Pd-Fe/SiO2 and Pd-Fe/Al2O3 catalysts for selective hydrodechlorination of 2,4-dichlorophenol into phenol

Article abstract of DOI:10.1016/j.molcata.2014.06.022

The effect of iron introduction on the activity and selectivity of chemically precipitated supported palladium catalysts in the hydrodechlorination of 2,4-dichlorophenol in liquid phase at room temperature was studied. Bimetallic Pd-Fe catalysts supported

Full text of DOI:10.1016/j.molcata.2014.06.022

Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Pd–Fe/SiO2 and Pd–Fe/Al2O3 catalysts for selective
hydrodechlorination of 2,4-dichlorophenol into phenol
Izabela A. Witon´ skaa, Michael J. Walockb, Michał Binczarskia, Magdalena Lesiaka,
Andrei V. Stanishevskyb, Stanisław Karskia,∗
a Institute of General and Ecological Chemistry, Lodz University of Technology, Zeromskiego 116, 90-924 Lodz, Poland
b Department of Physics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 April 2014
Received in revised form 29 May 2014
Accepted 17 June 2014
Available online 28 June 2014
The effect of iron introduction on the activity and selectivity of chemically precipitated supported pal-
ladium catalysts in the hydrodechlorination of 2,4-dichlorophenol in liquid phase at room temperature
was studied. Bimetallic Pd–Fe catalysts supported on silica and alumina were characterized by using XPS,
XRD, ToF-SIMS and TPR-H2 techniques. The dispersion of active phase in catalytic systems was exam-
ined by XRD and chemisorption of CO gas. Bimetallic Pd–Fe/SiO2 and Pd–Fe/Al2O3 catalysts containing
5 wt.% of Pd and 1–20 wt.% of Fe demonstrated high activity and high selectivity to phenol. However,
Pd–Fe/Al2O3 catalysts with higher dispersion of the active phase were less active in the studied reaction
than Pd–Fe/SiO2 systems, but selectivity to phenol was comparable for both types of bimetallic catalysts.
The stability of Pd–Fe/SiO2 systems was higher than the bimetallic Pd–Fe/Al2O3 catalysts but selectivity
to phenol decreases for that system systematically in each cycle of reaction, reaching only about 40% in
the tenth cycle. It was also found that the addition of Fe to palladium catalysts limited the formation of
cyclohexanone in the reaction medium.
Keywords:
Pd–Fe/SiO2 catalysts
Pd–Fe/Al2O3 catalysts
Catalytic hydrodechlorination
2,4-Dichlorophenol
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
were investigated for the treatment of waste streams containing
toxic chlorinated organic contaminants. The widely used chemi-
Chlorinated organic compounds (COCs) that were widely
utilized in 20th century [1] currently constitute the main contam-
ination components in nature. Because of the fact that they are
resistant to biological factors, systematic increase of their concen-
tration in the environment has been observed [2]. The presence of
significant amounts of COCs in air, soil, and also in the tissues of
living organisms may pose a threat to people’s health and it may
negatively influence the functioning of whole ecosystems.
Among the COCs, chlorophenols (CP’s) are still regarded as
useful industrial materials with a broad range of applications.
Chlorophenols are used as intermediates for organic synthesis, pes-
ticides, herbicides, biocides, dyes and wood preservatives [3,4].
Yet, these useful compounds are listed as priority pollutants by
the United States Environmental Protection Agency [5,6], due
to their high toxicity and resistance to decomposition. Due to
the harmful activity of chlorophenols [7], effective methods for
their decomposition need to be worked out. Several techniques
cal method of incineration often leads to the formation of highly
toxic by-products such as dioxins [8,9]. The methods based on
electrochemistry [10,11], photochemistry [12–14] and also on
biotechnology [15–18] result in low conversion. On the other hand,
the thermal methods, which include pyrolysis and hydrogenol-
ysis, require high energy. Another approach used to eliminate
those compounds from the environment is through catalytic
hydrodechlorination (HDC) with hydrogen, which is attractive
since it can be carried out at low temperature [19–21]. Among these
techniques catalytic hydrodechlorination provides a promising
non-destructive alternative technology whereby the chlorinated
waste is converted into products with commercial value [19–33].
Phenol, obtained in the HDC process of 2,4-DCP over supported
catalysts based on noble metals, is safer compound which may be
used as a substrate in various industrial processes. Phenol is com-
mercially used to make synthetic resins, dyes, pharmaceuticals,
pesticides, synthetic tanning agents, perfumes, lubricating oils and
solvents [34].
The catalytic hydrodechlorination of chlorophenols was con-
ducted on supported mono- and bimetallic catalysts based on Pd
[7,19–21,30,31,35–37], Pt [38–40] and Rh [7,32,39,41]. Among the
∗
Corresponding author. Tel.: +48 42 631 30 94.
E-mail address: stanislaw.karski@p.lodz.pl (S. Karski).
http://dx.doi.org/10.1016/j.molcata.2014.06.022
1381-1169/© 2014 Elsevier B.V. All rights reserved.

