Communications
and Pt for hydrogenation reactions and proposed that partial
decoordination of unsaturated hydrocarbons from the metal–
substrate species may allow hydrogenation with a low-energy
barrier on the noninteracting olefinic bond with the cata-
lyst.[26c] However, very low reactivity of the clay/Pt catalyst
under the optimized reaction conditions (Table 1, entry 13)
suggests the role of metal–substrate coordination for activa-
tion of double bonds by adsorption on the metal surface for
effective hydrogenation, as supported by XRD analysis of the
squalene-mixed clay/Pt. Substrate-dependent reactivity of the
double bonds on the Pd(111) and Pt(111) surfaces and their
interactions have already been investigated.[26a,27] Further stud-
ies will be undertaken to understand the role of the substrate
on the adsorption and reactivity of these catalysts.
General procedure for the hydrogenation of squalene
Catalysts were prehydrogentated at 3008C for 3 h under a hydro-
gen atmosphere. The hydrogenation reaction was performed in
a Berghof HR-100 high-pressure vessel equipped with a steel con-
tainer. The catalyst (100 mg) and squalene (1 g) were taken in an
air-dried container. A vacuum was created in the container, which
was followed by purging the hydrogen gas and the pressure was
maintained. The reaction temperature was raised from 258C at
58CminÀ1 to attain the desired temperature and was maintained
for several hours. The mixture was allowed to reach room tempera-
ture and was diluted with n-heptane (10 mL). The thus-obtained
solution was centrifuged, and the liquid fraction was separated.
The precipitated catalyst was diluted with n-heptane (2 10 mL),
shaken, and centrifuged to remove most of the product. The thus-
obtained liquid fractions were collected and used for analysis. Re-
action conversion and selectivity were measured by GC. The forma-
tion of squalane was further supported by 1H NMR spectroscopy.
In conclusion, metal-intercalated clay catalysts with metal
(Pt, Pd, and Ni) loadings of approximately 6 wt% were pre-
pared, and their catalytic activity in the hydrogenation of squa-
lene was tested. Simultaneous surface modification of the clay
and metal intercalation were observed during wet impregna-
tion in dilute nitric acid, which resulted in a change in the mor-
phology of the clay. Highly faceted Pd(111) intercalated in the
clay showed the highest catalytic activity and selectivity in the
chemoselective full reduction of squalene under solvent-free
conditions. The effectiveness of this catalyst was attributed to
the formation of Pd nanoparticles with a dominating (111)
plane, which promoted the reaction at a low Pd/squalene ratio
(0.06 mmolPd gsqualeneÀ1). Clay/Pd was stable under the optimized
reaction conditions, and a very small amount of Pd was leach-
ed (0.0311 ppm). The amount of Pd used in the hydrogenation
reaction could be reduced further to 0.015 mmol if it was per-
formed at higher temperatures and pressures.
Acknowledgements
Financial assistance by the DBT-PAN IIT Centre for Bioenergy (BT/
EB/PANIIT/2012) is gratefully acknowledged.
Keywords: chemoselectivity
nanoparticles · palladium
·
clays
·
hydrogenation
·
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[3] For selected examples see: a) P. Kumar, R. V. Jasra, T. S. G. Bhat, Ind. Eng.
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[4] a) S. Nishimura, Handbook of Heterogeneous Catalytic Hydrogenation for
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F. Dobert, J. Gaube, Handbook of Heterogeneous Catalysis (Eds.: G. Ertl,
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Experimental Section
Materials
Natural montmorillonite clay was procured from a local source in
Rajasthan, India.[3b] Squalene (98%), palladium nitrate hydrate
(99.9%), and nickel nitrate hexahydrate (98%) were purchased
from Alfa Aesar. Chloroplatinic acid hexahydrate was purchased
from Sigma–Aldrich. Nitric acid was received from Fisher Scientific.
Preparation of the catalysts
The clay was successively treated with 1n HNO3 and 1n NH4OH
for 12 h each at RT. The resulting clay was washed thoroughly with
deionized water and was dried overnight in an oven at 1208C to
be used as the solid support. Metals were incorporated by using
the wet impregnation method.
[7] Squalane; Merck Index, 14th ed., Merck & Co. Inc: Whitehouse Station,
NJ, 2012.
[8] a) F. Laserson, T. M. Neossance, Expression CosmØtique 2013, 325; b) A.
Kaiya, T. Nakamura, H. Wada, US6165481A, 2000.
[9] a) E. ValØry, D. Guillaume, K. Surla, P. Galtier, J. Verstraete, D. Schweich,
A solution of the metal salt in 3n HNO3 (10 mL) was added to the
clay (1 g), and the mixture was dried at 1208C with stirring. The
powdered material was calcined at 5008C for 5 h under a nitrogen
atmosphere, which was followed by reduction of the metal at
3008C for 3 h under a hydrogen atmosphere. This afforded the cat-
alyst with a metal loading of approximately 6 wt%.
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