Kirill V Kovtunov

Publications (13)109.94 Total impact

• Article: Parahydrogen-Induced Polarization in Heterogeneous Catalytic Processes.

  Kirill V Kovtunov, Vladimir V Zhivonitko, Ivan V Skovpin, Danila A Barskiy, Igor V Koptyug
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  ABSTRACT:  : Parahydrogen-induced polarization of nuclear spins provides enhancements of NMR signals for various nuclei of up to four to five orders of magnitude in magnetic fields of modern NMR spectrometers and even higher enhancements in low and ultra-low magnetic fields. It is based on the use of parahydrogen in catalytic hydrogenation reactions which, upon pairwise addition of the two H atoms of parahydrogen, can strongly enhance the NMR signals of reaction intermediates and products in solution. A recent advance in this field is the demonstration that PHIP can be observed not only in homogeneous hydrogenations but also in heterogeneous catalytic reactions. The use of heterogeneous catalysts for generating PHIP provides a number of significant advantages over the homogeneous processes, including the possibility to produce hyperpolarized gases, better control over the hydrogenation process, and the ease of separation of hyperpolarized fluids from the catalyst. The latter advantage is of paramount importance in light of the recent tendency toward utilization of hyperpolarized substances in in vivo spectroscopic and imaging applications of NMR. In addition, PHIP demonstrates the potential to become a useful tool for studying mechanisms of heterogeneous catalytic processes and for in situ studies of operating catalytic reactors. Here, the known examples of PHIP observations in heterogeneous reactions over immobilized transition metal complexes, supported metals, and some other types of heterogeneous catalysts are discussed and the applications of the technique for hypersensitive NMR imaging studies are presented.
  Topics in current chemistry 10/2012; · 4.29 Impact Factor
• Article: Heterogeneous addition of H2 to double and triple bonds over supported Pd catalysts: a parahydrogen-induced polarization technique study.

  Kirill V Kovtunov, Irene E Beck, Vladimir V Zhivonitko, Danila A Barskiy, Valery I Bukhtiyarov, Igor V Koptyug
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  ABSTRACT: In this work, the contribution of the pairwise H(2) addition to the overall reaction mechanism was studied under the systematic variation of both the Pd particle size and the properties of the catalyst support using the hydrogenation of propene and propyne over supported Pd catalysts as representative examples. For Pd supported on alumina, silica and zirconia, only propene formed upon hydrogenation of propyne with para-H(2) exhibits hyperpolarization. In contrast, propane formed in hydrogenation of propyne or propene is not hyperpolarized. This demonstrates the existence of different routes of H(2) addition to double and triple bonds on supported Pd catalysts. The unique ability of Pd/TiO(2) catalysts to add H(2) in a pairwise manner not only to the triple but also to the double bond is demonstrated. This finding indicates that the Pd-support interaction is of primary importance in determining not only the magnitude of the hyperpolarization of the NMR lines of the reaction products but even the involvement of the pairwise H(2) addition and hence the mechanism of heterogeneous hydrogenation. The comparative analysis of the selectivities toward pairwise H(2) addition suggested the existence of different surface active sites responsible for all three reaction routes: the direct total hydrogenation of propyne into propane, its selective hydrogenation into propene, and hydrogenation of propene into propane. A reaction scheme which accounts for the formation of the observed hyperpolarized and non-polarized reaction products in propyne and propene hydrogenation with para-H(2) over supported Pd catalysts is suggested. For the first time, application of the PHIP technique allowed us to demonstrate that hydrogenation of propene does not take place in the presence of propyne on supported Pd catalysts.
  Physical Chemistry Chemical Physics 07/2012; 14(31):11008-14. · 3.57 Impact Factor
• Article: Role of Different Active Sites in Heterogeneous Alkene Hydrogenation on Platinum Catalysts Revealed by Means of Parahydrogen-Induced Polarization

