Table 1 Hydrogenation of carboxylic acids under the reaction conditions in Fig. 1
Selectivity (%)
aAcid conv. (%)
Alcohol
Alkanes
Substrate
Catalyst metal/TiO2
Time/h
Octadecanoic acid
Hexadecanoic acid
Tetradecanoic acid
Decanoic acid
Cyclohexanecarboxylic acid
3-Cyclohexylpropanoic acid
Octadecanoic acid
Hexadecanoic acid
Tetradecanoic acid
4%Pt
4%Pt
4%Pt
4%Pt
4%Pt
4%Pt
4%Pt–4%Re
4%Pt–4%Re
4%Pt–4%Re
4%Pt–4%Re
4%Pt–4%Re
4%Pt–4%Re
12
14
6
8
6
18
2.5
2.5
3
4
1
82
79
83
79
80
80
86
84
83
79
84
85
93
90
91
90
88
8
67
61
90
75
70
6
7
10
9
10
12
92
33
39
10
25
30
94
Decanoic acid
Cyclohexanecarboxylic acid
3-Cyclohexylpropanoic acid
3
a
Using 4%Pt–4%Re/TiO2, all reactions went to completion in o5h, while using 4%Pt/TiO2 all reactions went to completion in o20 h.
the Pt–Re/TiO2 catalysts were found to have a significantly
reduced selectivity towards the respective alcohol compared
with the monometallic Pt/TiO2 catalyst.
under nitrogen atmosphere. The liquid phase hydrogenation
methodology reported here shows a huge potential for such
difficult hydrogenations under safer and more economical
reaction conditions.
The reusability of 4%Pt/TiO2 and 4%Pt–4%Re/TiO2
catalysts was studied with the recovered catalyst regenerated
by washing with acetone followed by an in situ pre-reduction
in H2 at 393 K for 1 h and then the hydrogenation of stearic
acid repeated. The regenerated 4%Pt/TiO2 catalyst showed
good reusability with similar reaction rates and the selectivity
towards stearyl alcohol on the recycle (ESIw). In contrast, the
regenerated 4%Pt–4%Re/TiO2 catalyst showed loss in the
hydrogenation activity with an associated decrease in reaction
rate. A further loss in the hydrogenation activity was observed
on recycling the catalyst for a second time. However, the
selectivity towards stearyl alcohol remained constant on recycle
(ESIw). Some of the decrease in activity is likely to be due to
the presence of strongly adsorbed carbonaceous residue on the
catalyst. The temperature programmed oxidation profile of
the spent catalyst showed a broad peak located at 140–370 1C
and calcination of the catalyst at 773 K and then pre-reduction
in H2 at 393 K did lead to some recovery of the activity but not
to the rate of the fresh catalyst (ESIw). N2 sorption analysis of
fresh and recovered 4%Pt–4%Re/TiO2 catalysts did not show
any pore blocking or reduction of the surface area and ICP
results showed that the leaching of the active metal was below
1 ppm. Therefore, it is most likely that the majority of the
deactivation is due to a loss of the interaction between the Re
and Pt. It should be noted that since the selectivity does not
change on recycle, it is unlikely that complete loss of contact
between the Re and Pt occurs as this would lead to an increase
in the selectivity for stearyl alcohol.
The authors would like to thank the EPSRC and Johnson
Matthey for funding this work under the CASTech project.
RP acknowledges studentship funding from Petronas.
Notes and references
1 E. Ucciani, in Heterogeneous Catalysis and Fine Chemicals, ed.
M. Guisnet, J. Barrault, C. Bouchoule, D. Duprez, C. Montassier
and G. Perot, Elsevier, Amsterdam, 1988, p. 33.
´
2 L. H. Tan Tai and V. Nardello-Rataj, in Handbook of detergents
part E: Applications, ed. U. Zoller, CRC press, Taylor and Francis
group, Boca Raton, 2009, p. 110.
3 J. L. Hargrove, P. Greenspan and D. K. Hartle, Exp. Biol. Med.,
2004, 229, 215.
4 S. Gupta, Dynamics of the Global Fatty Alcohol Market, Frost and
Sullivan Market Insight, 2004.
5 J. Pohl, F.-J. Carduck and G. Goebel, U.S. Patent, 4935556, 1990.
6 T. Turek and D. L. Trimm, Catal. Rev. Sci. Eng., 1994, 36, 645.
7 (a) J. E. Carnahan, T. A. Ford, W. S. Gresham, W. E. Grisby and
G. F. Hager, J. Am. Chem. Soc., 1955, 77, 3766; (b) K. Toshiyuki
and H. Tadao, Nippon Kagakkai Koen Yokoshu, 1998, 75, 260;
(c) W. Schrauth, O. Schenck and K. Stickdorn, Ber. Dtsch. Chem.
Ges. B, 1931, 64, 1314; (d) A. Guver, A. Bieler and K. Jabere, Helv.
Chim. Acta, 1947, 30, 39; (e) H. S. Broadbent, G. C. Campbell,
W. J. Martley and J. H. Johnson, J. Org. Chem., 1959, 24, 1847;
(f) M. Toba, S.-i. Tanaka, S.-i. Niwa, F. Mizukamia, Z. Koppany,
´
L. Guczi, K.-Y. Cheah and T.-S. Tang, Appl. Catal., A, 1999, 189,
243; (g) D.-H. He, N. Wakasa and T. Fuchikami, Tetrahedron
Lett., 1995, 36(7), 1059.
8 (a) H. G. Manyar, D. Weber, H. Daly, J. M. Thompson,
D. W. Rooney, L. F. Gladden, E. H. Stitt, J. J. Delgado,
S. Bernal and C. Hardacre, J. Catal., 2009, 265, 80;
(b) L. McLaughlin, E. Novakova, R. Burch and C. Hardacre,
Appl. Catal., A, 2008, 340, 162; (c) E. Novakova, L. McLaughlin,
R. Burch, P. Crawford, K. Griffin, C. Hardacre, P. Hu and
D. W. Rooney, J. Catal., 2007, 249, 93; (d) K. Anderson,
P. Goodrich, C. Hardacre and D. W. Rooney, Green Chem.,
2003, 5, 448.
9 R. Pestman, R. M. Koster, J. A. Z. Pieterse and V. Ponec,
J. Catal., 1997, 168, 255.
10 M. Watanabe, T. Iida and H. Inomata, Energy Convers. Manage.,
2006, 47, 3344.
Pt and Pt–Re supported on titania catalysts have shown
excellent activity for the reduction of various carboxylic acids
under low hydrogen pressures and reaction temperature com-
pared with that for previously reported catalysts. In particular,
the monometallic 4%Pt/TiO2 demonstrates excellent selecti-
vity towards corresponding alcohols. The reaction condi-
tions can also be successfully tuned with 100% selectivity
to obtain alkanes by decarboxylation of carboxylic acids
11 M. J. Mendes, O. A. A. Santos, E. Jordao and A. M. Silva, Appl.
Catal., A, 2001, 217, 253.
c
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 6279–6281 6281