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

Article abstract of DOI:10.1002/chem.201705644

Pd?In/Al₂O₃ 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/Al₂O₃ 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 ¹H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH₂ and CH₃ 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.

Full text of DOI:10.1002/chem.201705644

A Journal of
Accepted Article
Title: Selective single-site Pd-In hydrogenation catalyst for production
of enhanced magnetic resonance signals using parahydrogen
Authors: Dudari Burueva, Kirill Viktorovich Kovtunov, Valerii
Bukhtiyarov, Andrey Bukhtiyarov, Danila Barskiy, Igor
Prosvirin, Igor Mashkovsky, Galina Baeva, Aleksandr
Stakheev, and Igor Koptyug
This manuscript has been accepted after peer review and appears as an
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using the Digital Object Identifier (DOI) given below. The VoR will be
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the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201705644
Link to VoR: http://dx.doi.org/10.1002/chem.201705644
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COMMUNICATION
Selective single-site Pd-In hydrogenation catalyst for production
of enhanced magnetic resonance signals using parahydrogen
Dudari B. Burueva, Kirill V. Kovtunov,* Andrey V. Bukhtiyarov, Danila A. Barskiy, Igor P. Prosvirin, Igor
S. Mashkovsky, Galina N. Baeva, Valerii I. Bukhtiyarov, Aleksandr Yu. Stakheev, and Igor V. Koptyug
population of nuclear spin energy levels.[9] Nowadays the most
Abstract: Pd-In/Al2O3 single-site catalyst was able to show high
popular and common hyperpolarization methods are spin-
exchange optical pumping of noble gases (SEOP)[10], dynamic
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/Al2O3 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 1H MR images of flowing
hyperpolarized propene gas selectively for protons in CH-, CH2-
and CH3- 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.
nuclear polarization (DNP)[11]
,
chemically induced dynamic
nuclear
polarization
(CIDNP)[12]
, parahydrogen-induced
polarization (PHIP)[13] and signal amplification by reversible
exchange (SABRE)[14] - a form of non-hydrogenative PHIP.[15]
The latter approach (PHIP) is based on the conversion of the
high spin order of parahydrogen (p-H2), a nuclear spin isomer of
hydrogen with the total nuclear spin I = 0, into the polarization of
target molecules through a catalytic hydrogenation reaction.[16,17]
When two hydrogen atoms of p-H2 molecule are added to an
unsaturated substrate as a pair (pairwise hydrogen addition) in
magnetically nonequivalent positions, only those nuclear spin
levels in the target product molecule get populated that
correspond to the symmetry of parahydrogen. In this case, the
spin population distribution in the product molecule dramatically
deviates from the Boltzmann distribution, leading to significantly
enhanced (up to 104-105) absorptive and emissive NMR signals
at high magnetic field.[16] Depending on the magnetic field in
which the catalytic reaction takes place, two types of PHIP
experiments are distinguished – PASADENA (parahydrogen and
synthesis allow dramatically enhanced nuclear alignment)[13] and
ALTADENA (adiabatic longitudinal transport after dissociation
engenders net alignment)[18]. In a PASADENA experiment, the
hydrogenation product is formed directly in the high magnetic
field of an NMR spectrometer and polarized signals with
antiphase patterns are observed. In the case of an ALTADENA
experiment, the hydrogenation product is formed in a low (e.g.,
Earth’s, 0.05 mT) magnetic field with a subsequent transfer of
the product to the high magnetic field of an NMR spectrometer
(several T) for detection. As a result, NMR signals are observed
Nuclear magnetic resonance (NMR) phenomenon underlies
numerous modern spectroscopic analytical methods and is now
routinely used in chemistry, biology, materials science and
medicine.[1–4] NMR is a highly informative method to study
structures, properties and even spatial distribution of various
compounds.[5] In addition, magnetic resonance imaging (MRI) is
a
routine instrument for modern medical diagnostics.[6,7]
However, the energies of interaction between spins and
magnetic field are rather small, which results in the major
disadvantage of NMR/MRI methods, namely the low nuclear
spin polarization even in relatively high magnetic fields. For
example, at 298 K, for 1H nuclei exposed to a 7.1 T field the
polarization in thermal equilibrium is only 2.4×10-5 (0.0024%).
