性氧化为MAA的过程，从而首次阐明了与水相关的反应路径。在瞬态转换实验过程中使用D ₂ O而不是H ₂ O比较光谱和活度数据，使我们能够评估D ₂ O被激活的可能的活性位点。已经发现，在循环中，D ₂ O进出MAL + O _2的切换。在320°C的气体进料中，分别添加和除去D ₂ O时，MAA-OD产物的形成增加或减少。这表明来自D ₂ O的氘参与了气相MAA–OD的生产。另外，从D ₂ O和H ₂ O之间的同位素转换获得的原位DRIFTS-MS结果揭示了Keggin单元的特征红外波段在1200和600 cm ^{-1之间的变化}。已经发现，同位素交换可能发生在Mo–O–Mo单元的桥接氧上，在那里水被活化形成MAA。基于原位通过瞬态转换实验的DRIFTS-MS分析，提出了与水影响在Keggin型H ₃ PMoO ₁₂ O ₄₀催化剂上将MAL选择性氧化为MAA的反应机理。