DOI: 10.1002/cctc.201403005
Full Papers
Continuous Transfer Hydrogenation of Sugars to Alditols
with Bioderived Donors over Cu–Ni–Al Catalysts
David Scholz, Christof Aellig, Cecilia Mondelli, and Javier Pꢀrez-Ramꢁrez*[a]
The transfer hydrogenation of sugars to alditols with biobased
alcohol donors was studied over hydrotalcite-derived
Cu6ÀxNixAl2 catalysts prepared by coprecipitation at different
pH and featuring variable Cu/Ni ratios. Their evaluation, after
in situ activation in pure H2 at 773 K, in the ethanol-assisted
upgrading of glucose in a continuous-flow fixed-bed reactor
identified the solid synthesized at pH 9–10 and with Cu/Ni=
1 as the best performer. Based on textural, structural, and
redox analyses, this is related to an enhanced intermetallic in-
teraction. Upon screening alternative donors, a sorbitol yield as
high as 67% was achieved with 1,4-butanediol. The catalytic
system displayed a stable behavior during 48 h on stream and
proved suitable to hydrogenate also fructose, mannose, xylose,
and arabinose to the corresponding polyols (yields up to
65%), thus standing as a more sustainable and economical al-
ternative to Ru-based catalysts for sugar reductive upgrading.
Introduction
In the last two decades, the conversion of biobased feedstocks
into commodity and platform chemicals has become a central
area of research across multiple scientific disciplines.[1] Among
the routes explored to transform (hemi)cellulose-derived C5
and C6 sugars,[2] reductive upgrading has recently gained in-
creasing attention. This technology not only allows enhancing
the stability of saccharide feedstocks in view of further proc-
essing along alternative value chains but also leads to industri-
ally relevant products. Indeed, the polyols obtained from hexo-
ses and pentoses find wide application in the food, pharma-
ceutical, cosmetic, and polymer sectors.[3] Specifically, sorbitol,
xylitol, and arabinitol, that is, the hydrogenation products of
glucose, xylose, and arabinose, respectively, have been includ-
ed by the US Department of Energy within the 12 top added-
value chemicals that can be attained from biomass.[4]
strated in various works,[13] of using a hydrotalcite precursor for
attaining high dispersion and excellent metal interaction and
thus generating efficient multimetallic hydrogenation catalysts.
Still, in spite of the promising sorbitol yield, the stability of this
material was not evaluated.
The use of a hydrogen donor instead of molecular hydrogen
can be instrumental in view of developing a more industrially
viable hydrogenation process. This would circumvent safety-re-
lated issues, for example, storage and handling of pressurized
hazardous gases, and alleviate the environmental footprint,
that is, saving of the energy required for H2 production, espe-
cially if not obtained from renewable sources. So far, transfer
hydrogenation has been attempted only using furfural as the
substrate in the presence of formic acid[14] or alcohols.[15]
Whereas the former donor has shown to undermine the stabili-
ty of catalytic materials owing to its corrosiveness and reduce
the efficiency of the transformation through decomposition
with the concomitant formation of CO2, alcohols have the ad-
vantage to be largely available biobased substrates. Besides,
they form upon dehydrogenation carbonyl compounds that
can serve as feedstock or auxiliary chemical for the preparation
of valuable products.
The reduction of glucose and xylose has been studied over
Ni,[5,6] Ru,[7,8] Co,[6,9] Pd,[6] and Pt[10,11] catalysts. Ru-containing
systems have displayed the best performance, reaching almost
100 and 98% sorbitol and xylitol yields in batch mode, respec-
tively, and being recyclable in successive runs. Nevertheless,
the high market price of ruthenium represents a hurdle for
a prospective large-scale implementation of these solids. Con-
sidering more economical metals, catalysts such as Raney-Ni
have a limited industrial scope because metal leaching strong-
ly impacts their lifetime.[5e] Recently, Zhang et al.[12] reported
that a ternary Cu–Ni–Al catalyst achieved a sorbitol selectivity
of 93% at a glucose conversion of 73% after 3 h at 393 K and
30 bar H2. This result highlights the benefits, already demon-
Herein, we explored the application of hydrotalcite-derived
Cu–Ni–Al catalysts for the transfer hydrogenation of glucose in
the presence of ethanol using a continuous-flow fixed-bed re-
actor. An optimal catalytic system was attained identifying the
most adequate coprecipitation pH and the relative amount of
copper and nickel in the solid, and selecting suitable reaction
conditions in terms of temperature and contact time. There-
after, other biobased alcohols such as methanol, 1,4-butane-
diol, and glycerol were evaluated as hydrogen donors and the
stability of the catalyst assessed in a prolonged catalytic run.
Finally, the technology developed was extrapolated to the
transfer hydrogenation of other relevant sugars substrates, in-
cluding fructose, xylose, mannose, and arabinose.
[a] D. Scholz,+ Dr. C. Aellig,+ Dr. C. Mondelli, Prof. J. Pꢀrez-Ramꢁrez
Institute for Chemical and Bioengineering, ETH Zurich
Vladimir-Prelog-Weg 1, 8093 Zurich (Switzerland)
[+] These authors contributed equally to this work.
ChemCatChem 0000, 00, 0 – 0
1
ꢂ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