Formation from direct oxidation of H2 and destruction by decomposition/hydrogenation of H2O2 over Pd/C catalyst in aqueous medium containing different acids and halide anions
Formation from direct oxidation of H2 and destruction by decomposition/hydrogenation of H2O2 over Pd/C catalyst in aqueous medium containing different acids and halide anions
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DOI：
10.1016/j.apcata.2006.10.022
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发表时间：
2007-02-07
影响因子：
5.5
通讯作者：
Jana, Prabhas
中科院分区：
文献类型：
--
作者：
Choudhary, Vasant R.;Samanta, Chanchal;Jana, Prabhas
在酸性水反应介质中，使用不同的无机酸（即0.1 N H2SO4、H3PO4、H3BO3、HNO3、HCl、HBr或HI）和/或卤化物阴离子（即F-、Cl-、Br-或I-），覆盖其广泛的浓度范围（0-24 mmol/dm(3)），对O-2将H-2直接氧化为H2O2和H2O2的分解/加氢（在27℃和常压下）进行了彻底的研究。在没有任何外部添加卤化物的情况下，只有当介质中含有HCl时，H2氧化才会产生可观的H2O2。然而，由于酸的存在，H2O2的分解和加氢速率大大降低；然而，对H2O2分解的影响对光环酸的影响要大得多。在酸（0.1 N H3PO4或H2SO4）存在的情况下，外部添加卤化物阴离子达到最佳浓度，H-2-to-H2O2的生成反应大大增强。然而，在最佳卤化物阴离子浓度以上，它比h -2生成水（平行）反应更受抑制，导致H2O2产率和选择性下降。随着卤化物阴离子（除F-）浓度的增加，催化剂的H-2转化活性和H2O2破坏活性不断降低。在卤化物中，氯化物是Pd/C催化剂在H-2-to-H2O2氧化过程中最好的卤化物促进剂。在最佳cl浓度（5.4 mmol/dm(3)）下，H-2转化率和H2O2产率均达到最大值，且随着磷酸浓度的增加，H2O2分解受到极大抑制。在反应介质中没有氯阴离子或酸（或两者都没有）的情况下，在H-2氧化过程中只有很少或没有H2O2形成，H2O2的破坏速度非常快，特别是在H-2存在的情况下；H2O2的快速破坏主要是由于其分解而不是氢化。在酸和卤化物阴离子的最佳浓度下，h -2氧化成h2o2的效果最好。在酸和氯化物（或溴化物）启动子存在的情况下，H2O2的加氢作用主导H2O2的破坏作用，因此H2O2的净生成主要受H2O2加氢作用控制。(c) 2006年Elsevier B.V.出版
Direct oxidation of H-2 by O-2 to H2O2 and decomposition/hydrogenation of H2O2 (at 27 degrees C and atmospheric pressure) over Pd/C catalyst in an aqueous acidic reaction medium have been thoroughly investigated using different mineral acids (viz. 0.1 N H2SO4, H3PO4, H3BO3, HNO3, HCl, HBr or HI) and/or halide anions (viz. F-, Cl-, Br- or I-), covering their wide concentration range (0-24 mmol/dm(3)), in the reaction medium. In the absence of any externally added halide, appreciable H2O2 formation in the H2 oxidation occurred only when the medium contained HCl. However, the rates of H2O2 decomposition and hydrogenation are greatly reduced because of the presence of any acid; the influence on the H2O2 decomposition was, however, much larger for the halo acids. In the presence of acid (0.1 N H3PO4 or H2SO4), the H-2-to-H2O2 formation reaction is greatly enhanced by the externally added halide anions up to their optimum concentrations. However, above the optimum halide anion concentration, it is inhibited more than the H-2-to-water formation (parallel) reaction, causing a decrease in both the H2O2 yield and selectivity. Whereas, the H-2 conversion and H2O2 destruction activities of the catalyst are decreased continuously with increasing the halide anion (except F-) concentration. Among the halides, chloride is the best halide promoter for Pd/C catalyst in the H-2-to-H2O2 oxidation. At the optimum Cl-concentration (5.4 mmol/dm(3)), both the H-2 conversion and H2O2 yield are passed through a maximum and the H2O2 decomposition is greatly inhibited with increasing the phosphoric acid concentration. In the absence of either the chloride anions or the acid (or both) in the reaction medium, only a little or no H2O2 is formed in the H-2 oxidation and also the rate of H2O2 destruction is very fast, particularly in the presence of H-2; the rapid destruction of H2O2 is mainly due to its decomposition rather than its hydrogenation. The best H-2-to-H2O2 oxidation results are obtained at the optimum concentrations of both the acid and halide anions. In the presence of acid and chloride (or bromide) promoter, the H2O2 hydrogenation dominates the H2O2 destruction and hence the net H2O2 formation is mainly controlled by the H2O2 hydrogenation. (c) 2006 Published by Elsevier B.V.