Hydrogenation of diacetyl over composite-supported egg-shell noble metal catalysts

Article abstract of DOI:10.1007/s11696-017-0161-4

Two composite supports with a mixed inorganic-organic structure were synthesized: BTAl and UTAl. Hydrophilic-hydrophobic dual properties of the supports were suitable for preparing egg-shell-supported metal catalysts for selective hydrogenation reactions. The catalysts were characterized by ICP, XRD, OM, TEM, EPMA, XPS and TGA. Their mechanical resistance was assessed. Activity and selectivity were tested with the hydrogenation of 2,3-butanedione (diacetyl) to 3-hydroxy-2-butanoneacetoin (acetoin). The same order of increasing metal particle size was found for the two tested supports: Pt < Ru < Pd. The XPS analysis showed that the metal/composite catalysts reduced in H2 at 503 K had two kinds of active sites: reduced (Me°) and electron-deficient (Me⁺). It was rationalized that the hydrogen bond cleavage was performed on the Me° active sites, while reactant adsorption occurred on the Me⁺ sites. The differences in activity and selectivity between the composite catalysts were attributed to electronic effects on the different metals and to different adsorptive properties of the different polymers. The high selectivity to acetoin was attributed to the preferential adsorption of diacetyl as compared to the adsorption of acetoin. The BTAl catalysts were slightly more active and selective than the UTAl ones. This was attributed to electronic effects caused by remnant organic groups on the composite supports (urethane or biphenyl on UTAl or BTAl, respectively). Pd-BTAl was the most active and selective catalyst, a fact related to electronic effects of both palladium and the support.

Full text of DOI:10.1007/s11696-017-0161-4

Chem. Pap.
DOI 10.1007/s11696-017-0161-4
ORIGINAL PAPER
Hydrogenation of diacetyl over composite-supported egg-shell
noble metal catalysts
1
,2
1,3
4
1,3
1,3
N. Carrara
•
J. M. Badano
•
F. Coloma-Pascual
•
C. Vera
•
M. Quiroga
Received: 31 October 2016 / Accepted: 11 March 2017
Ó Institute of Chemistry, Slovak Academy of Sciences 2017
Abstract Two composite supports with a mixed inor-
ganic–organic structure were synthesized: BTAl and UTAl.
Hydrophilic–hydrophobic dual properties of the supports
were suitable for preparing egg-shell-supported metal cat-
alysts for selective hydrogenation reactions. The catalysts
were characterized by ICP, XRD, OM, TEM, EPMA, XPS
and TGA. Their mechanical resistance was assessed.
Activity and selectivity were tested with the hydrogenation
of 2,3-butanedione (diacetyl) to 3-hydroxy-2-bu-
tanoneacetoin (acetoin). The same order of increasing
metal particle size was found for the two tested supports:
Pt \ Ru \ Pd. The XPS analysis showed that the
metal/composite catalysts reduced in H2 at 503 K had two
adsorption of acetoin. The BTAl catalysts were slightly
more active and selective than the UTAl ones. This was
attributed to electronic effects caused by remnant organic
groups on the composite supports (urethane or biphenyl on
UTAl or BTAl, respectively). Pd-BTAl was the most active
and selective catalyst, a fact related to electronic effects of
both palladium and the support.
Keywords Composite support Á Egg-shell catalysts Á
Selective hydrogenation Á Metal effect
Introduction
kinds of active sites: reduced (Me°) and electron-deficient
?
Me ). It was rationalized that the hydrogen bond cleavage
(
Catalytic hydrogenation reactions are widely used for the
production of fine chemicals and specialties (Osawa et al.
2000). An important subset of these reactions involves the
transformation of vicinal diketones. The hydrogenation of
(a,b-diketones) is schematized as A ? B ? C, where A:
a,b-diketone, B: a-hydroxyketone and C: a,b-alkanediol.
In these reactions the control of the selectivity to a-hy-
droxyketones is difficult because the hydrogenation to the
a,b-alkanediol is usually favored or because the
hydrogenolysis to monoketones is also favored (Hayakawa
et al. 2000). a-Hydroxyketones are widely used as inter-
mediates for other products because its dual functionality
allows their use in several reactions (Hayakawa et al.
was performed on the Me° active sites, while reactant
adsorption occurred on the Me sites. The differences in
?
activity and selectivity between the composite catalysts
were attributed to electronic effects on the different metals
and to different adsorptive properties of the different
polymers. The high selectivity to acetoin was attributed to
the preferential adsorption of diacetyl as compared to the
&
J. M. Badano
jbadano@fiq.unl.edu.ar
1
INCAPE-CONICET, Instituto de Investigaciones en Cat a´ lisis
y Petroqu ´ı mica, Ruta 168 Km 0, S3000AOJ, Santa Fe,
Argentina
2000). For example a-hydroxyketones can be transformed
into vic-diols or a-aminoketones (Nakamura et al. 1996).
Vic-diol compounds can be used as solvents or interme-
diates for the synthesis of other products (Grafje et al.
2012).
2
3
4
Universidad Tecnol o´ gica Nacional, Facultad Regional Santa
Fe, Lavaise 610, S3004EWB, Santa Fe, Argentina
Facultad de Ingenier ´ı aQu ´ı mica (UNL), Santiago del Estero
2
829, S3000AOJ, Santa Fe, Argentina
Hydrogenation of (a,b-diketones) can be performed by
homogeneous (Hayakawa et al. 2000), heterogeneous
(Augustine 1997) or enzymatic catalysis(Nakamura et al.
Servicios T e´ cnicos de Investigaci o´ n, Facultad de Ciencias,
Universidad de Alicante, Apartado 99, 03080 Alicante, Spain
123

