A New Class of Heterogeneous Platinum Catalysts for the Chemoselective Hydrogenation
Table 8. X-ray powder diffraction (XRD) of SiliaCat Pt0-3. Table 9. 29Si solid state NMR spectra of SiliaCat Pt0-3 cata-
lyst.
Catalyst
Diffraction angle 2q
111 200 220
Mean particle
size [nm]
311
Catalyst[a]
Ref.[16]
T1 [ppm] T2 [ppm] T3 [ppm] T1:T2:T3 [%]
Pt(0)[a]
39.76 46.24 67.46 51.29 N.A.
À46
0
À56.00
À55.58
À55.42
À66.00
À66.38
À66.94
[b]
SiliaCat Pt0-1 39.76 46.16 67.74 81.12 1.7
SiliaCat Pt0-2 39.86 46.04 67.52 80.62 2.92
SiliaCat Pt0-3 39.76 46.16 67.62 81.25 3.15
MeSiO1/2
0:10:90
0:5:95
SiliaCat Pt0-3
0
[a]
Catalyst identified in Table 1.
[b]
[a]
The Powder Diffraction File of the International Centre
Silica gel support without platinum, (blank from our
measurements).
for Diffraction Data was used to identified the diffraction
peaks characteristic of crystalline Pt(0) with a face-cen-
tered cubic (fcc) lattice.
mum conversion. The catalyst was then filtered off and
washed with EtOH or MeOH. The filtrate was concentrated
to give a crude product and the conversion in the desired
product was determined by GC/MS analysis.
In the reusability test the hydrogenation was carried out
under a hydrogen balloon at room temperature in the pres-
ence of 0.5 mol% sol-gel catalyst. A two-necked flask con-
nected to a balloon of hydrogen was charged with the Silia-
Cat Pt-2 catalyst and degassed twice replacing each time the
vacuum with H2. The solution of the substrate in anhydrous
methanol (0.1M with respect to the substrate), kept under
inert conditions, was transferred via cannula to a flask
charged with the catalyst. The resulting mixture was de-
gassed once more and the vacuum was replaced with H2 fol-
lowed by 30 min stirring after which the catalyst was recov-
ered by filtration, rinsed with MeOH/THF solvents and
dried under vacuum prior to reuse. The conversion was as-
sessed by GC/MS analysis and the filtrate was concentrated
to give a crude product that was analyzed by ICP-MS for
leaching of Pt and Si.
Figure 4. 29Si NMR spectra of SiliaCat Pt0-3 heterogeneous
catalysts.
References
angle at room temperature in a 4 mm ZrO rotor. A Hahn
echo sequence synchronized with the spinning speed was
used while applying a TPPM15 composite pulse decoupling
during acquisition. 2400 acquisitions were recorded with a
recycling delay of 30 seconds. The catalyst analyzed
(Figure 4 and Table 9) was SiliaCat Pt0-3.
Nitrogen adsorption and desorption isotherms at 77 K
were measured using a Micrometrics TriStarꢄ 3000 system.
The data were analyzed using the Tristar 3000 model 4,01.
Both adsorption and desorption branches are used to calcu-
late the pore size distribution. The metal content in the
products was measured using the CAMECA SX100 instru-
ment equipped with EPMA analyse technique, a fully quali-
tative and quantitative method of non-destructive elemental
analysis of micron-sized volumes at the surface of materials,
with a sensitivity at the level of ppm.
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Catalyst Activity and Reusability
Reactions were performed on a 2-mmol scale. The substrate
was dissolved in 20 mL of MeOH and then treated with 0.1–
1 mol% sol-gel entrapped catalyst. The mixture was de-
gassed two times, replacing each time the vacuum by hydro-
gen. The reaction mixture, connected to a balloon of hydro-
gen, was stirred at room temperature until it showed maxi-
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1315