A comparison of ethanol and water as the liquid phase in the direct formation of H2O2 from H2 and O2 over a palladium catalyst
A comparison of ethanol and water as the liquid phase in the direct formation of H2O2 from H2 and O2 over a palladium catalyst
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DOI：
10.1007/s10562-004-0769-1
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发表时间：
2005
影响因子：
2.8
通讯作者：
Yi-fan Han;J. Lunsford
中科院分区：
文献类型：
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作者：
Yi-fan Han;J. Lunsford
乙醇和水作为 H2 和 O2 在钯催化剂上反应产生过氧化氢的介质进行了比较。两种介质中的反应在H2O2形成的净速率、活性Pd的状态和反应机理方面存在显着差异。反应在大气压和 10°C 下进行，通过玻璃料以 4/1 的比例引入 O2 和 H2。在乙醇中，使用 50 mg 5 wt% Pd/SiO2，7 小时内获得 1.8 wt% H2O2；然而，大约一半的量是在水中获得的。此外，水中的净形成速率并不保持恒定。两个体系的 HCl 浓度均为 0.17 N，这有助于在水中形成胶体 Pd，但在乙醇中则不然。水中活性的丧失归因于胶体的不稳定性，此前已证明胶体是钯的活性状态。相比之下，这些结果表明负载型钯是乙醇体系中金属的活性状态。非选择性产物水的形成机制也受到反应进行介质的影响。在乙醇中，水是通过 H2 和 O2 的直接反应形成的，而在水相中，水似乎是通过直接途径和 H2O2 的还原形成的。
Ethanol and water have been compared as the media in which hydrogen peroxide is produced from the reaction of H2and O2over a palladium catalyst. There are significant differences between the reaction in the two media with respect to the net rate of H2O2formation, the state of the active Pd and the mechanism of the reaction. The reactions were carried out at atmospheric pressure and at 10 °C, with O2and H2being introduced in a 4/1 ratio through a glass frit. In ethanol, using 50 mg of 5 wt % Pd/SiO2, 1.8 wt% H2O2was attained in 7 h; whereas, about half this amount was attained in water. In addition, the net formation rate did not remain constant in water. Both systems were 0.17 N in HCl, which facilitated the formation of colloidal Pd in water but not in ethanol. The loss of activity in water is attributed to the instability of the colloid, which has been shown previously to be the active state of Pd. By contrast, these results show that supported Pd is the active state of the metal in the ethanol system. The mechanism for the formation of the nonselective product, water, also is affected by the media in which the reaction is carried out. In ethanol, water is formed by the direct reaction of H2and O2, while in the aqueous phase, water appears to be formed both by the direct pathway and by the reduction of H2O2.