2D Mapping of NMR Signal Enhancement and Relaxation for Heterogeneously Hyperpolarized Propane Gas
2D Mapping of NMR Signal Enhancement and Relaxation for Heterogeneously Hyperpolarized Propane Gas
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DOI：
10.1021/acs.jpcc.7b02506
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发表时间：
2017-05-11
影响因子：
3.7
通讯作者：
Chekmenev, Eduard Y.
中科院分区：
文献类型：
--
作者：
Barskiy, Danila A.;Kovtunov, Kirill V.;Chekmenev, Eduard Y.
超极化（HP）丙烷是一种很有前途的对比剂，用于肺部磁共振成像（MRI）和研究多孔介质。在多相催化剂上进行丙烯仲氢加氢反应时，仲氢诱导极化（PHIP）技术是一种方便的制备具有增强质子极化的纯丙烷气体的方法。在这里，我们提出了一种新的方法的多维映射的成对仲氢加成效率使用PHIP回波脉冲序列。我们使用这种方法来研究三种模型的非均相Rh/TiO 2催化剂在高压丙烷气生产中的性能。三种催化剂与1.0，13.7，和23.2%（重量）的负载铑纳米粒子已通过X射线光电子能谱（XPS）和高分辨率透射电子显微镜（HRTEM）的特征。通过改变反应物混合物中仲氢和丙烯的含量以及混合气体的压力，获得了PHIP回波NMR信号的2D图和HP丙烷NMR信号增强的2D图。这些图清楚地表明，较低的金属覆盖率导致更有效的成对氢加成，产生更高水平的丙烷气体的质子极化。所提出的方法可以扩展到多维表征PHIP反应过程中的其他关键参数的影响，包括温度或添加惰性载气。还报道了在9.4 T下丙烷的2D T-1弛豫图作为丙烷分数（在与氢气的混合物中）和气体混合物压力的函数。
Hyperpolarized (HP) propane is a promising contrast agent for magnetic resonance imaging (MRI) of lungs and for studying porous media. The parahydrogen-induced polarization (PHIP) technique is a convenient approach to produce pure propane gas with enhanced proton polarization, when hydrogenation of propylene with parahydrogen is performed over heterogeneous catalysts. Here, we present a new approach of multidimensional mapping of the efficiency of pairwise parahydrogen addition using PHIP-echo pulse sequence. We use this approach to study the performance of three model heterogeneous Rh/TiO2 catalysts in the production of HP propane gas. The three catalysts with 1.0, 13.7, and 23.2 wt % of supported rhodium nanoparticles have been characterized by X-ray photoelectron spectroscopy (XPS) and high resolution transition electron microscopy (HRTEM). By varying the fractions of parahydrogen and propylene in the reactant mixture as well as the gas mixture pressure, 2D maps of PHIP-echo NMR signal and 2D maps of HP propane NMR signal enhancement were obtained. These maps clearly indicate that lower metal coverage results in more efficient pairwise hydrogen addition, producing greater levels of proton polarization of propane gas. The presented method can be extended to multidimensional characterization of the influence of other key parameters of PHIP reaction process including temperature or addition of an inert carrier gas. A 2D T-1 relaxation map of propane at 9.4 T is also reported as a function of propane fraction (in the mixture with hydrogen) and gas mixture pressure.