Chem. Pap.
1
996). The reduction of 1,2-, 1,3- and 1,4-diketones can be
performed by Clemmensen reduction (Di Vona et al.
990), zinc being used as the reducing agent in acid media.
Vulkollan (Grafje et al. 2012). The objectives of this work
are to evaluate the effect of the metallic active phase and
the composite support on the activity and selectivity during
the hydrogenation of 2,3-butanedione.
1
Hayakawa et al. (Hayakawa et al. 2000) carried out the
reduction of a 1,2-diketone using TiI in dichloromethane
4
as reducing agent, obtaining excellent yields (up to 92%) in
the synthesis of benzoin from diphenylglyoxal. Zuo et al.
Experimental
(
2001) studied the catalytic hydrogenation of 2,3-butane-
dione over Pt catalysts modified by other metal complexes,
finding that the modifiers had influence on both the reaction
activity and selectivity. Toukoniitty et al. (2003) studied
the solvent effect in the hydrogenation of phenyl-1,2-
propanedione. Gertosio et al. (1999) studied the effect of
the metal function in the hydrogenation of a steroid with a-
diketone functionality towards the a-hydroxyketone (11-
oxo,12b-OH) and obtained 100% yield.
Catalyst preparation
The composite supports BTAl and UTAl were prepared
following the technique described by Badano et al. (2010a).
A fine powder of c-Al O as inorganic phase was added to a
2
3
mixture of bifunctional monomers as organic phase and
benzoyl peroxide as polymerization initiator. The monomers
used were bisphenol A glycerolatedimethacrylate (BGMA),
Metal-based egg-shell catalysts are very important in
industry. A low contact time between reactives and active
sites and a better surface heat transfer are some of the good
qualities of these types of catalysts. Because of these
properties, they are appropriate for strongly exothermal
reactions where the intraparticle mass and heat diffusion
can decrease the catalyst selectivity or lifetime, e.g. by
coke formation (Lin and Chou 1994). Iglesia et al. (1995)
studied the preparation of cobalt egg-shell catalysts for
Fischer–Tropsch synthesis, and found that their use
triethylene
glycol
dimethacrylate
(TEG)
and
diurethanedimethacrylate (UDMA). A BTAl composite
support was prepared using BGMA and TEG. UTAl was
prepared using with UDMA and TEG. The mixture were
placed in an oven at 373 K for 1 h to activate the initiator and
start the polymerization and stored at 353 K for 12 h. The
supports were cut into cylinders of 1.2 mm diameter and
3 mm length. Finally the support was pretreated in N flow at
2
503 K for 2 h.
Metals were added to the supports by impregnation to
incipient wetness using an aqueous acidic solution of the
metal precursor (PdCl , RuCl or H PtCl ) at pH 1. The
increased the reaction rate and C selectivity. Badano et al.
5
(
2010a) developed new ‘‘composite’’ supports with a dual
2
3
2
6
phase matrix (organic–inorganic) with hydrophilic–hy-
drophobic nature and found that they could be advanta-
geously used for the preparation of egg-shell metal
catalysts (Carrara et al. 2014, 2015). This kind of support
was used to prepare low loaded palladium catalysts for the
selective hydrogenation of styrene and terminal and non-
terminal alkynes.
concentration of these solutions was adjusted to obtain a
metal loading on the catalysts of ca. 1 wt%. The catalysts
were named 1Pd-BTAl, 1Pd-UTAl, 1Pt-BTAl, 1Pt-UTAl,
1Ru-BTAl and 1Ru-UTAl. After the impregnation the
catalysts were ground to a size of 35–80 mesh and stored in
desiccator for further use. Prior to the reaction the catalysts
were activated in H flow at 503 K for 60 min.
2
In the present work two composite supports were used to
prepare different Pt, Pd and Ru noble metal catalysts. They
were evaluated in the reaction test of selective hydro-
genation of a diketone, 2,3-butanedione (diacetyl, DC), as
shown in Fig. 1. The intermediate product is 3-hydroxy-2-
butanone (acetoin, AC) and the total hydrogenated product
is 2,3-butanediol (BD). The intermediate product, AC, is
used in the flavor and fragrances industry, while the totally
hydrogenated BD is used in the cosmetic industry as
humectant or in the production of polymers such as
Characterization techniques
The catalysts were characterized by inductively coupled
plasma ICP-OES, X-ray diffraction, X-ray photoelectron
spectroscopy (XPS), microscopy (optical and TEM), elec-
tron probe micro-analysis (EPMA), and thermogravimetric
analysis (TGA and SDTA). The composite supports were
also subjected to mechanical tests for assessing their
compression and attrition resistance.
Fig. 1 Reaction scheme for
,3-butanedione hydrogenation
O
OH
OH
2
H C
H C
H C
3
3
3
H2
H2
CH3
CH3
CH3
Metal
Metal
O
O
HO
2
,3-butanedione (DC)
3-hydroxy-2-butanone (AC)
2,3-butanediol (BD)
1
23

