COMMUNICATION
www.rsc.org/greenchem | Green Chemistry
Selective transfer hydrogenolysis of glycerol promoted by palladium
catalysts in absence of hydrogen
a
a
b
a
Maria Grazia Musolino, Luciano Antonio Scarpino, Francesco Mauriello and Rosario Pietropaolo*
Received 4th June 2009, Accepted 31st July 2009
First published as an Advance Article on the web 11th August 2009
DOI: 10.1039/b915745j
◦
Selective conversion of glycerol into 1,2-propanediol in the
presence of a Pd/Fe catalyst, under inert atmosphere, is
reported for the first time; the hydrogen necessary for the
hydrogenolysis reaction derives from the dehydrogenation
of the solvent (2-propanol or ethanol), promoted by sup-
ported palladium, itself reduced “in situ” by alcohols.
then precipitated by adding Na
2
CO and dried at 80 C for
3
2
O
3
1 day. The XRD analysis reveals the amorphous structure of the
catalyst.
The experiments were carried out in an autoclave at 5 bar of
O (600 mg) poured into 50 ml
of ethanol or 2-propanol and 25 ml of an alcoholic solution of
glycerol (12 wt%). After 24 h, 12 h and 8 h of reaction time at
180 C (entries 1, 1¢, 2 and 3, respectively) and at 150 C (entry 4),
the reported results clearly indicate a very high conversion to
1,2-PDO, coupled with a small amount of EG. The other de-
tected products, as expected, mainly were acetaldehyde (derived
from ethanol) or acetone (derived from 2-propanol). Relevant
data of the investigated hydrogenolysis reaction, determined by
GC and GC-MS analysis, are reported in Table 1.
inert atmosphere using PdO/Fe
2
3
◦
◦
Catalytic processes converting biorenewable feedstocks to com-
modities and fuels are actually of large interest for industrial
1
chemical research. Glycerol is widely available from fatty esters
2
and easily obtained, as a byproduct, in biodiesel production.
Selective conversion of glycerol is a clean and economically
competitive process and represents one of the most attractive
routes, allowing formation of different valuable products, such
as 1,2-propanediol (1,2-PDO), 1,3-propanediol (1,3-PDO) or
Carrying out the reaction in 2-propanol, using the same
supported catalyst, previously reduced for 2 h at 200 C with
H , after 8 h and 4 h (entries 5 and 6, respectively) at 5 bar of
inert atmosphere, the results confirm the high yield, in a short
time, to 1,2-PDO.
3,4
◦
ethylene glycol (EG). So far, conventional hydrogenation
catalysts such as nickel, ruthenium and platinum have been used;
however, it seems difficult to obtain high conversion of glycerol
2
3,5
and/or high selectivity to propylene glycol in mild conditions.
On the other hand: (i) transfer hydrogenolysis, from aliphatic
to aromatic alcohols, promoted by nickel raney, is a known
reaction and (ii) oxidated palladium substrates are easily
In order to confirm the reduction reaction involving the
solvent, analogous studies were carried out adding 600 mg of
the catalyst to 50 ml of pure ethanol or 2-propanol at 180 C for
6
◦
reducible substances.
With the aim to take advantage of the peculiar palladium
properties we report, in this communication, on the transfer
24 h, in an inert atmosphere: acetaldehyde or acetone, besides
very small amounts of other products, were formed.
The most interesting peculiarity of the reported results rests
on the evidence that:
hydrogenolysis of glycerol in presence of 2-propanol or ethanol
◦
at 180 C, in an inert atmosphere, using the Pd/Fe
2
3
O catalyst.
The sample was tested both “as prepared” and reduced with
◦
hydrogen at 200 C.
The in situ hydrogen production, obtained by the dehydro-
genation of the reaction solvent, ensures several advantages such
us:
–
costs reduction related to the purchase, transport and
storage of the hydrogen;
use of only one solvent for the entire biodiesel process and
–
for the related chemical valorization of glycerol: ethanol, for
example, constitutes a typical solvent for glycerol and is actually
7–9
used in some innovative biodiesel production cycles.
The nominal 10% palladium catalyst, formulated as
PdO/Fe , was obtained by the co-precipitation technique
2
O
3
2
-
from PdCl
4
and Fe(NO ) , both dissolved in an acid solution,
3
3
a
Dipartimento di Meccanica e Materiali, Universit a` Mediterranea di
Reggio Calabria, loc. Feo di Vito, 89122, Reggio Calabria, Italy.
E-mail: rosario.pietropaolo@unirc.it; Fax: +39 0965 875248;
Tel: +39 0965 875256
Dipartimento di Scienza dei materiali e Ingegneria Chimica, Politecnico
di Torino, Corso Duca degli Abruzzi 24, 10129, Torino, Italy
b
Fig. 1 X-Ray photoemission spectra (Ar ion source) of Pd/Fe O3
catalysts before (full line) and after (dash line) hydrogenolysis reaction.
2
This journal is © The Royal Society of Chemistry 2009
Green Chem., 2009, 11, 1511–1513 | 1511