Water-soluble NHC-stabilized platinum nanoparticles as recoverable catalysts for hydrogenation in water

Article abstract of DOI:10.1039/d0cy00481b

The production of water-soluble and stable metallic nanoparticles that can act as recoverable catalysts still remains a challenge. Herein we report the behavior of a series of water-soluble platinum nanoparticles containing different sulfonated NHC ligands as recoverable catalysts for the hydrogenation of aromatic compounds in pure water. The NHC-protected nanoparticles are found to be active and, in general, can be reutilized with no loss of activity or selectivity, although differences are observed depending on the substitution of the NHC ligand or on the substrate being hydrogenated. Pt leaching was determined to be only 0.03-0.29%. TEM images reveal that the shape of the nanoparticles remains unaltered after catalysis. However, the size of the particles increased, although with no influence on their catalytic properties in many instances.

Full text of DOI:10.1039/d0cy00481b

View Article Online
View Journal
Catalysis
Science &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: A. M. Ruiz-Varilla,
E. A. Baquero, B. Chaudret, E. de Jesús, G. A. María del Camino and J. C. Flores, Catal. Sci. Technol.,
2020, DOI: 10.1039/D0CY00481B.
Volume
Number
21 January 2017
Pages 313-534
7
2
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
rsc.li/catalysis
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 2044-4761
PAPER
Chaoqiu Chen, Yong Qin et al.
Highly dispersed Pt nanoparticles supported on carbon
nanotubes produced by atomic layer deposition for hydrogen
generation from hydrolysis of ammonia borane
rsc.li/catalysis

Please do not adjust margins
Catalysis Science & Technology
Page 1 of 9
View Article Online
DOI: 10.1039/D0CY00481B
ARTICLE
Water-Soluble NHC-Stabilized Platinum Nanoparticles as
Recoverable Catalysts for Hydrogenation in Water
Received 00th January 20xx,
Accepted 00th January 20xx
Andrea M. Ruiz-Varilla,a Edwin A. Baquero,b* Bruno Chaudret,c Ernesto de Jesús,a Camino
Gonzalez-Arellano,a* and Juan C. Floresa*
DOI: 10.1039/x0xx00000x
The production of water-soluble and stable metallic nanoparticles that can act as recoverable catalysts still remains a
challenge. Herein we report the behavior of a series of water-soluble platinum nanoparticles containing different
sulfonated NHC ligands as recoverable catalysts for the hydrogenation of aromatic compounds in pure water. The NHC-
protected nanoparticles are found to be active and, in general, can be reutilized with no loss of activity or selectivity,
although differences are observed depending on the substitution of the NHC ligand or on the substrate being
hydrogenated. Pt leaching was determined to be only 0.03–0.29%. TEM images reveal that the shape of the nanoparticles
remains unaltered after catalysis. However, the size of the particles increased, although with no influence on their catalytic
properties in many instances.
robust ligand-metal bonds.4 Although the number of examples
of NHC-modified MNPs (M = Ir,5 Ag,6 Pd,7 Au,8 Ru,9 Pt,10 Ni,11
Cu12 and Rh13) that has been reported is relatively limited to
Introduction
Over the past few years, metal nanoparticles (MNPs) have
been extensively studied in catalysis and found to exhibit
desired activities and selectivities, and to potentially be
recyclable.1 Shape, size and size-distribution, and surface
composition strongly affect the reactivity and stability of
MNPs. In addition, the tendency to aggregate, which is usually
detrimental to catalytic performance, can be prevented by
using suitable stabilizers such as polymers, surfactants, and
phosphorus-, nitrogen- or sulfur-donor ligands.2 In addition to
the protective coverage and regulation of the solubility or
stability of the colloidal dispersion in a particular solvent, the
nature and quantity of the capping agent has a critical
influence on the accessibility and shape of the active centers
as it is expected to generate unsaturated surfaces with
available and selective sites.2,3
date, the subject has recently been reviewed.14
The majority of studies involving NHC-MNPs and their
applications have involved the use of organic solvents despite
the fact that the use of water as a reaction medium is very
attractive in a broader context. For chemical transformations,
water is considered both environmentally as a promising green
solvent and also brings a distinctive set of properties that often
offer different benefits (e.g., enhanced chemical reactivity and
selectivity, milder catalytic conditions, easier work-up
procedures or catalyst recovery).15 Nonetheless, to the best of
our knowledge, there are currently only a small number of
examples of water-soluble MNPs stabilized by NHCs, with only
a few reports for Pd,7d,e,f;8c Au,8c,d,e,f Ru,9d RuPt9f and PtNPs.10b,c
We have reported the synthesis of PtNPs 2a–d in water by
the thermally induced reduction of dimethyl complexes 1a–
d,16 which contain sulfonated NHC ligands (Scheme 1).10b The
synthetic methodology in water was subsequently successfully
expanded to prepare PtNPs by changing the thermal
procedure for the chemical reduction of Pt-NHC complexes,
under 3 bar of CO or H2, at room temperature.10c Direct
bonding of the NHC to the MNPs surface was corroborated by
determining the 13C–195Pt coupling constants by solid-state
NMR spectroscopy. Moreover, the fact that PtNPs 2a–d are
found to be fully stable while dispersed in water under air
highlights the great strength and inertness of the linkage
between the ligand and the metal surface. Taking advantage of
these features, the sulfonated NHCs were also found to be
suitable ligands for the synthesis, and stabilization of water-
soluble Pd7e,f and RuNPs9d under mild conditions.
Concurrently with these advances, the field of N-
heterocyclic carbenes (NHCs) has grown significantly, mainly
due to the easy and feasible modification of the N-heterocycle,
and the extraordinary capability of these ligands to bind to
metal centers, thus providing steric protection and, typically,
a. Departamento de Química Orgánica y Química Inorgánica, Instituto de
Investigación Química "Andrés M. del Río", Universidad de Alcalá, Campus
Universitario, 28871 Alcalá de Henares, Madrid, Spain. Email:
camino.gonzalez@uah.es, juanc.flores@uah.es
b. Departamento de Química, Facultad de Ciencias, Universidad Nacional de
Colombia, Sede Bogotá, Carrera 30 No. 45-03, 111321 Bogotá, Colombia. Email:
eabaquerov@unal.edu.co
c. LPCNO; INSA, CNRS, Université de Toulouse, 135, Avenue de Rangueil, 31077
Toulouse, France.
