314
J. A. Delgado and C. Godard
isolation. Other approaches attempted the functionalization or doping of the palladium surface with sulphur atoms. For instance, Perez-Ramirez et al. reported the
direct formation of a nanostructured Pd 3 S phase by a simple treatment of palladium
nanoparticles supported on graphitic carbon nitride with aqueous sodium sulphide
[77]. This material exhibited unparalleled performance in the semi-hydrogenation
of alkynes in liquid phase. According to the authors, sulphur displayed a multifunctional role in both the isolation of palladium trimers and weakening the binding of
organic intermediates.
10.3.2 Other Non-Pd-Based Formulations
De Vries et al. can be considered as one of the pioneers in applying Fe NPs in the
semi-hydrogenation of 1-octyne [79, 80]. As a mechanism to prevent the formation
of 1-octyne at early stages of the reaction (mechanistic selectivity) observed in the Fe
NPs, the authors opted for the preparation of Fe bimetallic with Ni, Co and Cu (1:1)
as well as all monometallic NPs [80]. The series displayed the following activity
order, Fe < Co < Ni, and the alkene selectivities obtained with the bimetallic systems
were intermediate compared to those obtained with the monometallic catalysts. Very
recently, Gregory et al. reported the facile preparation of FeNPs by reduction of
iron(II) acetylacetonate with diisobutylaluminum hydride (DIBAL-H) in THF in the
absence of stabilizer [81]. The formed nanoparticles and nanoclusters enabled the
synthesis of various Z-alkenes in high yields and with high stereocontrol under very
mild conditions (1–3 bar H 2 , 30 °C).
Moores et al. reported the application of iron@iron oxide core@shell nanoparticles of ca. 50 nm (Fe@FeO NPs) in the hydrogenation of alkynes in aqueous
media [82, 83]. Although the alkene selectivity of these NPs was not remarkable
(6% at 88% of conversion), they demonstrated to be stable and magnetically recoverable. The authors also suggested that the presence of an oxide shell did not block
the activity of the NPs but still provided protection against oxidation by oxygen or
water. According to other studies on iron-based catalysts [18, 79, 80, 84, 85], relevant
alkene selectivities were only accessible in the presence of additives or promoting
stabilizers.
Liu et al. reported the preparation of a layered double hydroxide-derived NiCu
alloy (NiCu/MMO) and its evaluation in the semi-hydrogenation of acetylene. The
bimetallic catalyst demonstrated improved alkene selectivity and longer stability
when compared to the monometallic Ni catalyst [86]. Very recently, Chandler et al.
reported a solution-phase synthesis for Ni and bimetallic NiAu NPs and its deposition
on alumina [87]. Gold was added to the initial Ni NPs via galvanic displacement of
Ni in organic solution in the presence of oleylamine as capping agent. In the hydrogenation of 1-hexyne, the alumina-supported NiAu catalysts provided intermediate
activity and selectivity when compared to the monometallic Ni and Au catalysts.
J. A. Delgado and C. Godard
isolation. Other approaches attempted the functionalization or doping of the palladium surface with sulphur atoms. For instance, Perez-Ramirez et al. reported the
direct formation of a nanostructured Pd 3 S phase by a simple treatment of palladium
nanoparticles supported on graphitic carbon nitride with aqueous sodium sulphide
[77]. This material exhibited unparalleled performance in the semi-hydrogenation
of alkynes in liquid phase. According to the authors, sulphur displayed a multifunctional role in both the isolation of palladium trimers and weakening the binding of
organic intermediates.
10.3.2 Other Non-Pd-Based Formulations
De Vries et al. can be considered as one of the pioneers in applying Fe NPs in the
semi-hydrogenation of 1-octyne [79, 80]. As a mechanism to prevent the formation
of 1-octyne at early stages of the reaction (mechanistic selectivity) observed in the Fe
NPs, the authors opted for the preparation of Fe bimetallic with Ni, Co and Cu (1:1)
as well as all monometallic NPs [80]. The series displayed the following activity
order, Fe < Co < Ni, and the alkene selectivities obtained with the bimetallic systems
were intermediate compared to those obtained with the monometallic catalysts. Very
recently, Gregory et al. reported the facile preparation of FeNPs by reduction of
iron(II) acetylacetonate with diisobutylaluminum hydride (DIBAL-H) in THF in the
absence of stabilizer [81]. The formed nanoparticles and nanoclusters enabled the
synthesis of various Z-alkenes in high yields and with high stereocontrol under very
mild conditions (1–3 bar H 2 , 30 °C).
Moores et al. reported the application of iron@iron oxide core@shell nanoparticles of ca. 50 nm (Fe@FeO NPs) in the hydrogenation of alkynes in aqueous
media [82, 83]. Although the alkene selectivity of these NPs was not remarkable
(6% at 88% of conversion), they demonstrated to be stable and magnetically recoverable. The authors also suggested that the presence of an oxide shell did not block
the activity of the NPs but still provided protection against oxidation by oxygen or
water. According to other studies on iron-based catalysts [18, 79, 80, 84, 85], relevant
alkene selectivities were only accessible in the presence of additives or promoting
stabilizers.
Liu et al. reported the preparation of a layered double hydroxide-derived NiCu
alloy (NiCu/MMO) and its evaluation in the semi-hydrogenation of acetylene. The
bimetallic catalyst demonstrated improved alkene selectivity and longer stability
when compared to the monometallic Ni catalyst [86]. Very recently, Chandler et al.
reported a solution-phase synthesis for Ni and bimetallic NiAu NPs and its deposition
on alumina [87]. Gold was added to the initial Ni NPs via galvanic displacement of
Ni in organic solution in the presence of oleylamine as capping agent. In the hydrogenation of 1-hexyne, the alumina-supported NiAu catalysts provided intermediate
activity and selectivity when compared to the monometallic Ni and Au catalysts.