Enhancement of catalytic activity of Pd-PVP colloid for direct H2O2 synthesis from H2 and O2 in water with addition of 0.5 atom% Pt or Ir
Enhancement of catalytic activity of Pd-PVP colloid for direct H2O2 synthesis from H2 and O2 in water with addition of 0.5 atom% Pt or Ir
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DOI：
10.1039/c7cy01890h
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发表时间：
2018-02
影响因子：
5
通讯作者：
T. Deguchi;H. Yamano;S. Takenouchi;M. Iwamoto
中科院分区：
文献类型：
--
作者：
T. Deguchi;H. Yamano;S. Takenouchi;M. Iwamoto
在H2SO4和NaBr存在下，pd -聚乙烯吡罗烷酮（PVP）胶体对H2和O2反应生成H2O2的催化活性随着极少量Pt或Ir的加入而大大增强。与普通合金催化剂相比，仅添加0.5原子%的Pt或Ir时，Pd的活性增加了一倍，但对H2O2形成的选择性有所降低。Ru、Rh或Au的加入对活性影响不大。对改性Pd-PVP反应的动力学分析表明，Pt和Ir的高h2活化能力提高了H2-O2反应速率，DFT研究支持了这一结论。相比之下，无论Pt或Ir的加入与否，H2O2的加氢速率几乎不变，这表明Pt或Ir上活化的氢很少参与H2O2的破坏。pt修饰的Pd-PVP在时间依赖性测量中表现出不连续的催化活性变化，导致H2-O2反应速率提高，H2O2选择性降低。在反应条件下较低的氢气分压或在没有氢气的情况下较高的温度会加速这一变化。结果表明，负载Pt和ir的Pd-PVP催化剂在反应过程中结构发生了变化；Pt或Ir原子最初会位于Pd粒子的配位更不饱和的位置，并进入表面Pd晶格以稳定。结果表明，在O2分压为360 kPa的条件下，负载Pt和ir的Pd-PVP催化剂的H2O2产生量可达数wt%。
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.