† Electronic Supplementary Information (ESI) available: Experimental details of the
synthesis and characterization of the PtNPs and of the catalysis. See
DOI: 10.1039/x0xx00000x
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 2 of 9
ARTICLE
Journal Name
catalytic performances of PtNPs 2b–d in the same reaction are
View Article Online
DOI: 10.1039/D0CY00481B
comparable to that of 2a, with no substantial differences
attributable to the nature of the NHC ligand coordinated to the
nanoparticle surface. Thus, conversions range from 99% (2a)
to 87% (2c), although TON values (mmol of phenylacetylene
converted/mmol of surface Pt = 250, 240, 290, and 245) and
average TOFs (TON/reaction time = 83, 80, 97 and 82 h-1 for
2a, 2b, 2c, and 2d, respectively) were all similar, with
approximately the same selectivity, and styrene:ethylbenzene
ratios of 70-80:30-20 (Entries 1–4, Table 1).
The selective hydrogenation of alkynes to alkenes is a
relevant reaction for polymer and fine chemistry that has
received increasing attention recently due to the use of well-
defined MNPs, mostly based on colloidal palladium(0), but also
on other metals.17 As for PtNPs, dispersed Pt nanoparticles,
Scheme 1. Synthesis of water-soluble NHC-stabilized PtNPs 2a-d.
The chemical behavior of this type of NPs is of particular
interest, especially for catalytic processes in water. We have
observed that the surface of such NPs is accessible to co-
ligands (e.g. CO)7e,f;9d;10c and to catalytic substrates in water.
Indeed, we have preliminarily communicated the
enantiospecific C–H deuteration of L-lysine on RuNPs,9d and
the hydrogenation of styrene as a model reaction carried out
with PtNPs in water.10b
Table 1: Hydrogenation of unsaturated substrates in water catalyzed by PtNPs 2a.
Inspired by these results, we envisioned that the water-
soluble PtNPs 2 could be attractive catalysts for the selective
hydrogenation of unsaturated compounds in water. As such,
herein we report the use of 2a–d as catalysts for the
hydrogenation of different substituted arenes under fairly mild
conditions in this solvent. In addition to the activity and
selectivity of the processes, the recoverability and durability of
the PtNPs, and the influence of the nature of the carbene
coordinated to the surface, have also been investigated.
R2
R2'
R2''
PtNPs 2a-d
+
H2
+
30 °C, H2O
R1
R1
R1'
Entry Cat. Substrate
Product
Conv (%)h Selectivity (A:B)h
1b
2b
2a
2b
2c
2d
2a
2b
2c
2d
2a
2b
2c
2d
>99
96
69:31
77:23
78:22
79:21
>99:<1
>99:<1
>99:<1
>99:<1
96:4
A
B
3b
87
4b
98
Results and discussion
Synthesis of PtNPs 2
5c
>99
92
OH
6c
O
A
The platinum nanoparticles 2a-d were prepared according to a
previously reported procedure,10b using the organometallic
approach, by heating complexes 1a-d at 80 °C in water for 18
hours (Scheme 1, see the Supporting Information, SI). The
PtNPs were found to be spherical in shape, with sizes ranging
from 1.3–2.0 ± 0.4 nm, depending on the NHC ligand. The
smallest nanoparticles resulted from the bulkiest ligands a and
b (both 1.3 nm), whereas the biggest ones resulted from
ligands c and d (1.6 and 2.0 nm, respectively; Figures S1-S4). It
should be noted that these nanomaterials are highly stable in
water, under air, remaining totally dispersed without
agglomeration or Pt0 precipitation for at least one year.
Hydrogenation of phenylacetylene
H
7c
94
OH
8c
92
B
9d
>99
>99
>99
>99
NH2
10d
11d
12d
99:1
A
NO2
NH2
99:1
byproducts
98:2
B
13e
14e
15d
16d
2a
2b
2a
2b
32
28
66
13
50:44f
64:26g
16:84
25:75
A
NO2
NO2
Having demonstrated the ability of PtNPs 2 to hydrogenate
styrene in water,10b the hydrogenation of phenylacetylene was
chosen as the model reaction to explore their catalytic
properties in aqueous media. The first set of experiments was
carried out using nanoparticles 2a under different reaction
conditions (temperature, hydrogen pressure, time; see Table
S1). The optimal conditions required for complete
hydrogenation of phenylacetylene (>99%) were 30 °C, 2 bar of
H2 and reaction for 3 h, with a Pt loading of 0.4 mol% (Entry 4,
Table S1). Interestingly, under the conditions tested, the
reaction is moderately selective towards semi-hydrogenation
of the alkyne, thus leading to product compositions containing
70-75% styrene and 25-30% ethylbenzene (Table S1). The
B
NH2
O
H
O
A
NO
O
H
H
NO2
B
NH2
a
Reaction conditions: 1 mmol substrate, surface Pt loading: 0.4 (2a,b,d) or 0.3 (2c)
mol% (see SI; total Pt loading: 0.6 (2a,b,d) or 0.4 (2c) mol%), 2 mL of water. b 2.0 bar
of H2, 3 h. 5.0 bar of H2, 8 h. 3.0 bar of H2, 3 h. 1.0 bar of H2, 2h. f 6% of 3-
c
d
e
vinylaniline was found. g 10% of 3-vinylaniline was found. h Determined by GC-MS.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 9
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
prepared by impregnation methods and supported on Zeolite-
templated carbon (ZTC)18a or on carbon nanotubes (CNT),18b
have been shown to be selective for styrene (up to 88%) in the
hydrogenation of phenylacetylene under optimized conditions
(4.0-5.0 bar of H2, 1 h, 50-80 °C) in organic solvents.