Chem. Pap.
The metal content of the catalysts was obtained by
C°DC = 0.188 M), and a certain mass of the activated
catalyst. Then the reactor was closed. Before the reaction,
digesting the sample and then analyzing the liquors in a
Perkin Elmer Optima 2100DV ICP-OES equipment.
the reactor was pressurized with N up to 5 bar and purged
2
X-ray diffractograms were obtained in a Shimadzu XD-
˚
3 times, to eliminate oxygen traces. The reaction begun
with the hydrogen entrance into the system. During the
reaction the stirring speed was maintained at 1200 rpm, the
pressure was kept constant at 20 bar and the temperature at
353 K. Runs were carried out in triplicates with an
experimental error of 3%. Reactants and products were
analyzed by gas chromatography in a Shimadzu 2014
equipment with a flame ionization detector and a
30 m J&W INNOWax 19091N-213 (cross-linked poly-
ethylene glycol phase) capillary column.
1
equipment, using Cu Ka radiation (k = 1.5405 A) fil-
tered with Ni. The 2h = 20–80° range was scanned at a
-
1
rate of 1° min . The samples were prepared by milling the
material to a fine powder and reducing it in hydrogen.
Optical micrographs were obtained with a Mitsubishi
Microwatcher VS-30H Microscope and a Sony Color
Video Printer. The samples used were either pellets or
powders with 35–80 meshes size.
For the transmission electron microscopy (TEM) the
samples were milled and then dispersed in a 50% v/v
ethanol:water solution for further analysis. The measure-
ments were performed in a JEOL JEM-1200 EXII
equipment.
Results and discussion
Characterization
XPS measurements were carried out with a Mul-
titechUniSpecs equipment. Measurements were done using
a VG-MicrotechMultilab equipment, with a MgK (hm
X-ray diffraction (XRD)
1
253.6 eV) radiation source and a pass energy of 50 eV.
The XPS system analysis pressure was kept at
The X-ray diffractograms of the supports and catalysts are
shown in Fig. 2a, b (1 M-UTAl and 1 M-BTAl catalysts).
In these figures the signals of the c-alumina phase and the
metal phase have been marked with symbols.
-
9 10 Pa. Samples were reduced ex situ 1 h with H at
7
5
5
2
03 K and treated in situ for 10 min in the instrument
chamber before recording the spectrum. A careful decon-
volution of the spectra was made. The areas of the peaks
were estimated by calculating the integral of each peak
after subtracting a Shirley background and fitting the
experimental peak to a combination of Lorentzian/Gaus-
sian lines of 30–70% proportions. The reference binding
energy (BE) was the Al 2p peak at 74.4 eV.
The diffractograms of the support UTAl and the UTAl-
based catalysts can be seen in Fig. 2a. In all cases the
typical signals of c-Al O are present at 33°, 37.7°, 46°,
2
3
62° and 67° (Huang et al. 2008). The organic portion of the
composite is amorphous, so it does not produce diffraction
peaks. In Fig. 2a the intense peak at 2h = 39.9° of the 1Pd-
UTAl catalyst was attributed to the (111) plane of metallic
Pd° (Ngamsom et al. 2004). In the 1Pt-UTAl catalyst a
small peak appears at 2h = 39.7°, which would correspond
to the (111) plane of Pt° (Onoe et al. 2007; Shul et al. 1986;
Huang et al. 2006). In the case of the 1Ru-UTAl catalyst no
peaks are observed, possibly due to the proximity of the
(101) main plane of Ru to a strong support peak at
2h = 43.3°, as reported by other authors (Marshall et al.
2005). Anyway small particles of Ru on the catalyst that
could be detected by TEM are well below the detection
limit of the X-ray diffraction technique.
Thermo gravimetric analysis (TGA) traces were also
obtained. The experiments were carried out in a TA
Instruments 2950 apparatus. The catalyst samples (about
-
1
1
0 mg) were heated in a 40 mL min air flow from room
-
1
temperature up to 1173 K at a heating rate of 5 K min
.
Values of the axial and radial mechanical resistance of
the pellets were obtained in an Instron Marks Universal
-
1
Rehearsals equipment. A rate of 1 mm min was used.
The reported values were the result of the averaging of ten
experiments with different samples. The attrition resistance
measurements were performed following the ASTM D
4
058-92 norm.
In Fig. 2b diffractograms of the BTAl support and its
catalysts can be seen. The main features and conclusions
that can be drawn are the same as those previously dis-
cussed for the BTAl catalysts.
Catalytic activity tests
The catalytic performance of the prepared catalysts was
tested in a semi-continuous stainless steel batch reactor
Optical microscopy (OM), electron probe micro-analysis
(EPMA) and transmission electron microscopy (TEM)
(
slurry), equipped with a magnetic stirrer and with PTFE-
coated internals. The catalysts were ground to a fine
powder to eliminate mass transfer limitations. The reactor
was charged with a solution of 2,3-butanedione (diacetyl,
DC) in isopropanol (initial concentration of diacetyl,
The results of optical microscopy (OM) of the composites
and the supported 1% Pt, 1% Pd and 1% Ru catalysts are
shown in Fig. 3a–h. The images were obtained with
123

