chemoselective hydrogenations of carbonyl, nitro, and alkynyl compounds while
retaining C¼C bonds, and the aerobic oxidation of alcohols and the Wacker type
oxidation of alkenes, which overcome the limitations of the conventional catalyst
systems. This improved catalytic performance is due to significant advances in the
precise fabrication of nanoscale metals, which has made it possible to explore novel
catalysis and design metal active centers.
Keywords Catalyst · Hydrogenation · Metal · Nanoparticle · Oxidation
1 Introduction
Reduction and oxidation reactions (redox reactions) are fundamental and important
transformations in both laboratory and industrial chemistries. In conventional redox
reaction systems, metal hydrides, such as NaBH 4 and LiAlH 4 , or heavy metal salts,
such as permanganate and dichromate, have been employed as reducing or oxidizing
agents. As these stoichiometric reagents have serious drawbacks, including high
costs, toxicity, and producing large amounts of waste, the development of promising
catalytic systems to replace these stoichiometric reactions has attracted much attention. With regard to atom economy and the environmental demands of chemical
reactions, an ultimate goal of redox reactions is to employ molecular hydrogen (H 2 )
or molecular oxygen (O 2 ) [1–6]. These inexpensive reagents are abundant and can
avoid the use of harmful reagents. In this context, transition metal complexes have
traditionally been employed as catalysts, because they are dissolved in reaction
media, which makes all active sites accessible to substrates, leading to exhibit high
catalytic activities. Despite these advantages, homogeneous catalyst systems have
fundamental problems, including short lifetimes (low stability), risk of contaminating products with metals (low recoverability), and tedious workups for reuse (low
reusability). Although heterogeneous catalysts are the most promising approach to
solving the above issues, they generally show low activity and require harsh reaction
conditions and have mainly been applied in gas-phase reactions. Therefore, highperformance heterogeneous catalysts with high activity, selectivity, recoverability,
and reusability would be ideal, leading to the development of green sustainable
redox reaction processes using H 2 or O 2 .
Using metal nanoparticles (NPs) is among the most promising strategies for the
design of high-performance heterogeneous catalysts because of their unusual properties compared to bulk metal. To date, metal NP catalysts have been employed to
refine petroleum, manufacture petrochemicals, clean exhaust gas, and produce
renewable clean energy, especially in gas-phase reactions [7–9]. Recently, the
advance of nanoengineering has enabled the precise construction of metal NP
catalysts. Sophisticated metal NP catalysts, obtained by controlling particle sizes
and shapes, tuning metal electronic states, and modulating metal–support
50
K. Jitsukawa and T. Mitsudome
retaining C¼C bonds, and the aerobic oxidation of alcohols and the Wacker type
oxidation of alkenes, which overcome the limitations of the conventional catalyst
systems. This improved catalytic performance is due to significant advances in the
precise fabrication of nanoscale metals, which has made it possible to explore novel
catalysis and design metal active centers.
Keywords Catalyst · Hydrogenation · Metal · Nanoparticle · Oxidation
1 Introduction
Reduction and oxidation reactions (redox reactions) are fundamental and important
transformations in both laboratory and industrial chemistries. In conventional redox
reaction systems, metal hydrides, such as NaBH 4 and LiAlH 4 , or heavy metal salts,
such as permanganate and dichromate, have been employed as reducing or oxidizing
agents. As these stoichiometric reagents have serious drawbacks, including high
costs, toxicity, and producing large amounts of waste, the development of promising
catalytic systems to replace these stoichiometric reactions has attracted much attention. With regard to atom economy and the environmental demands of chemical
reactions, an ultimate goal of redox reactions is to employ molecular hydrogen (H 2 )
or molecular oxygen (O 2 ) [1–6]. These inexpensive reagents are abundant and can
avoid the use of harmful reagents. In this context, transition metal complexes have
traditionally been employed as catalysts, because they are dissolved in reaction
media, which makes all active sites accessible to substrates, leading to exhibit high
catalytic activities. Despite these advantages, homogeneous catalyst systems have
fundamental problems, including short lifetimes (low stability), risk of contaminating products with metals (low recoverability), and tedious workups for reuse (low
reusability). Although heterogeneous catalysts are the most promising approach to
solving the above issues, they generally show low activity and require harsh reaction
conditions and have mainly been applied in gas-phase reactions. Therefore, highperformance heterogeneous catalysts with high activity, selectivity, recoverability,
and reusability would be ideal, leading to the development of green sustainable
redox reaction processes using H 2 or O 2 .
Using metal nanoparticles (NPs) is among the most promising strategies for the
design of high-performance heterogeneous catalysts because of their unusual properties compared to bulk metal. To date, metal NP catalysts have been employed to
refine petroleum, manufacture petrochemicals, clean exhaust gas, and produce
renewable clean energy, especially in gas-phase reactions [7–9]. Recently, the
advance of nanoengineering has enabled the precise construction of metal NP
catalysts. Sophisticated metal NP catalysts, obtained by controlling particle sizes
and shapes, tuning metal electronic states, and modulating metal–support
50
K. Jitsukawa and T. Mitsudome