Unsupported alkanethiolate-stabilized PtNPs have also been
used in this reaction, with the colloidal catalyst leading to full
conversion in chloroform, but after longer reaction times (24
h, room temp., atmospheric pressure), and showing a modest
selectivity (31:69% styrene/ethylbenzene).19
View Article Online
DOI: 10.1039/D0CY00481B
After biphasic separation of the catalytic products with the
help of an organic solvent (see SI), the aqueous dispersions of
PtNPs 2 were reutilized up to 10 more times in the
hydrogenation reaction under the same conditions. The
recovered water phases showed total conversions from one
run to the next in each of the eleven consecutive reactions,
thus indicating some degree of stability for the nanocatalysts
in the long term. This contrasts with the poor stability reported
for PtNPs grafted with the water-soluble phosphane PTA
(1,3,5-triaza-7-phosphaadamantane) in the hydrogenation of
octene in water (20 °C, 1 bar of H2), for which a sharp decrease
in conversion is observed upon catalyst recycling.20 With 2, the
cumulative TONs based on converted phenylacetylene
increased to around 3000 in these series of reactions, which is
almost twice the value based on consumed hydrogen as the
selectivity changed completely to ethylbenzene after the 2nd-
3rd cycle (see Figures S5 and S6 for PtNPs 2a and 2d,
respectively). Complete hydrogenation of the triple bond has
also been observed in reactions catalyzed with the
heterogenized Pt nanoparticles mentioned above, but as a
result of longer reaction times or higher H2 pressures.18
Moreover, PtNPs supported on ZTC have been reported to
show constant selectivity for styrene (ca. 80%) in recycling
experiments, although a 20% decrease in conversion is
recorded after four uses of the catalyst.18a In contrast, the
reactivity of PtNPs 2 in the catalytic hydrogenation in water
appears to increase with use concomitantly with a drastic
switch in the selectivity of the reaction towards ethylbenzene.
The outcomes are consistent with an initial activation of
the surface of nanoparticles 2 and with species in the resting
state that remain stable during the recycling operations, thus
providing pre-activated catalysts from the beginning of the
reaction in subsequent uses of their aqueous dispersions. With
this in mind, we monitored the composition of the reaction by
periodically performing GC analysis (see SI) using PtNPs 2a as
catalysts in a sequence of four cycles (Figure 1). Thus, a slower
reaction is observed in the first run, whereas in the
reutilization cycles the catalyst is clearly more active,
especially taking into account that conversion shifts to the
product with a fully hydrogenated triple bond.
Fig. 1. Reaction profile (conversion (%) vs. time) in the hydrogenation of
phenylacetylene catalyzed by PtNPs 2a during 4 consecutive cycles: 1 (■), 2
(●), 3 (▲), and 4 (▼).
(2.0 bar) and the tube containing the solid was sealed and
1
maintained at room temperature (24 h). The gas-phase H
NMR spectrum of the mixture showed the expected broad
resonance (∆1/2 = 1714 Hz) for H2 at 4.5 ppm (Figure 2a). The
tube was thoroughly evacuated under vacuum (10-6 bar, 24 h),
and the gas-phase spectrum recorded again to verify
disappearance of the resonance for the H2 gas (Figure 2b). The
NMR tube was then filled with D2 (2.0 bar, overnight) and the
1H NMR spectrum was recorded once more. A peak at 4.5 ppm
reemerged, but now with a narrower linewidth (∆1/2 = 382 Hz;
Figure 2c). The major component of the new peak was
assigned to protons in HD, which forms after the activation of
D2 by the PtNPs, recombination with already existing Pt-H
species, and desorption of HD gas (note that H2 can then be
formed as a minor component).21 These findings show that
PtNPs 2a can activate H2 (or D2) to afford tightly bound H
atoms that persist after prolonged high vacuum (or after
catalyst recovery), but can be readily transferred to D2 (or to
the substrate in hydrogenation reactions).
The PtNPs all behaved similarly, with constant conversion
(100%) to ethylbenzene in the recycling runs. Despite this,
some differences in degradation were apparent to the naked
eye, with the precipitation of tiny amounts of Pt black visible
after the first use for PtNPs 2d, the eighth for 2c, and after the
(H2)gas
a)
b)
c)
(HD)gas
In order to detect the formation of Pt-H species in
activation of the nanoparticles, we performed an NMR
experiment based on an H/D exchange reaction, which has
been reported to be useful for the indirect detection of H
atoms bound to MNPs.21 Thus, a sample of NPs 2a was
introduced into an empty high-pressure NMR tube equipped
with a Teflon valve, the atmosphere was replaced by H2 gas
Fig. 2. Sequence of gas-phase 1H NMR spectra showing the formation of HD
by treatment of PtNPs 2a with a) H2; b) after removal of H2 under vacuum;
and c) after treatment with D2.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 4 of 9
ARTICLE
Journal Name
tenth run with nanoparticles 2a or 2b. The suspected aging or
degradation of the catalysts was further inspected by TEM.
Indeed, TEM imaging analysis of the colloidal solutions after
recycling experiments confirmed that the spherical shape of
the particles remained unaltered in all systems at the end of
the sequence of eleven reactions, although the PtNPs
increased in size from 1.3±0.4 to 2.5±0.5 nm for 2a,b, or from
1.6±0.4 to 2.9±0.6 nm for 2c, whereas for 2d the polydispersity
increased from 0.3 to 0.7 nm (Figures S7–S10), showing a
bimodal size-distribution histogram with particles up to 4 nm
in diameter. This size increase can be assigned to an Ostwald
ripening process,22 which is thermodynamically more favorable
for NPs in a higher energy state due to decoordination of the
NHC ligands from the surface during catalysis. As such, all
these water-soluble NHC ligands seem to efficiently maintain
the activity of the PtNPs, although those containing an aryl ring
(a and b) appear to offer better surface protection, thereby
preventing degradation and aggregation/precipitation of the
NPs (vide infra).
The size change detected led us to investigate the possible
leaching and loss of platinum with the products; ICP-MS
analyses of the organic phases separated after all cycles using
NPs 2a showed that Pt leaching was negligible (Table 2, Entry
1). This finding demonstrates that our capping NHC ligands
provide robust systems that are able to efficiently retain the
PtNPs in the aqueous phase after each cycle. At the same time,
considering the total platinum content found in the products
(0.03%) and the total TON accumulated over the multiple runs
(ca. 3000), in the absence of any purification step, the resulting
Pt contamination in the crude reaction products is less than
0.2 or 0.3 ppm, expressed as a molar or as a mass fraction of
the metal, respectively.
View Article Online
DOI: 10.1039/D0CY00481B
Fig. 3. Recycling experiments in the hydrogenation of benzaldehyde with
PtNPs 2a (■), 2b (●), 2c (▲) and 2d (▼). Reaction conditions as in Table 1.
conditions selected, PtNPs 2a-d were found to be highly active
and selective towards the formation of benzyl alcohol as the
almost exclusive product (Entries 5–8, conv. 92–99%,
selectivity >99%, Table 1), with no difference in behavior
assignable to the nature of the NHC ligand present on the NP-
surface. The TOFs determined at the end of the first use of the
catalysts were 30-40 h-1, with 2c being the most active.