The value of polarization directly determines the signal-to-noise
ratio (SNR) in NMR and, among other consequences, limits
spatial resolution achievable in MRI.[8] In order to overcome this
low inherent sensitivity, several methods have been developed
to hyperpolarize nuclear spins, i.e., to create a non-Boltzmann
either in net absorption or in emission.
Since the PHIP technique is based on the catalytic activation
and addition of parahydrogen molecule, major emphasis is
placed on the screening of catalysts suitable for pairwise
hydrogen addition.[19,20] The PHIP effect was first observed for
homogeneous[21] and later for heterogeneous[22,23] hydrogenation
catalytic systems. However, heterogeneous PHIP (HET-PHIP)
catalysts appear most appropriate for the production of
hyperpolarized molecules not contaminated with the catalyst,
especially in the context of MRI applications.[24] The scope of
heterogeneous catalysts which are suitable for HET-PHIP
increased significantly in the past 10 years. For instance, PHIP
was successfully observed over various metal catalysts such as
[*]
D. B. Burueva, Dr. K. V. Kovtunov, Prof. I. V. Koptyug
Laboratory of Magnetic Resonance Microimaging
International Tomography Center, SB RAS
3A Institutskaya St., 630090 Novosibirsk (Russia)
Novosibirsk State University
2 Pirogova St., 630090 Novosibirsk (Russia)
E-mail: kovtunov@tomo.nsc.ru
Dr. A. V. Bukhtiyarov, Dr. I. P. Prosvirin, Prof. V. I. Bukhtiyarov
Boreskov Institute of Catalysis, SB RAS
5 Acad. Lavrentiev Pr., 630090 Novosibirsk (Russia)
Novosibirsk State University
2 Pirogova St., 630090 Novosibirsk (Russia)
Dr. D. A. Barskiy
Department of Chemistry, University of California at Berkeley,
Berkeley, CA 94720-3220 (USA)
, , , , , , bimetallic
Rh[25,26] Pt[22,27,28] Pd[29,30] Ir[31,32] Au[33] Cu[34]
systems Pt-Sn[35], Pd-Au[15], Pd-M (M=Sn, Zn, Ag, Mn, Pb, Au)[36]
supported on support materials such as SiO2, ZrO2, Al2O3, TiO2,
Al-Si fiberglass[30], chitosan[26], carbon nanotubes[33]. Moreover,
the PHIP effect was demonstrated for bulk Pt metal[37] and
several metal oxides (PtO2, PdO[37] and CeO2[38]).
Dr. I. S. Mashkovsky, G. N. Baeva, Prof. A. Yu. Stakheev
N.D. Zelinsky Institute of Organic Chemistry, RAS
47 Leninsky Pr., 119991 Moscow (Russia)
Utilization of heterogeneous catalytic systems for
observation of PHIP effects requires catalysts with a substantial
contribution of the pairwise route of hydrogen addition during
Supporting information for this article is given via a link at the end of
the document.
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catalytic hydrogenation. Although the contribution of the pairwise
hydrogen addition in the case of HET-PHIP catalysts does not
atoms, which do not chemisorb CO, on the nanoparticle
surface.[55,58] Moreover, FTIR spectrum of CO adsorbed on the
reference monometallic Pd/Al2O3 sample exhibits two absorption
bands, while the spectrum of CO adsorbed on bimetallic Pd-
In/Al2O3 catalyst exhibits only one intensive band at 2073 cm-1
attributed to linearly adsorbed CO on metallic Pd (Figure S2).
