confined NPs, NPs stabilised by ionic liquids and polymers and NPs generated in
situ without stabilising agent. A key issue is the role of the stabiliser in the catalytic
process (activity, selectivity and recyclability). General trends in the use of conditions, stabilisers, additives and co-catalysts were also observed. In spite of the
advances achieved in the last decade, there is still a quest for Ir NP-based catalysts
with sufficient selectivity to be industrially applied in fine chemistry.
Keywords Carbon materials · Cyclohexene hydrogenation · Hydrogenation
reactions · Ionic liquids · Iridium nanoparticles (Ir NPs) · Ligand-stabilised Ir NPs ·
Metal oxide supports · Nanocatalysis · Polymer supports · α,β-unsaturated carbonyl
compounds
1 Introduction
Catalysis is crucial for green (or sustainable) chemistry, which has the objective to
reduce or eliminate the use and generation of hazardous substances. Apart from
being potentially selective, catalytic processes permit the use of stoichiometric
amounts of reagents, which reduces the amount of by-products and residues. Catalysis can be homogeneous or heterogeneous, depending on whether the substrates
and catalysts are in the same phase or not. Each type of catalysis presents a series of
advantages and disadvantages. For example, homogeneous catalysts tend to be more
selective and active than heterogeneous ones, but often they are less stable and
recyclable. In between, we can find metal nanoparticles (MNPs), which combine the
benefits of heterogeneous and homogeneous catalysts [1–3]. MNPs, as well as
heterogeneous catalysts, possess the possibility to be easily recovered and subsequently reused. Besides, MNPs present a large number of active sites due to their
high surface/volume ratio, which makes them very active in catalysis approaching
homogeneous ones [4–6]. Their high conversions and selectivities together with an
easy product separation make MNPs ideal catalysts for catalytic processes. For all
this, MNP catalysis is gaining a lot of interest in both academia and industry.
The main objective in MNP catalysis is to develop appropriate tools to produce
well-defined nano-objects with controlled size, morphology and catalytic properties.
To this end, stabilisers are the best way to control these parameters. Among all
stabilising agents used for MNP stabilisation, we can find surfactants [7–10], polymers [11, 12], ionic liquids [13, 14], ligands [15, 16] and supports [17, 18], which
substantially improve the MNP stability. In addition to protecting MNPs through
electronic and/or steric stabilisations, they also are able to modify the catalytic
properties. For example, through a synergistic effect with the nanoparticle surface,
stabilising ligands are able to enhance the stability and activity of MNPs [19, 20].
Hydrogenation of unsaturated compounds using molecular H 2 is one of the most
efficient and atom-economical way for the formation of high added value
398
L. M. Martínez-Prieto et al.
situ without stabilising agent. A key issue is the role of the stabiliser in the catalytic
process (activity, selectivity and recyclability). General trends in the use of conditions, stabilisers, additives and co-catalysts were also observed. In spite of the
advances achieved in the last decade, there is still a quest for Ir NP-based catalysts
with sufficient selectivity to be industrially applied in fine chemistry.
Keywords Carbon materials · Cyclohexene hydrogenation · Hydrogenation
reactions · Ionic liquids · Iridium nanoparticles (Ir NPs) · Ligand-stabilised Ir NPs ·
Metal oxide supports · Nanocatalysis · Polymer supports · α,β-unsaturated carbonyl
compounds
1 Introduction
Catalysis is crucial for green (or sustainable) chemistry, which has the objective to
reduce or eliminate the use and generation of hazardous substances. Apart from
being potentially selective, catalytic processes permit the use of stoichiometric
amounts of reagents, which reduces the amount of by-products and residues. Catalysis can be homogeneous or heterogeneous, depending on whether the substrates
and catalysts are in the same phase or not. Each type of catalysis presents a series of
advantages and disadvantages. For example, homogeneous catalysts tend to be more
selective and active than heterogeneous ones, but often they are less stable and
recyclable. In between, we can find metal nanoparticles (MNPs), which combine the
benefits of heterogeneous and homogeneous catalysts [1–3]. MNPs, as well as
heterogeneous catalysts, possess the possibility to be easily recovered and subsequently reused. Besides, MNPs present a large number of active sites due to their
high surface/volume ratio, which makes them very active in catalysis approaching
homogeneous ones [4–6]. Their high conversions and selectivities together with an
easy product separation make MNPs ideal catalysts for catalytic processes. For all
this, MNP catalysis is gaining a lot of interest in both academia and industry.
The main objective in MNP catalysis is to develop appropriate tools to produce
well-defined nano-objects with controlled size, morphology and catalytic properties.
To this end, stabilisers are the best way to control these parameters. Among all
stabilising agents used for MNP stabilisation, we can find surfactants [7–10], polymers [11, 12], ionic liquids [13, 14], ligands [15, 16] and supports [17, 18], which
substantially improve the MNP stability. In addition to protecting MNPs through
electronic and/or steric stabilisations, they also are able to modify the catalytic
properties. For example, through a synergistic effect with the nanoparticle surface,
stabilising ligands are able to enhance the stability and activity of MNPs [19, 20].
Hydrogenation of unsaturated compounds using molecular H 2 is one of the most
efficient and atom-economical way for the formation of high added value
398
L. M. Martínez-Prieto et al.