Comparable TOF values have been reported in this reaction for
Pt and Pt/Pd NPs stabilized by silsesquioxanes in EtOH/H2O
mixtures. The mono- or bimetallic NPs were recovered from
the products by adjusting the pH of the medium in order to
precipitate the particles and were reutilized, with a minor drop
in activity being observed after five runs.25 Nanosystems 2
were also recycled up to 10 times by simple liquid-liquid
extraction. Moreover, while PtNPs 2a and 2b showed well-
conserved performances over the 11 cycles of the recycling
series, PtNPs 2d exhibited some fatigue after the eighth run,
and 2c showed a sharp decrease in activity, with conversions
of 80% after the fourth cycle and 29% in the last one (Figure
Hydrogenation of other substituted benzenes
Next, we guided the study of catalytic hydrogenation with 3). Interestingly, Figure 3 also shows that the conversions
PtNPs 2 in water towards the hydrogenation of other aromatic achieved with 2b-d in the second use of the catalyst were
model substrates, such as benzaldehyde, acetophenone and higher than in the initial one, in agreement with the activation
nitrobenzene. The selective hydrogenation of aromatic period mentioned above for the PtNPs, and with resting
carbonyl or nitro compounds is of great interest because the species tolerant to the recycling work-up.
products of this reaction, particularly the corresponding
Selective formation of the aromatic alcohol remained
aromatic alcohols or anilines, are valuable intermediates in the unaltered in all these series of reactions, with only traces of
pharmaceutical, polymer, agro-, and specialty chemical cyclohexylmethanol being detected as byproduct (<1%). The
industries.10a,23,24
hydrogenation of aromatic carbonyl compounds is a challenge
After testing different reaction conditions with NPs 2a in in terms of chemoselectivity as Pt particles usually favor
the hydrogenation of benzaldehyde (4-5 bar, 30-60 °C, 5-15 h), reduction of the C=O bond,23c,26 whereas simultaneous
we obtained optimized results at 5.0 bar of H2, 30 °C and 8 h, hydrogenation of the aromatic ring is a common side-reaction
and observed that higher temperatures are detrimental to the with Ru23b,27,28 or Rh28 NPs.
stability and activity of the nanoparticles. Under the mild
Some Pt black was noticeable after the first use for PtNPs
2c,d, the fifth use for 2b, and after the ninth run with
nanoparticles 2a. TEM images of PtNPs 2a used in the recycling
experiments revealed that the particle size increased from
1.3±0.4 to 2.8±0.6 nm, with no change in the spherical shape
(Figure S11) or loss of activity after 11 cycles. Again, Pt
contamination of the products, as measured for NPs 2a by ICP-
MS, was insignificant (Table 2, Entry 2).
Table 2: Percentage of the initial Pt leached in the sequence of hydrogenation runs with
phenylacetylene (entry 1), benzaldehyde (2) and nitrobenzene (3) catalyzed by PtNPs 2a.a
Entry\Run
1
2
3-10
0.01
0.02
0.25
11
Total %Pt leached
1
2
3
0.01
0.01
0.01
0.01
0.00
0.01
0.00
0.00
0.02
0.03
0.03
0.29
A similar diameter and dispersity enlargement, with no
alteration of the catalytic activity, has been reported in the
a Found in the organic phases with the products. Determined by ICP-MS (RSD ≤2%).
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 9
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
same hydrogenation reaction using Pd-based nanocatalysts.25c 91% to 84% yield in the first and fifth cycles, respectively).24b
View Article Online
In the case of 2c, the activity of which decreased after the fifth No metallic precipitates were observedDaOtI:t1h0e.10e3n9/dD0oCfYa0n04y81oBf
cycle, TEM analyses of the Pt black precipitated after the the reactions carried out with 2a, although Pt black was visible
recycling series revealed that the PtNPs increased in size from after the seventh use for PtNPs 2b, and after the last five runs
1.6±0.4 to 2.9±0.5 nm (Figure S12a), and also showed the for 2c and 2d. TEM images recorded for PtNPs 2a and 2c after
formation of large conglomerates (Figure S12b), which are eleven cycles showed an increment in the size of the particles
likely to reduce the active surface available and, consequently, to 2.5 and 2.6±0.4 nm (Figures S14 and S15, respectively).
the activity of this system.
However, this increase did not affect the catalytic activity. An
The results for the hydrogenation of acetophenone were increase in mean diameter after recycling was also reported
difficult to interpret. Thus, after some preliminary testing using for the NPs supported on the ionic polymer mentioned
2a (Table S2), we selected the same operating conditions used above.24a ICP-MS measurements performed for PtNPs 2a
for the reaction with benzaldehyde (i.e., 5.0 bar of H2, 30 °C, 8 revealed a Pt leaching to the organic phases of 0.29% (Table 2,
h). The selectivity for 1-phenylethanol (80-95%; combined with Entry 3). Although higher than that found in the reactions with
3-15% of cyclohexyl methyl ketone, and 0-5% of 1- phenylacetylene or benzaldehyde, this metal leaching is still
cyclohexylethanol) was higher than that typically found for low considering the eleven uses of the catalyst (33 h),
Ru23b,27,28 or Rh28 NPs and in the same range observed for including the corresponding biphasic separations, thus
supported Pt NPs,26 although the conversion of the reaction showing that this system also comprises highly recoverable
was poorly reproducible. For instance, conversions in a range catalysts for the hydrogenation of nitrobenzene.
