Annotated Bibliography for Ru Nanoparticles Catalysis Research

Annotated Bibliography
Your annotated bibliography should be prepared according to
ACS format, using The ACS Style Guide: Effective
Communication of Scientific Information, 3rd edition. One or
more copies of this book are held on reserve in the library.
The Purdue Online Writing Lab (OWL) at
http://owl.english.purdue.edu/owl/resource/614/01/ offers
further information regarding annotated bibliographies.
This annotated bibliography, along with a correctly formatted
citation, should include a summary of the content of the source
and a two-pronged critical analysis of the source. The first part
of the critical analysis will be your objective evaluation of the
source and the second part will be your subjective evaluation.
Even if a source is found to be credible, if it does not contribute
to your research question, it should not be included.
Prepare your annotated bibliographic entry according to the
following guidelines:
1. Bibliography Entry: Include the complete bibliographic
information correctly formatted according to the ACS style
guidelines
1. Summary of Content: Include a descriptive paragraph
summarizing the source. Include key concepts and quotations
when appropriate.
Objective Evaluation: Objectively evaluate the credibility of the
source using the criteria that are most relevant. Use the
questions presented in the TRAAP criteria found under
“Evaluate Sources” at
https://youtu.be/zzTBBm1HXvM
1. to stimulate your ideas, but don’t feel as if you need to
address each criteria as a checklist. Use the criteria that are

appropriate for your source. When relevant, address such things
as bias or lack of bias, outdated material or current material,
author’s point of view, and author’s credentials and
qualifications to write on the topic. What is the author’s
purpose in writing the information? Is the information
presented without prejudice? Or does the author, publisher, or
research funding organization have a stake in the outcome or
the controversy you are investigating?
1. Subjective Evaluation: Include a summary of the relevance of
the source to your research topic or question. How will the
source contribute to your research, and how useful will it be?
Does it offer a unique perspective? Does it offer a contradictory
viewpoint to another source?
Photochemistry Assignment #2
This assignment covers material from Chapter 2 section 1 to
Chapter 2 Section 14.
1) According to the principles of quantum mechanics, what is
the wave function?
2) What is the Born-Oppenheimer approximation?
3) Under what two types of interactions does the approximation
given in equation 2.4
break down?
4) (a) What is the four-letter abbreviation for the highest energy
occupied molecular
orbital?
(b) What is the four-letter abbreviation for the lowest energy

unoccupied molecular
orbital?
5) To what does the square of a wave function relate?
6) What is an expectation value?
7) What is meant by an electronic configuration?
8) An alkene like ethylene will usually have only one low-
energy electronic transition.
What is it?
9) An organic molecule which contains a carbonyl functional
group, like formaldehyde,
typically has two relatively low-energy electronic transitions.
What are they?
10) What are the two possible spin states for the configurations
shown for ethylene and
formaldehyde in Figure 2.1-b?
11) A single electron configuration is often adequate to
approximate the electronic
characteristics of an electronic state. In some cases, however, a
combination of two or
more configurations are required to achieve a good
approximation of a single state.
When does this occur?
12) (a) What is Hund’s rule for organic photochemistry?
(b) What is the physical basis for this rule?
13) (a) What is the symbol for the Coulomb integral?
(b) What is the symbol for the electron exchange integral?
(c) Are both of these integrals positive quantities? Why?

(d) Which integral is purely a quantum mechanical
phenomenon?
14) According to equation 2.18, the difference in the electronic
energy between singlet
and triplet states derived from the same electron orbital
configuration (ΔEST) is equal to
what?
15) In Section 2.14, the text says that the
2
12
e
r term can be factored out of the electron
exchange integral leaving the overlap integral. The text then
states that the quantum
mechanical mathematical overlap integral corresponds to the
degree of physical overlap
of the orbitals in space. Thus, the smaller the overlap, the
smaller the value of the
overlap integral; and the larger the overlap, the larger the value
of the overlap integral.
(a) So, in a carbonyl containing compound, which is larger: ,
(b) Since the value of ΔEST is related to the value of the
electron exchange integral J,
which

configuration in formaldehyde?
16) Does increasing conjugation increase or lower ΔEST from
alkenes? (Refer to Table 2.3.)
Ru Metal application
Final presentation
Here is the name of the authors
Represented by my name
Introduction
Main topic Focus on first general information about Ru
application then second, Ru nanoparticles as catalysis in
different
application(Ru Nanoparticles: Application in Catalysis)
Please, use one example from each article if possible, or if there
is one example summarize it.
General Application of Ru
Application 2
Ruthenium Nanoparticles Decorated Tungsten Oxide as a
Bifunctional Catalyst for Electro catalytic and Catalytic
Applications

Application 3
Catalysis with Colloidal Ruthenium Nanoparticles
Application 4
Sensitive Colorimetric Assay of H2S Depending on the High-
Efficient
Inhibition of Catalytic Performance of Ru Nanoparticles
Application 5
Synthesis of PtRu Nanoparticles from the Hydrosilylation
Reaction and Application as
Catalyst for Direct Methanol Fuel Cell
Application 6
Role of Ru Oxidation Degree for Catalytic Activity in
Bimetallic Pt/Ru
Nanoparticles
Conclusion

(6 References) page
Please, summarize the all 6 articles (5 articles and part of
chapter of book) in two pages, with the third page of references.
Then complete the power point. Example from each article (one
article in each slide).
Please, no space between lines.
Write the whole two pages.
Please, take the information of ( general application of Ru) from
this chapter of this book(Properties and Applications of
Ruthenium)
Please, note that I will ask you to use those 6 articles with other
new 6 articles and 2 parts of chapters of books) to write short
research (about 15 to 20 pages) of this topic( Ru element:
application catalysis with other information).
Catalysis with Colloidal Ruthenium Nanoparticles
M. Rosa Axet and Karine Philippot*
UPR8241, Universite ́ de Toulouse, UPS, INPT, CNRS, LCC
(Laboratoire de Chimie de Coordination), 205 Route de
NarbonneF-31077 Toulouse cedex 4, France
ABSTRACT: This review provides a synthetic overview of the
recent research
advancements addressing the topic of catalysis with colloidal
ruthenium metal
nanoparticles through the last five years. The aim is to
enlighten the interest of
ruthenium metal at the nanoscale for a selection of catalytic
reactions performed in

solution condition. The recent progress in nanochemistry
allowed providing well-
controlled ruthenium nanoparticles which served as models and
allowed study of how
their characteristics influence their catalytic properties.
Although this parameter is not
enough often taken into consideration the surface chemistry of
ruthenium nanoparticles
starts to be better understood. This offers thus a strong basis to
better apprehend
catalytic processes on the metal surface and also explore how
these can be affected by
the stabilizing molecules as well as the ruthenium
crystallographic structure. Ruthenium
nanoparticles have been reported for their application as
catalysts in solution for diverse
reactions. The main ones are reduction, oxidation,
Fischer−Tropsch, C−H activation,
CO2 transformation, and hydrogen production through amine
borane dehydrogenation
or water-splitting reactions, which will be reviewed here.
Results obtained showed that ruthenium nanoparticles can be
highly
performant in these reactions, but efforts are still required in
order to be able to rationalize the results. Beside their catalytic
performance, ruthenium nanocatalysts are very good models in
order to investigate key parameters for a better controlled
nanocatalysis. This is a challenging but fundamental task in
order to develop more efficient catalytic systems, namely more
active and more selective catalysts able to work in mild
conditions.
CONTENTS
1. Introduction 1086
2. Interests of Ruthenium and Metal Nanoparticles 1087

2.1. Physicochemical Properties and Interests of
Ruthenium 1087
2.2. Interests of Metal Nanoparticles in Catalysis 1087
2.3. Present Challenges in Nanocatalysis and
Place of Ruthenium Nanocatalysts 1088
3. Synthesis Methods of Ruthenium Nanoparticles 1088
3.1. Reduction of Ruthenium(III) Chloride Hy-
drate 1089
3.2. Polyol Method 1090
3.3. Use of an Organometallic Precursor 1090
3.4. Supported Nanoparticles 1092
4. Ruthenium Nanoparticles As Catalysts 1092
4.1. Reduction Reactions 1092
4.1.2. Reduction of Nitro Compounds 1097
4.1.3. Hydrodeoxygenation 1100
4.1.4. Reductive Amination of Carbonyl Com-
pounds, Amination of Alcohols, and
Other Miscellaneous Reduction Reac-
tions 1105
4.2. Oxidation Reactions 1106
4.3. Fischer−Tropsch Reaction 1111
4.4. C−H Activation and Other Reactions 1113
4.5. Transformation of CO2 1113
4.5.1. Transformation of CO2 into HCOOH 1113

4.5.2. Transformation of CO2 into CO, CH4, or
C2+ Hydrocarbons 1119
4.5.3. Conclusions on CO2 Transformation 1123
4.6. Dehydrogenation of Amine Boranes 1124
4.6.1. Dehydrogenation of Amine Boranes by
Dehydrocoupling 1125
Methanolysis 1127
Hydrolysis 1128
Supported Ruthenium Nanocatalysts 1130
4.6.5. Conclusions on Amineborane Dehydro-
genation 1130
4.7. Water Splitting 1130
4.7.1. Ru NPs as Electrocatalysts for HER 1131
4.7.2. Ru NPs as (Photo)catalysts for HER 1133
4.7.3. Conclusions on Water Splitting 1133
5. Concluding Remarks and Outlook 1133
Author Information 1135
Corresponding Author 1135
ORCID 1135
Notes 1135
Biographies 1135
Special Issue: Nanoparticles in Catalysis

Received: July 6, 2019
Published: January 3, 2020
Review
pubs.acs.org/CRCite This: Chem. Rev. 2020, 120, 1085−1145
© 2020 American Chemical Society 1085 DOI:
10.1021/acs.chemrev.9b00434
Chem. Rev. 2020, 120, 1085−1145
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Acknowledgments 1136
References 1136
1. INTRODUCTION
With symbol Ru and the 44th position in the periodic table of
elements, ruthenium is part of the transition metals group. It is
considered as a scarce metal with limited availability. This may
be hindering wider commercial applications involving
ruthenium due to its high price (even if still the least expensive
precious metal) and wide fluctuations in the market. The
applications of ruthenium mainly concern technological
devices and catalysis sectors. In 2018, ruthenium consumption
has achieved 42 tons for industrial applications concerning
electronics (33%), electrochemistry (17%), and chemistry
(37%).1 For instance, ruthenium is commonly added at a small
quantity in alloys given its ability to harden them. This is the
case of super alloys used for the manufacture of turbine blades
of jet engines. It reinforces the rhodium, palladium, and
platinum-based alloys used for wear-resistant electrical contacts
(high-end spark plugs have electrodes coated with a Pt−Ru
alloy; pen tips are made with alloys containing ruthenium).
Ruthenium dioxide, RuO2, and ruthenates of lead and bismuth
are involved in resistive chips. In electronics, ruthenium is used
in the manufacture of hard disks as a coating between two
magnetic layers.
Regarding catalysis, ruthenium is a polyvalent metal because
it can easily adopt formal oxidation states in a wide range
(from II to VIII), leading to a multitude of complexes that
display interesting and often unique properties. These
properties can be tuned by an appropriate choice of the
ligands because these latter strongly affect the reactivity as well
as stability of ruthenium complexes. A molecular level
understanding of structure−activity relationships in complexes
is a key parameter for the development of better catalysts. For

instance bipyridines- and terpyridine-containing ruthenium
complexes are known for their luminescent and photoredox
properties. Such properties are at the basis of the photo-
dissociation of water into O2 and H2 (water splitting)
2 and of
the development of new generation photovoltaic cells.3
Another important application of ruthenium is the catalytic
production of added-value chemicals like acetic acid.4
Carbene-based ruthenium complexes are well-known for
their central role in olefin metathesis that provides active
molecules or functionalized polymers among others. Ru
complexes with phosphorus-containing ligands (for example
phosphines, diphosphines as the so-called BINAP, or
phosphites) are active for hydrogenation reactions such as
others, including the enantioselective version.5 Ru complexes
are also known for their catalytic performance in the synthesis
of formic acid and its decomposition into H2 and CO2 or also
the dehydrogenation of alcohols, two important reactions
regarding hydrogen storage.6 Finally Ru species are also
catalysts of oxidation reactions.7 In heterogeneous conditions,
ruthenium is the most active catalyst for the production of
ammonia.8 It is also active in the hydrogenation of diverse
substrates. As ligands in molecular catalysis, supports play a
key-role in the properties of supported ruthenium catalysts due
to metal−support interactions. The fine understanding of
microscopic properties of the heterogeneous catalysts, in
particular, the nature of surface active sites and their chemical
or sterical environment is of utmost importance in order to
improve catalytic performances. Finally, the oxidized form of
ruthenium, RuO2, is known for its performance in heteroge-
neous oxidation catalysis and in electrocatalysis.

