S.-H. Ahn et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 55–60
59
Augustine catalyst appeared to correspond with the high tem-
perature peak of its associated NH3 TPD diagram (Fig. 3). On the
other hand, no strong acid sites formed from PTA on the Augustine
catalyst due to degradation of Keggin structure of PTA during its
adsorption in ethanol solvent.
Of these strong PTA acid sites, the sites uncovered by the Ru
complex might have behaved as additional sites for MAA hydro-
genation as the acid was added to the reaction mixture, as described
previously by Wolfson[14], who demonstrated the enhanced rate
and enantioselectivity of asymmetric hydrogenation of MAA. The
formation of EHB from the reaction (3% yield) also supported this
conclusion. It was previously reported [15] that EHB is produced by
transesterification during the hydrogenation of -ketoesters with
added acid. Therefore, the acid sites on the catalysts prepared by the
modified Augustine method likely produced the transesterification
product EHB.
(
d)
(
c)
(
b)
(
a)
5
10
15
20
25
30
35
40
45
50
2
θ(degrees)
It may also be possible that the electronic state of the Ru metal
adsorbed over strongly acidic PTA might have been changed due to
the higher electron withdrawing power of PTA, which could have
led to the increased activity and selectivity of the modified Augus-
tine catalyst. In support of this possibility, Augustine reported that
there is direct interaction between HPA and the metal atoms of
organometallic complexes, which results in an enhancement of
catalytic reactivity [9].
Fig. 5. XRD patterns of (a) pure Al2O3, (b) PTA/Al2O3 prepared by Augustine method,
c) PTA/Al2O3 prepared by modified Augustine method, and (d) PTA.
(
W Ot (983 cm−1), W Oc W (898 cm ), W Oe W (797 cm ))
−1
−1
−
1
are clearly identifiable in addition to the alumina peak (1650 cm ).
On the other hand, absorption peak at 1080 cm was only observed
in the spectrum of PTA/Al O prepared by Augustine method, while
−
1
2
3
the other peaks were broad. These observations were in agreement
with a previous report [16] showing that Keggin structures are pre-
served by impregnation of PTA on alumina in a 0.5 M HCl aqueous
solution, whereas they are degraded by impregnation in EtOH.
Differences in the properties of the PTA immobilized supports
were also evaluated using XRD patterns. Fig. 5 shows the XRD pat-
4
. Conclusions
In this work, we attempted to prepare Ru-BINAP catalysts by the
well-known Augustine method of immobilization using PTA as the
anchoring agent. The catalyst was then applied to high-pressure
reactions of -ketoester hydrogenation. We also developed a mod-
ified Augustine method employing HCl as the impregnating solvent
instead of ethanol. With respect to asymmetric hydrogenation of
terns of modified Al O3 and pure Al O . The XRD pattern of the
2
2
3
PTA/Al O prepared by Augustine method (b) was similar to that
2
3
◦
of alumina (a) except for a broad peak at 3–7 , whereas in the case
of the PTA/Al O prepared by modified Augustine method (c), sharp
2
3

-ketoesters, the overall catalytic activities of the modified Augus-
◦
XRD peaks corresponding to crystalline PTA were observed at 6–9 .
It was apparent that the Keggin structure was better maintained
during impregnation of PTA in 0.5 M HCl (modified Augustine
method) than in EtOH (Augustine method). It is well known that
PTA with a Keggin structure behaves as a strong Bröensted acid
tine catalysts were superior to those of the Augustine catalysts and
were similar to those of the homogeneous catalyst. NH -TPD anal-
3
ysis of the modified Augustine catalyst revealed the presence of
a significant number of strong acid sites when compared to the
Augustine catalyst. The FT-IR spectra of the PTA/alumina of the
modified Augustine catalyst showed that the Keggin structure of
PTA remained intact during impregnation, which was also con-
firmed by XRD. The strong acid sites formed by HPA with Keggin
structure on the modified Augustine catalyst appeared to enhance
the rate and enantioselectivity of asymmetric hydrogenation of
[
18]. Therefore, the additional acidities of the modified Augustine
catalyst appeared to be related to PTA with well-preserved Keggin
structure.
3.3. Evaluation of enhanced performance of modified Augustine
catalysts

-ketoesters through formation of additional active sites or an elec-
tronic effect on Ru metal. Furthermore, these results showed that
the modified Augustine method was efficient for preparing active
supported metal catalysts for high-pressure reaction of asymmetric
hydrogenation of -ketoesters.
Based on the results shown above, the improved activity and
selectivity of the modified Augustine catalysts was considered to
be due to the strong acid sites of PTA. Specifically, acid sites on
the surface of the modified Augustine catalyst were thought to
be formed as follows. In preparing the modified Augustine cata-
lyst, PTA dissolved in HCl solution was impregnated on alumina
and the recovered PTA/alumina powder was subsequently impreg-
nated with Ru-BINAP in EtOH. Therefore, various kinds of acid sites
could have been formed including adsorbed PTA and HCl on the
support of the modified Augustine catalyst. PTA is known to adsorb
on Al O very strongly due to electrostatic interactions between
References
[1] E.I. Klabunovskii, R.A. Sheldon, CatTech 2 (1997) 153–160.
[2] T. Osawa, T. Harada, A. Tai, Catal. Today 37 (1997) 465–480.
[3] D.E. De Vos, I.F.J. Vankelecom, P.A. Jacobs (Eds.), Chiral Catalyst Immobilization
and Recycling, Wiley-VCH, Weinheim, 2000, p. 123.
[4] C.E. Song, S.-g. Lee, Chem. Rev. 102 (2002) 3495–3524.
2
3
[
[
5] A. Zsigmond, I. Balatoni, K. Bogar, F. Notheisz, F. Joo, J. Catal. 227 (2004) 428–435.
6] R. Augustine, S. Tanielyan, S. Anderson, H. Yang, Chem. Commun. (Camb.)
(1999) 1257–1258.
acidic proton-Keggin polyanions and pairs of basic-Lewis acid sites
on Al O as suggested by Rao et al. [17]. Thus, PTA could have
2
3
remained intact on the surface even after metal deposition, to form
acid sites on alumina. HCl was also thought to weakly adsorb on
alumina, but was likely washed out by EtOH during the washing
step following deposition of the metal complex.
During the adsorption step in HCl solution, strong acid sites of
PTA with definite Keggin structure may have formed on the mod-
ified Augustine catalyst. These strong acid sites on the modified
[7] R.L. Augustine, S.K. Tanielyan, S. Anderson, H. Yang, Y. Gao, Chem. Ind. (Dekker)
2 (2000) 497–508.
8
[
[
8] J.A.M. Brandts, P.H. Berben, Org. Proc. Res. Dev. 7 (2003) 393–398.
9] R.L. Augustine, S.K. Tanielyan, N. Mahata, Y. Gao, A. Zsigmond, H. Yang, Appl.
Catal. A 256 (2003) 69–76.
[
[
[
10] R. Augustine, Spec. Chem. Mag. (April) (2004) 19–21.
11] J.A.M. Brandts, J. Donkervoort, Spec. Chem. Mag. 24 (2004) 26–27.
12] C.F.J. Barnard, J. Rouzaud, S.H. Stevenson, Org. Proc. Res. Dev. 9 (2005) 164–167.
[13] S.H. Ahn, Y.H. Park, P.A. Jacobs, Stud. Surf. Sci. Catal. 159 (2006) 349–352.