I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
249
studied supported bimetallic systems, those promoted with Ru
[22], Rh [43–45], Bi [46,47] showed the best catalytic character-
istics. In those publications, the influence of dispersion of active
phase [48–50], the kind of support [36,37,42], addition of the sec-
ond metal [42–45,51] and the role of natural water components
like humic acid [52] and different kinds of ions [53] on the catalytic
properties of supported systems in HDC of chlorophenols have been
discussed.
Catalytic properties of nanoparticulate, bimetallic Pd/Fe have
been also described in literature [37,54,55]. The authors of those
publications have established the optimal composition of bimetal-
lic systems and they have also studied the influences of reaction
temperature, the pH of the reaction environment, and other natu-
ral factors, such as the presence of humic acids or saltiness of the
water, on the catalytic properties in the process of HDC.
hydrochloric acid (CHEMPUR, 35–38%, pure p.a.). The water was
evaporated at an elevated temperature (T = 60 ◦C) under vacuum.
Monometallic catalysts were dried in air at 110 ◦C for 6 h, calcined
at 500 ◦C for 4 h in an oxygen atmosphere (O2, Air Products, 99,5%,
at rate 20 mL/min), cooling in an argon to room temperature (Ar,
Linde 5.0, at rate 20 mL/min), and then reduced in a hydrogen atmo-
sphere (H2, Air Products, Premium Plus, at rate 20 mL/min) for 2 h
at 300 ◦C before catalytic measurements. The linear temperature
increase rate was 20 ◦C/min between the thermal processing steps.
Bimetallic Pd–Fe/support catalysts containing 5 wt.% Pd and 1, 8,
20 wt.% Fe were obtained by coimpregnation of supports with water
solution of Fe(NO3)3·9H2O (POCH, pure p.a.) and PdCl2 (POCH,
anhydrous, pure p.a.) acidified to pH about 5 with hydrochloric
acid (CHEMPUR, 35–38%, pure p.a.), according to the procedure
described above.
However, supported Pd–Fe catalysts have not been researched
deeply in the hydrodechlorination reaction of polichlorophenols
in the liquid phase, especially mutual interactions between pal-
ladium and iron in catalytic systems were not studied. Munoz
et al. [56] used bimetallic Pd–Fe/␥-Al2O3 catalysts in degradation of
chlorophenols by sequential combination of hydrodechlorination
(HDC) and catalytic wet peroxide oxidation (CWPO). The Pd–Fe/␥-
Al2O3 catalyst showed a high activity in both processes, however
a decrease in activity was observed in each reaction HDC and
CWPO cycle, which can be attributed to iron leaching and active
site blockage by carbonaceous deposits. Complete dechlorination
of chlorophenol and negligible ecotoxicity of final effluents were
maintained upon successive applications in a four-cycles test with
2,4-DCP.
On the other hand, Golubina et al. [57] studied multiphase
hydrodechlorination of 1,4-dichlorobenzene, hexachlorobenzene
and 2,4,8-trichlorodibenzofurane over Pd/C and Pd–Fe/C catalysts.
Metal-metal interaction and structure of bimetallic particles were
studied by TPR and XPS techniques. Based on the obtained results,
two aspects of the influence of iron addition were considered: (1)
formation of Pd-enriched PdFe alloy, which resulted in an increase
of catalytic activity of bimetallic catalysts in comparison with Pd/C;
(2) formation of FeCl3 under HDC reaction condition, which pre-
vented complete chlorination of palladium, possibly leading to its
deactivation.
2.2. Catalytic measurements
In our studies the reaction conditions were optimized for
mono- and bimetallic catalysts. The mass-transfer limitations have
been evaluated experimentally using the diagnostic criteria asso-
ciated with varying hydrogen flow rate (0.05–0.5 L/min), stirring