The exaltation of properties at the nanoscale regime can
increase the relevance of ruthenium for catalysis. The recent
progress in nanochemistry allowed having at disposal better
controlled Ru NPs in terms of size, dispersion, shape,
composition, and surface state, etc. All these characteristics
may influence strongly their surface properties and con-
sequently their catalytic performance (both reactivity and
selectivity), and numerous efforts are presently made in this
sense. Using a molecular approach, namely studying the
interface between surface atoms and stabilizers (ligands) by a
combination of techniques from molecular chemistry (like
nuclear magnetic resonance) to theoretical studies allows a
better understanding of the surface chemistry of ruthenium
nanoparticles. As will be seen in the next sections, these
findings give thus a strong basis to better apprehend catalytic
processes on the metal surface as well as how these can be
affected by the presence of stabilizing molecules or by the
crystallographic structure of the ruthenium cores, eventually by
taking benefit of these parameters.
This review will start by summarizing the physicochemical
properties and interests of ruthenium together with those of
metal nanoparticles (section 2) and following, the main
synthesis methods to produce ruthenium metal nanoparticles
in solution (section 3). Then, the purpose is to provide a
synthetic overview of the recent advancements in research that
address the investigation of ruthenium metal nanoparticles (Ru
NPs) in catalysis in solution (or suspension) conditions in the
period 2014−2019 (section 4). The aim is to highlight the
potential of ruthenium metal when it is divided at the
nanoscale in a controlled manner, namely under the form of
well-defined Ru NPs, in colloidal catalysis. Ru NPs have been
reported for their application as catalysts in diverse reactions.
The reactions reviewed here include reduction, oxidation,
Fischer−Tropsch, C−H activation and amine borane dehy-

drogenation reactions where Ru NPs show to be very
performant. Even if at a lesser extent, Ru NPs have been
also investigated for the reduction of carbon dioxide and water
splitting process. Relevant works involving Ru NPs in these
catalytic reactions will be described. Selection of examples was
governed by the degree of control of the characteristics of the
described Ru NPs that was made possible by solution synthesis
methods, thus allowing precise catalytic investigations.
Heterogeneous catalysts are not considered due to the fact
the metal nanoparticles they contain are generally poorly
controlled due to drastic conditions applied for their
preparation. However, a few examples of supported Ru NP-
based catalysts are presented. This is justified either by their
initial preparation method, which enabled to obtain well-
controlled nanostructures, thus providing complementary
information to the discussed subjects or by the relevant or
pioneering character of the contribution to the field of
catalysis. Also, a few papers from earlier years are included
due to their high input. Finally concluding remarks and
perspectives will be given for each type of reaction treated.
Chemical Reviews Review
DOI: 10.1021/acs.chemrev.9b00434
Chem. Rev. 2020, 120, 1085−1145
1086
2. INTERESTS OF RUTHENIUM AND METAL
NANOPARTICLES
2.1. Physicochemical Properties and Interests of
Ruthenium

Identified and isolated by Karl Karlovich Klaus in 1844,9
ruthenium has as its symbol Ru and the 44th position in the
periodic table of elements. Ruthenium is the 74th most
abundant metal, a rare element, and is part of the precious
metals, being the first of the series beside rhodium, palladium,
osmium, iridium, and platinum. With a current price of ca.
7000 €/kg,10 ruthenium is still the least expensive precious
metal.
Ruthenium is a hard, silvery white metal which is unalterable
in the ambiant air and does not tarnish at room temperature
(rt). Ruthenium is a transition metal with electronic
configuration [Kr]4d75s1 for the isolated atom in ground
state. The oxidation states of ruthenium range from II to VIII,
the most common ones being II, III, and IV. These different
oxidation states provide a large number of stable ruthenium
catalysts (at 16 or 18 electrons). Ruthenium is not easily
oxidized at atmospheric condition but RuO2, a stable oxide,
may be formed under oxygen pressure. Ruthenium tetroxide
(RuO4), a volatile compound, is a powerful oxidizing and very
toxic.9 The dissolution of ruthenium is not easy and requires
use of aqua regia in heating conditions. Crystalline structure of
bulk ruthenium is hexagonal closed-packed (hcp) but at the
nanoscale, face-centered cubic (fcc) structure is also
known.11−13 Ruthenium is the only noble metal that can
crystallize in the nanometer scale with the hcp structure or the
fcc one. The anisotropy of the hexagonal system is expected to
lead more easily to anisotropic crystals, but there are only a few
papers reporting anisotropic Ru NPs, and none with a high
aspect ratio.14
The applications of ruthenium mainly concern technological
devices and catalysis sectors.15 In catalysis, ruthenium is a
polyvalent metal which proved to be active in both
homogeneous and heterogeneous conditions. RuCl3·3H2O is

often the starting point of a rich coordination and organo-
metallic chemistry, thus leading to a wide variety of ruthenium
complexes of high interest for homogeneous catalysis.
Ruthenium complexes are able to activate unique and multiple
bonds and make possible selective C−C, C−H, or C-
heteroatom bond formation and cleavage.16 Ruthenium
catalysts are thus involved in a great variety of organic
reactions, such as alkylation, allylation, arylation, cyclization,
cyclopropanation, hydrogenation, hydroformylation, hydro-
silylation, hydroxylation, isomerization, olefin metathesis,
oxidation, transfer hydrogenation, tandem reactions, water
splitting, etc. Ru-catalysis is effectively exploited in the
synthesis of natural and biologically active organic compounds,
to access recognized chemotherapeutic agents, supramolecular
assemblies, smart materials, specialty polymers, biopolymers,
agrochemicals, and, increasingly, in valorization of renewable
resources as platform chemicals for polymers. Presently,
intensive research efforts are devoted in C−H and C−X
bond activation, olefin metathesis, and newest trends of green
chemistry, such as water oxidation and hydrogen production,
reduction of CO2 to CO, oleochemistry, and reactions in eco-
friendly media.17 Because of their matter state, heterogeneous
transition metal catalysts are also of high interest in catalysis
and largely exploited at the industrial level. Heterogeneous
catalysts are extended inorganic solids where the d orbitals play
a key role in the adsorption and transformation of substrates.
The catalytic activity of transition metals shows a strong
periodic effect with a maximum of reactivity for group-VIII
transition metals among which ruthenium. Ruthenium is able
to chemisorb diverse small molecules such as O2, C2H2, CO,
H2, N2, and CO2. In heterogeneous and colloidal conditions,
ruthenium is reputed to be active in hydrogenation of nitrogen
for ammonia synthesis, hydrogenation of diverse substrates like
olefins, and carbonylated molecules but also of aromatics for
which molecular ruthenium is not known, as well as for

dehydrogenation of amine boranes and hydrogen evolution
reactions. Interestingly, it is not very known for hydrogenation
of CO2 and dehydrogenation of formic acid. RuO2 turned out
to be an excellent oxidation catalyst in heterogeneous catalysis
(mainly oxidation of CO) and electrocatalysis (oxidation of
water).18
2.2. Interests of Metal Nanoparticles in Catalysis
Heterogeneous transition metal catalysts are extended
inorganic solids where the d orbitals play a key role in the
adsorption of substrates due to their ability to donate and
accept electron density to and from the substrates. This is
particularly true for the degenerate states in band structures.
The electronic flexibility provided by the d electrons of the
metal surface has to be such that the bond with the substrate
atoms is intermediate between weak and strong. The metal
surface must be able to bind the substrate atoms strongly
enough to provoke their dissociation in the chemisorption
process. But the surface-atom bond created has to be not too
strong, for the bonded substrate atom to be able to further
react with other surface-bonded atoms and form the products
that can rapidly desorb. If the surface-atom bond is too strong,
further reaction will be precluded. The catalytic activity of
transition metals shows a strong periodic effect with a
maximum of reactivity for group-8 transition metals where
ruthenium is located.19
Being part of heterogeneous catalysts, metal nanoparticles
(MNPs) have been known for a long time, but a renewed
interest emerged in the last three decades for the design of
better defined systems.20 Numerous research efforts are
devoted to the design of well-controlled MNPs and even at
an atomic precision level.21,22 This keen interest for MNPs
derives from the particular matter state (finely divided metals)
and exalted electronic properties, influencing physical and

chemical properties that they present in comparison to bulk
metals and molecular complexes. Besides fundamental aspects
of research, this interest is also governed by the specific
properties and the potential applications that MNPs may find
in various domains including optoelectronics, sensing,
biomedicine, catalysis, energy conversion, and storage, as
nonexhaustive examples.23−26 Several books focus specifically
on nanocatalysis.27−37 For catalysis, MNPs are attractive
species due to the high surface to volume ratio they display.
This ratio is even more pronounced when MNPs are at a size
as close as one nanometer, or even below, because the number
of surface atoms can be >90%, thus providing a vast number of
potential active sites. It is thus of prime importance to have
synthesis tools that enable obtaining ultrasmall NPs in order to
promote high surface area. Besides the size, other key
parameters need also to be controlled. The crystalline structure
is important because depending on it, different types of
crystalline plans can be exposed at the nanoparticle surface,
which can lead to different catalytic properties. Controlling the
Chem. Rev. 2020, 120, 1085−1145
1087
shape of MNPs is another way to orientate the crystalline plans
exposed.38−40 The last key parameter but not the least is the
composition of MNPs. The composition has to be adjusted
depending on the catalysis target. Apart from the nature of the
metallic core that may govern the reactivity (some metals are
well-known for certain catalyzes but not for others), the
surrounding stabilizer for colloidal catalysis (ionic liquids (IL),

polymers, surfactants, polyols, ligands, etc.) or the support for
supported catalysis (metal oxides, metal organic frameworks
(MOFs), carbon derivatives, etc.) may also influence or even
orient the catalytic performance. If calcination is usually
applied in heterogeneous catalysis in order to suppress any
organics and liberate the active sites, such treatment on small
nanoparticles can be critical because of sintering. Moreover,
naked MNPs are not always optimal catalysts. In modern
nanocatalysis, the presence of organic ligands at the NP surface
is not seen as detrimental but instead is a way to improve or
even modify the chemoselectivity.41 Using ligands as
stabilizers
allows to make a parallel with molecular catalysis; the ligand
interaction with surface metal atoms of the nanoparticles can
be compared to ligand interactions with the metal centers in
homogeneous catalysts, which is of paramount importance for
stability and catalytic properties (activity and selectivity).
Ligands can be chosen in order to tune the surface properties
of MNPs through steric or electronic effects.42,43 The
challenge
is to find ligands able to stabilize well-defined MNPs while
controlling accessibility at the metal surface and
reactivity.41,44
Strongly bound capping ligands (like thiols or phosphines) can
result in the poisoning of a nanocatalyst at high surface
coverage. But a limited amount of ligand can be beneficial. The
coordination of a ligand at a metal surface can also be a way to
block selectively some active sites in order to orientate the
catalysis evolution. Compared to the investigation of facet
dependency,40,45 the ligand influence on the catalytic activity
has been less intensively studied but recent results illustrate
well the interest to do so.46−50 Ligand-stabilized MNPs can be
applied to catalysis as stable colloidal suspensions but also in
heterogeneous conditions when deposited on the surface or
confined in the pores of a solid support.51 Ionic liquids52 are

