Han Geun-Ho, Lee Seok-Ho, Seo Myung-Gi, Lee Kwan-Young
Department of Chemical and Biological Engineering, Korea University 145 Anam-ro Seoul 02841 Republic of Korea
Lotte Chemical 115 Gajeongbuk-ro Daejeon 34110 Republic of Korea
RSC Adv. 2020 May 27;10(34):19952-19960. doi: 10.1039/d0ra03148h. eCollection 2020 May 26.
When synthesizing nanoparticles in the liquid phase, polymeric materials (mainly polyvinylpyrrolidone, PVP) are applied as capping and/or stabilizing agents. The polymer layer on the nanoparticles must likely be removed since it blocks the active sites of the catalyst and inhibits mass transfer of the reactants. However, we have found that the polymer can have a positive effect on the direct synthesis of hydrogen peroxide. By testing Pd/SiO catalysts with different amounts of PVP, it was revealed that an adequate amount of PVP resulted in a higher rate of hydrogen peroxide production (1001 mmol g h) than pristine Pd/SiO did (750 mmol g h), unlike other PVP added Pd/SiO catalysts containing excess PVP (less than 652 mmol g h). The effect of PVP on the catalysts was examined by transmission electron microscopy, Fourier transform infrared spectroscopy, CO chemisorption, thermogravimetric analysis, and X-ray photoelectron spectroscopy. For the catalysts containing PVP, the oxidation state of the palladium 3d shifted to high binding energy due to electron transfer from Pd to the PVP molecules. Consequently, the presence of PVP on the catalysts inhibited oxygen dissociation and decomposition of the produced hydrogen peroxide, resulting in a high selectivity and high production rate of hydrogen peroxide.
在液相中合成纳米颗粒时，聚合物材料（主要是聚乙烯吡咯烷酮，PVP）被用作封端和/或稳定剂。纳米颗粒上的聚合物层很可能需要去除，因为它会阻碍催化剂的活性位点并抑制反应物的传质。然而，我们发现该聚合物对过氧化氢的直接合成可能具有积极作用。通过测试含有不同量PVP的Pd/SiO催化剂，发现适量的PVP比原始的Pd/SiO催化剂（750 mmol g⁻¹ h⁻¹）产生过氧化氢的速率更高（1001 mmol g⁻¹ h⁻¹），这与其他添加了过量PVP（小于652 mmol g⁻¹ h⁻¹）的Pd/SiO催化剂不同。通过透射电子显微镜、傅里叶变换红外光谱、CO化学吸附、热重分析和X射线光电子能谱研究了PVP对催化剂的影响。对于含有PVP的催化剂，由于电子从Pd转移到PVP分子，钯3d的氧化态向高结合能移动。因此，催化剂上PVP的存在抑制了氧的解离和所产生过氧化氢的分解，从而导致过氧化氢的高选择性和高生产率。
