Catalytic activity of Pd-polyvinylpyrrolidone (PVP) colloid for the reaction of H₂ and O₂ to H₂O₂ in the presence of H₂SO₄ and NaBr was greatly enhanced with the addition of a very small quantity of Pt or Ir. In contrast to ordinary alloy catalysts, the activity of Pd was doubly increased with the addition of only 0.5 atom% Pt or Ir, although the selectivity for the H₂O₂ formation somewhat decreased. Addition of Ru, Rh, or Au affected little the activity. Kinetic analyses of the reactions over modified Pd-PVP indicated that the high H₂-activating abilities of Pt and Ir increased the H₂–O₂ reaction rate, which was supported by DFT study. In contrast, H₂O₂ hydrogenation rates were almost constant irrespective of Pt or Ir addition, indicating little participation of the hydrogen activated on Pt or Ir in H₂O₂ destruction. Pt-modified Pd-PVP showed a discontinuous change in catalytic activity in the time dependency measurement, resulting in higher H₂–O₂ reaction rates and lower H₂O₂ selectivity. Lower partial pressure of hydrogen under the reaction conditions or higher temperatures in the absence of H₂ accelerated the change. Structures of the Pt- and Ir-loaded Pd-PVP catalysts were suggested to change during the reaction; the Pt or Ir atoms would initially be located at coordinatively more unsaturated sites of the Pd particles and move into the surface Pd lattice to be stabilized. It is shown that the amount of H₂O₂ produced reaches several wt% when estimated using the Pt- and Ir-loaded Pd-PVP catalysts under an O₂ partial pressure of 360 kPa.

中文翻译：

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添加0.5％（原子）的Pt或Ir †，可以 增强Pd-PVP胶体从水中的H ₂和O ₂直接合成H ₂ O ₂的催化活性。

添加少量Pt或Ir可以大大提高Pd-聚乙烯吡咯烷酮（PVP）胶体在H ₂ SO ₄和NaBr存在下对H ₂和O ₂转化为H ₂ O _2的催化活性。与普通合金催化剂相比，尽管仅对H ₂ O ₂形成的选择性有所降低，但仅添加0.5原子％的Pt或Ir，Pd的活性就增加了两倍。Ru，Rh或Au的添加对活性几乎没有影响。修饰的Pd-PVP上反应的动力学分析表明，Pt和Ir的高H ₂活化能力增加了H ₂-O ₂反应速率，得到DFT研究的支持。相反，H ₂ O _2的氢化速率几乎恒定，而与添加Pt或Ir无关，这表明在Pt或Ir上活化的氢很少参与H ₂ O _2的破坏。Pt修饰的Pd-PVP在时间依赖性测量中显示出催化活性的不连续变化，从而导致更高的H ₂ -O ₂反应速率和更低的H ₂ O ₂选择性。在反应条件下较低的氢气分压或在不存在H ₂的情况下较高的温度加速了变化。建议在反应过程中改变载有Pt和Ir的Pd-PVP催化剂的结构。Pt或Ir原子最初将位于Pd颗粒的更多不饱和位置，并进入表面Pd晶格中以使其稳定。结果表明，当在360 kPa的O ₂分压下，使用载有Pt和Ir的Pd-PVP催化剂估算时，H ₂ O _2的生成量达到了几个wt％。