of 20-81% were observed for PtNPs 2a in the first use of the
In addition to aniline as the major product (95-99%),
catalyst (61-84%, 9-16%, and 4-7% for 2b, 2c, 2d, respectively) variable amounts of several minor by-products, such as
with reproducibility varying in all recycling series (Table S2). hydrogenation intermediates (i.e., nitrosobenzene ≤2%, and
Moreover, the conversion decreased to values of 1-23% in the azobenzene ≤4%), the fully hydrogenated product (i.e.,
last run of 2a (11th use). In addition, large amounts of Pt black cyclohexylamine ≤0.3%), or condensation compounds resulting
formed in most of these reactions, with complete precipitation from hydrogen-borrowing amination coupling reactions (i.e.,
leading to colorless final solutions in some cases. The lack of N,N-dicyclohexylamine <1%, N-cyclohexylaniline ≤4%), were
reproducibility and stability of the NPs can be tentatively detected in the catalytic cycles.31 For the hydrogenation of
attributed to deactivation caused by the presence of 1- nitroarenes, it is well known that partially hydrogenated
phenylethanol. It has been reported that nucleophilic alcohols intermediates,
including
nitrosoarenes
or
N-
such as 1-phenylethanol can inhibit metal catalysts in water by arylhydroxylamine, and other derivatives such as azoarenes
forming stable adducts with the active species.29 Another from condensation processes, are formed, particularly under
explanation, although less likely considering the results in the mild conditions. Hydroxylamines are problematic due to their
hydrogenation of benzaldehyde, is self-poisoning of the Pt NPs toxicity and tendency to undergo highly exothermic
by CO, which strongly binds to the active sites and is generated decomposition, even when accumulated at low levels.10a,24c,32
by decarbonylation of the alcohol produced at the NP Immobilized Pt catalysts have been associated with this
surface.30 After the eleven uses of 2a, the average diameter problem.32a,b However, the presence of the undesirable N-
increased to 3.0±0.7 nm (3.5±0.7 nm for 2c) for the particles phenylhydroxylamine was never detected at the end of the
remaining dispersed in water, and to 4.4±1.4 nm for those reaction using PtNPs
2 in water. Therefore, if the
observable by TEM in the precipitated solid, which was hydroxylamine is formed, it apparently reacts rapidly under
strongly agglomerated (Figure S13).
the mild conditions applied.
The catalytic hydrogenation of nitrobenzene was
Taking into account the superior stability of 2a and 2b, we
performed at 3.0 bar of H2 and 30 °C for 3 h, with incomplete also briefly tested the chemoselectivity of these NPs in the
conversions being observed at lower pressures or with shorter hydrogenation of 3-nitrostyrene and 3-nitrobenzaldehyde. The
reaction times. We found that 2a–d were all highly active and hydrogenation of substituted nitroarenes containing other
selective for the formation of aniline as the major product reducible functionalities is a challenging task because the
(conv. >99% with selectivity >96%, Table 1, Entries 9–12). TOF chemoselectivity of the process is very sensitive to the metal in
values after the first cycle were found to be in the range 85- use, the support, and other conditions (solvent, stabilizers,
110 h-1 (calculated based on converted substrate), similar to reductant, pH, etc.),24,32,33,34 or to the metallic nanocrystal
that reported by Lara et al. (100 h-1) under similar conditions in faces exposed.32a In an attempt to favor selective
water for PtNPs stabilized by an IPr ligand, namely 1,3-bis(2,6- hydrogenation of the vinyl group of 3-nitrostyrene, we used
diisopropylphenylimidazol-2-ylidene), although no recycling very mild conditions (1.0 bar of H2, 30 °C, 2 h of reaction) and
data were disclosed.10a Particles 2 were found to be very active obtained low conversions (32% and 28%, for 2a and 2b,
after 11 reaction cycles, maintaining the initial activity (conv. respectively, Entries 13–14, Table 1), with a selectivity in
95–99%) and selectivity (>96%), with cumulative TONs of agreement with a process in which hydrogenation of the C=C
2750-3600. PtNPs dispersed on an ionic polymer have also double bond of the vinyl group is easier than reduction of the
shown almost intact performances in this reaction in THF after nitro group (50:44:6 and 64:26:10 of 3-ethylnitrobenzene:3-
been recovered five times,24a whereas some loss of activity has ethylaniline:3-vinylaniline for 2a and 2b, respectively).34
been observed in water for gum arabic-supported PtNPs (from Indeed, a shorter reaction time (1 h) or a lower pressure (0.5
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 6 of 9
ARTICLE
bar,
Journal Name
2
h) resulted in increased selectivity for 3- maintained for NPs with ligands containing an aryVlireiwnAgrt(ic2leaOanlninde
DOI: 10.1039/D0CY00481B
ethylnitrobenzene (78-83%), but at the cost of negligible 2b), probably because they offer better surface protection and
conversions (3-5%). The conditions for the reaction with 3- prevent degradation of the particles. Nevertheless, aging due
nitrobenzaldehyde were tentatively established in an attempt to reuse results in an increase in the size of the spherical NPs,
to provoke selective reduction of the nitro group (3.0 bar of even for 2a and 2b.
H2, 30 °C, 3 h). Better conversions were obtained for PtNPs 2a
This study highlights the use of hydrophilic NHC ligands as
(66%, Entry 15, Table 1), whereas for 2b a value of only 13% stabilizers of water-soluble PtNPs that make them efficient and
was achieved (Entry 16, Table 1). Reduction occurred only at more robust recoverable catalysts for hydrogenation reactions
the nitro group, with the carbonyl group remaining intact after in water than other ligands such as PTA,20 in processes where
catalysis, thus leading to mixtures of only two products (3- contamination of the product with Pt, when measured, was
aminobenzaldehyde and 3-nitrosobenzaldehyde, 84:16 and below the specification limits for metal impurities (ppm levels)
75:25 for 2a and 2b, respectively). Although conversions of in the production of many pharmaceuticals and fine
both substrates were not completed, the shape and dispersity chemicals.35
of PtNPs 2a were not modified after catalysis, as shown by the
TEM images. However, the size of the particles increased
slightly after just one use (1.9±0.4 and 1.8±0.3 nm for NPs used
Conflicts of interest
with 3-nitrostyrene and 3-nitrobenzaldehyde, respectively;
Figures S16 and S17). It is worth mentioning that no
arylhydroxylamines were detected in any of the hydrogenation
reactions of nitroarenes performed with NPs 2 in water.
There are no conflicts to declare.
Acknowledgements
We gratefully acknowledge support from the Spanish
Ministerio de Economía y Competitividad (project CTQ2017-
85203-P), the Ministerio de Educación (FPU grant to A. M. R.-
V.), and the Universidad de Alcalá (project CCGP2017/EXP-
018).
