the hydrogen transfer to the co-adsorbed cyclohexene. On the other hand, AgIr NPs
supported on Co 3 O 4 present a linear dependence between metal composition and
selectivity in the hydrogenation of α,β-unsaturated aldehydes. The more Ag rich the
catalyst is, the more selective is the catalyst towards C¼O hydrogenation (Fig. 23b).
Moreover, the Co 3 O 4 support plays an important role in the hydrogenation mechanism, since the use of mesoporous Co 3 O 4 considerably increases the selectivity.
DFT calculations explain this trend through different synergic factors: (1) Ag-rich
NPs present higher proportion of weak H-binding sites due to their larger size, which
promote the hydrogen spillover to the Co 3 O 4 support; (2) Ag-rich NPs present more
Ag atoms which are weaker C¼C adsorption sites; and (3) the larger Ag-rich NPs
also present a higher weak surface/strong edge adsorption site ratio; thus C¼C
hydrogenation is more hindered in larger NPs.
In addition to carbon-based materials, metal oxides and silica supports, one can
find another less used material for MNP stabilisation such as clays. For example,
Dutta et al. generated Ir NPs (~4 nm) inside the nanopores of a modified montmorillonite clay by an incipient wetness impregnation method (Ir NPs/montmorillonite), by using IrCl 3 as metal precursor and ethylene glycol as reductant [133]. This Ir
catalysts presented a high catalytic activity in the hydrogenation of a great number of
aromatic compounds under solvent-free conditions (maximum TOF ¼ 79 h
À1 ;
Table 21). Moreover, the catalyst was easily recovered from the reaction media by
filtration and was reused many times without any significant loss of catalytic activity.
6.4 Zeolite-Supported Ir NPs
Zeolites are rigid anionic frameworks of aluminosilicates with well-defined channels
and cavities. Zeolites have numerous applications; one of the most important is the
Fig. 23 (a) TOFs as a function of %Ir composition in AgIr alloy NPs (red) and compared to pure Ir
NPs (black plot and grey line). (b) Selectivity to crotyl alcohol over Ag x Ir (100-x) /a-Co 3 O 4 (orange)
and Ag x Ir (100-x)/ m-Co 3 O 4 (blue) as a function of %Ir composition. Reprinted with permission from
ref. [132]. Copyright 2018 American Chemical Society
442
L. M. Martínez-Prieto et al.
supported on Co 3 O 4 present a linear dependence between metal composition and
selectivity in the hydrogenation of α,β-unsaturated aldehydes. The more Ag rich the
catalyst is, the more selective is the catalyst towards C¼O hydrogenation (Fig. 23b).
Moreover, the Co 3 O 4 support plays an important role in the hydrogenation mechanism, since the use of mesoporous Co 3 O 4 considerably increases the selectivity.
DFT calculations explain this trend through different synergic factors: (1) Ag-rich
NPs present higher proportion of weak H-binding sites due to their larger size, which
promote the hydrogen spillover to the Co 3 O 4 support; (2) Ag-rich NPs present more
Ag atoms which are weaker C¼C adsorption sites; and (3) the larger Ag-rich NPs
also present a higher weak surface/strong edge adsorption site ratio; thus C¼C
hydrogenation is more hindered in larger NPs.
In addition to carbon-based materials, metal oxides and silica supports, one can
find another less used material for MNP stabilisation such as clays. For example,
Dutta et al. generated Ir NPs (~4 nm) inside the nanopores of a modified montmorillonite clay by an incipient wetness impregnation method (Ir NPs/montmorillonite), by using IrCl 3 as metal precursor and ethylene glycol as reductant [133]. This Ir
catalysts presented a high catalytic activity in the hydrogenation of a great number of
aromatic compounds under solvent-free conditions (maximum TOF ¼ 79 h
À1 ;
Table 21). Moreover, the catalyst was easily recovered from the reaction media by
filtration and was reused many times without any significant loss of catalytic activity.
6.4 Zeolite-Supported Ir NPs
Zeolites are rigid anionic frameworks of aluminosilicates with well-defined channels
and cavities. Zeolites have numerous applications; one of the most important is the
Fig. 23 (a) TOFs as a function of %Ir composition in AgIr alloy NPs (red) and compared to pure Ir
NPs (black plot and grey line). (b) Selectivity to crotyl alcohol over Ag x Ir (100-x) /a-Co 3 O 4 (orange)
and Ag x Ir (100-x)/ m-Co 3 O 4 (blue) as a function of %Ir composition. Reprinted with permission from
ref. [132]. Copyright 2018 American Chemical Society
442
L. M. Martínez-Prieto et al.