Chem. Pap.
the metal concentration decreases drastically towards the
center of the pellet.
(
a)
Electronic transmission micrographs of the BTAl and
UTAl supports and catalysts can be seen in Fig. 5. In
Fig. 5a, b the inorganic phase of the BTAl and UTAl
composite support can be distinguished as the region in
gray shade while the organic phase has a light color or it is
white. In Fig. 5c–h the Pt, Ru and Pd phases can be dis-
tinguished as the dark-colored zone surrounding the alu-
mina phase. It must be noted that in these micrographs no
metal phase is observed on the polymeric phase.
1
Pd-UTAl
1
Ru-UTAl
1Pt-UTAl
UTAl
Optical and transmission electron microscopy images
corroborate that the main features of the impregnation
mechanism of the metal precursor are dictated by the
hydrophilic–hydrophobic nature of the alumina–polymer
matrix. In the preparation procedure an acidic aqueous
solution of the precursor metal was used. This solution
would wet the hydrophilic particles (alumina) located more
near the external surface. The hydrophobic polymeric
material would act as a barrier preventing the impregnation
of the inner particle core by the aqueous solution.
Figure 6 shows the distribution of particle diameters on
each composite catalyst. The values of the average volume-
surface diameter (DVA) as calculated using Eq. (1) are
given in Table 1.
2
0
30
40
50
60
70
80
2
(
b)
1Pd-BTAl
1
1
Ru-BTAl
Pt-BTAl
P
3
i
2
n Á d
i
DVA ¼ P
:
ð1Þ
ni Á di
Taking this average volume-surface diameter for each
catalyst, the dispersion (D) on the surface of the catalysts
was estimated following a procedure explained by Badano
et al. (2010b). The estimated D values are also given in
Table 1.
BTAl
2
0
30
40
50
60
70
80
2
Metal content and X-ray photoelectronic spectroscopy
Fig. 2 X-ray diffractograms. a UTAL support and catalysts. b BTAl
support and catalysts
Results of metal content are presented in Table 1. The
content of each composite catalyst was between 0.86 and
1.1%. The metal content, as measured by ICP, gives
information on the effectiveness of the incipient wetness
technique for impregnating catalysts with a precise desired
amount of metal. The results indicate that the error of the
technique was ± 14%.
pelletized catalysts. The metal phase of the catalyst can be
seen in the periphery, indicating an egg-shell metal distri-
bution. The polymeric phase of the support matrix can be
appreciated in dark color, while the inorganic phase is seen
in light color. In all the photos the organic phase is seen
surrounding the alumina particles.
Values of the Pd/Al mass ratio inside the catalyst pellets
were obtained by means of EPMA. The catalyst pellets
were coated with a layer of carbon by vacuum deposition.
The Pd 3d5/2, Pt 4d5/2 and Ru 3p3/2 XPS spectra of the
Me-composite catalysts, previously reduced in H
at
2
503 K, are shown in Fig. 7. The spectra had a peak at about
198.5 eV that corresponds to Cl 2p3/2. This would be due to
chloride species that were not eliminated during the ther-
mal treatment (Badano et al. 2010b; NIST 2016). From the
position, maximum intensity and area of the peaks of the
XPS spectra, binding energies and relative concentration of
surface metal species were determined. From the analysis
-
1
The scanning speed was 0.02 mm min and the acceler-
ation voltage of the electron beam was 20 kV. Results of
EPMA are presented in Fig. 4. Plots of metal concentration
as a function of the pellet radius are presented, for the 1Pd-
BTAl and 1Pd-UTAl catalysts. As it can be seen, both
catalysts exhibit egg-shell distributions of the metal phase,
1
23

Chem. Pap.
Fig. 3 Optical microscopy
images of different metal
catalysts. a 1Pt-BTAl, b 1Pt-
UTAl, c 1Ru-BTAl, d 1Ru-
UTAl, e 1Pd-BTAl, f 1Pd-
UTAl, g BTAl, h UTAl
of the chlorine signals also the Cl/Al atomic ratio was
determined. Binding energies and atomic ratios can be
found in Table 1.
both samples (1Pt-BTAl and 1Pt-UTAl) two peaks were
detected, one at 313.5 eV and another at 315.5 eV that
n?
can be assigned to Pt° and to electron-deficient Pt
The XPS results of the Pt-composite catalysts can be
seen in Table 1. For these samples the low-intensity Pt
(n ? 2) chloride species (Serrano-Ruiz et al. 2006; La
Surface 2016). In both cases, Pt° is present in a concen-
tration of ca. 50% indicating that the reduction treatment
was insufficient or that a strong interaction with the
support was present and precluded an easy reduction. The
4
d5/2 signals were studied and not the stronger Pt 4f7/2
ones because the latter are overlapped with the signals
due to the alumina component of the support, Al 2p. In
123

Chem. Pap.
Fig. 4 Metal radial
(
a)
(b)
concentration pattern of the Pd
catalysts as obtained by EPMA.
r° is the external pellet radio.
a 1Pd-BTAl, b 1Pd-UTAl.
(
Badano et al. 2010a)
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
r/r°
0.8
1.0
r/r°
BTAl catalysts had a higher surface chlorine content than
the UTAl-supported ones.
pretreatment and reaction. The obtained results are plotted
in Fig. 8a–d.
With respect to the XPS results of the Ru/composite
catalysts, the region analyzed was that of the Ru 3p3/2
binding energy, because the Ru3d band overlaps with the
C1s band. In both samples two Ru species could be
detected, one with binding energy at about 461.0 ± 0.3 eV
and another species with binding energy at about 463.3 eV.
According to the literature reports they would be due to
Figure 8a shows the thermal degradation pattern of the
UTAl support and the UTAl catalysts. It can be seen that
these materials begin to lose weight noticeably at about
523 K. The presence of metal in the catalysts contributes to
speed up the decomposition of the organic matrix of the
support. The order of stability is: UTAl [ 1Ru-
UTAl [ 1Pd-UTAl [ 1Pt-UTAl. For all samples at the
end of the test a residue remains of about 50% the initial
mass. This residue corresponds to the inorganic portion of
the support, c-Al O .
Figure 8c shows the thermal gravimetry traces of the
BTAl support and catalysts. In all cases it can be seen that
the samples are stable up to 523 K. At temperatures higher
than this value a rapid decomposition of the organic part of
the sample occurs. As it was the case with the UTAl sup-
port and catalyst these materials are more rapidly decom-
posed in the presence of the noble metal. The order of
thermal stability for the samples was: BTAl [ 1Ru-
BTAl & 1Pd-BTAl [ 1Pt-BTAl. In all cases the final
residue of about 50% the original mass, corresponded to
the inorganic portion of the support.
d?
Ru° and to Ru (d ? 3) chloride species (Badano et al.
2
010b; NIST 2016). The amount of Ru° on both compos-
ites is very similar. With respect to the Cl/Al ratio the
greater residual chlorine content is found on the BTAl
support. Ruthenium catalysts had the highest Cl/Al surface
atomic ratios which is consistent with the higher oxidation
state of ruthenium.
2
3
Two peaks due to Pd were detected in the spectra of the
catalysts, one at about 335.3 ± 0.2 eV and another at
n?
3
36.7 ± 0.3 eV, attributed to Pd° and Pd (n ? 2). The
signal of oxidized Pd would be related to the presence of
chloride species (Badano et al. 2010b; NIST 2016). In both
catalysts the dominant surface species was metallic Pd, a
desired feature for efficient hydrogenation catalysts. With
respect to the Pd oxidized species, it could be formed by
non-reduced Pd atoms, stabilized by neighboring chlorine
atoms that were not eliminated during the reduction treat-
ment at 503 K (Badano et al. 2010b). The Cl/Al ratios of
the Pd/composite catalysts shown in Table 1 indicate the
presence of surface chlorine, not eliminated during the
thermal pretreatment of the catalysts. The composite Pd-
Figure 8b, d shows the differential thermal analysis
(SDTA) traces of the UTAl and BTAl supports and cata-
lysts. In these tests the temperature difference between the
sample and a reference is registered, thus allowing to detect
if the process is endothermal or exothermal. The traces of
the supports show three distinctive zones:
•
•
•
From room temperature to 523 K the process is
endothermal.
-
BTAl had a higher content of superficial Cl than Pd-
UTAl.
The 523–773 K zone is exothermal, correlating with
the decomposition of the organic matrix.
Above 773 K no temperature differences between the
sample and the reference were recorded. This coincides
with the evolution at constant mass of the inorganic
phase.
Thermal gravimetry
The thermal gravimetry tests give information on the
thermal stability of the supports and catalysts and they
allow determining the appropriate temperatures for thermal
1
23