also very efficient to stabilize metal NPs, and colloidal
suspensions in ionic liquids can even be deposited onto
inorganic supports.53
2.3. Present Challenges in Nanocatalysis and Place of
Ruthenium Nanocatalysts
Having at disposal synthesis strategies that allow access, in a
reproducible manner, to well-defined MNPs in terms of size,
crystalline structure, composition (metal cores and stabilizing
agents), chemical order (bimetallic or multimetallic systems),
shape, and dispersion is a beneficial condition to investigate
finely their catalytic properties and define structure/properties
relationships. Taking advantage of recent developments in
nanochemistry in solution, and in particular of the use of
molecular chemistry tools, nanocatalysis is now well-
established as a borderline domain between homogeneous
and heterogeneous catalysis. Nanocatalysts can be seen as
assemblies of individual active sites where metal−metal and
metal−stabilizer bonds will both have influence.54 Precisely
designed MNPs are expected to present benefits from both
homogeneous and heterogeneous catalysts, namely high
reactivity and better selectivity together with high stability.55
The understanding of structure−properties relationships is
required for the design of more performant nanocatalysts in
order to develop more efficient and eco-compatible chemical
production.56 If a certain progress has been done in the past
decade, this topic remains very challenging. Model nano-
catalysts are needed in order to better understand the link
between the characteristics of MNPs and their catalytic
performance and thus bridge the gap between model surfaces
and real catalysts. Each progress that contributes to reduce the
gap of knowledge between nanocatalysts and homogeneous
catalysts constitutes a step forward the development of more

efficient and selective catalytic systems. Intensive efforts in
this
direction are needed in order to one day be able to anticipate
the design of suitable catalysts for a given reaction.
Various metals are investigated in nanocatalysis toward these
principles, with a huge number of studies dedicated to gold
which is highly reputed for CO oxidation and emerges now in
hydrogenation catalysis,57,58 or palladium which intervenes in
various C−C coupling reactions and also in hydrogenation
catalysis.59,60 Other metals like rhodium, platinum, iridium,
nickel, cobalt, and iron, among others, are also the object of
numerous studies. Compared to all these metals, the number
of works focusing on the use of Ru metal NPs in nanocatalysis
may appear to be lower. This may be quite surprising given the
large and successful application of this metal in homogeneous
catalysis but can be explained by the fact it is an expensive
metal. However, as it will be seen hereafter, ruthenium proved
to be an interesting metal to carry out precise studies in order
to establish structure−properties relationships in diverse
catalytic reactions, mainly hydrogenation, hydrodeoxygenation,
Fischer−Tropsch, C−H activation, amine borane dehydrogen-
ation, water splitting, and carbon dioxide reduction.
3. SYNTHESIS METHODS OF RUTHENIUM
NANOPARTICLES
Being part of heterogeneous catalysts, metal NPs have been
known for a long time, but a renewed interest emerged in the
last three decades for the design of better defined systems,
studies in which Ru NPs stand at a good place.33 This arises
from fundamental hurdles met in scientific research with badly
defined NPs such as the common issue of size dispersity (e.g.,
5% in even highly monodispersed samples), the unascertained
surfaces of NPs, the unknown core−ligand interfaces, the
defects and elusive edge structures in 2D materials, and the still

missing information on alloy patterns in bi- and multimetallic
NPs. Such imprecisions preclude deep understanding of many
fundamental aspects of NPs, including the atomic-level
mechanism of surface catalysis.22 Developing synthesis
strategies that allow preparing, in a reproducible manner,
well-defined MNPs in terms of size, crystalline structure,
composition (metal cores and stabilizing agents), chemical
order, shape, and dispersion is a prerequisite in order to
investigate finely their catalytic properties and determine the
links between structural features and catalytic properties. For
this purpose, bottom-up liquid-phase techniques are very
attractive because they are versatile and easy to use,
necessitating straightforward equipment than physic routes.
Recent developments in nanochemistry offer efficient tools to
reach these objectives and make nanocatalysis to be a
recognized domain at the frontier between homogeneous
and heterogeneous catalyzes, thanks to better-controlled NPs
that allow progressively to take benefit of advantages of both
types of catalysts.33 Metal NPs stabilized by ligands allow
performing fine surface studies as done with homogeneous
catalysts. Indeed such NPs display a metal surface with an
Chem. Rev. 2020, 120, 1085−1145
1088
interface close to that of molecular complexes (isolated surface
atoms can be seen like metal centers with their coordination
sphere) while benefiting from the influence of neighboring
metal atoms. It is also worth to mention that recent
developments of theoretical tools allow to bring computational

chemistry applied to small NPs to the same level of accuracy
and relevance as in molecular chemistry.61 All together
nanochemistry and computational chemistry enable to have
precise mapping of the surface properties of MNPs.
At the nanoscale level, ruthenium showed to be of interest in
diverse catalytic reactions and different synthesis tools have
been developed to access well-defined Ru NPs. The synthesis
of ruthenium NPs62 is often performed by chemical reduction
of ruthenium(III) chloride hydrate because of its availability,
using various reagents such as amines, carbon monoxide,
hydride salts (NaBH4, LiAlH4), hydrazine, alcohols, citrate
salts, or hydrogen. The drawback of these methods is the
presence of surface contaminants resulting from the reaction
conditions, such as water, salts, organic residues, or even an
oxide shell, which can alter the NP properties and limit access
to their surface. An elegant approach to circumvent these
difficulties is the use of organometallic (or metal−organic)
complexes as metal sources which are generally decomposed
under hydrogen atmosphere in mild conditions (low temper-
ature and pressure) in organic solution.63 The main
disadvantages of this approach is the access to the metal
precursors and the need to handle them in inert conditions and
in degassed organic solvents in order to preserve their initial
properties. The gain is the high quality of the obtained NPs
which display well-controlled characteristics and allow precise
surface studies. In between, the polyol method allows the
access to MNPs starting from metal complexes, similarly to the
organometallic approach, but usually using harsher synthesis
conditions.14 Whatever the preparation method followed, the
particles are generally stabilized by a polymer, an ionic liquid,
a
surfactant, or a ligand added to the reaction mixture for
preventing undesired metal agglomeration and precipitation. A
large interest is presently devoted to ligand-protected particles

due to the intrinsic physicochemical properties of these ligands
which can contribute to tune those of the particles.41 Before
describing the catalytic applications of Ru NPs, we will
summarize in the next subparts the main strategies developed
in order to access Ru NPs in colloidal solutions, namely the
reduction of ruthenium trichloride, polyol method, and the use
of an organometallic precursor. It is important to note that
apart from these very often used methods, others are reported
in the literature, such as the usage of ultrasounds or
microwaves, microemulsion systems, coprecipitation techni-
ques, sol−gel method, and hydrothermal/solvothermal pro-
cessing. These synthesis approaches will not be here described
because they are not applied for the preparation of the Ru
nanocatalysts cited in the following parts of this review.
3.1. Reduction of Ruthenium(III) Chloride Hydrate
The reduction of ruthenium(III) chloride hydrate in water is
the most used method to prepare Ru NPs because of its low
cost, ease of implementation, and scalability. This method
(Figure 1) consists in treating an aqueous solution of
commercial RuCl3·xH2O (with x = 3 depending on purity;
hereafter referred as RuCl3) by a reducing agent in the
presence of a stabilizer, at ambient conditions (room
temperature; rt) and without taking specific cautions.64 Diverse
reductants …
Role of Ru Oxidation Degree for Catalytic Activity in
Bimetallic Pt/Ru
Nanoparticles
Huanhuan Wang,† Shuangming Chen,*,† Changda Wang,† Ke
Zhang,† Daobin Liu,† Yasir A. Haleem,†
Xusheng Zheng,† Binghui Ge,‡ and Li Song*,†

†National Synchrotron Radiation Laboratory, CAS Center for
Excellence in Nanoscience, University of Science and
Technology of
China, Hefei 230029, China
‡Beijing National Laboratory for Condensed Mater Physics,
Institute of Physics, Chinese Academy of Sciences, Beijing
100190, China
*S Supporting Information
ABSTRACT: Understanding the intrinsic relationship between
the catalytic activity of bimetallic
nanoparticles and their composition and structure is very
critical to further modulate their
properties and specific applications in catalysts, clean energy,
and other related fields. Here we
prepared new bimetallic Pt−Ru nanoparticles with different
Pt/Ru molar ratios via a solvothermal
method. In combination with X-ray diffraction (XRD),
transmission electron microscopy (TEM)
coupled with energy-dispersive X-ray spectroscopy (EDX), X-
ray photoelectron spectroscopy
(XPS), and synchrotron X-ray absorption spectroscopy (XAS)
techniques, we systematically
investigated the dependence of the methanol electro-oxidation
activity from the obtained Pt/Ru
nanoparticles with different compositions under annealing
treatment. Our observations revealed
that the Pt−Ru bimetallic nanoparticles have a Pt-rich core and
a Ru-rich shell structure. After
annealment at 500 °C, the alloying extent of the Pt−Ru
nanoparticles increased, and more Pt atoms
appeared on the surface. Notably, subsequent evaluations of the
catalytic activity for the methanol
oxidation reaction proved that the electrocatalytic performance
of Pt/Ru bimetals was increased

with the oxidation degree of superficial Ru atoms.
■ INTRODUCTION
Among various kinds of fuel cells, direct methanol fuel cells
(DMFCs) have been considered to be promising power sources
for future energy needs due to their high energy densities, low
emissions, and facile fuel distribution and storage.1−3 Pt-based
catalysts are the most efficient anode catalysts for the methanol
oxidation reaction (MOR) in DMFCs.4 Nevertheless, challeng-
ing issues of Pt-based catalysts such as the high cost, low
abundance, and poison formation are the main obstacles to the
commercialization of DMFCs.5 This has led to the develop-
ment of Pt-based binary metallic systems, such as PtRu, PtMo,
and PtSn, and ternary compounds, such as PtRuW, PtRuMo,
and PtRuSn.6−8 PtRu alloy nanocrystals have been recognized
as being greatly efficient electrocatalysts for methanol
oxidation
reaction.9 The effect of PtRu structural characteristics, such as
composition, degree of alloying and Ru oxidation state, on the
electrocatalytic activity for methanol oxidation has been
reviewed.10 Guo et al. stated that the Pt−Ru (1:1) catalyst
exhibited a highest methanol oxidation current and a lower
poisoning rate.11 But Selda et al. found that a 0.25 Ru/Pt ratio
is optimum at room temperature.12 An optimum ratio of 10−
30% Ru at room temperature for methanol oxidation has also
been reported.13 There is also a debate on whether a PtRu
bimetallic alloy or a Pt and Ru oxide mixture is the most
effective methanol oxidation catalyst. Gasteiger et al. concluded
that the high catalytic activity of Pt−Ru alloys for the
electrooxidation of methanol is described very well by
bifunctional action of the alloy surface.14 Huang et al.
suggested
that the presence of crystalline RuO2 is essential to have a
better methanol oxidation from Pt nanoparticles.15 On the
other hand, Rolison et al. found that a commercial Pt−Ru

