368
I. Cano and P. W. N. M. van Leeuwen
20 s
−1 ). However, the Pt NPs show moderate activity for aldehyde and ketone hydrogenation, which results in the reduction of the C=C bond in both substrates with
81% and 68% selectivity, respectively, at total conversion, the remainder being the
doubly hydrogenated product, the saturated alcohol. It is thought that the electronrich surface coordinates only weakly to the ketone function, while back-donation
enhances alkene coordination.
Rodionov and co-workers prepared bimetallic PtFe MNPs stabilized by carboxylic
acids and perfluorinated carboxylic acids from Pt(acac) 2 and Fe(CO) 5 with 1,2hexadecanediol as reducing agent [50]. Particle sizes varied from 3.2 to 3.6 nm,
independent of the metal ratio. It was proposed that the carboxylic acids coordinate
to Fe, leaving Pt free. The selectivity of CAL to COL depends strongly on Fe content
and the type of acid used (perfluorodecalin, n-hexane, 1 bar H 2 , 50 °C). High Fe
contents (0.33) and long-chain (C10) perfluoroacids gave the highest selectivity, up
to 94%, much higher than that shown by the Fe (0.13) catalyst prepared this way,
64%.
Zheng, Fu, et al. studied the effect of the nature of the capping amine ligand on
Pt 3 Co NPs in the hydrogenation of CAL [51]. Thus, for oleylamine a very homogeneous monodispersion of NPs with 8.2 nm size was obtained by CO reduction
of acetylacetonate precursors. The truncated octahedrally shaped NPs gave a highly
ordered TEM as shown in Fig. 11.6. An 8 nm NP contains about 3000 surface atoms
and analysis shows slightly less than 500 oleylamine molecules on the surface which,
according to DFT, can form ordered arrays on the surface. >90% COL was obtained in
the hydrogenation of CAL (n-butanol, 25 °C, 1 bar H 2 ), which the authors explained
by the coordination of the carbonyl group to the surface interchelating in the stacks,
while coordination of the alkene is prohibited by the stacked amines. For shorter chain
amines the selectivity gradually diminished (octylamine 80%, butylamine 20% COL
in addition to HCAL and HCOL) while the rate increased, in support of the mechanism proposed. This catalytic system also provided >90% selectivity towards the
unsaturated alcohol in the hydrogenation of citral.
11.4.2 Organic Supports
Polymerization of 4-tritylaniline and formaldehyde with FeCl 3 as a catalyst yields
hollow polymeric tubes with a diameter of 80–100 nm [52]. They were used as
support for Pt NPs (3–4 nm) generated the usual way in water from chloroplatinate
and sodium borohydride. This catalytic system (2 wt% metal) was explored for
the hydrogenation of unsaturated aldehydes (isopropanol, 60 °C, 20 bar). Modest
selectivities for cinnamaldehyde (COL < 72%) and 3-methyl-2-butenal (3-methyl-2butenol < 50%) were observed, whereas furfural was converted selectively (100%)
to furfuryl alcohol.
I. Cano and P. W. N. M. van Leeuwen
20 s
−1 ). However, the Pt NPs show moderate activity for aldehyde and ketone hydrogenation, which results in the reduction of the C=C bond in both substrates with
81% and 68% selectivity, respectively, at total conversion, the remainder being the
doubly hydrogenated product, the saturated alcohol. It is thought that the electronrich surface coordinates only weakly to the ketone function, while back-donation
enhances alkene coordination.
Rodionov and co-workers prepared bimetallic PtFe MNPs stabilized by carboxylic
acids and perfluorinated carboxylic acids from Pt(acac) 2 and Fe(CO) 5 with 1,2hexadecanediol as reducing agent [50]. Particle sizes varied from 3.2 to 3.6 nm,
independent of the metal ratio. It was proposed that the carboxylic acids coordinate
to Fe, leaving Pt free. The selectivity of CAL to COL depends strongly on Fe content
and the type of acid used (perfluorodecalin, n-hexane, 1 bar H 2 , 50 °C). High Fe
contents (0.33) and long-chain (C10) perfluoroacids gave the highest selectivity, up
to 94%, much higher than that shown by the Fe (0.13) catalyst prepared this way,
64%.
Zheng, Fu, et al. studied the effect of the nature of the capping amine ligand on
Pt 3 Co NPs in the hydrogenation of CAL [51]. Thus, for oleylamine a very homogeneous monodispersion of NPs with 8.2 nm size was obtained by CO reduction
of acetylacetonate precursors. The truncated octahedrally shaped NPs gave a highly
ordered TEM as shown in Fig. 11.6. An 8 nm NP contains about 3000 surface atoms
and analysis shows slightly less than 500 oleylamine molecules on the surface which,
according to DFT, can form ordered arrays on the surface. >90% COL was obtained in
the hydrogenation of CAL (n-butanol, 25 °C, 1 bar H 2 ), which the authors explained
by the coordination of the carbonyl group to the surface interchelating in the stacks,
while coordination of the alkene is prohibited by the stacked amines. For shorter chain
amines the selectivity gradually diminished (octylamine 80%, butylamine 20% COL
in addition to HCAL and HCOL) while the rate increased, in support of the mechanism proposed. This catalytic system also provided >90% selectivity towards the
unsaturated alcohol in the hydrogenation of citral.
11.4.2 Organic Supports
Polymerization of 4-tritylaniline and formaldehyde with FeCl 3 as a catalyst yields
hollow polymeric tubes with a diameter of 80–100 nm [52]. They were used as
support for Pt NPs (3–4 nm) generated the usual way in water from chloroplatinate
and sodium borohydride. This catalytic system (2 wt% metal) was explored for
the hydrogenation of unsaturated aldehydes (isopropanol, 60 °C, 20 bar). Modest
selectivities for cinnamaldehyde (COL < 72%) and 3-methyl-2-butenal (3-methyl-2butenol < 50%) were observed, whereas furfural was converted selectively (100%)
to furfuryl alcohol.