The absence of any other signals within the multi-bonded CO
range (2000-1800 cm-1) provides the evidence that single Pd
atoms are present on the surface of Pd-In nanoparticles and
these Pd atoms are able to bind CO in linear form only, without
participation of neighboring Pd atoms (the μ-bridge form of
absorbed CO). The absence of bridged CO species can be the
result of the increase in Pd-Pd interatomic distances due to Pd
site isolation by In atoms, similar to the Pd-Ga system reported
earlier.[59]
usually exceed 1-3%[20]
, the HET-PHIP technique can be
successfully applied for the hyperpolarization of prospective
contract agents for MRI. For instance, MR visualization of model
systems with various geometries was demonstrated with the use
of hyperpolarized propane gas produced by heterogeneous
hydrogenation of propene with p-H2 over supported Rh
catalysts.[25,39,40] As high level of pairwise hydrogen addition
corresponds to the high level of NMR signal, synthesis and
utilization of new heterogeneous hydrogenation catalysts with
significant percentages of the pairwise hydrogen addition level is
a highly important task. One of the promising ways is to use
catalysts with well-defined single-site structure of active
centers.[33] These single-site centers behave similarly to the
metal centers of homogeneous catalysts[41–43] in catalytic
reactions and, thus, can be expected to accomplish pairwise
addition of H2 to a substrate. So far the largest contribution of
pairwise hydrogen addition (10.9%) was observed with the use
of silica-encapsulated Pt-Sn intermetallic nanoparticles[35] in
propene hydrogenation, but the overall conversion estimated as
0.5% is too low for MRI applications. Here, a Pd-based catalyst
with the single-site character of the distribution of active sites
was utilized for the production of propene with significant levels
of both hyperpolarization and conversion (9.3% (1.7%
observable, without corrections) and 20%, respectively) during
selective heterogeneous hydrogenation of propyne and for
subsequent MR visualization of this hyperpolarized propene.
For the synthesis of palladium catalysts with isolated Pd
atoms, one of the promising approaches is the modification of
monometallic Pd-based catalysts with another metal (Ag, Cu,
Ga) which leads to an intermetallic structure formation.[44–46] It
was shown that isolation of Pd atoms on the surface of an
intermetallic compound enables significantly improved product
selectivity and catalyst stability.[47,48] The presence of a second
metal in Pd-based catalysts is able to reduce the size of Pd
nanoparticles and thus to prevent palladium hydride (PdHx)
formation.[49] The latter is the key to high product selectivity
because palladium hydride is the known active species for side
reactions such as isomerization or over-hydrogenation.[50,51] Pd-
In catalyst has been shown to be an effective catalyst for
semihydrogenation of a triple to a double carbon-carbon bond in
Pd-In/Al2O3 catalyst was tested earlier in the liquid-phase
hydrogenation of terminal and internal alkynes (phenylacetylene,
diphenylacetylene, and 1-phenyl-1-propyne) and demonstrated
high selectivity to the formation of alkenes (up to 98%).[54]
In the current study, the catalytic activity of single-site Pd-
In/Al2O3 catalyst was tested in the gas-phase hydrogenation of
propyne gas. To this end, propyne was premixed with
parahydrogen in the molar ratio of 1:4. The reaction was
conducted in a continuous flow regime at various temperatures
(mcat = 30 mg, T = 100-500 °C, u = 0.4-8.8 mL/s), with the
reactor outflow continuously supplied to the probe of an NMR
1
spectrometer and analyzed by H NMR. The obtained propyne
conversion and selectivity to propene are presented in Table 1
and Table S1. At 100 °C, the Pd-In/Al2O3 catalyst was inactive
and no products could be detected in the thermal 1H NMR
spectra. At 200-300 °C the catalyst activity increased and a 35%
conversion was achieved at the gas flow rate of ~0.4 mL/s. The
highest conversion levels were observed at 400 °C. Notably, the
Pd-In catalyst maintains the high selectivity to propene, up to
98%, over a wide range of temperatures (200-400 °C) even at
high propyne conversion (62% yield of propene was observed at
0.4 mL/s gas flow and 400 °C). It is important to note that at
500 °C the conversion to propene dropped down dramatically to
~39% which can be explained by catalyst deactivation and/or
propadiene formation (selectivity to allene formation was about
~60%).
