DOI: 10.1002/cssc.201500722
Communications
Deuterium-Labeling Study of the Hydrogenation of 2-
Methylfuran and 2,5-Dimethylfuran over Carbon-
Supported Noble Metal Catalysts
Jungshik Kang,[a] Anne Vonderheide,[b] and Vadim V. Guliants*[a]
2-Methylfuran and 2,5-dimethylfuran were deuterated over Pd
and Pt catalysts at 90–2208C. Furan ring saturation over a Pd/C
catalyst occurred at low reaction temperatures, which led to
deuterated THFs, followed by progressive D exchange in the
THF ring at higher temperatures. Finally, H/D exchange oc-
curred in the methyl groups on the THF ring. Cleavage of the
CÀO bond also occurred over a Pd/C catalyst at elevated tem-
peratures, which resulted in deuterated ketones, for which all
H atoms were exchanged for D. Alcohols were produced over
a Pt/C catalyst at low temperatures because they are more
stable than the corresponding ketones. D replaced H on all
carbon atoms of the furan ring and saturated the O and C
atoms of the broken CÀO bond in both deuterated 2-pentanol
and 2-hexanol. At low temperatures (90–1058C), all H atoms in
the deuterated alcohols were exchanged for D except for the
last two hydrogen atoms on the methyl groups.
Further upgrading of these substituted furans to valuable
chemicals involves hydrogenation of the aromatic furan ring
and its opening by hydrogenolysis, which typically result in
mixtures of substituted tetrahydrofurans (THFs), ketones, and
alcohols.[5] Although the highly selective hydrogenation of 5-
hydroxymethylfurfural to 2,5-dimethylfuran and furfural to 2-
methylfuran has been reported,[6] improving the selectivity of
the 2,5-dimethylfuran and 2-methylfuran hydrogenation and
hydrogenolysis reactions is crucial for producing the desired
products in high yields. Moreover, whereas many studies
report Pt and Pd to be highly promising catalysts for these re-
actions,[7] the current understanding of the hydrogenation
pathways of 2-methylfuran and 2,5-dimethylfuran are still
rather limited.
In this study, the hydrogenation pathways of 2-methylfuran
and 2,5-dimethylfuran over two carbon-supported Pt and Pd
catalysts were investigated by using D2- and D-labeled prod-
ucts analyzed by GC–MS by employing chemical ionization.
Deuterium labeling is frequently used in the chemical sciences
to elucidate reaction pathways,[8] whereas MS can distinguish
deuterated diastereomers by means of rearrangements involv-
ing five- and six-membered cyclic transition states.[9] Moreover,
chemical ionization used in MS largely preserves the parent
molecular ions and, therefore, is particularly promising for the
identification of D-labeled molecules in complex product mix-
tures.[10]
The catalytic transformations of biomass into fuels and value-
added chemicals have received considerable attention in the
past decade as green alternatives to the petrochemical pro-
cesses. From an environmental standpoint, such processes
based on renewable feedstocks result in lower carbon dioxide
emissions, which contribute to global warming.[1] For instance,
substituted furans and their derivatives are important chemical
intermediates derived from biomass that can be hydrogenated
into a variety of specialty chemicals, solvents, and alternative
fuels.[2] In particular, two hemicellulose- and cellulose-derived
molecules, 2-methylfuran and 2,5-dimethylfuran, have highly
promising physical and chemical properties for applications as
alternative fuels.[3] They possess energy densities of 31.2 and
32.9 MJkgÀ1, respectively, which are approximately 40% great-
er than the energy density of ethanol; furthermore, they pos-
sess high research octane numbers of 103 and 101, respective-
ly.[4]
THFs, alcohols, and ketones were observed over Pt/C and
Pd/C catalysts under different reaction conditions (Tables 1 and
2). The main differences in the catalytic behavior between the
Pd and Pt catalysts were observed at low temperatures. The
hydrogenation of 2-methylfuran and 2,5-dimethylfuran over
the Pd/C catalyst at low reaction temperatures resulted in ring
saturation and formation of THFs, whereas linear alcohols were
Table 1. Product yields during the hydrogenation of 2,5-dimethylfuran.[a]
Catalyst Temperature
Yield [mol%]
2,5-dimethyltetra- 2-hexanone 2-hexanol others
hydrofuran
[8C]
[a] Dr. J. Kang, Prof. V. V. Guliants
Department of Biomedical, Chemical, and Environmental Engineering
University of Cincinnati
Cincinnati, OH 45221-0012 (USA)
Pt/C
95
105
130
220
95
125
150
220
82.3
50.1
37.1
13.5
100
100
98.6
41.3
9
35.5
43.8
70.2
0
0
0
45
8.7
14.4
19.1
2.1
0
0
0
0
0
0
0
14.2
0
0
[b] Dr. A. Vonderheide
Pd/C
Department of Chemistry
University of Cincinnati
Cincinnati, OH 45221-0037 (USA)
1.4
13.8
Supporting Information (experimental details) for this article is available
[a] The conversion of 2,5-dimethylfuran was 100% in all cases.
ChemSusChem 2015, 8, 3044 – 3047
3044
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim