specific rates of HMF hydrogenation (ESI,† Table 6). Pd showed
the highest rate of HMF hydrogenation relative to Pt and Ru.
This behavior can be detrimental to the overall production of
DHMTHF if the rate of DHMF hydrogenation is slow and
permits time for this reactive intermediate to undergo degra-
dation reactions. The relative rates of DHMF hydrogenation were
estimated using furfuryl alcohol (FA) hydrogenation as a model
reaction. Indeed, Ru showed a faster rate than Pd for FA hydro-
genation. Accordingly, the overall selectivity to DHMTHF is
dependent on both the rates of hydrogenation as well as solution
acidity.
4. Conclusions
Fig. 8 HMF hydrogenation over Vulcan supported Ru, Pd, or Pt at
various time points. Feed was purified with 1.5 g Amberlite IRA-400
(OH) before reaction. Products observed DHMF (black), DHMTHF
(white), polyols (grey), and unidentified products (striped).
The selectivity for hydrogenation of HMF to DHMTHF is
affected by the acidity of the aqueous solution containing HMF.
In particular, the selectivity to DHMTHF decreases when acidic
impurities (for example levulinic acid, an HMF degradation
product) are present in the reaction mixture, or when metal
oxides with low-isoelectric point are used as supports for Ru
hydrogenation catalysts. The primary by-products observed are
1,2,5-HT, 1,2,5,6-HT, and 1,2,6-HT. These molecules appear to
be formed by the hydrogenation of acid-catalyzed degradation
products of dihydroxymethylfuran (DHMF). Importantly, high
selectivities to DHMTHF can be achieved when the hydrogen-
ation catalyst is comprised of ruthenium deposited on a support
with a high isoelectric point oxide (e.g., ceria).
3.4 Effect of metal catalyst
Studies were conducted to probe how the selectivity for hydro-
genation of HMF is affected by changing the nature of the metal
component of the hydrogenation catalyst. All catalysts were
studied using a biphasic system of water and 1-butanol, and the
feed was contacted with Amberlite IRA-400(OH) before reaction
to eliminate the effect of impurities in solution. The results are
shown in Fig. 8. Using either palladium or platinum as the cata-
lyst, the majority of the HMF was converted to unidentified pro-
ducts except when using higher loading of Pd. The HPLC
spectra of the product mixture did not reveal any significant
peaks, which may indicate that the undetected carbon is in the
form of insoluble polymers. These polymers may be formed
through the loss of formaldehyde from DHMF, followed by fur-
furyl alcohol polymerization, which is well known in the litera-
ture.18,19 As evidence for this chemistry, we have detected the
formation of formaldehyde dibutyl acetal (which was identified
by GC/MS) when reacting DHMF in butanol under acidic
conditions.
Acknowledgements
This work was supported by the NSF under the auspices of the
Center for Enabling New Technolgies through Catalysis
(CENTC).
References
1 B. F. M. Kuster, Starch, 1990, 42, 314–321.
2 J. N. Chheda, Y. Roman-Leshkov and J. A. Dumesic, Green Chem.,
2007, 9, 342–350.
After a reaction time of 2 hours, DHMF was observed from
the hydrogenation of HMF when using palladium and platinum
as catalysts, whereas DHMF had been fully consumed when
using ruthenium, indicating that at the same weight loading pal-
ladium and platinum catalysts were less active compared to the
ruthenium catalyst (at least in terms of DHMF hydrogenation).
As was seen in Table 1 when using a lower loading of Ru/
Vulcan, a decrease in rate of hydrogenation is accompanied by a
decrease in selectivity due to an increased relative rate of degra-
dation reactions in solution. This behavior is consistent with an
increased yield of unidentified products when using both a lower
amount and/or weight loading of Ru/Vulcan or when using Pd/
Vulcan or Pt/Vulcan.
The irreversible uptake of CO was measured for each catalyst
(ESI,† Table 6) to calculate metal dispersion and particle size. Pt
is known to catalyze both hydrogenation and C–C scission reac-
tions during aqueous phase reforming, which can account for the
lower selectivity to DHMTHF using Pt.20,21 To probe the differ-
ence between Ru and Pd, HMF hydrogenation was studied using
low catalyst amounts (50 mg) and low reaction times to calculate
3 Y. Roman-Leshkov, J. N. Cheda and J. A. Dumesic, Science, 2006, 312,
1933–1937.
4 A. J. Sanborn and P. D. Bloom, US Pat. 7579490, 2008.
5 C. Moreau, M. N. Belgacem and A. Gandini, Top. Catal., 2004, 27, 11–
30.
6 T. J. Connolly, J. L. Considine, Z. Ding, B. Forsatz, M. N. Jennings, M.
F. MacEwan, K. M. McCoy, D. W. Place, A. Sharma and K. Sutherland,
Org. Process Res. Dev., 2010, 14, 459–465.
7 T. Buntara, S. Noel, P. H. Phua, I. Melián-Cabrera, J. G. de Vries and H.
J. Heeres, Angew. Chem., Int. Ed., 2011, 50, 7083–7087.
8 M. Chia, Y. J. Pagan-Torres, D. Hibbitts, Q. Tan, H. N. Pham, A.
K. Datye, M. Neurock, R. J. Davis and J. A. Dumesic, J. Am. Chem.
Soc., 2011.
9 M. Faber, US Pat. 4400498, 1983.
10 S. Koso, N. Ueda, Y. Shinmi, K. Okumura, T. Kizuka and K. Tomishige,
J. Catal., 2009, 267, 89–92.
11 Y. Nakagawa and K. Tomishige, Catal. Commun., 2010, 12, 154–156.
12 J. D. Garber, US Pat. 3025307, 1962.
13 V. Schiavo, G. Descotes and J. Mentech, Bull. Soc. Chim. Fr., 1991, 128,
704–711.
14 E. I. Gürbüz, E. L. Kunkes and J. A. Dumesic, Appl. Catal., B, 2010, 94,
134–141.
15 M. A. Aramendía, V. Boráu, C. Jiménez, A. Marinas, J. M. Marinas, J.
A. Navío, J. R. Ruiz and F. J. Urbano, Colloids Surf., A, 2004, 234, 17–
25.
1418 | Green Chem., 2012, 14, 1413–1419
This journal is © The Royal Society of Chemistry 2012