Table 1. Hydrogenation of propyne with parahydrogen over Pd-In/Al2O3
catalyst: propyne conversion, selectivity to propene, 1H NMR signal
enhancements (SE) and estimates of percentages of pairwise hydrogen
addition calculated for CH and CH2 protons of propene at 5.1 mL/s
hydrogenation
of
acetylene,[52,53]
phenylacetylene,
diphenylacetylene and 1-phenyl-1-propyne[54]. Moreover, it was
established that Pd was present as single atoms.[52,55]
Temperature, °C
100
200
1
300
7
400
21
500
18
Pd-In/Al2O3 single-site catalyst was prepared by incipient-
wetness impregnation of Al2O3 with bimetallic acetate complex
PdIn(CH3COO)5 with subsequent reduction (for details, see
Supporting Information). Recently it was shown that the use of a
bimetallic complex as a precursor of the active component
combined with high-temperature reduction enables the formation
of bimetallic particles in the catalyst.[55–57] The size of Pd-In
nanoparticles was determined by TEM after pre-reduction in H2
atmosphere at 550 °C. TEM images of a reference Pd/Al2O3
sample and Pd-In/Al2O3 sample are shown in Figure S1. TEM
experiments show that spherical Pd-In particles with an average
size of ~3.5 nm are formed. The dispersion of Pd in the catalysts
was determined from the CO uptake in CO chemisorption
analysis (assuming a stoichiometry of CO:Pd = 1:1). In particular,
for the monometallic Pd/Al2O3 catalyst the dispersion was about
~36%, but for Pd-In/Al2O3 catalyst the dispersion value was
approximately ~5.6%.This fact indicates direct influence of In
Conversion, %
-
-
Selectivity to propene, %
72
95
93
43
SE for CH group of
propene
27*
592
429
214
155
202
145
219
159
SE for CH2 group of
propene
-
-
-
Percentage of pairwise H2
addition (CH)
1.64
1.19
0.59
0.43
0.56
0.40
0.61
0.44
Percentage of pairwise H2
addition (CH2)
* signal-to-noise ratio was used for SE estimation
High selectivity with respect to the target alkene can be
explained by the fact that formation of the Pd-In intermetallic
compound considerably decreases the formation of palladium
hydrides (PdHx), which contain hydrogen source responsible for
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complete hydrogenation.[60] In our case, the observed high
selectivity to propene during gas phase propyne hydrogenation
is consistent with the fact that no signals assignable to the
decomposition of palladium hydride PdHx were observed via
TPD analysis of Pd-In/Al2O3 catalyst.[55] Furthermore, the
catalyst has proven to be able to achieve significant levels of
pairwise hydrogen addition.
(SE) were obtained by using the approach previously reported
for propene hydrogenation (see SI for details).[61] Thus, the
percentage of pairwise hydrogen addition at 400 °C was found
to be 9.3% (Figure S5b). To the best of our knowledge, this is
the highest percentage of pairwise addition reported to date for
heterogeneous catalytic systems that can achieve significant
conversion levels (~20%).
1
Although at 100 °C no products were observed in thermally
polarized NMR spectra (the spectra acquired after an abrupt
interruption of the gas flow and subsequent spin relaxation to
thermal equilibrium), the small hyperpolarized signals of CH and
Both high H NMR signal enhancement and high conversion
level obtained using Pd-In/Al2O3 catalyst during hydrogenation of
propyne with parahydrogen allowed us to use MRI for selective
visualization of reaction product, propene. For MRI experiments
the concentration of protons is critical, and the amount of
catalyst was increased 3–fold in order to increase conversion.
2D MR images of propene were acquired using chemical shift
selective RF pulses (Figure 2). Selective excitation of different
groups of protons overcomes the problem of NMR signals
cancelation due to the presence of separate multiplets with
opposite phases (ALTADENA experiment). Also, such technique
paves the way to determine the spatial distribution of a particular
compound in the complex mixture (i.e., reagents and products).
For MRI experiments, conventional FLASH[62] pulse sequence
was modified and used (see SI for details). The results
convincingly demonstrate that dramatically enhanced NMR
signals of the flowing hyperpolarized propene, produced via
propyne hydrogenation with parahydrogen over Pd-In/Al2O3
single-site catalyst, are strong enough for selective 1H MR
imaging, while after an abrupt interruption of the gas flow and
relaxation to thermal equilibrium, the NMR signals are not strong
enough for acquiring good quality MR images for protons of the
CH and CH2 groups of propene produced in the reaction (Figure
2).
