Direct Oxidation of Hydrogen to Hydrogen Peroxide over Pd (or PdO)/Al2O3 in Aqueous Reaction Medium: Influence of Different Acids and Halide Anions in Reaction Medium on Formatio

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• 作者：Vasant R. Choudhary ; Yugesh V. Ingole ; Chanchal Samanta ; Prabhas Jana
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2007
• 出版时间：December 5, 2007
• 年：2007
• 卷：46
• 期：25
• 页码：8566 - 8573
• 全文大小：119K
• 年卷期：v.46,no.25(December 5, 2007)
• ISSN：1520-5045

文摘

Effects of different mineral acids (viz. H₂SO₄, H₃PO₄, HNO₃, HCl, HBr, and HI), acid (H₃PO₄) concentration,different halide anions (viz. F^-, Cl^-, Br^-, and I^-), and halide anion concentration in aqueous reaction mediumon the H₂O₂ formation (in H₂-to-H₂O₂ oxidation) and/or on the H₂O₂ destruction (by H₂O₂ decompositionand hydrogenation) activities of Pd (or PdO)/Al₂O₃ catalyst (at 300 K and atmospheric pressure) have beenthoroughly investigated. Among the different halide anions, Br^- anions are most effective for promoting theH₂O₂ formation and inhibiting the H₂O₂ destruction by both the H₂O₂ decomposition and/or hydrogenation.The cations associated with the halide anions, however, have only a little or no influence on both the H₂O₂formation and destruction. The concentration of the different halide anions has a strong influence on the H₂conversion and H₂O₂ formation and destruction activities of the Pd/Al₂O₃. The H₂O₂ formation activity in thepresence of Br^- or Cl^- anions is highest at the optimum concentration of halide (about 1.0 mmol/dm³). It isalso highest at the optimum concentration of phosphoric acid (between 0.1 and 0.3 mol/dm³). In general, theH₂O₂ formation is increased with decreasing the H₂O₂ destruction activity of the catalyst, indicating a closerelationship between the two. Br^- anions act as an excellent catalyst promoter for Pd/Al₂O₃ catalyst, but theyshow only a small promoting effect for PdO/Al₂O₃ catalyst. The next choice for halide promoter for Pd/Al₂O₃ catalyst is Cl^- anions. F^- and I^- anions are, however, catalyst inhibitor and strong poison, respectively,for the H₂O₂ formation. At the same concentration, Br^- anions are more effective than Cl^- anions for inhibitingthe H₂O₂ destruction reactions over Pd/Al₂O₃ catalyst. For both halide promoters (Cl^- and Br^-), the net H₂O₂formation is controlled by the H₂O₂ hydrogenation rather than by the H₂O₂ decomposition.