Chem. Pap.
Fig. 5 TEM images of some
catalyst fragments. a BTAl,
b UTAl, c1Pt-BTAl, d 1Pt-
UTAl, e 1Ru-BTAl, f 1Ru-
UTAl, g 1Pd-BTAl, h 1Pd-
UTAl
Decomposition of the organic matrix in the 523–773 K
range would correspond to the occurrence of cracking,
depolymerization and oxidation reactions. Andrzejewska
et al. (1993) have reported that during the thermal
decomposition of highly interlinked polymers a competi-
tion occurs between the phenomena of depolymerization
and decomposition.
Figure 8b, d shows a shift of the SDTA traces to lower
temperatures. The effect is more important for the UTAl
support and would indicate that the noble metals promote
the decomposition of the polymeric phase and that Pt has
the strongest promoting effect.
123

Chem. Pap.
Fig. 6 Metal particle size
distribution of catalysts
(
a)
(b)
observed with TEM. a 1Pt-
BTAl, b 1Pt-UTAl, c 1Ru-
BTAl, d 1Ru-UTAl, e 1Pd-
BTAl and f 1Pd-UTAl
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
dp (nm)
dp (nm)
(
c)
(
d)
0
1
2
3
4
5
6
7
8
dp (nm)
0
1
2
3
4
5
6
7
8
dp (nm)
(
e)
(f)
0
1
2
3
4
5
6
7
8
dp (nm)
0
1
2
3
4
5
6
7
8
dp (nm)
Mechanical properties of the supports
resistance was UTAl [ BTAl [ a-Al O [ c-Al O [
2
3
2 3
carbon, and the order of attrition resistance (long test)
Figure 9 shows the results of resistance to diametral
compression (RDC), resistance to longitudinal compression
was UTAl [ BTAl [ c-Al O [ a-Al O [ carbon. The
2
3
2 3
greater resistance of the composite supports can be
explained by their preparation method. The polymer covers
the inorganic particles and prevents its attrition.
(
RLC), and resistance to attrition of the tested commercial
supports (carbon, alumina) and the composite supports
UTAl, BTAl). Attrition resistance tests were made in
(
Parent et al. (2011) developed ceramic catalysts that had
better attrition resistance due to the presence of metal
accordance with ASTM D4058–92 norm (1800 turns). One
special test had a longer duration (18,000 turns).
oxides in their structure (e.g. NiO, MgO, K O), achieving
2
w
up to 0.3% / attrition loss in a 48-h test in a laboratory-
As it can be seen in Fig. 9a–d the results of the
mechanical properties indicate that the commercial sup-
ports have a lower resistance than the composite supports,
UTAl being the most resistant. The order of compression
w
scale fluidized-bed reactor system. However, their prepa-
ration procedure was somewhat cumbersome and involved
long thermal treatments and high temperatures. Scherzer
1
23