1
CH2 groups of propene were observed in the H NMR spectra
acquired while the gas was flowing (Figure S3). During
hydrogenation at 200-500 °C, both PHIP and thermally polarized
1H NMR signals were detected. The signal enhancement factors
and the percentages of pairwise hydrogen addition were
estimated by comparing the PHIP 1H NMR signals with the
thermal ones (see SI for details), and the results are shown in
Table 1. Importantly, at 400 °C the Pd-In/Al2O3 catalyst
demonstrated highly intensive PHIP effects along with
a
relatively high conversion level. Thus, the highest amount of
hyperpolarized propene was produced during propyne
hydrogenation at 400 °C and the mixture flow rate of ~5.1 mL/s
(Figure 1).
It should be noted that Pd-In/Al2O3 catalyst can produce
PASADENA polarization at 130 °C (Figure S6) even without
pretreatment (high-temperature reduction in H2 gas) which was
used in the experiments described above.
To study the influence of reduction treatment conditions on
catalytic activity and the catalyst active sites structure, the
chemical state of the catalyst was investigated by X-ray
photoelectron spectroscopy (XPS) during the reduction in
hydrogen atmosphere at different temperatures (Figure 3). Pd3d
and In3d core-level spectra demonstrated formation of different
sites on the catalyst surface during reduction. For the fresh
catalyst (before reduction treatment), Pd3d XPS spectrum
shows the presence of two different Pd states with binding
energies of 334.9±0.1 and 335.9±0.1 eV. The peak at 334.9 eV
was assigned to the metallic Pd.[63,64] According to the literature
data, the peak with a higher binding energy (~335.9 eV) could
Figure 1. (a) Reaction scheme of propyne hydrogenation; (b) 1H NMR
ALTADENA spectra acquired during propyne hydrogenation with
parahydrogen at 400 °C over Pd-In/Al2O3 catalyst while the gas was flowing
with the flow rate of 5.1 mL/s (green line) and after an abrupt interruption of
the gas flow and relaxation to thermal equilibrium (purple line). All spectra
were acquired with 8 signal accumulations and are presented on the same
vertical scale.
be
assigned
to
the
indium-palladium
intermetallic
compound.[50,65,66] In3d XPS spectrum of non-reduced catalytic
sample shows the presence of two indium states with binding
energies of 443.4±0.1 eV and 445.2±0.1 eV. The peak at 445.2
eV is assigned to indium in the 3+ state (In2O3).[50,65,66] The state
with a lower binding energy could be related to the presence of
PdxIny intermetallic compound on the catalyst surface. Thus, we
can conclude that for the non-reduced Pd-In/Al2O3 catalyst In
and Pd are partially present in the form of intermetallic PdxIny
compound. The rest of palladium is present in metallic form and
the rest of indium in the form of In2O3, which can potentially
cover the bimetallic (intermetallic) particles.
The signal enhancements estimated for Pd-In/Al2O3 catalyst
presented in Table 1 are lower than the actual values because
polarization losses caused by nuclear spin relaxation
1
dramatically reduce the intensities of enhanced H NMR signals
for propene. Therefore, the percentages of the pairwise
hydrogen addition were reevaluated taking due account of spin
relaxation effects. The corrected values of signal enhancement
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Figure 2. (a) Reaction scheme of propyne hydrogenation; (b) and (c) 1H NMR spectra acquired during propyne hydrogenation over Pd-In/Al2O3 catalyst (b) while
the gas was flowing and (c) after an abrupt interruption of the gas flow and the subsequent relaxation of nuclear spins to thermal equilibrium. The spectra are
presented on the same vertical scale. The reaction temperature was 400 °C, and the gas flow rate was 8.8 mL/s. (d) MR images of a 10-mm NMR tube filled with
gaseous thermal and hyperpolarized propene in the transverse orientation. MR images of hyperpolarized propene were acquired while the gas was flowing. For
all MR images, the matrix size and spatial resolution were equal to 64×64 and 0.8×0.8 mm2 per pixel, respectively.
