Factors influencing decomposition of H2O2 over supported Pd catalyst in aqueous medium
Factors influencing decomposition of H2O2 over supported Pd catalyst in aqueous medium
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DOI：
10.1016/j.molcata.2006.07.009
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发表时间：
2006-12-15
影响因子：
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通讯作者：
Choudhary, T. V.
中科院分区：
文献类型：
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作者：
Choudhary, V. R.;Samanta, C.;Choudhary, T. V.
由于H2 O2分解可导致在负载型Pd催化剂上由H-2和O-2直接合成H2 O2的过程中的选择性/产率损失，因此重要的是增强对影响H2 O2分解反应的因素的理解。在此，已经进行了详细的研究以研究不同因素的影响，例如（a）反应介质中酸的性质和浓度，（B）反应介质中存在和不存在酸时卤化物的性质和浓度，（c）预处理程序和（d）通过掺入不同卤化物的催化剂改性，在25 ℃下，在水介质中，在5%Pd/C催化剂上的H2 O2分解反应。本研究表明，H2 O2分解活性受到上述所有因素的深刻影响。酸对H_2O_2分解活性的抑制效果依次为：氢碘酸>氢溴酸>盐酸>乙酸>磷酸>硫酸>高氯酸。酸的能力，以降低H2 O2分解活性被认为是非常强烈地依赖于其相关的阴离子的性质。卤化物，如碘化物，溴化物和氯化物在抑制H2 O2分解活性方面特别有效。催化剂的氧化预处理强烈抑制了其H2 O2分解活性，而还原处理则促进了其活性。随着每次连续使用，观察到催化剂的H2 O2分解活性逐渐降低，这是由于Pd被H2 O2原位亚表面氧化。通过反应介质或先前的催化剂改性的卤化物掺入对H2 O2分解活性具有类似的定性效果。(c)2006 Elsevier B. V.保留所有权利。
Since H2O2 decomposition can result in selectivity/yield loss in the direct H2O2 synthesis process from H-2 and O-2 over supported Pd catalysts, it is important to have an enhanced understanding about the factors affecting the H2O2 decomposition reaction. Herein, detailed studies have been undertaken to investigate the influence of different factors, such as (a) nature and concentration of acid in reaction medium, (b) nature and concentration of halide in presence and absence of acid in reaction medium, (c) pretreatment procedures and (d) catalyst modification by incorporation of different halides, on the H2O2 decomposition reaction over a 5% Pd/C catalyst in aqueous medium at 25 degrees C. This study has shown that the H2O2 decomposition activity is profoundly influenced by all the above factors. The effectiveness of the acids in suppressing the H2O2 decomposition activity decreased in the following order: hydroiodic acid > hydrobromic acid > hydrochloric acid >> acetic acid > phosphoric acid > sulfuric acid > perchloric acid. The ability of the acid to decrease the H2O2 decomposition activity was found to very strongly depend on the nature of its associated anion. Halides, such as iodide, bromide and chloride were particularly effective in suppressing the H2O2 decomposition activity. Oxidation pretreatment of the catalyst was found to strongly suppress its H2O2 decomposition activity, while a reduction treatment was found to promote its activity. A gradual decrease in the H2O2 decomposition activity of the catalyst was observed with each successive usage due to in situ sub-surface oxidation of Pd by H2O2. Halide incorporation either via the reaction medium or prior catalyst modification had a similar qualitative effect on the H2O2 decomposition activity. (c) 2006 Elsevier B.V. All rights reserved.