catalyst composed of oxides of Pt and Ru could deliberately
control the chemical state of Ru to form RuOxHy rather than
Ru metal or particularly anhydrous RuO2 because of poor
proton conduction.16 However, no unanimous conclusion has
been reached until now. Therefore, understanding the intrinsic
relationship between the catalytic activity of bimetallic
nanoparticles and their composition and structure is very
critical for further modulating their properties and specific
applications in catalysts, clean energy, etc.
The primary goal of the present work is to conclusively
establish the relative methanol oxidation activity of bimetallic
Pt−Ru nanoparticles with different compositions and annealing
treatments, using a consistent experimental approach. The
catalyst samples were thoroughly characterized by physical and
electrochemical technologies. Our detailed analysis of the
bimetal’s catalytic activity for methanol oxidation reaction
revealed that Pt/Ru nanoparticles with a Pt-rich core and Ru-
rich shell structure promote increased electro-oxidation of
methanol with the oxidation state of Ru atoms. This study
provides useful insight for understanding the intrinsic relation-
ship between catalytic property and structure/composition,
Received: December 15, 2015
Revised: February 26, 2016
Published: February 29, 2016
Article
pubs.acs.org/JPCC
10.1021/acs.jpcc.5b12267
J. Phys. Chem. C 2016, 120, 6569−6576
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■ EXPERIMENTAL SECTION
Sample Preparation. In a typical procedure for PtRu,
0.0889 g of poly(vinylpyrrolidone) (PVP), 400 μL of 0.2 M
RuCl3(aq), and 800 μL of 0.1 M H2PtCl6(aq) were dissolved in
38.8 mL of ethylene glycol (EG) under constant magnetic
stirring for 30 min. Then the mixed solution was transferred
into a stainless autoclave having a 50 mL Teflon liner and
heated in an oven at 200 °C for 12 h. After the autoclave was
naturally cooled to room temperature, 23.68 mg of acetylene
black was added to the resulting black solution and
continuously stirred for 30 min. The final product was obtained
by centrifugation, washed several times with deionized water
and absolute ethanol, and dried in a vacuum oven at 60 °C for
12 h. The procedure for Pt2Ru and PtRu2 was the same as that
for PtRu except that the molar ratio of RuCl3 and H2PtCl6 was
changed to 1:2 and 2:1. To investigate the influence of
annealing process, the resulting PtRu powder was calcined at
500 °C under 100 sccm H2/Ar flow for 4 h.
Sample Characterization and XAFS Data Analysis. X-
ray diffraction was performed on a TTR-III high-power X-ray
powder diffractometer employing a scanning rate of 0.02 s−1 in
a 2θ range from 30° to 90° with Cu Kα radiation. The
morphology of samples was characterized by transmission
electron microscopy (TEM, JEM-2100F), equipped with
energy-dispersive X-ray spectroscopy (EDX). The sample for
TEM was prepared by placing a drop of ultrasonically dispersed
ethanol solution onto a carbon-coated copper grid and allowing
the solvent to be evaporated in air at room temperature. Metal
concentrations were measured by inductively coupled plasma
(ICP) atomic emission spectroscopy (AES) using an Atomscan
Advantage Spectrometer. HAADF-STEM and EDX elemental
mapping analysis were carried out in a JEOL ARM-200
microscope at 200 kV. X-ray photoelectron spectroscopy (XPS)
experiments were performed at the Photoemission Endstation

at the BL10B beamline in the National Synchrotron Radiation
Laboratory (NSRL) in Hefei, China. This beamline is
connected to a bending magnet and equipped with three
gratings that cover photon energies from 100 to 1000 eV with a
typical photon flux of 1 × 1010 photons/s and a resolution (E/
ΔE) better than 1000 at 244 eV. The Pt L3-edge and Ru K-edge
XAFS measurements were made in transmission mode at the
beamline 14W1 in Shanghai Synchrotron Radiation Facility
(SSRF) and 1W1B station in Beijing Synchrotron Radiation
Facility (BSRF). The X-ray was monochromatized by a double-
crystal Si(311) monochromator, and the energy was calibrated
using a platinum metal foil for the Pt L3-edge and a ruthenium
metal foil for the Ru K-edge. The monochromator was detuned
to reject higher harmonics. XAFS data were analyzed with
WinXAS3.1 program.17 The energy thresholds were deter-
mined as the maxima of the first derivative. Absorption curves
were normalized to 1, and the EXAFS signals χ(k) were
obtained after the removal of pre-edge and postedge back-
ground. The Fourier transform (FT) spectra were obtained as
k3χ(k) with a Bessel window in the range 3−12.5 Å−1 for the Pt
L3-edge and 3.2−13.2 Å
−1 for the Ru K-edge. Theoretical
amplitudes and phase-shift functions of Pt−Pt, Ru−Ru, Pt−O,
and Ru−O were calculated with the FEFF8.2 code18 using the
crystal structural parameters of the Pt foil, Ru foil, PtO2, and
RuO2.
19−21 On the basis of a face-centered cubic (fcc) model,
the Pt−Ru bond was modeled. The S0
2 values were found to be
1.06 and 0.93 for Pt and Ru, respectively.
Electrochemical Measurements. Electrochemical meas-

urements were taken using a conventional three-electrode
system, with a Pt mesh electrode as counter electrode, a silver/
silver chloride electrode (Ag/AgCl) as the reference electrode,
and a 3 mm diameter glassy carbon electrode as working
electrode. The working electrode was prepared by coating a
small amount of catalyst ink on glassy carbon electrode.
Carbon-supported PtRu catalyst (2.0 mg) was dispersed into a
solution containing 1 mL of ethanol and 10 μL of Nafion
solution (5 wt %), followed by ultrasonic treatment for 30 min,
and then the resultant suspension (ca. 10 μL) was pipetted
onto glassy carbon electrode and dried at room temperature for
20 min. Prior to coating with catalyst ink, the glassy carbon
electrode was polished with alumina paste and washed with
deionized water. Cyclic voltammetry was carried out to study
the methanol oxidation reaction (MOR) at room temperature
in an electrolyte containing 1.0 M KOH and 1.0 M CH3OH
between −0.8 and 0.3 V (vs Ag/AgCl) at a scan rate of 50 mV/
s. Prior to each cyclic voltammetry measurement, the
electrolytic solution was purged with pure N2 for 30 min to
remove dissolved oxygen.
■ RESULTS AND DISCUSSION
XRD and TEM Characterization. Figure 1 shows the
comparison of XRD patterns for different samples. The
characteristic peaks for a face-centered cubic phase (fcc) were
clearly observed in all samples. No additional peaks, such as
those attributed to Pt or Ru oxides, can be detected.
Interestingly, the characteristic peaks shifted to a higher angle
with increasing Ru percentage, indicating the contraction of the
lattice parameter due to formation of the Pt−Ru alloy. In
addition, the diffraction peaks shifted to higher angles and
became slightly sharper after annealing. This suggests that the
annealing process can reduce the lattice parameter and slightly
increase the grain size and the alloying extent of the Pt/Ru

nanocrystals.
The particle size and corresponding histograms of size
distribution of different samples are shown in Figure 2. Most
particles of PtRu, Pt2Ru, and PtRu2 are monodisperse with an
average size about 3−4 nm. After annealing, the particles
became slightly larger in size (Figure 2d). The compositions of
the catalyst were measured by ICP-AES and EDX and are
Figure 1. XRD patterns of PtRu, PtRu-annealed, Pt2Ru, and
PtRu2.
The Journal of Physical Chemistry C Article
DOI: 10.1021/acs.jpcc.5b12267
J. Phys. Chem. C 2016, 120, 6569−6576
6570
shown in Figure S1 and Table S1 (Supporting Information), in
which the overall chemical compositions for PtRu, Pt2Ru, and
PtRu2 alloy nanoparticle electrocatalysts are well confirmed
with 1:1, 2:1, and 1:2 Pt:Ru atomic ratios. The high angle
annular dark field scanning transmission electron microscopy
(HAADF-STEM) image and the corresponding EDX elemental
mapping image of PtRu are shown in Figure 2e and Figure 2f.
These observations reveal that the prepared PtRu particles are
formed by Ru and Pt elements. The EDX elemental mapping
image indicates that Ru atoms have a degree of dispersion
higher than that of Pt atoms.
XANES and XPS Analysis. To identify the microstructure
of Pt/Ru bimetals, we performed synchrotron-based X-ray
absorption spectroscopy (XAS) of the samples. The X-ray

absorption near-edge structure (XANES) spectra of the Pt L3-
edge and Ru K-edge are shown in Figure 3. In the Pt L3-edge of
Figure 3a, all samples exhibited more intense white line peaks
than that of Pt foil. It is known that the Pt L3-edge white line
corresponds to the excitation of 2p3/2 electrons to empty 5d
orbitals,22 which means more unoccupied 5d states of Pt atoms
in these Pt/Ru alloy nanoparticles in contrast to Pt foil. In
general, this explanation can be ascribed to three effects: size
effect, alloying effect, and surface oxidation effect. However,
as
the Pt atoms in pure Pt nanoparticles have more d electrons
than that in bulk,23 the influence of the size effect can be
eliminated.
To clarify the alloying effect, we investigated the Pt L3-edge
XANES spectrum of Pt−Ru alloy and compared it with the
spectrum of pure Pt. In the calculations, we modeled the Pt L3-
edge XANES spectra of Pt−Ru alloy by replacing some of the
12 nearest-neighbored Pt atoms around the central Pt atom
with Ru atoms. As shown in Figure 3b, Pt/Ru alloy has a
slightly weaker white line peak compared to pure Pt. That
means the alloying effect cannot cause the increase in white line
peak intensity. Finally, we suggest that the increase can be
attributed to a surface oxidation effect. More precisely, it
originates from the oxidation of some surface Pt atoms. Besides,
it is worth noting that the white line intensity for PtRu, Pt2Ru,
and PtRu2 was almost constant while PtRu-annealed exhibited a
distinct increase, which can be explained by the increased
oxidized Pt atoms after annealing. However, strong oxidation of
Pt in these Pt−Ru alloy nanoparticles should be ruled out based
on the direct comparison with bulk Pt and PtO2. For the Ru K-
edge XANES spectra in Figure 3c, the Ru atoms in sample
PtRu, Pt2Ru, and PtRu2 were partially oxidized where the order
of oxidation degree is Pt2Ru > PtRu > PtRu2. Similarly, strong
oxidation of Ru should also be eliminated. Notably, there is

almost no oxidation of Ru in PtRu after annealing. This means
that oxidized Ru atoms in PtRu were reduced by the annealing
process.
To further investigate the electronic structure of these Pt−Ru
nanoparticles, XPS spectra for the Pt 4f and Ru 3d core level
region for all samples were measured as shown in Figure 4. As
shown in Figure 4a, the binding energies (BE) of Pt 4f7/2 for all
PtRu, Pt2Ru, and PtRu2 are almost the same while a slight right
shift to higher BE can be observed for PtPu-annealed,
Figure 2. TEM images and histograms of particle-size
distributions of (a) PtRu, (b) Pt2Ru, (c) PtRu2, and (d) PtRu
after annealing treatment. (e)
HAADF-STEM image. (f) The corresponding EDX elemental
mapping image of PtRu.
DOI: 10.1021/acs.jpcc.5b12267
J. Phys. Chem. C 2016, 120, 6569−6576
6571
suggesting an increase in the d-vacancy of the Pt atoms.24 The
Ru 3d core level region was deconvoluted as shown in Figure
4b−e, as described by Roblison et al.25 The corresponding
deconvoluted results are summarized in Table 2. The XPS data
suggest that there are three Ru species (Ru metal, RuO2, and
RuO2·xH2O) present on the surface of the Pt−Ru catalyst. The
percentages of Ru−OH species (RuO2·xH2O) and Ru-oxide
increase in the following trend: Pt2Ru > PtRu > PtRu2 > PtRu-
annealed, consistent with the XANES analysis.
EXAFS Analysis. To further study the structure, the

