通过仲氢诱导极化研究丙炔在负载型 Pd-Ag 催化剂上的成对立体选择性氢化,The Journal of Physical Chemistry C

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通过仲氢诱导极化研究丙炔在负载型 Pd-Ag 催化剂上的成对立体选择性氢化
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2021-08-03 , DOI: 10.1021/acs.jpcc.1c02560
Weiyu Wang ₁ , Qiang Wang ₁ , Yueying Chu ₁ , Guodong Qi ₁ , Shenhui Li ₁ , Jun Xu ₁ , Feng Deng ₁

Affiliation

炔烃半氢化为立体分子的合成提供了一种关键方法。通过使用仲氢诱导极化 (PHIP) NMR 技术研究了丙炔在 Al ₂ O ₃负载的 Pd-Ag 双金属催化剂上立体选择性氢化成丙烯。负载型催化剂采用初湿浸渍法制备，通过改变 Pd 和 Ag 组分系统调节其性能。X 射线衍射、红外光谱和透射电子显微镜的结构表征表明，在 Al ₂ O ₃上形成了具有随机合金结构的高度分散的双金属 Pd-Ag 纳米颗粒支持。对于具有较高 Ag 浓度的 Pd-Ag 催化剂上的丙炔加氢，吸附的质子主要限制在活性 Pd 系综上，这有利于丙炔成对加氢量更高，从而导致更强的 PHIP 效应。产物立体选择性测量表明，丙炔的成对合成加成随着 Pd-Ag 合金中 Ag 含量的增加而增加。反应条件影响成对加氢立体选择性。反应物流量的较低 H ₂ /丙炔比或较高的总反应物流量增强了表观成对顺式加成立体选择性，这可以通过抑制顺反异构化过程和/或较高的内在成对顺式加成选择性来解释.

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Pairwise Stereoselective Hydrogenation of Propyne on Supported Pd–Ag Catalysts Investigated by Parahydrogen-Induced Polarization

Alkyne semihydrogenation offers a key approach for the synthesis of stereodefined molecules. The stereoselective hydrogenation of propyne to propene over Al₂O₃-supported Pd–Ag bimetallic catalysts is studied by using parahydrogen-induced polarization (PHIP) NMR technique. The supported catalysts were prepared by an incipient-wetness impregnation method, and their properties were systemically tuned by altering Pd and Ag components. Structural characterization by X-ray diffraction, infrared spectra, and transmission electron microscope shows the formation of highly dispersed bimetallic Pd–Ag nanoparticles with random alloy structures on Al₂O₃ support. For the hydrogenation of propyne over Pd–Ag catalysts with higher Ag concentration, the adsorbed protons are mostly restricted on the active Pd ensembles, which favors a higher pairwise hydrogen addition to propyne, leading to a stronger PHIP effect. The product stereoselectivity measurements show that the pairwise syn-addition to propyne increases with Ag content in the Pd–Ag alloy. The reaction conditions impact the pairwise hydrogenation stereoselectivity. A lower H₂/propyne ratio of reactant flow or a higher total reactant flow rate enhances the apparent pairwise syn-addition stereoselectivity, which can be accounted for by the suppressed cis–trans isomerization process and/or a higher intrinsic pairwise syn-addition selectivity.

更新日期：2021-08-12

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