Chem. Pap.
Table 1 Metal content as determined by ICP, metal particle size and dispersion, and XPS results
Catalyst
Metal loading (wt%) Metal dispersion (%) Average particle diameter (nm) XPS
BE and atomic ratio Cl/Al atomic ratio ( /at
at
)
1
1
1
1
1
1
Pt-BTAl
0.86
75.50
80.89
40.43
44.48
22.86
24.89
1.4
1.3
3.3
3.0
4.3
4.2
313.6 eV (55%)
15.5 eV (45%)
313.5 eV (48%)
15.5 eV (52%)
461.3 eV (76%)
63.3 eV (24%)
460.8 eV (77%)
63.2 eV (23%)
335.5 eV (75%)
37.0 eV (25%)
335.0 eV (80%)
36.4 eV (20%)
0.0142
0.0134
0.0551
0.0263
0.0131
0.0088
3
Pt-UTAl 0.90
Ru-BTAl 0.95
Ru-UTAl 0.90
Pd-BTAl 1.10
Pd-UTAl 1.00
3
4
4
3
3
et al. (1991) developed high attrition resistant cracking
catalysts for FCC that were prepared by spray drying of an
aqueous solution of molecular sieves, kaolin (clay) or silica
their selectivity to 3-hydroxy-2-butanone (SAC) as a func-
tion of time. Figure 10c shows plots of total conversion of
2,3-butanedione (XBD) for UTAl catalysts and Fig. 10d
shows their selectivity to 3-hydroxy-2-butanone (SAC) as a
function of time.
and aluminum chloride hydroxide. The best catalyst pre-
w
sented an attrition loss lower than 1% / and was formed
w
by 20% zeolite (CREY), 15% silica (NALCO 2326), 15%
alumina and 50% kaolin.
Table 2 shows values of total conversions of DC and
selectivities to 3-hydroxy-2-butanone at 60 and 120 min of
reaction time. The turn over frequencies (TOF) were cal-
culated using values of metal dispersion calculated from
the TEM average particle size, and the initial reaction rates,
estimated from the plots of Fig. 10a, c by extrapolation to
zero reaction time.
Not only the composite supports have many advantages,
but their preparation is simple and they do not need any
thermal treatments. However, composite supports have a
maximum temperature limit of 503 K, their use being
restricted to reactions performed at temperatures lower
than this limit.
The analysis of the results of Fig. 10 and Table 2 indi-
cates that the active metal phase more appropriate for
obtaining the intermediate product in high yield is Pd,
while the metal that provides the highest selectivity to 2,3-
butanediol is Pt. The order of selectivity to 3-hydroxy-2-
butanone is: 1Pd-BTAl [ 1Pd-UTAl ꢀ 1Ru-UTAl -
C 1Ru-BTAl [ 1Pt-BTAl ꢀ 1Pt-UTAl. Meanwhile, the
order of activity is: 1Pd-BTAl ꢀ 1Pt-BTAl [ 1Pt-
UTAl ꢀ 1Ru-BTAl [ 1Pd-UTAl [ 1Ru-UTAl.
Catalytic activity results
All catalysts were active in the reaction of hydrogenation
of 2,3-butanedione (DC). The only reaction products found
were 3-hydroxy-2-butanone (AC) and butanediol (BD). No
traces of reaction products coming from the total hydro-
genation of one or two carbons (2-butanone, 2-butanol or
butane) were detected. This can be explained by a rapid
desorption of the products of partial hydrogenation and
their lower affinity for the surface, their subsequent
hydrogenolysis or oligomerization being precluded (Ry-
lander 1985).
Gertosio et al. (1999) studied the metal effect in the
hydrogenation of a steroid with diketonic functionality and
obtained similar results. They obtained the following
activity order as based on the initial volumetric reaction
rate: Pt [ Ru [ Pd. The Pd catalyst had an induction
period much higher than the rest of catalyst. However, total
conversion over the Pd catalyst was got, once the induction
period was reached. If values of the reaction rate order are
compared almost identical values can be seen for the sys-
tem of this work and the system of Gertosio et al. (1999).
The high selectivity to the intermediate product could be
the results of several factors:
The results of the reaction tests are shown in Fig. 10a, c
in terms of total conversion of 2,3-butanedione (XDC) as a
function of reaction time for all catalysts, and in Fig. 10b, d
in terms of selectivity to AC as a function of time. No
induction period can be seen in the activity plots.
Figure 10a shows plots of total conversion of 2,3-bu-
tanedione (XBD) for BTAl catalysts and Fig. 10b shows
123

Chem. Pap.
(
a)
(
b) 2000
Pt°
Pt
Data
3
2
2
1
1
000
500
000
500
000
Pt°
+
Pt
1500
Data
1
000
5
00
0
5
00
0
3
05
310
315
320
3
05
310
315
320
Binding energy (eV)
Binding energy (eV)
(
c) 6000
(d)
Ru°
Ru
5000
4000
Ru°
Ru
Data
5
4
3
2
1
000
000
000
000
000
0
Data
3
000
2000
1
000
0
4
55
460
465
470
4
55
460
465
470
Binding energy (eV)
Binding energy (eV)
(
e)
(f)
1
6000
Pd°
Pd
Data
8
6
4
2
000
000
000
000
0
Pd°
Pd
Data
14000
1
2000
0000
8000
1
6
4
2
000
000
000
0
3
30
335
340
345
3
30
335
340
345
Binding energy (eV)
Binding energy (eV)
Fig. 7 Metal species distribution in catalysts as determined by XPS. a 1Pt-BTAl, b 1Pt-UTAl, c 1Pd-BTAl, d 1Pd-UTAl, e 1Pd-BTAl, f 1Pd-
UTAl
•
•
The high affinity of AC for the IPA solvent that precludes
the adsorption of AC, first step for the consecutive
hydrogenation to the diol (Nakamura et al. 1996).
Because of electronic effects, the desorption of acetoin
•
The presence of an egg-shell metal distribution, that
favors a rapid desorption of the intermediate product,
3-hydroxy-2-butanone, thus decreasing the possibility
of over hydrogenation to 2,3-butanediol (Carrara
et al. 2014). This is a known result for systems of
consecutive reactions under diffusive or chemical
control.
(
with one p bond in its structure) would be favored
while in the reaction medium enough 2,3-butanedione
2 p bonds) were present.
(
1
23