corresponding extended X-ray absorption fine structure
(EXAFS) of the samples was analyzed. The k3-weighted
EXAFS signals of the Pt L3-edge and Ru K-edge are shown
in Figure S2 (Supporting Information). It has been noted that
EXAFS oscillations of all samples were lower in amplitude
compared to that of bulk Pt and bulk Ru in both the Pt L3-edge
and Ru K-edge, which can be attributed to the size effect of the
nanoparticles. In contrast to amplitude, the phase of EXAFS
oscillations of PtRu, Pt2Ru, and PtRu2 were similar to that of
bulk sample, which indicates that these nanoparticles are more
likely to be a core−shell structure rather than an alloying
structure. For the control sample, the EXAFS oscillations of
PtRu-annealed were slightly phase-shifted at each edge,
indicating the increased alloying extent after the annealing
process. Particularly, the comparison with the EXAFS signals of
standard Pt and Ru oxides further confirmed that strong
oxidation of Pt and Ru could be eliminated in our samples.
Figure 5a and 5b shows the corresponding Fourier-
transformed EXAFS spectra of the Pt L3-edge and Ru K-
edge. It is observed that the Pt L3-edge for PtRu, Pt2Ru, and
PtRu2 exhibit similar local structure around Pt. However, there
is a significant change in local structure around Pt in PtRu after
annealing. On the basis of the Ru K-edge, we can conclude that
Ru atoms in Pt2Ru have the highest oxidation degree. EXAFS
data analysis was carried out by simultaneously fitting both the
Pt L3-edge and the Ru K-edge. The comparisons of
experimental and fitting data for the Pt L3-edge and Ru K-
edge are shown in Figures S3 and S4 (Supporting Information),
and corresponding fitting parameters are summarized in Table
S2 (Supporting Information).
According to previously reported literature,26 we can
determine atomic distribution and alloying extent in bimetallic

nanoparticles based on four parameters:
Pobserved(NPt−Ru/NPt‑i),
Robserved(NRu−Pt/NRu‑i), Prandom, and Rrandom. For PtRu
and PtRu-
annealed samples, Prandom and Rrandom can be taken as 0.5, as
the
atomic ratio of Pt and Ru is 1:1. For the Pt2Ru sample, Prandom
and Rrandom can be taken as 0.33 and 0.67, respectively, as the
atomic ratio of Pt and Ru is 2:1. Conversely, Prandom and
Rrandom
can be taken as 0.67 and 0.33 for PtRu2. Then alloying extents
of Pt (JPt) and Ru (JRu) can be calculated using the following
equations:
= ×J P P( / ) 100%Pt observed random (1)
= ×J P P( / ) 100%Ru observed random (2)
All the calculated results based on this method are
summarized in Table 1. The observed parameter relationships
∑NPt−M > ∑NRu−M and JRu, JPt < 100% indicate that all of
the
as-synthesized Pt−Ru nanoparticles adopt a Pt-rich core and
Ru-rich shell structure. The larger JPt and JRu values in PtRu-
annealed indicate the increased extent of atomic dispersion and
alloying extent after the annealing process, which is consistent
with the above analysis. The higher values of Robserved and
JRu
suggest a higher alloying extent of Ru atoms compared with Pt.
Figure 3. XANES spectra at the (a) Pt L3-edge and (c) Ru K-
edge for Pt foil, Ru foil, PtO2, RuO2, and all samples. (b) The
comparison of the
calculated Pt-L3 edge XANES spectra of pure Pt and Pt−Ru
alloy with some Pt atoms substituted by Ru atoms in the first
shell.

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This means that most of the Ru atoms were reduced and
involved in alloying after the annealing process. Meanwhile,
some Pt atoms migrated to the surface and were then oxidized
by air, according to the XANES and XPS analysis. Here we can
summarize that as-grown Pt/Ru nanoparticles have a Pt-rich
core and Ru-rich shell structure. After the annealing process,
the alloying extent of Pt/Ru nanoparticles had been increased,
and more Pt atoms appeared on the surface. The structures of
Pt/Ru nanoparticles are schematically shown in Figure 5c.
Catalytic Performance in the Methanol Electro-
oxidation. Cyclic voltammetry experiments were performed
in N2-saturated freshly prepared 1 M KOH solution by
sweeping the electrode potential from −0.8 to 0.3 V vs Ag/
AgCl at a scan rate of 50 mV/s, to measure the electrochemical
active surface area (ECSA) of the catalysts, as shown in Figure
S5 (Supporting Information). The integrated charge in the
hydrogen adsorption/desorption peak area in the CV curves
represents the total charge concerning H+ adsorption, QH, and
has been used to determine ECSA by employing the following
equation:27
μ
μ
=

×
Q
ECSA [m /g of Pt]
charge [ , C/cm ]
210 [ C/cm ] electrode loading [g of Pt/m ]
2
H
2
2 2
The trend in ECSA values varied in the following order: Pt2Ru
(80.71 m2/g) > PtRu (64.01 m2/g) > PtRu2 (52.08 m
2/g) >
PtRu-annealed (27.63 m2/g). Among these electrocatalysts,
Pt2Ru was ascertained to possess the greatest electrochemical
activity. Accordingly, it is rational to assume that the higher
ECSA value may signify the better electrocatalyst that has more
catalyst sites available for electrochemical reaction.
To investigate the effect of Pt/Ru bimetal structure on the
catalytic property, a methanol electro-oxidation experiment was
carried out. Figure 6a displays cyclic voltammograms (CVs) of
methanol oxidation on Pt2Ru, PtRu, PtRu2, and PtRu-annealed
in 1.0 M KOH containing 1.0 M CH3OH solution. Two well-
defined oxidation peaks can be clearly observed: one in the
forward scan is produced because of oxidation of freshly
chemisorbed species coming from methanol adsorption, and
the other in the reverse scan is primarily ascribed to removal of

incompletely oxidized carbonaceous species formed during the
forward scan. As known, the oxidation peak during the forward
Figure 4. XPS spectra of (a) Pt 4f and C 1s + Ru 3d for (b)
PtRu, (c) PtRu-annealed, (d) Pt2Ru, and (e) PtRu2. The entire
Ru 3d + C 1s envelope
was deconvolved for all spectra, but for clarity, only the fits for
Ru 3d5/2 lines are shown. The envelopes are fitted with three
Ru 3d5/2 peaks.
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J. Phys. Chem. C 2016, 120, 6569−6576
6573
scan can be used to evaluate the catalytic activity of the
catalyst.
It is estimated that the values of current density increase in the
following trend: Pt2Ru > PtRu > PtRu2. This phenomenon is
attributed to two probable reasons: one is increasing oxidation
degree of surface Ru atoms in these samples (Pt2Ru > PtRu >
PtRu2), which is consistent with the order of catalytic activity
of
the catalysts, while the other is increasing Pt concentration in
these Pt/Ru catalysts. However, with the same composition, the
PtRu-annealed sample with the lowest oxidation degree of Ru
atoms and more Pt atoms on the surface exhibits the worst
catalytic activity. Thus, we can suggest that the higher methanol
oxidation catalytic activity originates from the increasing
oxidation degree of surface Ru atoms in Pt/Ru bimetals. This
is probable due to the content of Ru−OH increasing with the

oxidation degree of surface Ru atoms, as Ru−OH is a critical
component of the MOR of the Pt−Ru catalyst which
determines the electrocatalytic activity of Pt−Ru.25 Further-
more, the ratio of the forward anodic peak current density (If)
to the reverse anodic peak current density (Ib), If/Ib, can be
used as an important index to evaluate the catalyst tolerance to
CO accumulation.28,29 Our calculation indicates that Pt2Ru,
PtRu, and PtRu2 have almost the same If/Ib value, while the If/
Ib value of PtRu-annealed is obviously larger. This may be
attributed to the increasing alloying extent after the annealing
process, as it has been proved that the tolerance to CO
accumulation by the Pt−Ru alloying catalyst will increase with
the alloying degree.30 Thus, the best catalyst for oxidation of
accumulated CO is not necessarily the best one for methanol
oxidation.10
Moreover, chronoamperometry (CA) was also performed to
investigate the long-term stability of those catalysts under the
same conditions. Figure 6b shows CA curves performed in 1.0
M KOH + 1.0 M CH3OH at −0.2 V (vs Ag/AgCl) for 2500 s.
After a sharp drop in the initial period of around 300 s, the
currents decay at a much slower speed and then approach a flat
line. During the whole time, it was clear that current density
produced on the Pt2Ru catalyst was higher than the current
density produced on the PtRu, PtRu2, and PtRu-annealed
catalysts. These results are in agreement with those of the cyclic
voltammetry measurements, indicating that Pt/Ru bimetals
Figure 5. Fourier-transformed EXAFS spectra of the (a) Pt L3-
edge and (b) Ru K-edge for Pt foil, Ru foil, PtO2, RuO2, and all
samples. (c)
Schematic representation of the structure of the Pt−Ru
nanoparticles having different molar ratios synthesized by EG
reduction and after annealing.
Table 1. Alloying Extent Values of All Samples

sample ∑NPt‑M ∑NRu‑M Pobserved Robserved JPt(%) JRu(%)
PtRu 10.2 7.3 0.09 0.26 0.18 0.52
PtRu-annealed 10.1 6 0.19 0.53 0.38 1.06
PtRu2 10.8 7.5 0.1 0.2 0.15 0.61
Pt2Ru 10.1 7.5 0.07 0.12 0.21 0.18
Table 2. Binding Energies of Ru Species Obtained from
Curve-Fitted Ru 3d5/2 XPS Spectra for PtRu Catalysts
catalysts
binding energy/
eV assignment
relative
concentration/%
PtRu 280.0 Ru metal 58.25
280.9 RuO2 19.42
282.2 RuO2·xH2O 22.33
PtRu-annealed 279.8 Ru metal 62.16
280.8 RuO2 21.62
282.2 RuO2·xH2O 16.22
Pt2Ru 280 Ru metal 45.46
280.9 RuO2 27.27
282.3 RuO2·xH2O 27.27
PtRu2 280 Ru metal 61.54
280.9 RuO2 19.23
282.2 RuO2·xH2O 19.23

DOI: 10.1021/acs.jpcc.5b12267
J. Phys. Chem. C 2016, 120, 6569−6576
6574
with higher Ru oxidation degree can pose better methanol
oxidation catalytic activity.
■ CONCLUSIONS
Bimetallic Pt−Ru nanoparticles with different Pt/Ru molar
ratios were synthesized by a solvothermal method and
characterized by various methods. Our observations revealed
that these Pt−Ru nanoparticles have a Pt-rich core and a Ru-
rich shell structure. After annealing at 500 °C, the alloying
extent of Pt/Ru nanoparticles increased, a portion of Pt atoms
migrated to surface, and most of the surficial oxidized Ru atoms
were reduced and involved in alloying. The evaluations of
methanol electro-oxidation activity elucidated that electro-
catalytic performance improved with the increasing oxidation
degree of superficial Ru atoms. This study provides useful
information and deep insight for understanding the relationship
of electrocatalytic performance of bimetallic nanoparticles with
their structure, which may help us to further tune the bimetal
structure, composition, and catalytic activity for specific
applications.
■ ASSOCIATED CONTENT
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jpcc.5b12267.
EDX analyses of Pt2Ru, PtRu, and PtRu2. Comparison of
compositions determined from EDX and ICP. Compar-

ison of k3-weighted EXAFS signals, experimental data,
and the fitting curves for Pt L3-edge and Ru K-edge.
Cyclic voltammograms (CVs) of all samples in 1 M
KOH. Best fit parameters of the Pt L3-edge and Ru K-
edge EXAFS spectra (PDF)
■ AUTHOR INFORMATION
Corresponding Authors
*E-mail: [email protected]
*E-mail: [email protected]
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
Financial support comes from 973 program (2014CB848900),
NSF (U1232131, U1532112, 11375198, 11574280), the
Postdoctoral Science Foundation of China (2015M581990),
the Fundamental Research Funds for the Central Universities
(WK2310000053), and User with Potential from CAS Hefei
Science Center (CX2310000080). We also thank the SSRF
(BL14W1), BSRF (1W1B), MCD, and Photoemission
Endstations in NSRL for help with synchrotron-based
measurements and the USTC Center for Micro and Nanoscale
Research and Fabrication.
■ REFERENCES
(1) Wang, D. Y.; Chou, H. L.; Lin, Y. C.; Lai, F. J.; Chen, C.
H.; Lee,
J. F.; Hwang, B. J.; Chen, C. C. Simple replacement reaction for
the
preparation of ternary Fe(1−x)PtRu(x) nanocrystals with
superior
catalytic activity in methanol oxidation reaction. J. Am. Chem.
Soc.
2012, 134, 10011−10020.
(2) Eid, K.; Wang, H.; He, P.; Wang, K.; Ahamad, T.; Alshehri,

