Glycerol Hydrogenolysis promoted by Supported Palladium Catalysts
PdZn, PdNi, PdCoI and PdFeI catalysts, confirming that it is an
intermediate in glycerol hydrogenolysis. Finally, the best per-
forming samples (PdCo and PdFe) were tested on a large-scale
reaction at a higher H2 pressure (4 MPa). In addition, after sev-
eral recycles, PdCo appeared to be an efficient catalyst suitable
for use on an industrial scale.
were performed on samples reduced at 473 K for 2 h and regis-
tered in the 2q range of 10–808 at a scan speed of 0.58 minÀ1. Dif-
fraction peaks were compared with those of standard compounds
reported in the JPCDS Data File. XPS analysis was performed on re-
duced, at 473 K for 2 h, samples, by using a Physical Electronics
GMBH PHI 5800-01 spectrometer, equipped with a monochromatic
AlKa X-ray source. The binding energy was calibrated by taking the
C 1s peak (284.6 eV) as a reference.
Catalytic activity measurements: Glycerol hydrogenolysis was car-
ried out in a 250 mL stainless-steel batch reactor (Parr instrument)
equipped with an electronic temperature controller and a magnet-
ic stirrer. The reaction was normally conducted at 453 K, 0.5 MPa of
initial hydrogen pressure, with the catalyst (0.600 g) in dioxane or
2-propanol (50 mL) and added to a solution of glycerol (25 mL;
12 wt%), for 24 h, using a 500 rpm stirring speed (initial molar
ratio H2/glycerol ffi1.6). The reaction sequence was as follows:
Once the reactor was loaded as reported above, it was heated at
the reaction temperature and set aside for the time established.
Then, the system was cooled and, when at room temperature, the
liquid was analyzed. Product analysis was performed with a gas
chromatograph (HP model 5890) equipped with a wide bore capil-
larity column (CP-WAX 52CB, 50 m, inner diameter 0.53 mm) and a
flame ionization detector. When the experiments were carried out
using a higher amount of glycerol (45 wt%, 50 mL isopropanol),
0.900 g of catalyst and a higher pressure (4 MPa) were used (initial
molar ratio of H2/glycerol ffi1). The conversion and selectivity of
glycerol were calculated on the basis of Equations (1) and (2):
Experimental Section
Catalyst preparation: Supported palladium catalysts were obtained
by using two different techniques: coprecipitation and impregna-
tion. Catalysts prepared by using the coprecipitation technique,
with a nominal palladium loading of 5 wt%, were obtained from
aqueous solutions of the corresponding inorganic precursors. An-
hydrous palladium chloride (Fluka, purum, 60% palladium) was dis-
solved in HCl and cobalt(II) nitrate hexahydrate (Fluka, purity
ꢁ99%), nickel(II) nitrate hexahydrate (Aldrich, purity 98%), zinc(II)
nitrate hexahydrate (Aldrich, purity 98%), and iron(III) nitrate nona-
hydrate (Fluka, purity ꢁ98%) were added. The obtained aqueous
metal salt solutions were added dropwise into a 1m aqueous solu-
tion of Na2CO3. After filtration and washing until chloride was re-
moved, samples were dried for 1 day under vacuum at 353 K and
further reduced at 473 K for 2 h under a flow of hydrogen. In the
Pd/CoO specimen, the formation of small cobalt particles made it
unstable when exposed to air. Therefore, after the reduction treat-
ment, contact with air was avoided as good as possible.
Nominal 5% Pd/CoO and Pd/Fe2O3 were also prepared by incipient
wetness impregnation of the commercial supports CoO (Aldrich,
S
lution of palladium(II) acetylacetonate (Aldrich, purity 99%) in ace-
tone. After impregnation, the samples were dried for 1 day under
vacuum at 353 K and further reduced at 473 K for 2 h under a flow
of hydrogen.
moles of reacted glycerol
moles of glycerol feed
ð1Þ
ð2Þ
glycerol conversion ½% ¼
glycerol selectivity ½% ¼
 100
BET =7 m2 gÀ1) and Fe2O3 (Sigma–Aldrich, SBET =4 m2 gÀ1) with a so-
moles of defined product
moles of reacted glycerol
 100
Catalysts characterization: BET surface areas were determined by
using N2 adsorption–desorption isotherms at liquid nitrogen tem-
perature using a Micromeritics Chemisorb 2750 instrument. The
composition of the flow of gas was N2/He=30:70. Samples were
outgassed under a flow of nitrogen for 1 h at 473 K before meas-
urements were taken. The catalyst particle sizes and relative mor-
phologies were analyzed by performing TEM measurements using
a JEOL 2000 FX instrument operating at 200 kV and directly inter-
faced with a computer for real-time image processing. The speci-
mens were prepared by grinding the reduced catalyst powder in
an agate mortar and then suspending it in isopropanol. A drop of
the suspension, previously dispersed in an ultrasonic bath, was de-
posited on a copper grid coated by a holey carbon film. After
evaporation of the solvent, the specimens were introduced into
the microscope column. Particle size distributions were obtained
by counting several hundred particles visible on the micrographs
on each sample. From the size distribution, the number average di-
ameter was calculated: dn =ꢀnidi/ni in which ni is the number of
particles of diameter di. TPR measurements were performed by
using a conventional TPR apparatus. The dried samples (50 mg)
were heated at a linear rate of 10 KminÀ1 from 298 to 1273 K in a
5 vol% of H2/Ar mixture at a flow rate of 20 cm3 minÀ1. H2 con-
sumption was monitored by using a thermal conductivity detector
(TCD). A molecular sieve cold trap (maintained at 193 K) and a
tube filled with KOH, placed before the TCD, were used to block
water and CO2, respectively. The calibration of signals was done by
injecting a known amount of H2 into the carrier. XRD data were ac-
quired at room temperature on a Philips X-Pert diffractometer by
using the Ni b-filtered CuKa radiation (l=0.15418 nm). Analyses
Keywords: glycerol
hydrogenolysis · palladium · sustainable chemistry
·
heterogeneous
catalysis
·
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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