Chem. Pap.
Fig. 8 Thermogravimetry
results. a TGA of UTAl support
and catalysts, b SDTA of UTAL
support and catalysts, c TGA of
BTAl support and catalysts,
d SDTA of BTAL support and
catalysts
1.0
1Pt-UTAl
1Pd-UTAl
1
Ru-UTAl
0
0
0
0
0
0
.9
.8
.7
.6
.5
.4
UTAl
1Pt-UTAl
1Pd-UTAl
1
Ru-UTAl
UTAl
(
a)
(b)
600
3
00
400
500
700
800
900
3
00
400
500
600
700
800
900
T (K)
T (K)
1
0
0
0
0
0
0
.0
.9
.8
.7
.6
.5
.4
BTAl
Pd-BTAl
1Pt-BTAl
Ru-BTAl
1
1
BTAl
1
1
Pd-BTAl
Pt-BTAl
1Ru-BTAl
(
c)
(
d)
3
00
400
500
600
700
800
900
300
400
500
600
700
800
900
T (K)
T (K)
Fig. 9 Mechanical properties
of commercial and composite
supports. a Diametral
compression resistance (DCR).
b Longitudinal compression
resistance (LCR). c Mass loss
by attrition at 1800 turns.
d Mass loss by attrition at
(
a)400
(
b) 5000
4
3
2
1
000
000
000
000
0
300
2
1
00
00
0
1
8,000 turns
Carbon RX3 g-Al2O3
a-Al2O3
UTAl
BTAl
Carbon RX3 g-Al2O3
a-Al2O3
UTAl
BTAl
(c)
(
d)
1
1
1
1
0
0
0
0
0
.6
7
6
5
4
3
2
1
0
.4
.2
.0
.8
.6
.4
.2
.0
Carbon RX3 g-Al2O3 a-Al2O3
UTAl
BTAl
Carbon RX3 g-Al2O3 a-Al2O3
UTAl
BTAl
Analysis of the effect of the type of metal used, kind of
RuCl and H PtCl , so the stabilized species at this pH are
3 2 6
2
-
-
support and chloride is now presented:
the tetrahedral complexes [PdCl ]
4
and [RuCl ] ,and
4
2
-
octahedral [PtCl6] . All of these complexes are electron
donor Lewis bases (Greenwood and Earnshaw 1997) and it
is expected than during impregnation they get chemisorbed
on the basic sites (Lewis sites) of alumina. In the case of
composite supports the interaction between the metal and
Effect of the type of metal
As stated in the ‘‘Experimental’’ section, a solution of HCl
was used to reach pH 1 in the case of the precursors PdCl2,
123

Chem. Pap.
Fig. 10 Catalytic test results.
Pd, Pt and Ru catalysts.
a Conversion as a function of
time, BTAl catalysts.
b Selectivity to AC, BTAl
catalysts. c Conversion as a
function of time, UTAl
catalysts. d Selectivity to AC,
UTAl catalysts
(
a) 100
(b) 100
8
0
80
60
40
20
0
60
40
1
1
1
Pd-BTAl
Pt-BTAl
Ru-BTAl
1Pd-BTAl
1Pt-BTAl
1Ru-BTAl
2
0
0
0
240
480
720
960
1200
0
240
480
720
960
1200
Time (min)
Time (min)
(
c) 100
(d) 100
1
1
1
Pd-UTAl
Pt-UTAl
Ru-UTAl
80
60
40
20
0
80
60
40
20
0
1Pd-UTAl
Pt-UTAl
1Ru-UTAl
1
0
240
480
720
960
1200
0
240
480
720
960
1200
Time (min)
Time (min)
Table 2 Values of conversion
and selectivity to acetoin at
selected values of reaction time,
and turnover frequency
-1
TOF (s ) 9 10
-2
Catalyst
X
DC (%)
S
t = 60 min
AC (%)
X
DC (%)
t = 120 min
S
AC (%)
t = 60 min
t = 120 min
1
1
1
1
1
1
Pt-BTAl
Pt-UTAl
45.12
37.22
11.05
7.09
69.80
66.31
81.45
83.94
97.15
80.41
60.33
44.12
19.35
13.06
46.04
8.18
68.64
62.08
82.32
85.12
98.10
94.50
7.90
6.29
1.80
1.08
11.48
1.21
Ru-BTAl
Ru-UTAl
Pd-BTAl
Pd-UTAl
36.79
4.34
Experimental conditions: VIPA = 60 mL, C°DC = 0.188 M, T = 353 K, PH2 = 20 bar, WCAT = 500 mg
the support surface is a consequence of dispersion forces
Cagnola et al. 2012). Shape and the size of the molecules
Two active sites were detected by XPS, Me° and Med?.
The results seem to indicate that both are necessary during
the hydrogenation of DC:
(
affect the magnitude of the dispersion forces between them.
Larger and heavier atoms and molecules exhibit stronger
dispersion forces than smaller and lighter ones, so the
dispersion forces are proportional to the size of the ion. In
our case taking into account the sizes of these complexes
(a) Me° sites: during hydrogenation reactions, metallic
centers rich in electrons can cleave the hydrogen bond by
means of the interaction of a filled d metal orbital (HOMO)
with the empty sigma antibonding molecular orbital of H2
(LUMO) (Shriver et al. 1994). The rupture of the hydrogen
bond is more easily done on metals with a high amount of
available electrons in the external d orbital, as it is the case
2
-
the dispersion forces order would be: [PtCl6]
-
-
2-
RuCl ] [ [PdCl ] . As the shape of the platinum pre-
[
4
4
cursor complex is octahedral, quite bigger size than the
tetrahedral palladium or ruthenium complexes, this species
would have higher dispersion. On the composite support
there would be geometrical effects causing the highest
dispersions of Pt-BTAl and Pt-UTAl.
1
0
of palladium (d ). This rupture should be less likely on
9
metals with fewer d electrons, as in the case of Pt (d ) or
8
Ru (d ) (Badano et al. 2010b). Therefore, the differences in
activity during the hydrogenation of DC between the
1
23

