Heterogeneous hydrogenation of phenylalkynes with parahydrogen: hyperpolarization, reaction selectivity, and kinetics
Heterogeneous hydrogenation of phenylalkynes with parahydrogen: hyperpolarization, reaction selectivity, and kinetics
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苯炔与仲氢的多相氢化：超极化、反应选择性和动力学
DOI：
10.1039/c9cp02913c
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发表时间：
2019
影响因子：
3.3
通讯作者：
Koptyug, Igor V.
中科院分区：
文献类型：
--
作者：
Pokochueva, Ekaterina V.;Kovtunov, Kirill V.;Salnikov, Oleg G.;Gemeinhardt, Max E.;Kovtunova, Larisa M.;Bukhtiyarov, Valerii I.;Chekmenev, Eduard Y.;Goodson, Boyd M.;Koptyug, Igor V.
仲氢诱导极化（PHIP）是研究气相和液相中氢化反应的一种有效技术。成对添加仲氢的氢化底物赋予核自旋秩序的反应产物，表现为增强的1H NMR信号从新生质子网站。固定在载体上的纳米级金属催化剂包括一类有前途的催化剂，用于产生PHIP效应;然而，在这样的催化剂上，进行成对添加路线的基板的百分比-观察PHIP的必要条件-通常是低的。在本文中，我们提出了一个系统的研究几种金属催化剂（Rh，Pt，Pd和Ir）负载在TiO 2上的不同原型苯炔（苯乙炔，1-苯基-1-丙炔，3-苯基-1-丙炔）与仲氢的液相加氢。催化剂的活性和选择性被认为是由活性金属的性质和金属负载的百分比的影响。结果表明，最佳的催化剂用于生产超极化的产品是Rh/TiO 2与4wt%的金属负载，而Pd/TiO 2提供了最大的选择性苯炔的半氢化。在液相加氢反应动力学的研究中，结果表明，相对于氢的反应顺序几乎是相同的成对和非成对H2加成-与这些反应途径的催化活性位点的类似性质一致。
Parahydrogen-induced polarization (PHIP) is a powerful technique for studying hydrogenation reactions in gas and liquid phases. Pairwise addition of parahydrogen to the hydrogenation substrate imparts nuclear spin order to reaction products, manifested as enhanced 1H NMR signals from the nascent proton sites. Nanoscale metal catalysts immobilized on supports comprise a promising class of catalysts for producing PHIP effects; however, on such catalysts the percentage of substrates undergoing the pairwise addition route—a necessary condition for observing PHIP—is usually low. In this paper, we present a systematic study of several metal catalysts (Rh, Pt, Pd, and Ir) supported on TiO2 in liquid-phase hydrogenation of different prototypical phenylalkynes (phenylacetylene, 1-phenyl-1-propyne, and 3-phenyl-1-propyne) with parahydrogen. Catalyst activity and selectivity were found to be affected by both the nature of the active metal and the percentage of metal loading. It was demonstrated that the optimal catalyst for production of hyperpolarized products is Rh/TiO2 with 4 wt% metal loading, whereas Pd/TiO2 provided the greatest selectivity for semihydrogenation of phenylalkynes. In a study of liquid-phase hydrogenation reaction kinetics, it was shown that reaction order with respect to hydrogen is nearly the same for pairwise and non-pairwise H2 addition—consistent with a similar nature of the catalytically active sites for these reaction pathways.