S. M.;
Yamauchi, Y.; Wang, L. One-step synthesis of porous bimetallic
PtCu
nanocrystals with high electrocatalytic activity for methanol
oxidation
reaction. Nanoscale 2015, 7, 16860−16866.
(3) Zhang, H.; Jin, M.; Xia, Y. Enhancing the catalytic and
electrocatalytic properties of Pt-based catalysts by forming
bimetallic
nanocrystals with Pd. Chem. Soc. Rev. 2012, 41, 8035−8049.
(4) Sau, T. K.; Lopez, M.; Goia, D. V. Method for preparing
carbon-
supported Pt−Ru nanoparticles with controlled internal
structure.
Chem. Mater. 2009, 21, 3649−3654.
(5) Bing, Y.; Liu, H.; Zhang, L.; Ghosh, D.; Zhang, J.
Nanostructured
Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction
reaction.
Chem. Soc. Rev. 2010, 39, 2184−2202.
(6) Figueiredo, M. C.; Sorsa, O.; Arań-Ais, R. M.; Doan, N.;
Feliu, J.
M.; Kallio, T. Trimetallic catalyst based on PtRu modified by
irreversible adsorption of Sb for direct ethanol fuel cells. J.
Catal. 2015,
329, 69−77.
(7) Uribe-Godínez, J.; García-Montalvo, V.; Jimeńez-Sandoval,
O. A
novel Rh−Ir …
Sensitive Colorimetric Assay of H2S Depending on the High-
Efficient
Inhibition of Catalytic Performance of Ru Nanoparticles
Yuan Zhao,† Yaodong Luo,† Yingyue Zhu,‡ Yali Sun,† Linyan

Cui,† and Qijun Song*,†
†Key Lab of Synthetic and Biological Colloids, Ministry of
Education, School of Chemical and Material Engineering,
Jiangnan
University, 1800 Lihu Road, Wuxi, Jiangsu 214122, China
‡School of Biotechnology and Food Engineering, Changshu
Institute of Technology, No. 99 3dr South Ring Road,
Changshu, Jiangsu
215500, China
ABSTRACT: Nanocatalysts depended colorimetric assay
possesses the
advantage of fast detection and provides a novel avenue for the
detection of
hydrogen sulfide (H2S). The exploration of nanocatalysts with
superior catalytic
activity is challenging to achieve ultrasensitive colorimetric
assay of H2S. Herein,
1.7 ± 0.2 nm ruthenium nanoparticles (Ru NPs) were prepared
and exhibited
outstanding catalytic hydrogenation activity. The degradation
rate constants of
orange I in the presence of Ru NPs were 4-, 47- and 165-fold
higher than those
of platinum (Pt) NPs, iridium (Ir) NPs and control groups
without catalysts.
H2S-induced deactivation of Ru NP catalysts was designed for
the sensitive
colorimetric assay of H2S, attributing to the poor thiotolerance
of Ru NPs. A
standard linear curve between the rate constants and the
concentration of H2S
was established. The limit of detection (LOD) was as low as 0.6

nM. A Ru NPs
based colorimetric principle was also used to fabricate
colorimetric paper strips
for the on-site visual analysis of H2S. The proposed approach
shows potential
prospective for the preparation of highly selective colorimetric
NP sensors for specific purposes.
KEYWORDS: Ru nanoparticles, Catalytic activity, H2S
detection, Colorimetric assay, Paper strips
■ INTRODUCTION
H2S along with nitric oxide and carbon monoxide are well-
known environmental pollutants and the endogenous gaso-
transmitter.1,2 H2S as one of the most important exhaled
gaseous signaling molecules plays a significant role in a variety
of physiological and pathological processes.3 Its level is not
only
an important environmental index but also is linked to various
diseases (e.g., Alzheimer’s disease, Down’s syndrome, diabetes
and liver cirrhosis).4−6 It is necessary to propose a powerful
monitoring sensor for the precise investigation of H2S.
Currently, the most common analysis for H2S detection
mainly focuses on the instrumental analysis (such as gas
chromatography, gas chromatography−mass spectrometry),
fluorescence methods and colorimetric sensors, etc.1,5,7,8
However, instrumental analysis often requires tedious sample
preparation or sophisticated equipment, and is not suitable for
routine laboratory and on-site analyses.1,9 Fluorescence
methods mainly depend on the fluorescence of probes, which
are easily interrupted by the quenching effects due to the
oxygen, humidity and foreign species.5,10 Alternatively,
colorimetric assay gains increasing attention, attributing to
the simple detection by naked eyes, short assay time, relatively

low cost and no requirements for skillful technicians.3 Due to
the unique fluorescence properties, localized surface plasmon
resonance and catalytic performances of NPs,2,5,6,11−13 NPs
based colorimetric methods have been widely exploited for the
detection of H2S (Table 1).
Nanocatalysts depended colorimetric assay, by contrast,
possesses the advantages of simple operation, fast responses
and high sensitivity, and is convenient to achieve on-site visual
analysis of H2S. However, the conventional and reported
catalysts are mainly limited to Au NPs, Ag NPs,
[email protected] NPs
and graphene, etc.3,6,14−16 The detection sensitivity of
colorimetric assay is still far from satisfying, and its
performance
is still restricted due to the limited catalytic property of the
used
NPs. With the rapid development of nanocatalysts, Ru NPs as a
transition metal show superior catalytic hydrogenation
activities, and have been investigated and employed in the
reduction of nitroaromatic compounds and azo dyes.17
Nevertheless, studies on Ru NPs are limited to the exploration
of novel synthetic methods and the investigation of shape-
determined catalytic properties,18−22 but Ru NP catalysts as a
signal amplifier for the colorimetric assay are not explored. The
mechanism of H2S induced Ru NP catalysts deactivation is not
fully understood, and it is imperative and challenging to
evaluate the deactivation degrees using Ru NPs-triggered
catalytic system.
Received: May 8, 2017
Revised: July 15, 2017
Published: August 14, 2017

Research Article
pubs.acs.org/journal/ascecg
10.1021/acssuschemeng.7b01448
ACS Sustainable Chem. Eng. 2017, 5, 7912−7919
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In this paper, uniform Ru NPs were synthesized and showed
superior catalytic hydrogenation activities for the degradation
of
orange I. Orange I−Ru NPs as an amplifier system was first
designed for the sensitive and selective colorimetric monitoring
of H2S, depending on H2S-induced poisoning of the catalytic
active sites of Ru NPs. The degradation kinetic curves of orange
I−Ru NPs amplifier were investigated in the presence of
different concentrations of H2S, and the color fading process of
orange I was monitored. The relationship between H2S
concentration and the degradation rate constants of orange I
was established, and the LOD was as low as 0.6 nM. The
proposed Ru NPs based colorimetric assay can be served as an
innovative signal transduction and amplification method for the
sensitive detection of H2S.
■ EXPERIMENTAL SECTION
Materials and Reagents. Ruthenium chloride hydrate (RuCl3·
nH2O) was purchased from J&K Chemical CO., Ltd. Poly-
(vinylpyrrolidone) (PVP), ethylene glycol, hydrazine hydrate
(N2H4,
85%), orange I, anhydrous acetone, histidine (His), alanine
(Als),
threonine (Thr), arginine (Arg), aspartic acid (Asp), glutamic
acid
(Glu), tyrosine (Tyr), phenylalanine (Phe), cysteine (Cys) and
glutathione (GSH), NaCO3, NaHCO3, NaNO2, NaNO3, NH4Cl,
NaSO4, NaSO3, Na2S2O8 and Na2S were all purchased from
Sinopharm Chemical Reagent Co., Ltd. All reagents were of

analytical-reagent grade and were used without further
purification.
Synthesis of Ru NPs. 12.3 mg of RuCl3 and 55.5 mg of PVP
were
dissolved in 10 mL of ethylene glycol at room temperature. The
mixture was heated at 170 °C for 6 h. The color of the solution
changed from dark red to dark brown and finally to dark brown.
An
aliquot of 10 mL Ru NPs solution was purified by anhydrous
acetone
for three times and then dispersed to 625 μL of ultrapure water.
The
concentration of Ru NPs was calculated to be about 1.6 μM
according
to the previous reported procedures.14 PVP stabilized Pt NPs
and Ir
NPs were respectively prepared according to the previous
methods.17,23 The average sizes of Pt NPs and Ir NPs were 3.8
±
1.3 nm and 1.9 ± 0.5 nm (Figure S1, Supporting Information).
Catalytic Hydrogenation Performance of Ru NPs. An aliquot
of 4 μL 10 mM orange I was mixed with 2 mL of 0.8 M N2H4
solution.
And then, an amount of 10 μL Ru NPs, Pt NPs, Ir NPs was
added into
the above solution, respectively. The final concentration of Ru
NPs in
the system was about 8 nM. The catalytic performances of Ru
NPs, Pt
NPs and Ir NPs at the same concentration were compared by
measuring the degradation kinetic curves at 512 nm in the
reduction of
orange I.

Colorimetric Sensor for the Detection of H2S. Na2S generally
exists in the form of HS− under alkaline condition, and is
widely used
as the source of H2S in solution.
2,4,11,24 An amount of 20 μL different
concentrated stock solution of Na2S (0, 5, 10, 20, 40, 60, 80,
100, 200,
400, 600 and 800 nM) was mixed with 10 μL of Ru NPs,
respectively.
The Na2S−Ru NPs solution was added into the mixtures of 4 μL
of 10
mM orange I and 2 mL of 0.8 M N2H4. UV−vis absorption
spectrum
of orange I was measured at 512 nm by monitoring the
degradation
kinetic curves in the presence of different concentration of
Na2S
donors.
Specificity and Reproducibility. The specificity of the
developed
method was explored for the detection of other sulfhydryl
compounds,
such as Cys and GSH. An amount of 20 μL of 2 μM Na2S
donors and
amino acids (His, Als, Thr, Arg, Asp, Glu, Tyr, Phe, Cys and
GSH)
were added to the mixture of Ru NPs, orange I and N2H4,
respectively.
The degradation kinetic curves of orange I were monitored. The
selectivity of the proposed colorimetric assay was assessed in
the
presence of other interfering substances, including NaCO3,
NaHCO3,

NaNO2, NaNO3, NH4Cl, NaSO4, Na2S2O8 and NaSO3. An
amount of
20 μL of 200 nM Na2S donors and 20 μL of 2 μM different
interfering
substances were added to the mixtures of Ru NPs, orange I and
N2H4,
respectively. The mixtures were applied to evaluate the
selectivity in
the monitoring of H2S.
The reproducibility of the developed colorimetric sensor was
investigated for the detection of H2S in Tai lake water. An
aliquot of 1
mL of negative Tai lake water was filtrated three times to
remove other
substances. An amount of Na2S donors was spiked into the
mentioned
1 mL of negative Tai lake water with the final concentration of
30, 50,
70, 90, 300 and 500 nM. The concentration of Na2S was
measured by
the developed colorimetric sensors at the same detection
procedures.
Fabrication of Paper Strip for H2S Gas Detection. A paper
strip was fabricated for the visual detection of H2S gas.
Generally, an
aliquot of 10 μL of 1 M NaOH solution was added into 1 mL of
4 mM
orange I, and the color of orange I was red under alkaline
conditions.
Filter papers (1 cm × 1 cm) were soaked with the above
solution.
After 1 min, filter papers were got out, and then 5 μL of Ru NPs
was
injected onto the filter papers. The prepared filter papers were

dried at
40 °C oven for 10 min, and then were placed in a clear glass
container
(500 mL in volume).
H2S gas is prepared by a stoichiometric reaction between Na2S
and
diluted H2SO4. An amount of 0.5 mmol Na2S was added into a
sealed
flask (500 mL), and then 0.4 mL of H2SO4 (0.1 mmol) was
slowly
injected. Different amounts of H2S gas were obtained by a
micro
syringe and separately injected into the above container with the
prepared filter papers. The final concentration of H2S gas was
0, 1, 10
and 100 μM. After incubatiion for 5 min, an aliquot of 5 μL of
0.8 M
N2H4 solution was added onto the surface of orange I−Ru NPs
modified filter papers. The color changes of filter papers were
recorded
at 2 min for visual detection of H2S gas. The fabricated paper
strips
were also applied to study the effect of the interference gases
using
their dissolved forms, involving CO3
2−, HCO3
−, NO2
−, NO3
−, NH4
+,
SO4