Conclusions
In this work, we have explored the use of PtNPs 2a–d
stabilized with hydrophilic NHC ligands as catalysts for the
hydrogenation of aromatic compounds in water. The particles
are able to activate H2 on the surface, as demonstrated by gas-
phase NMR experiments and by their catalytic behavior in
water. Thus, PtNPs 2 are found to be efficient catalysts for the
hydrogenation of several substituted benzenes in this solvent
under very mild conditions.
All nanoparticles exhibit a chemoselectivity that favors
hydrogenation of the substituents over reduction of the
aromatic ring, in a study that also unveils preferences
following the trend unsaturated C-C bond > nitro > carbonyl
group, for the functionalities present in the aryl rings. The
process is selective towards ethylbenzene when
phenylacetylene is the substrate, although the semi-
hydrogenated alkene is the major product when using fresh
nanoparticles, the corresponding alcohol is formed in the
hydrogenation of carbonyl groups, and anilines result from the
reduction of nitrobenzenes, with no noticeable formation of
arylhydroxylamines under the conditions applied.
The outcomes of the recycling experiments turned out to
be quite informative. Thus, the NPs can be reused after
recovery by biphasic separation, retaining most of their
catalytic activity (in at least 11 cycles), with the exception of
acetophenone, which was a harmful substrate and deactivated
the NPs with precipitation of Pt black. As such, the NHC ligands
provide water-solubility and, in general, stability to the NPs
during catalysis. Moreover, some findings are in agreement
with the ligands also stabilizing the species in the resting state
during the recycling operations, thus providing pre-activated
catalysts for subsequent use of the NPs in aqueous dispersion.
No significant differences in activity or selectivity can be
attributed to the nature of the NHC ligand with any substrate.
However, the durability of the catalysts is more efficiently
Notes and references
1
Nanomaterials in Catalysis, eds. P. Serp and K. Philippot,
Wiley-VCH, Weinheim, 2013.
2
a) Nanoparticles and Catalysis Vol. 1, ed. D. Astruc, Wiley-
VCH, 2008; b) Nanoparticles From Theory to Application, 2nd
completely revised and updated Edition, ed. G. Schmid,
Wiley-VCH, Weinheim 2010; c) P. Lara, K. Philippot and B.
Chaudret, ChemCatChem, 2013, 5, 28-45; d) C. Amiens, D.
Ciuculescu-Pradines and K. Philippot, Coord. Chem. Rev.,
2016, 308, 409-432; e) L. M. Martinez-Prieto and B.
Chaudret, Acc. Chem. Res., 2018, 51, 376-384.
3
4
a) L. M. Rossi, J. L. Fiorio, M. A. S. García and C. P. Ferraz,
Dalton Trans., 2018, 47, 5889-5915; b) A. Heuer-Jungemann,
N. Feliu, I. Bakaimi, M. Hamaly, A. Alkilany, I. Chakraborty, A.
Masood, M. F. Casula, A. Kostopoulou, E. Oh, K. Susumu, M.
H. Stewart, I. L. Medintz, E. Stratakis, W. J. Parak and A. G.
Kanaras, Chem. Rev., 2019, 119, 4819-4880.
a) M. N. Hopkinson, C. Richter, M. Schedler and F. Glorius,
Nature, 2014, 510, 485-496; b) V. Nesterov, D. Reiter, P. Bag,
P. Frisch, R. Holzner, A. Porzelt and S. Inoue, Chem. Rev.,
2018, 118, 9678-9842; c) N-Heterocyclic Carbenes: From
Laboratory Curiosities to Efficient Synthetic Tools 1 and 2, ed.
S. Díez-González, RSC Catalysis Series, The Royal Society of
Chemistry, 2011 and 2017; d) The Organometallic Chemistry
of N-heterocyclic Carbenes, ed. H. V. Huynh, Wiley-VCH,
2017.
5
6
a ) L. S. Ott, M. L. Cline, M. Deetlefs, K. R. Seddon and R. G.
Finke, J. Am. Chem. Soc., 2005, 127, 5758-5759; b) L. S. Ott,
S. Campbell, K. R. Seddon and R. G. Finke, Inorg. Chem.,
2007, 46, 10335-10344.
a) A. Melaiye, Z. Sun, K. Hindi, A. Milsted, D. Ely, D. H.
Reneker, C. A. Tessier and W. J. Youngs, J. Am. Chem. Soc.
2005, 127, 2285-2291; b) X. Ling, N. Schaeffer, S. Roland and
M.-P. Pileni, Langmuir, 2013, 29, 12647-12656; c) H. Lu and
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 9
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
R. L. Brutchey, Chem. Mater., 2017, 29, 1396-1403; d) J. Cao
and H. Tian, Chem. Asian J., 2018, 13, 1561-1569.
127; b) B. L. Tran, J. L. Fulton, J. C. Linehan, J. A. Lercher and
View Article Online
R. M. Bullock, ACS Catal., 2018, 8, 8441-8449.
DOI: 10.1039/D0CY00481B
7
a) K. V. S. Ranganath, J. Kloesges, A. H. Schäfer and F. Glorius, 14 a) A. V. Zhukhovitskiy, M. J. MacLeod and J. A. Johnson,
Angew. Chem. Int. Ed., 2010, 49, 7786-7789; b) C. J. Serpell,
J. Cookson, A. L. Thompson, C. M. Brown and P. D. Beer,
Dalton Trans., 2013, 42, 1385-1393; c) M. Planellas, Y.
Moglie, F. Alonso, M. Yus, R. Pleixats and A. Shafir, Eur. J.
Chem. Rev., 2015, 115, 11503-11532; b) Y.-Y. An, J.-G. Yu and
Y.-F. Han, Chin. J. Chem., 2019, 37, 76-87; c) C. A. Smith, M.
R. Narouz, P. A. Lummis, I. Singh, A. Nazemi, C.-H. Li and C.
M. Crudden, Chem. Rev., 2019, 119, 4986-5056.
Org. Chem., 2014, 3001-3008; d) A. Rühling, K. Schaepe, L. 15 See for instance: a) B. H. Lipshutz, Chem., 2018, 4, 2004-
Rakers, B. Vonhören, P. Tegeder, B. J. Ravoo and F. Glorius,
Angew. Chem. Int. Ed., 2016, 55, 5856-5860; e) J. M. Asensio,
S. Tricard, Y. Coppel, R. Andrés, B. Chaudret and E. de Jesús,
Angew. Chem. Int. Ed., 2017, 56, 865-869; f) J. M. Asensio, S.