  Vladimir V. Zhivonitko, Kirill V. Kovtunov, Irene E. Beck, Artem B. Ayupov, Valerii I. Bukhtiyarov, Igor V. Koptyug
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  ABSTRACT: Substantial NMR signal enhancements provided by parahydrogen-induced polarization (PHIP) are associated with the ability of a catalyst to incorporate both H atoms of a dihydrogen molecule into the same product molecule. Therefore, PHIP can provide valuable information about the mechanisms and kinetics of catalytic hydrogenation reactions as well as produce hyperpolarized molecules for sensitivity enhancement in NMR. In this work, the PHIP technique was applied to study the structure sensitivity and the support effects on the degree of pairwise H2 addition in propene hydrogenation over supported platinum catalysts. Four series of Pt catalysts supported on Al2O3, SiO2, ZrO2, and TiO2 were examined. A nontrivial dependence of the selectivity toward pairwise H2 addition on the Pt particle size was found. Its analysis indicates that at least three types of different active sites coexist on the catalysts surface. Among them, the major one is responsible for the nonpairwise H2 addition to the double bond, whereas pairwise addition can proceed on the other two minor active sites. An explanation of the nature of these active sites is proposed. A substantial increase in the pairwise addition selectivity was found for Pt/TiO2 catalysts as compared to other catalyst series, possibly due to a strong metal–support interaction taking place even after low temperature catalyst reduction.
  The Journal of Physical Chemistry C 06/2011; 115(27):13386. · 4.80 Impact Factor
• Article: Microfluidic gas-flow imaging utilizing parahydrogen-induced polarization and remote-detection NMR.

  Ville-Veikko Telkki, Vladimir V Zhivonitko, Susanna Ahola, Kirill V Kovtunov, Jukka Jokisaari, Igor V Koptyug
  Angewandte Chemie International Edition 11/2010; 49(45):8363-6. · 13.45 Impact Factor
• Article: New perspectives for parahydrogen-induced polarization in liquid phase heterogeneous hydrogenation: an aqueous phase and ALTADENA study.

  Igor V Koptyug, Vladimir V Zhivonitko, Kirill V Kovtunov
  ChemPhysChem 10/2010; 11(14):3086-8. · 3.41 Impact Factor
• Article: Parahydrogen-induced polarization in alkyne hydrogenation catalyzed by Pd nanoparticles embedded in a supported ionic liquid phase.

  Kirill V Kovtunov, Vladimir V Zhivonitko, Lioubov Kiwi-Minsker, Igor V Koptyug
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  ABSTRACT: Parahydrogen-induced polarization was observed in the gas phase heterogeneous hydrogenation of propyne catalyzed by Pd(0) nanoparticles embedded in an ionic liquid phase supported on activated carbon fibers (Pd(0)/SILP/ACF). The results were markedly different from those obtained with a reference catalyst, Pd(0)/ACF, demonstrating the important role of the ionic liquid.
  Chemical Communications 08/2010; 46(31):5764-6. · 6.17 Impact Factor
• Article: Parahydrogen-Induced Polarization in Heterogeneous Hydrogenations Catalyzed by an Immobilized Au(III) Complex

  Kirill V. Kovtunov, Vladimir V. Zhivonitko, Avelino Corma, Igor V. Koptyug
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  ABSTRACT: Hydrogenation of unsaturated compounds with parahydrogen can lead to an enhancement of the NMR signals of reaction products by several orders of magnitude. Parahydrogen-induced polarization (PHIP) of nuclear spins is useful for developing both novel MRI applications as well as hypersensitive tools for operando studies in catalysis, but until recently, PHIP was observed only in homogeneous hydrogenations. To assess the potential of combining PHIP with heterogeneous catalysis, heterogeneous gas-phase hydrogenation of propene and propyne with parahydrogen was carried out using a Au(III) Schiff base complex immobilized within a metal−organic framework material IRMOF-3. Observation of PHIP in the 1H NMR spectra of reaction products implies that both hydrogen atoms of a single H2 molecule are transferred as a pair to the same product molecule and supports the conclusions made earlier that the well-defined isolated Au(III) centers of this catalyst are the active sites involved in hydrogen activation.Keywords (keywords): heterogeneous catalysis; hydrogenation; immobilized Au(III) complex; pairwise hydrogen addition; parahydrogen-induced polarization
  Journal of Physical Chemistry Letters 05/2010; · 6.21 Impact Factor
• Chapter: Parahydrogen‐Induced Polarization in Heterogeneous Catalytic Hydrogenations

  Kirill V. Kovtunov, Igor V. Koptyug
  02/2009: pages 99 - 115; , ISBN: 9783527626052
• Article: Observation of parahydrogen-induced polarization in heterogeneous hydrogenation on supported metal catalysts.

  Kirill V Kovtunov, Irene E Beck, Valery I Bukhtiyarov, Igor V Koptyug
  Angewandte Chemie International Edition 02/2008; 47(8):1492-5. · 13.45 Impact Factor
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  Article: NMR imaging of catalytic hydrogenation in microreactors with the use of para-hydrogen.