2−, S2O8
2−, SO3
2−. To explore the efficacy of colorimetric paper
strips, the concentration was designed to 2 μM for interfering
substances and 200 nM for Na2S.
Instrumentation and Measurements. The UV−vis spectra were
recorded in the range of 200−900 nm using a double beam
UV−vis
spectrophotometer with a 1 cm quartz cuvette (Model TU-1901).
XPS
analysis was performed on a PHI5000 Versa Probe high-
performance
electron spectrometer (Japan), using monochromatic Al Kα
radiation
(1486.6 eV), operating at accelerating voltage of 15 kV. Phase
identification of the Ru NPs were conducted with X-ray
diffraction
(XRD, D8, Bruker AXS Co., Ltd.) using Cu Kα radiation source
(λ =
1.54051 Å) over the 2θ range of 3−90°. High-resolution
transmission
electron microscopy (HRTEM, JEM-2100, Japan Electron
Optics
Laboratory Co., Ltd.) was performed at 200 kV to characterize
the
structure of NPs. The ζ-potential of Ru NPs was surveyed by
using ζ-
Table 1. Comparison of LODs of NPs Based Colorimetric
Sensors for H2S Detection
Signals NPs
Linear
range LODs refs

Luminescence Upconversion
NPs
0−100 μM / 4
Fluorescence Carbon
nanodots
5−100 μM 0.7 μM 37
Fluorescence Au nanoclusters 7−100 μM 0.73
μM
7
UV−vis absorption Au NPs 3−45 μM 2.4 μM 3
UV−vis absorption Ag NPs 0.8−6.4
μM
0.35
μM
38
UV−vis absorption Ag NPs 0.7−10 μM 0.2 μM 11
UV−vis absorption Au nanorods 0.5−5 μM 0.2 μM 36
Localized resonance
scattering
[email protected] NPs 0.05−100
μM
50 nM 5
Catalytic properties Graphene 40−400

μM
25.3
μM
6
Catalytic properties [email protected] NPs 10−100
nM
7.5 nM 14
Catalytic properties Au NPs 0.5−10 μM 80 nM 15
Catalytic properties Ru NPs 5−100 nM 0.6 nM this
work
ACS Sustainable Chemistry & Engineering Research Article
DOI: 10.1021/acssuschemeng.7b01448
7913
potential/nanometer particle size analytical instrument
(Brookhaven
Instruments Corporation).
■ RESULTS AND DISCUSSION
Ru NPs Based Colorimetric Principle for H2S Assay. A
schematic diagram illustrated the mechanism of the proposed
Ru NPs based colorimetric assay of H2S (Scheme 1). Ru NPs

exhibited superior catalytic hydrogenation performance in the
degradation of azo dyes. Ru NPs were applied to attack the azo
bonds of orange I, leading to the rapidly degradation of orange
I to aromatic amines or hydrazine derivatives through the
hydrogenation reduction (Scheme 1a). Red colored orange I
could be rapidly degraded to colorless using Ru NPs as catalysis
and N2H4 as reducing agents. When H2S existed, the poor
thiotolerance of Ru NPs induced the poisoning of the catalytic
active sites of Ru NPs and deactivated the catalytic perform-
ances of Ru NPs. With the increasing concentration of H2S, the
degradation kinetic curves of orange I became slow and the
degradation rate constants decreased (Scheme 1b). There was a
linear relationship between the concentration of H2S and the
degradation rate constants. The color of orange I gradually
faded under the H2S triggered Ru NPs catalytic system, and a
paper strip sensor was fabricated for successful detection of
H2S
using the optimized sensor solutions.
Preparation and Characterization of Ru NPs. Ru NPs
stabilized by PVP were synthesized by the reduction of RuCl3
in the presence of ethylene glycol at 170 °C for 6 h. As
illustrated in TEM images (Figure 1a), Ru NPs showed good
monodispersity and uniform morphology. The average
diameter of Ru NPs was 1.7 ± 0.2 nm, which was statistically
analyzed from about 85 Ru NPs (Figure 1b). Representative
HR-TEM images revealed that the lattice fringes of Ru NPs
were separated by 0.236 nm. Ru NPs exhibited hexagonalclose-
packed (hcp) crystal structures, which was in accordance with
the XRD patterns (Figure 1c,d).17,18
The oxidation state of Ru NPs was characterized by XPS
spectra (Figure 2a,b). Two peaks at 280.2 and 285.3 eV were
attributed to the binding energies of 3d5/2 for Ru NPs in the
zero oxidation state, and the binding energy at 281.1 and 287.1

eV was assigned to the high valence state of RuO2 3d5/2, owing
to surface oxidized of Ru(0) during the XPS sampling
procedure (Figure 2a).25,26 C 1s exhibited a peak located at
284.8 eV in the XPS spectra. Figure 2b shows two peaks at
462.0 and 463.5 eV, corresponding to the binding energies of
Ru(0) 3p3/2 and RuO2 3p3/2, respectively.
25−27 Additionally,
when Ru3+ was reduced to Ru0, the absorption peak at 308 nm
for Ru3+ generally decreased and finally disappeared, and the
color of the solution changed from dark red to dark brown,
indicating the formation of Ru NPs (Figure 2c). The ζ-
potential of Ru NPs solution was measured to be −22.0 mV
(Figure 2d), indicating the excellent stability of Ru NPs.23 The
hydroxyl from PVP endowed Ru NPs with negatively charge,
which further stabilized them against agglomeration by
electrostatic repulsion.
Catalytic Hydrogenation Performances of Ru NPs.
Orange I as an azo dye could be quickly degraded to aromatic
amines in the presence of Ru NPs and N2H4, ascribing to the
Information).17 The catalytic performances of Ru NPs in the
reduction of orange I were compared with Pt NPs, Ir NPs and
the control group without catalysts. Under alkaline conditions,
the color of orange I was red with the maximum absorbance of
512 nm (Figure S2, Supporting Information). The changes in
the absorption at 512 nm as a function of time were monitored
in the presence of different catalysts. As demonstrated in Figure
3a, the absorption at 512 nm showed no obvious changes for
the control groups and Ir NPs within 2.0 min, and the
degradation process generally took around 12 h. However, the
absorption at 512 nm exhibited a sharp decline under the
catalysis of Ru NPs. Even though orange I could also be
degraded using Pt NPs as catalysts, the degradation kinetics
curve was much slower than that of Ru NPs (Figure S3,

Supporting Information). The degradation rate constants of
orange I for Ru NPs were 4-, 47- and 165-fold higher than that
of Pt NPs, Ir NPs and control groups (Figure 3a).
The superior catalytic hydrogenation performances of Ru
NPs can be ascribed to the vacant orbitals and the strong
coordination effect with N2H4. Ru NPs acted as an electron
mediator transferred the electron and hydrogen from N2H4 to
azo bonds, leading to the degradation and decolorization of
orange I.17,28 Meanwhile, the catalytic degradation reaction
could also be inhibited after the addition of H2S, due to H2S-
triggered catalytic poisoning and the deactivation efficiency of
Ru NP catalysts.3,29,30 Therefore, the degradation kinetics
curve
became slower after the addition of H2S, and the color of
orange I did not change to colorless but became lighter when
Ru NPs and H2S both existed (Figure 3b).
Ru NPs Based Colorimetric Assay of H2S. The catalytic
hydrogenation reaction of orange I using Ru NPs as catalysts
could be applied to detect H2S. The logarithm plot of the
absorbance at 512 nm with reaction time in the presence of
different concentrations of Na2S donors was investigated. As
demonstrated in Figure 4a, with the increasing concentration of
Scheme 1. Schematic Illustration of Colorimetric Assay of
H2S Depending on the Catalytic Hydrogenation Activity of
Ru NPs
7914

Na2S donors, the degradation kinetics curve of orange I became
slower, and the color of orange I became deepened. As
illustrated in Figure 4b, the kinetic rate constants decreased
with the increasing concentration of Na2S donors.
31 The
standard linear curves between rate constants and the
concentration of Na2S donors was established with a good
correlation in the range of 5−100 nM (R2 = 0.9923) and 200−
800 nM (R2 = 0.9981) (Figure 4c,d). The LOD was calculated
to be 0.6 nM based on 3σ criterion (Supporting Information),
which was much sensitive than those of previous reported
approaches (Table 1).
The sensitivity for the specific H2S detection was determined
by the superior catalytic activity of Ru NPs and H2S-triggered
catalytic deactivation efficiency of Ru NPs. The single Ru NPs
Figure 1. (a) TEM images of synthesized Ru NPs. (b) Statistic
analysis of the size of Ru NPs. (c) Respective HR-TEM images
of Ru NPs. (d) XRD
patterns of Ru NPs.
Figure 2. (a,b) XPS spectra of Ru NPs. (c) UV−vis spectra of
RuCl3 and Ru NPs. Inset: photograph of Ru NPs solution. (d) ζ-
potential of Ru NPs.
7915

without the utilization of an acidic support or the addition of a
second metal showed poor thiotolerance, which weakened the
thioresistance of Ru NPs in the catalytic hydrogenation of
orange I.30 Na2S donor generally exists in the form of HS
−
under alkaline condition.24 A number of HS− absorbed on the
surfaces of Ru NPs, and the catalytic active sites on Ru NPs
were reduced, resulting in the formation HS−-induced catalytic
deactivation of Ru NPs.3,29 To validate this, other biological
thiols, such as GSH and Cys, were employed to discuss the
responses of the absorption of orange I at the same conditions.
As shown in Figure 5a, a significant decreased absorption
occurred for the control groups and other amino acids without
sulfhydryl groups. An obvious absorption at 512 nm for orange
I was observed for GSH, Cys and H2S, convincingly suggesting
the interaction between Ru NPs and HS−. The different
absorption at 512 nm under the same concentration of GSH,
Cys and H2S was due to the spatial effect and steric hindrance
from various molecules. H2S molecules were easy to expose
HS−, and thus could directly contact Ru NP catalysts to
deactivate the catalytic active sites on the surface.
Selectivity Evaluation. The developed colorimetric assay
was planned to achieve ultrasensitive detection of H2S in the
atmosphere, and thus the existing biological thiols in bio-
logicalsystem could not interfere the detection results. The
selectivity of the developed colorimetric assay was further
assessed by challenging the system with interfering gases using
their dissolved forms, involving CO3

2−, HCO3
−, NO2
−, NO3
−,
NH4
+, SO4
2−, S2O8
2−, SO3
2−. As illustrated in Figure 5b, there
were no obvious changes in the absorbance except for H2S,
revealing that the present sensing system exhibited excellent
Figure 3. (a) Time-dependent absorbance of orange I at 512 nm
in the presence of Ru NPs, Pt NPs and Ir NPs. (b) Time-
dependent absorbance of
orange I at 512 nm under the catalysis of Ru NPs before and
after the addition of H2S. Inset: corresponding photographs of
orange I at different
conditions.
Figure 4. (a) Time-dependent absorbance of orange I at 512 nm
in the presence of Ru NPs and different concentration of Na2S
donors. Inset:
photographs of orange I within 2 min after the addition of Ru
NPs and different concentration of Na2S. (b) Linear fit plots of
ln(A0/At) vs time at
different concentration of Na2S. (c) Rate constants as a function
of Na2S concentration ranging from 5 to 100 nM. (d) The rate
constants as a
function of Na2S concentration ranging from 200 to 800 nM.

