Semihydrogenation of Propyne over Cerium Oxide Nanorods, Nanocubes, and Nano‐Octahedra: Facet‐Dependent Parahydrogen‐Induced Polarization

Zhao, Evan Wenbo; Xin, Yan; Hagelin‐Weaver, Helena E.; Bowers, Clifford R.

doi:10.1002/cctc.201600270

Cited by 27 publications

(33 citation statements)

References 36 publications

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“…For instance, PHIP was successfully observed over various metal catalysts such as Rh, Pt, Pd, Ir, Au, Cu, bimetallic systems Pt−Sn, Pd−Au, Pd−M (M=Sn, Zn, Ag, Mn, Pb, Au) supported on support materials such as SiO 2 , ZrO 2 , Al 2 O 3 , TiO 2 , Al−Si fiberglass, chitosan, carbon nanotubes . Moreover, the PHIP effect was demonstrated for bulk Pt metal and several metal oxides (PtO 2 , PdO and CeO 2 ).…”

Section: Hydrogenation Of Propyne With Parahydrogen Over Pd−in/al2o3 mentioning

confidence: 96%

Selective Single‐Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

Burueva

Kovtunov

Bukhtiyarov

et al. 2018

Chemistry A European J

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Pd-In/Al O single-site catalyst was able to show high selectivity (up to 98 %) in the gas phase semihydrogenation of propyne. Formation of intermetallic Pd-In compound was studied by XPS during reduction of the catalyst. FTIR-CO spectroscopy confirmed single-site nature of the intermetallic Pd-In phase reduced at high temperature. Utilization of Pd-In/Al O in semihydrogenation of propyne with parahydrogen allowed to produce ≈3400-fold NMR signal enhancement for reaction product propene (polarization=9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd-In catalyst allowed to acquire H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH and CH groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.

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Section: Hydrogenation Of Propyne With Parahydrogen Over Pd−in/al2o3 mentioning

confidence: 96%

Selective Single‐Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

Burueva

Kovtunov

Bukhtiyarov

et al. 2018

Chemistry A European J

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“…Capping of metal nanoparticles with organic ligands may hinder surface mobility, as shown for PHIP in the gas phase, [83] organic solvents [84] and water, [4b, 7, 85] with the latter yielding ~1 mM of HP product with up to 1.2% polarization ( 1 H and 13 C) in 10 s. Reduced surface mobility of H atoms is also expected on metal oxides. Indeed, PHIP effects were observed using many such materials [80j, 86] (e.g., CeO 2 , Cr 2 O 3 , CaO, ZrO 2 ).…”

Section: How To Make It Work: the Hyperpolarizer And Chemistry Of mentioning

confidence: 99%

“…[77] The resulting significant 1 H NMR signal enhancement facilitated the MR imaging of various model objects, [122] and was later used to image production of hyperpolarized propane in an operating heterogeneous catalytic reactor using both conventional [122b] and remote-detection MRI. [123] Efforts to increase the efficiency of pairwise hydrogen addition to unsaturated hydrocarbons by modifying the heterogeneous catalyst structure [80g] and varying the nature of catalytically active sites [80k, 86b] helped identify Rh/TiO 2 as an efficient hydrogenation catalyst for the production of HP propane for 3D MRI with micro-scale spatial resolution (625×625×625 μm 3 ). [81] …”

Section: How To Make Use Of Parahydrogen-induced Polarization: Conmentioning

confidence: 99%

Parahydrogen‐Based Hyperpolarization for Biomedicine

et al. 2018

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Magnetic resonance (MR) is one of the most versatile and useful physical effects used for human imaging, chemical analysis, and the elucidation of molecular structures. However, its full potential is rarely used, because only a small fraction of the nuclear spin ensemble is polarized, that is, aligned with the applied static magnetic field. Hyperpolarization methods seek other means to increase the polarization and thus the MR signal. A unique source of pure spin order is the entangled singlet spin state of dihydrogen, parahydrogen (pH ), which is inherently stable and long-lived. When brought into contact with another molecule, this "spin order on demand" allows the MR signal to be enhanced by several orders of magnitude. Considerable progress has been made in the past decade in the area of pH -based hyperpolarization techniques for biomedical applications. It is the goal of this Review to provide a selective overview of these developments, covering the areas of spin physics, catalysis, instrumentation, preparation of the contrast agents, and applications.

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“…However, the most interesting fact was that polarization of the 1 H NMR signals of the reactant's CH groups was also detected, whereas the signals of the CH 2 groups showed no PHIP effects. We can explain this on the basis of the “pairwise replacement” phenomenon, which was previously demonstrated for the hydrogenation of propene and cyclohexene over supported metal catalysts and for the hydrogenation of propene over immobilized Rh complexes and bulk CeO 2 , and arises from reversible p ‐H 2 addition. Notably, the exact mechanism for “pairwise replacement” is often debated.…”

Section: Resultsmentioning

confidence: 97%

Mechanistic Insight into the Heterogeneous Hydrogenation of Furan Derivatives with the use of Parahydrogen

et al. 2018

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Parahydrogen‐induced polarization (PHIP) was shown to be a useful and unique technique to study the mechanisms of catalytic reactions involving hydrogen. In this paper, PHIP was utilized for mechanistic investigation of the gas‐phase hydrogenation of furan, 2,3‐dihydrofuran, and 2,5‐dihydrofuran over titania‐supported Rh, Pd, and Pt catalysts. In the hydrogenation of all three substrates over the Rh/TiO2 catalyst, the PHIP technique revealed the possibility of pairwise addition of two H atoms from the same H2 molecule with the formation of tetrahydrofuran molecules while retaining spin correlation between the added protons. In the hydrogenation of 2,3‐dihydrofuran over the Rh/TiO2 catalyst, PHIP effects were detected not only for tetrahydrofuran but also for the reactant (2,3‐dihydrofuran) at positions 2 and 3 of the heterocyclic ring. Such unexpected results are direct evidence for the pairwise replacement of the hydrogen atoms in 2,3‐dihydorfuran. A probable mechanism for this pairwise replacement includes sequential steps of addition and elimination of hydrogen atoms. In contrast, if the hydrogenation of 2,5‐dihydrofuran was performed over Rh/TiO2, PHIP effects were detected for all protons of 2,3‐dihydrofuran, implying that 2,3‐dihydrofuran could be formed from 2,5‐dihydrofuran not only through isomerization of the C=C bond but also through dehydrogenation of 2,5‐dihydrofuran to furan with subsequent semihydrogenation.

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Semihydrogenation of Propyne over Cerium Oxide Nanorods, Nanocubes, and Nano‐Octahedra: Facet‐Dependent Parahydrogen‐Induced Polarization

Cited by 27 publications

References 36 publications

Selective Single‐Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

Selective Single‐Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

Parahydrogen‐Based Hyperpolarization for Biomedicine

Mechanistic Insight into the Heterogeneous Hydrogenation of Furan Derivatives with the use of Parahydrogen

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