Chem. Pap.
composite catalysts could be partly attributed to differences
in the electronic density of the external d orbital of each
metal that promotes the dissociative chemisorption of
electrons from the carbonyl group, forming new r bonding
and antibonding orbital fragments. In the synthetized cat-
alysts, the chloride ions are those of the metal precursors
that remain on the catalysts, after the thermal treatments
hydrogen.
n?
b) Me sites: these species are necessary as Lewis acid
n?
(
performed. The fraction of electropositive M was higher
sites to chemisorb diacetyl, a Lewis base. The lowest
activity shown by Pd-UTAl could be explained by an
electronic effect because Pd-UTAl had the lowest amount
in almost all Me-BTAl catalysts (25, 24 and 45% for Pd,
Ru and Pt, see Table 1) as compared to the Me-UTAl ones
(20, 23 and 52 for Pd, Ru and Pt). The BTAl catalysts had
the highest activity of metal catalyst series. A clear pattern
of relative higher activity for those materials with higher
n?
of electrodeficient Pd species.
In a previous work of our group (Carrara et al. 2014) it
was proved that during the hydrogenation of 2,3-butane-
dione the reaction kinetics could be explained by a Horiuti–
Polanyi mechanism in which the addition of an H atom to
the carbonyl group in the adsorbed state is the rate limiting
step. The lower selectivity to AC of the Pt-composite or the
Ru-composite catalysts could be related to the small par-
ticle size of the metal function in these materials. This
would promote the overhydrogenation of DC.
-
n?
Cl content can be found that stabilize electropositive M
sites, where diacetyl is chemisorbed.
Regarding the selectivity, the pattern is not clear
because Pd and Pt catalysts with lower chloride content
were, respectively, the highest and the least selective to
acetoin. The lower selectivity to AC of Pt-composite cat-
alysts could be related to the higher fraction of electrode-
n?
ficient Pt , ca. 50%, that favors overhydrogenation.
Effect of the support
When comparing the results of the metals supported over
BTAl in comparison to the same metal supported over
UTAl it is seen in all cases that the total conversion of DC
and the selectivity to acetoin are higher for the BTAl cat-
alysts. This result was also previously found when com-
paring composite-supported Pd catalysts of different metal
loading for the hydrogenation of styrene, 1-heptyne or
Conclusions
Two composite supports were used to prepare different Pt-,
Pd- and Ru-supported noble metal catalysts. The effects of
the type of metal and the type of composite support on the
activity and selectivity during the hydrogenation of 2,3-
butanedione were studied. The catalysts were characterized
by ICP, XRD, OM, TEM, EPMA, XPS, TGA and
mechanical resistance tests.
3
-hexyne (Badano et al. 2010a; Carrara et al. 2015).
The difference in activity could be due to the presence
of different groups, specifically basic Lewis sites that
remain on the surface of the support after the polymer-
ization step of the support preparation procedure. These
would be amide groups in the case of UTAl and aromatic
groups in the case of BTAl. Lewis sites would generate
electronic and geometric effects that in turn would favor
the formation of metal species of different electronic
density. Metal particles under this interaction could reach
different final sizes. This interaction could also be
responsible for the lower concentration of surface chlorine
over the UTAl support.
An egg-shell metal distribution was observed by OM
and EPMA. TEM allowed to distinguish the Pt, Ru and Pd
metal phases surrounding the alumina phase. OM, EPMA
and TEM micrographs confirmed that the metal deposition
mechanism is related to the dual hydrophilic–hydrophobic
action of the alumina–polymer matrix. The acidic aqueous
solution of the metal precursor would wet the hydrophilic
particles (alumina) located more near the external surface
while the hydrophobic polymeric material would act as a
barrier preventing the impregnation of the inner particle
core. Different dispersion forces of the precursor complex
metals would lead to different particle sizes on the surface,
the order being Pt \ Ru \ Pd.
Effect of the chloride
XPS results indicated that the composite-supported
metal particles have both Me° and Med?. after the high-
temperature treatment in hydrogen. These species would be
important necessary sites collaborating during the hydro-
genation reactions. It was rationalized that the hydrogen
bond cleavage is performed on the totally reduced Me°
active sites while the substrate adsorption occurs on the
electron-deficient Med? site. The synergism between these
sites for undertaking a selective hydrogenation transfor-
mation seems not to have been reported before.
Chloride had a clear influence in enhancing the activity of
the composite catalysts. Chloride ions would stabilize
n?
electropositive M surface atoms. Metal atoms bearing a
partial positive charge would form bonds with the CO
groups of diacetyl and would be important both for
adsorption and hydrogenation. From the classical Bly-
holder model for CO interaction with transition metal
surface atoms, electronic depletion of the d band would
leave empty orbitals available for accommodating 5r
123

Chem. Pap.
The prepared composite-supported noble metal catalysts
were found to be active and selective for the hydrogenation
of 2,3-butanedione. The following order of activity was
obtained: Pd [ Pt [ Ru. The differences in activity during
the hydrogenation of DC between the composite catalysts
could be partly attributed to differences in the electronic
density of the external d orbital of each metal that promotes
the dissociative chemisorption of hydrogen. This cleavage
is more easily performed on the metal with the highest
amount of electrons in the external d orbital (Pd) and more
difficultly on the metal with the smallest number of
d electrons (Ru).
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Palladium, platinum and ruthenium catalysts with low
metal loading displayed high selectivity values ([75%), the
order of selectivity to AC being Pd [ Ru [ Pt. The high
selectivity to the intermediate product could be partly
related to the preferential location of the metal particles
near the catalyst surface. Diffusion into long pores could
lead to overhydrogenation of DC.
supported Pd catalysts.
8
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Higher values of catalytic activity and selectivity to AC
were got when supporting the metal over the BTAl support.
These results could be related to a different surface con-
centration of basic Lewis sites remaining after the poly-
merization step. The basic groups would be amides in the
case of the UTAl support and aromatic nuclei in the case of
BTAl. These groups would interact with the metal pre-
cursor species during impregnation and would influence the
final distribution of metal particle sizes. After reducing at
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The most active and selective catalyst was Pd-BTAl
related to electronic effects of both palladium and the
support.
Composite BTAl and UTAl supports proved to have
excellent mechanical properties, even better than those of
commercial c-Al O , a-Al O and carbon. Both supports
displayed a higher resistance to diametral and longitudinal
compression and to attrition. The improved properties were
attributed to the intimate contact between the organic and
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increases their resistance.
2
3
2 3
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