Tricard, Y. Coppel, R. Andrés, B. Chaudret and E. de Jesús,
Chem. Eur. J., 2017, 23, 13435-13444.
2007; b) M.-O. Simon and C.-J. Li, Chem. Soc. Rev., 2012, 41,
1415-1427; c) Metal-Catalyzed Reactions in Water, ed. P. H.
Dixneuf and V. Cadierno, Wiley-VCH, Weinheim, 2013; d) T.
Kitanosono, K. Masuda, P. Xu and S. Kobayashi, Chem. Rev.,
2018, 118, 679-746.
16 E. A. Baquero, J. C. Flores, J. Perles, P. Gómez-Sal and E. de
Jesús, Organometallics, 2014, 33, 5470-5482.
8
a) E. C. Hurst, K. Wilson, I. J. S. Fairlamb and V. Chechik, New
J. Chem., 2009, 33, 1837-1840; b) J. Vignolle and T. D. Tilley, 17 a) J. A. Delgado, O. Benkirane, C. Claver, D. Curulla-Ferré
Chem. Commun., 2009, 46, 7230-7232; c) A. Ferry, K.
Schaepe, P. Tegeder, C. Richter, K. M. Chepiga, B. J. Ravoo
and F. Glorius, ACS Catal., 2015, 5, 5414-5420; d) M. J.
and C. Godard, Dalton Trans., 2017, 46, 12381-12403; b) A.
Reina, I. Favier, C. Pradel and M. Gómez, Adv. Synth. Catal.
2018, 360, 3544-3552.
MacLeod and J. A. Johnson, J. Am. Chem. Soc., 2015, 137, 18 a) C. Jiang, K. Hara, K. Namba, H. Kobayashi, S.
7974-7977; e) G. A. Monti, G. A. Fernández, N. M. Correa, R.
D. Falcone, F. Moyano and G. F. Silbestri, R. Soc. open sci.,
2017, 4, 170481; f) K. Salorinne, R. W. Y. Man, C.-H. Li, M.
Ittisanronnachai, H. Nishihara, T. Kyotani and A. Fukuoka,
Chem. Lett., 2014, 43, 1794-1796; b) C. Li, Z. Shao, M. Pang,
C. T. Williams and C. Liang, Catal. Today, 2012, 186, 69-75.
Taki, M. Nambo and C. M. Crudden, Angew. Chem Int. Ed., 19 K. A. San, V. Chen and Y.-S. Shon, ACS Appl. Mater.
2017, 56, 6198-6202; g) R. W. Y. Man, C.-H. Li, M. W. A. Interfaces, 2017, 9, 9823-9832.
MacLean, O. V. Zenkina, M. T. Zamora, L. N. Saunders, A. 20 P.-J. Debouttière, Y. Coppel, A. Denicourt-Nowicki, A.
Rousina-Webb, M. Nambo and C. M. Crudden, J. Am. Chem.
Soc., 2018, 140, 1576-1579; h) R. Ye, A. V. Zhukhovitskiy, R.
Roucoux, B. Chaudret and K. Philippot, Eur. J. Inorg. Chem.,
2012, 8, 1229-1236.
V. Kazantsev, S. C. Fakra, B. B. Wickemeyer, F. D. Toste and 21 T. Pery, K. Pelzer, G. Buntkowsky, K. Philippot, H.-H. Limbach
G. A. Somorjai, J. Am. Chem. Soc., 2018, 140, 4144-4149. and B. Chaudret, ChemPhysChem, 2005, 6, 605-607.
a) P. Lara, O. Rivada-Wheelaghan, S. Conejero, R. Poteau, K. 22 a) P. Parthasarathy and A. V. Virkar, J. Power Sources, 2013,
9
Philippot and B. Chaudret, Angew. Chem. Int. Ed., 2011, 50,
12080-12084; b) P. Lara, L. M. Martínez-Prieto, M. Roselló-
Merino, C. Richter, F. Glorius, S. Conejero, K. Philippot and B.
Chaudret, Nano-Struct. Nano-Objects, 2016, 6, 39-45; c) L. M.
234, 82-90; b) T. W. Hansen, A. T. DeLaRiva, S. R. Challa and
A. K. Datye, Acc. Chem. Res., 2013, 46, 1720-1730; c) Z.
Zhang, Z. Wang, S. He, C. Wang, M. Jin and Y. Yin, Chem. Sci.,
2015, 6, 5197-5203.
Martínez-Prieto, A. Ferry, L. Rakers, C. Richter, P. Lecante, K. 23 a) W. Zhang, G. Li, L. Wang and X. Zhang, Catal. Sci. Technol.,
Philippot, B. Chaudret and F. Glorius, Chem. Commun., 2016,
52, 4768-4771; d) L. M. Martínez-Prieto, E. A. Baquero, G.
Pieters, J. C. Flores, E. de Jesús, C. Nayral, F. Delpech, P. W.
N. M. van Leeuwen, G. Lippens and B. Chaudret, Chem.
2015, 5, 2532-2553; b) L. Song, X. Li, H. Wang, H. Wu and P.
Wu, Catal. Lett., 2009, 133, 63-69; c) P. Maity, S. Basu, S.
Bhaduri and G. K. Lahiri, Adv. Synth. Catal., 2007, 349, 1955-
1962.
Commun., 2017, 53, 5850-5853; e) L. Rakers, L. M. Martínez- 24 a) K. Xu, Y. Zhang, X. Chen, L. Huang, R. Zhang and J. Huang,
Prieto, A. M. López-Vinasco, K. Philippot, P. W. N. M. van
Leeuwen, B. Chaudret and F. Glorius, Chem. Commun., 2018,
54, 7070-7073; f) D. Bouzouita, G. Lippens, E. A. Baquero, P.
F. Fazzini, G. Pieters, Y. Coppel, P. Lecante, S. Tricard, L. M.
Martínez-Prieto and B. Chaudret, Nanoscale, 2019, 11, 16544-
16552.
Adv. Synth. Catal., 2011, 353, 1260-1264; b) B. Sreedhar, D.
K. Devi and D. Yada, Catal. Commun., 2011, 12, 1009-1014; c)
P. Lara and K. Philippot, Catal. Sci. Technol., 2014, 4, 2445-
2465; d) N. Arai, N. Onodera, A. Dekita, J. Hori and T.
Ohkuma, Tetrahedron Lett., 2015, 56, 3913-3915.