The spectra presented in Figure 3 clearly verify that the
content of Pd-In intermetallic component increases with the
temperature of reduction treatment, while the contents of Pd0
and In2O3 decrease.
catalyst sample decreases with reduction temperature increase
while the Pd/Al atomic ratio remains constant (Figure S7). This
represents the direct evidence of indium diffusion from the
surface to the bulk of intermetallic particles.
The build-up of the intermetallic state of Pd with the increase
in reduction temperature was detected up to 300 C, and further
increase of reduction temperature does not lead to changes in
the Pd(Intermetallic)/Pd0 atomic ratio (see Table S3). At the
same time, the In(Intermetallic)/In3+ ratio gradually increases
with reduction temperature increase. It means that indium oxide
requires higher temperatures for the reduction and intermetallic
compound formation (Figure 3b). Thus, for the intermetallic Pd-
In compound formation the reduction of Pd-In/Al2O3 catalyst is
necessary. The data obtained in this work is in a good
agreement with the results reported previously.[55]
In conclusion, the single-site Pd-In/Al2O3 catalyst was
found to be a promising catalyst for the semihydrogenation of
propyne, which exhibits up to 98% propene selectivity and the
high catalytic activity. The redistribution of both palladium and
indium atoms on the catalyst surface associated with the
formation of Pd-In intermetallic compounds were observed by
XPS during catalyst reduction. It was shown that Pd sites
isolation by In atoms leads to improved selectivity of the triple
carbon-carbon bond hydrogenation. Moreover, Pd-In/Al2O3
Figure 3. Pd3d and In3d XPS spectra for the Pd-In/Al2O3 sample reduced in
10 mbar of H2 at various temperatures.
catalyst was found to show
a unique behavior in PHIP
The atomic concentrations of active sites calculated from
XPS data are presented in Table S3. The surface Pd/In atomic
ratio of the Pd-In/Al2O3 catalyst increases with increasing the
temperature of reduction from RT to 250 C, pointing to a
redistribution of both palladium and indium atoms on the catalyst
surface (Figure S7b). This increase can be explained by the
formation of intermetallic Pd-In sites, diffusion of reduced In into
the catalytic particles, and/or Pd isolation by In on the surface of
the bimetallic particles. Under higher reduction temperatures
(>250 C), the surface Pd/In atomic ratio remains constant. At
the same time, the aggregation of In and Pd sites to intermetallic
Pd-In compound still occurs. Moreover, In/Al atomic ratio of
experiments. A ~3400-fold signal enhancement was estimated
by taking due account of relaxation processes. This high signal
enhancement corresponds to the high percentage (9.3%) of
pairwise H2 addition and represents the highest value reported
to date for heterogeneous gas phase hydrogenation with
significant conversion (about 20%). The high catalytic activity of
Pd-In/Al2O3 single-site catalyst allows one to produce significant
amounts of hyperpolarized gas with polarization levels that are
unprecedented for heterogeneous PHIP, making it possible to
utilize MRI for selective imaging. MR images of flowing
hyperpolarized propene were obtained with 0.8x0.8 mm2 spatial
resolution, selectively for each of the three groups of hydrogen
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atoms in propene. The MRI of thermally polarized propene at the
same conditions is impossible due to an insufficient
concentration of protons. Therefore, these demonstrations of the
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[29]
[30]
[31]
[32]
[33]
[34]
[35]
Acknowledgements
D.B.B., K.V.K thank the Russian Science Foundation (grant #
17-73-20030) for the support of MRI and NMR experiments.
I.S.M., G.N.B., A.Yu.S. thank the Russian Science Foundation
(grant #16-13-10530) for supporting the catalyst synthesis.
D.B.B. is also grateful to Haldor Topsøe A/S Ph.D. program for
financial support. D.B.B. and K.V.K. thank Alexey Romanov for
his contribution to MRI experiments.
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D.B. Burueva, K.V. Kovtunov,* A.V.
Bukhtiyarov, D.A. Barskiy, I.P.
Prosvirin, I.S. Mashkovsky, G.N.
Baeva, V.I. Bukhtiyarov, A.Yu.
Stakheev, I.V. Koptyug
Page No. – Page No.
Selective single-site Pd-In
hydrogenation catalyst for
production of enhanced magnetic
resonance signals using
parahydrogen
This article is protected by copyright. All rights reserved.