7916
selectivity and antijamming capability for the monitoring of
H2S in the atmosphere.
Analysis of Real Samples and Evaluation of Method
Accuracy. The application of the developed colorimetric assay
was investigated by detecting H2S in negative Tai lake water.
Different amounts of Na2S donors were spiked into negative
Tai lake water, and the H2S level was calculated referring to the
regression equation in Figure 4c,d. It was reported that the
heavy metal ions existed in water could deactivate the catalytic
activity of metal catalysts,32−34 but the heavy metal ions
would
be precipitated by the formation of hydroxide under alkaline
conditions, which systematically indicated the accuracy and
precision of the developed colorimetric sensor for H2S
detection in the polluted water. As demonstrated in Table S1
of the Supporting Information, the recovery for the samples
was in the range of 97.5%−102.3%, and the RSD was within
1.9%.
Colorimetric Assay of H2S Using Fabricated Paper
Strip Sensor. It was clearly seen that Ru NPs depended
colorimetric assay of H2S showed laudable advantages against
the literature procedures, in terms of response times, sensitivity
and selectivity. The proposed colorimetric principle was
devoted to fabricate a colorimetric paper strip for H2S gas
assay. H2S gas was generated by a stoichiometric reaction
between Na2S and diluted H2SO4 (Na2S + 2H

+ = H2S↑ +
2Na+).35 The sensing pH was controlled at acidic con-
ditions.2,11,35,36 As demonstrated in Figure 6a, an obvious red
color was observed for the paper strips when just orange I was
existed under alkaline conditions. However, the red colored
paper strip rapidly faded to colorless in the presence of Ru NPs
and N2H4 (Figure 6e), attributed to the superior catalytic
hydrogenation performances of Ru NPs. Interestingly, with
increasing amounts of H2S gas (from Figure 6d to 6b), more
catalytic active sites on Ru NPs were deactivated, introducing
the varying degrees of color fading. The fabricated paper strips
were also applied to study the effect of gases using their
dissolved forms. As illustrated in Figure 6f−n, no color changes
were observed for ions other than H2S. The favorable
selectivity
for H2S was well suitable for processing complex sample
matrixes for the environmental samples. The fabricated paper
strip sensor was appropriate for the specific and reliable
colorimetric monitoring H2S with the concentration of above 1
μM in the atmosphere, and has the potential to be a convenient
and portable detection kit without the need of sophisticated
instrumentation.
■ CONCLUSION
In summary, a simple Ru NPs depended colorimetric principle
was proposed for the specific and ultrasensitive detection of
H2S. Ru NPs were synthesized and exhibited superior catalytic
performances, which were 4- and 47-fold higher than that of Pt
NPs, Ir NPs. Red-colored orange I could be rapidly degraded to
colorless by Ru NPs, but slowly degraded to pink by the
introduction of H2S to Ru NPs solution, due to the weak
thioresistance of Ru NPs and the poisoning of the catalytic
active sites of Ru NPs. The deactivation degrees were evaluated
by kinetic rate constants of H2S−Ru NPs triggered catalytic

system. Attributing to the superior catalytic activity of Ru NPs
Figure 5. (a) Absorbance intensities of orange I at 512 nm
toward the same concentration of biological thiols and other
amino acids without
sulfhydryl groups. Inset: corresponding photographs of orange I
within 2 min in the presences of Ru NPs and biological
thiols/amino acids. (b)
Selectivity of the proposed colorimetric assay against Na2S
donors and the interfering substances. Inset: the corresponding
photographs of orange I
within 2 min in the presence of Ru NPs and interfering
substances.
Figure 6. (a−e) Visual responses of different concentration of
H2S toward fabricated paper strip sensors. (a) Control group of
orange under alkaline
condition; (b−e) addition of Ru NPs and 100, 10, 1, 0 μM Na2S
donors. (f−n) Visual responses of different interfering
substances toward fabricated
paper strip sensors. f−n, CO3
2−, HCO3
−, NO2
−, NO3
−, NH4
+, SO4
2−, S2O8
2−, SO3
2− and H2S.

7917
and the rapid H2S-induced specific response, the developed
assay for H2S detection displayed a high sensitivity with a wide
linear range of 5−100 nM and a low LOD of 0.6 nM. The
proposed principle for colorimetric assay enabled the visual
readout with the naked eyes, and showed potential as a novel
detection paper strip for point-of-care testing of H2S.
■ ASSOCIATED CONTENT
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acssusche-
meng.7b01448.
Photographs of orange I before and after the addition of
Ru NPs, UV−vis spectra of orange I at different pH,
TEM images of Pt NPs and Ir NPs, table of colorimetric
assay of H2S spiked in Tai lake water (PDF)
■ AUTHOR INFORMATION
Corresponding Author
*Q. Song. E-mail: [email protected]
ORCID
Qijun Song: 0000-0002-7579-885X
Notes
The authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This work is financially supported by the National Natural
Science Foundation of China (21403090), China Postdoctoral

Science Foundation (2015M570405, 2016T90417), the
foundation of Key Lab of Synthetic and Biological Colloids,
Ministry of Education, Jiangnan University (No. JDSJ2015-08
and JDSJ2016-01) and the 111 Project (B13025).
■ REFERENCES
(1) Jarosz, A. P.; Yep, T.; Mutus, B. Microplate-Based
Colorimetric
Detection of Free Hydrogen Sulfide. Anal. Chem. 2013, 85,
3638−
3643.
(2) Yuan, Z. Q.; Lu, F. N.; Peng, M. H.; Wang, C. W.; Tseng,
Y. T.;
Du, Y.; Cai, N.; Lien, C. W.; Chang, H. T.; He, Y.; Yeung, E. S.
Selective Colorimetric Detection of Hydrogen Sulfide Based on
Primary Amine-Active Ester Cross-Linking of Gold
Nanoparticles.
Anal. Chem. 2015, 87, 7267−7273.
(3) Fan, W.; Lee, Y. H.; Pedireddy, S.; Zhang, Q.; Liu, T.; Ling,
X. Y.
Graphene oxide and shape-controlled silver nanoparticle hybrids
for
ultrasensitive single-particle surface-enhanced Raman scattering
(SERS) sensing. Nanoscale 2014, 6, 4843−4851.
(4) Peng, J. J.; Teoh, C. L.; Zeng, X.; Samanta, A.; Wang, L.;
Xu, W.;
Su, D. D.; Yuan, L.; Liu, X. G.; Chang, Y. T. Development of a
Highly
Selective, …
Chapter 17
Properties and Applications of Ruthenium

Anil K. Sahu, Deepak K. Dash, Koushlesh Mishra,
Saraswati P. Mishra, Rajni Yadav and
Pankaj Kashyap
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/intechopen.76393
Provisional chapter
Properties and Applications of Ruthenium
Anil K. Sahu, Deepak K. Dash, Koushlesh Mishra,
Saraswati P. Mishra, Rajni Yadav and
Pankaj Kashyap
Additional information is available at the end of the chapter
Abstract
Ruthenium (Ru) with atomic number of 44 is one of the
platinum group metals, the others
being Rh, Pd, Os, Ir and Pt. In earth’s crust, it is quite rare,
found in parts per billion
quantities, in ores containing some of the other platinum group
metals. Ruthenium is silvery
whitish, lustrous hard metal with a shiny surface. It has seven
stable isotopes. Recently,
coordination and organometallic chemistry of Ru has shown
remarkable growth. In this
chapter, we review the application of Ru in diverse fields along
with its physical and
chemical properties. In the applications part of Ru we have
primarily focused on the
biomedical applications. The biomedical applications are
broadly divided into diagnostic

and treatment aspects. Ru and their complexes are mainly used
in determination of ferritin,
calcitonin and cyclosporine and folate level in human body for
diagnosis of diseases. Treat-
ment aspects focuses on immunosuppressant, antimicrobial and
anticancer activity.
Keywords: ruthenium, platinum group, biomedical application,
rare element, cancer,
isotopes
1. Discovery of ruthenium
Ruthenium is one of the 118 chemical elements given in the
periodic table. Out of these 118
elements, 92 elements originated from natural sources and
remaining 26 elements have been
synthesized in laboratories [1, 2]. The last naturally occurring
element to be discovered was
Uranium in 1789 [1, 3]. Technetium was the first man-made
element to be synthesized in the
year 1937 [2]. Recently in the year 2016, four of the man-made
elements were included in
periodic table. The four newly added elements goes by the name
nihonium (Nh), moscovium
(Mc), tennessine (Ts), and oganesson (Og), respectively for
element 113, 115, 117 and 118 [4].
© 2016 The Author(s). Licensee InTech. This chapter is
distributed under the terms of the Creative Commons
Attribution License
(http://creativecommons.org/licenses/by/3.0), which permits
unrestricted use,
distribution, and eproduction in any medium, provided the

original work is properly cited.
DOI: 10.5772/intechopen.76393
© 2018 The Author(s). Licensee IntechOpen. This chapter is
distributed under the terms of the Creative
Commons Attribution License
(http://creativecommons.org/licenses/by/3.0), which permits
unrestricted use,
distribution, and reproduction in any medium, provided the
original work is properly cited.
Discovery of Ruthenium had many twist and turns. A polish
Chemist Jedrzej Sniadecki
(1768–1838) in 1808 was first to announce the discovery of an
element which he named
Vestium after an asteroid called Vesta [3]. However, none of
the contemporary Chemists
were able to confirm his discovery. Later he again reported
discovery of element 44 while
working on the platinum ores from South America and
published his results but again none
of the fellow chemist were able to confirm the element 44 [4].
Due to repeated failures of his
claim, Sniadecki got depressed and dropped the idea of further
research on this element [1,
5]. After 20 years, a Russian chemist, Gottfried W. Osann,
claimed the discovery of element
44. His discovery had the same fate as that of Sniadecki as none
of his fellow chemist could
repeat his results [5].
At last in the year 1844, another Russian chemist Carl Ernst
Claus [also known in Russian as

Karl Karlovich Klaus (1796–1864)] tried his luck on discovery
of element 44. He succeeded in it
as he gave positive proof about the new element extracted from
platinum ores obtained from
the Ural Mountains in Russia [6]. Claus had suggested the name
of newly discovered element
as Ruthenium after the name Ruthenia which was the ancient
name of Russia. Earlier Osann
had also suggested the same name for the element 44 [2, 5].
Ruthenium with atomic number 44
was given the symbol Ru. It is included in group 8, period 5 and
block d in modern periodic
table and it is a member of the platinum group metals [5].
2. Occurrence in nature
Like other platinum group metals, Ruthenium is also one of the
rare metals in the earth’s crust.
It is quite rare in that it is found as about 0.0004 parts per
million of earth crust [6]. This fraction
of abundance makes it sixth rarest metal in earth crust. As other
platinum group metals, it is
obtained from platinum ores [7]. For instance, it is also
obtained by purification process of a
mineral called osmiridium [5].
3. Electronic configuration of Ru
In the modern periodic table, group 8 consists of four chemical
elements. These elements are
Iron (Fe), Ruthenium (Ru), Osmium (Os) and Hassium (Hs) [7].
Ruthenium has atomic
number of 44, that is, it contains 44 electrons distributed in
atomic orbitals and its nucleus
has 44 protons and 57 neutrons (Figure 1). Electron distribution
in atomic or molecular

Annotated Bibliography for Ru Nanoparticles Catalysis Research

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Annotated Bibliography for Ru Nanoparticles Catalysis Research