Direct synthesis of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in an aqueous acidic medium over halide-modified Pd/Al2O3 catalysts
Direct synthesis of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in an aqueous acidic medium over halide-modified Pd/Al2O3 catalysts
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DOI：
10.1016/j.apcata.2007.06.030
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发表时间：
2007-10
影响因子：
5.5
通讯作者：
C. Samanta;V. Choudhary
中科院分区：
文献类型：
--
作者：
C. Samanta;V. Choudhary
在酸性水性反应介质中，在卤化物改性的氧化和还原 Pd/Al2O3 催化剂上，在非常温和的条件下（27°C 和大气压），从其元素直接合成 H2O2。通过将卤化物离子引入负载型 Pd/γ-Al2O3 催化剂中或通过在 Pd 沉积之前将卤化物离子沉积在载体 (γ-Al2O3) 上，将卤化物离子引入催化剂中。为了阐明直接 H2O2 过程中强烈影响 H2O2 产率/选择性的因素，也在相应的催化剂上进行了与 H2O2 合成相似的反应条件下的 H2O2 分解和加氢。卤化物改性的 Pd/Al2O3 催化剂在直接 H2O2 合成中的性能表明，在 Pd 沉积在载体上之前或之后，在催化剂体系中插入卤化物对 H2O2 的形成具有相当的定性影响。 Pd 氧化态和卤离子的性质对 H2 转化（在直接 H2O2 合成过程中）和 H2O2 分解和/或氢化反应有很大影响。虽然 Pd 氧化态对 H2O2 形成的影响对于含有 F− 和 Cl− 离子的催化体系很重要，但发现 Pd 氧化态的影响对于含有 Br− 离子的催化剂体系不太重要；由于 Br− 离子的存在，无论 Pd 的氧化态如何，H2O2 的形成选择性都显着增加。发现在卤化物改性 Pd/Al2O3 催化剂上，在氢气存在下，H2O2 破坏途径（即氢化和/或分解）的性质强烈依赖于催化剂卤化物改性过程中掺入催化剂中的卤化物离子的性质。
Direct synthesis of H2O2from its elements was carried out in an acidic aqueous reaction medium over halide-modified oxidized and reduced Pd/Al2O3catalysts under very mild conditions (at 27°C and atmospheric pressure). The halide ions were introduced into the catalyst by incorporating halide ions into supported Pd/γ-Al2O3catalyst or via depositing halide ions on the support (γ-Al2O3)prior to Pd deposition. The H2O2decomposition and hydrogenation over the corresponding catalysts were also carried out under the reaction conditions similar to those employed for the H2O2synthesis in order to elucidate the factors strongly affecting the H2O2yield/selectivity in the direct H2O2process. The performance of halide-modified Pd/Al2O3catalysts in the direct H2O2synthesis revealed that halide insertion in the catalyst system prior to or after Pd deposition on the support had comparable qualitative effect on the H2O2formation. Both the Pd oxidation state and the nature of the halide ions had strong influences on the H2conversion (in direct H2O2synthesis process) and H2O2decomposition and/or hydrogenation reaction. While the effect of Pd oxidation state on the H2O2formation was significant for the catalytic system containing F−and Cl−ions, the influence of the Pd oxidation state was found less important for the catalyst system containing Br−ions; the H2O2formation selectivity increased significantly due to the presence of Br−ions, irrespective of the Pd oxidation state. The nature of the H2O2destruction pathway (i.e. hydrogenation and/or decomposition) in the presence of hydrogen over halide-modified Pd/Al2O3catalysts was found to be strongly dependent upon the nature of the halide ions incorporated in the catalyst during halide-modification of the catalyst.