  Louis-S Bouchard, Scott R Burt, M Sabieh Anwar, Kirill V Kovtunov, Igor V Koptyug, Alexander Pines
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  ABSTRACT: Catalysis is vital to industrial chemistry, and the optimization of catalytic reactors attracts considerable resources. It has proven challenging to correlate the active regions in heterogeneous catalyst beds with morphology and to monitor multistep reactions within the bed. We demonstrate techniques, using magnetic resonance imaging and para-hydrogen (p-H2) polarization, that allow direct visualization of gas-phase flow and the density of active catalyst in a packed-bed microreactor, as well as control over the dynamics of the polarized state in space and time to facilitate the study of subsequent reactions. These procedures are suitable for characterizing reactors and reactions in microfluidic devices where low sensitivity of conventional magnetic resonance would otherwise be the limiting factor.
  Science 02/2008; 319(5862):442-5. · 31.20 Impact Factor
• Article: para-Hydrogen-induced polarization in heterogeneous hydrogenation reactions.

  Igor V Koptyug, Kirill V Kovtunov, Scott R Burt, M Sabieh Anwar, Christian Hilty, Song-I Han, Alexander Pines, Renad Z Sagdeev
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  ABSTRACT: We demonstrate the creation and observation of para-hydrogen-induced polarization in heterogeneous hydrogenation reactions. Wilkinson's catalyst, RhCl(PPh3)3, supported on either modified silica gel or a polymer, is shown to hydrogenate styrene into ethylbenzene and to produce enhanced spin polarizations, observed through NMR, when the reaction was performed with H2 gas enriched in the para spin isomer. Furthermore, gaseous phase para-hydrogenation of propylene to propane with two catalysts, the Wilkinson's catalyst supported on modified silica gel and Rh(cod)(sulfos) (cod = cycloocta-1,5-diene; sulfos = -O3S(C6H4)CH2C(CH2PPh2)3) supported on silica gel, demonstrates heterogeneous catalytic conversion resulting in large spin polarizations. These experiments serve as a direct verification of the mechanism of heterogeneous hydrogenation reactions involving immobilized metal complexes and can be potentially developed into a practical tool for producing catalyst-free fluids with highly polarized nuclear spins for a broad range of hyperpolarized NMR and MRI applications.
  Journal of the American Chemical Society 06/2007; 129(17):5580-6. · 9.91 Impact Factor
• Article: Para-hydrogen-enhanced hyperpolarized gas-phase magnetic resonance imaging.

  Louis-S Bouchard, Kirill V Kovtunov, Scott R Burt, M Sabieh Anwar, Igor V Koptyug, Renad Z Sagdeev, Alexander Pines
  Angewandte Chemie International Edition 02/2007; 46(22):4064-8. · 13.45 Impact Factor
• Article: NMR microimaging of fluid flow in model string-type reactors

  Igor V. Koptyug, Kirill V. Kovtunov, Edo Gerkema, Lioubov Kiwi-Minsker, Renad Z. Sagdeev
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  ABSTRACT: Magnetic resonance microimaging (MRM) was employed to obtain quantitative velocity maps of water flowing in the channels possessing unconventional cross-section shapes formed by a bundle of parallel fibers within a tubular string-type reactor. The maps obtained demonstrate the presence of large amounts of an almost stagnant liquid in the stretched corners of the cross-sections representing distorted triangles or squares. This fact together with the irregularity of the filaments packing in the model string-type reactor was demonstrated to lead to a broad residence time distributions (RTDs) for liquid flow. Next, the pulsed field gradient NMR (PFG NMR) technique was employed to compare transport of water with that of butane gas in the same model string-type reactor. The experimentally measured average propagators (travel distance probability density functions) have demonstrated that Taylor dispersion can lead to much better RTDs for gas as compared to liquid in channels with sub-millimeter equivalent diameters. The PFG NMR data were compared with the RTD obtained using the conventional tracer time-of-flight transient response method. It is concluded that due to the differences in the quantities actually measured by the two techniques, and the significant differences in the measurement length scales (microns to 1–2 cm for NMR/MRM, tens of centimeters for transient response methods), there is no reliable way of directly comparing these results. The information obtained by NMR/MRM and more conventional techniques such as time-of-flight should be considered as complementary. In particular, NMR/MRM can reveal the reasons for the observed overall reactor performance by providing access to the transport processes on short length scales inside the reactor and by revealing structure–transport interrelations.
  Chemical Engineering Science.