25 a) X. Li, B. Li, M. Cheng, Y. Du, X. Wang and P. Yang, J. Mol.
Catal. A: Chem., 2008, 284, 1-7; b) W. Zhou, J. Wang, C.
Wang, Y. Du, J. Xu and P. Yang, Mater. Chem. Phys. 2010,
122, 10-14; c) X. Li, Y. Du, J. Dai, X. Wang and P. Yang, Catal.
Lett., 2007, 118, 151-158.
10 a) P. Lara, A. Suárez, V. Collière, K. Philippot and B. Chaudret,
ChemCatChem, 2014, 6, 87-90; b) E. A. Baquero, S. Tricard, J.
C. Flores, E. de Jesús and B. Chaudret, Angew. Chem. Int. Ed.,
2014, 53, 13220-13224; c) E. A. Baquero, S. Tricard, Y.
Coppel, J. C. Flores, B. Chaudret and E. de Jesús, Dalton 26 a) I. Schrader, J. Warneke, J. Backenköhler and S. Kunz, J. Am.
Trans., 2018, 47, 4093-4104; d) L. M. Martínez-Prieto, L.
Rakers, A. M. López-Vinasco, I. Cano, Y. Coppel, K. Philippot,
F. Glorius, B. Chaudret and P. W. N. M. van Leeuwen, Chem.
Eur. J., 2017, 23, 12779-12786; e) C.-Y. Wu, W. J. Wolf, Y.
Levartovsky, H. A. Bechtel, M. C. Martin, F. D. Toste and E.
Gross, Nature, 2017, 541, 511-515.
Chem. Soc., 2015, 137, 905-912; b) Y. Ding, X. Li, B. Li, H.
Wang and P. Wu, Catal. Commun., 2012, 28, 147-151; c) P.
Maity, S. Basu, S. Bhaduri and G. K. Lahiri, J. Mol. Catal. A:
Chem., 2007, 270, 117-122; d) A. Chaiyanurakkul, L. Gao, T.
Nishikata, K. Kojima and H. Nagashima, Chem. Lett., 2014,
43, 1233-1235.
11 a) J.-F. Soulé, H. Miyamura and S. Kobayashi, J. Am. Chem. 27 a) M. Guerrero, A. Roucoux, A. Denicourt-Nowicki, H.
Soc., 2013, 135, 10602-10605; b) M. Díaz de los Bernardos, S.
Pérez-Rodríguez, A. Gual, C. Claver and C. Godard, Chem.
Commun., 2017, 53, 7894-7897.
Bricout, E. Monflier, V. Collière, K. Fajerwerg and K.
Philippot, Catal. Today, 2012, 183, 34-41; b) D. Gonzalez-
Galvez, P. Lara, O. Rivada-Wheelaghan, S. Conejero, B.
Chaudret, K. Philippot and P. W. N. M. van Leeuwen, Catal.
Sci. Technol., 2013, 3, 99-105; c) L. M. Martínez-Prieto, A.
Ferry, P. Lara, C. Richter, K. Philippot, F. Glorius and B.
Chaudret, Chem. Eur. J., 2015, 21, 17495-17502.
12 a) A. Fedorov, H.-J. Liu, H.-K. Lo and C. Copéret. J. Am. Chem.
Soc., 2016, 138, 16502-16507; b) N. Kaeffer, H.-J. Liu, H.-K.
Lo, A. Fedorov and C. Copéret, Chem. Sci., 2018, 9, 5366-
5371.
13 a) F. Martinez-Espinar, P. Blondeau, P. Nolis, B. Chaudret, C. 28 J. Llop Castelbou, E. Bresó-Femenia, P. Blondeau, B.
Claver, S. Castillón and C. Godard, J. Catal., 2017, 354, 113-
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 8 of 9
ARTICLE
Journal Name
Chaudret, S. Castillón, C. Claver and C. Godard,
ChemCatChem, 2014, 6, 3160-3168.
View Article Online
DOI: 10.1039/D0CY00481B
29 D. Jantke, M. Cokoja, M. Drees, W. A. Herrmann and F. E.
Kühn, ChemCatChem 2013, 5, 3241-3248.
30 a) A. J. Wain, M. A. O’Connell and G. A. Attard, ACS Catal.,
2018, 8, 3561-3570; b) J. Pritchard, A. Ciftci, M. W. G. M.
(Tiny) Verhoeven, E. J. M. Hensen and E. A. Pidko, Catal.
Today, 2017, 279, 10-18; c) M. E. Grass, R. M. Rioux and G. A.
Somorjai, Catal. Lett., 2009, 128, 1-8.
31 P. Rubio-Marqués, A. Leyva-Pérez and A. Corma, Chem.
Commun., 2013, 49, 8160-8162.
32 a) A. Corma, P. Serna, P. Concepción and J. J. Calvino, J. Am.
Chem. Soc., 2008, 130, 8748–8753; b) A. Corma and P. Serna,
Science, 2006, 313, 332-334; c) A. Corma, C. González-
Arellano, M. Iglesias, F. Sánchez, Appl. Catal. A: Gen., 2009,
356, 99-102.
33 a) M. J. Beier, J. -M. Andanson and A. Baiker, ACS Catal.,
2012, 2, 2587-2595; b) L. Huang, P. Luo, W. Pei, X. Liu, Y.
Wang, J. Wang, W. Xing and J. Huang, Adv. Synth. Catal.,
2012, 354, 2689-2694; c) H. Goksu, Y. Yıldız, B. Çelik, M.
Yazici, B. Kilbas and F. Sen, Catal Sci. Technol., 2016, 6, 2318-
2324.
34 C. Campos, C. Torres, M. Oportus, M. A. Peña, J.L.G. Fierro
and P. Reyes, Catal. Today, 2013, 213, 93-100.
35 See, for instance: International Council for Harmonisation of
Technical Requirements for Pharmaceuticals for Human Use
(ICH). Guideline for Elemental Impuriries Q3D(R1), 2019;
bit.ly/2HGfF5T, (accessed date 09/09/2019).
8 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 9 of 9
View Article Online
DOI: 10.1039/D0CY00481B
ARTICLE
Only for Table of Contents Entry
Aromatic compounds have been hydrogenated in water using
recoverable catalysts based on water-soluble platinum
nanoparticles capped with NHC ligands.
Please do not adjust margins