speed (50–750 rpm), catalyst concentration (0.5–2 g/L) and parti-
cle size (0.5–0.075 mm). All the HDC reactions of 2,4-DCP solution
(0.4 L, 100 mg 2,4-DCP/L) were performed at the room tempera-
ture (20 ◦C) and at neutral pH (pH = 7 0.1). Experimental results
have revealed the influence of mass transfer at the liquid/solid
interface and intraparticle diffusion in limiting HDC rate. However,
these effects were not observed when hydrogen flow was higher
than 0.15 L/min, reaction mixture was stirred at least at 400 rpm,
the catalysts concentration was higher than 0.75 g/L and particle
sizes of catalysts were lower than 0.15 mm. For these reasons, all
HDC reactions over mono- and bimetallic catalysts were performed
under conditions described below in order to eliminate diffusion
restriction.
The HDC of 2,4-dichlorophenol (2,4-DCP) solution (2,4-DCP con-
centration was 100 mg/L) was performed in a 400-mL thermostated
glass reactor at the room temperature (20 ◦C). The hydrochloric
acid formed during the HDC of 2,4-DCP was neutralized by the
addition of an aqueous solution of sodium hydroxide (0.1 mol/L) to
maintain constant pH = 7 0.1 in the reaction medium. The reaction
was conducted with equal amount of catalyst (mcat = 0.4 g) in each
experiment. The mixture was stirred at 500 rpm and hydrogen was
bubbled through at 0.2 L/min. Samples of the reaction medium were
taken systematically, filtered and analyzed using high performance
liquid chromatography (HPLC), coupled to a variable wavelength
UV (210 nm) detector. The reaction products were separated on
a Zorbax SB-C18 column (mobile phase MeOH/H2O). In addition,
further products of phenol hydrogenation were detected by gas
chromatography (GC) (with FID detection; packed column 8% Car-
bowax 1540 on Chromosorb W).
In the present work the activity and the selectivity of chemically
precipitated supported palladium catalysts modified with Fe in the
hydrodechlorination of 2,4-dichlorophenol at room temperature
were investigated. These systems were characterized by XRD, XPS,
ToF-SIMS, AAS, TPR-H2 and CO gas chemisorption techniques.
2. Materials and methods
2.1. Catalyst preparation
Palladium catalysts characterized with good resistance to chlo-
rides deactivation are identified as the most efficient systems in
HDC reaction [25,58]. What is more, metal dispersion has been
identified as being critical [48]. Supported metal particle size can be
modified by the synthesis method, the support used, metal loading,
activation procedure and addition of second metal. In our studies
we concentrated on the influence of iron addition on the activity
and selectivity of 5%Pd/SiO2 and 5%Pd/Al2O3. The incorporation of
more than 5-wt.% of Pd into catalytic systems does not cause a sig-
nificant increase in the activity of palladium catalysts and is not
justified from an economical point of view [47].
For a group of selected catalysts (5%Pd/Al2O3, 5%Pd–8%Fe/Al2O3
and 5%Pd–8%Fe/SiO2), the stability in the reaction of hydrodechlori-
nation of 2,4-dichlorophenol was studied. Ten cycles of the 2,4-DCP
(100 mg/L, 400 mL total volume) HDC reaction were performed on
the same portion of catalyst (mcat = 0.4 g). Each cycle of the reaction
was conducted for 1.5 h at room temperature using H2, flowing
at 0.2 L/min. After this time, the product mixture was removed
from above the catalyst, filtered and analyzed by HPLC, GC-FID and
atomic absorption spectrometry (AAS). Over the course of the entire
process, including particular catalytic cycles, the catalysts were not
removed from the reactor. After the 10-th cycle of the reaction,
the catalyst was quantitatively transferred into a weighing vessel,
washed with deionized water, dried at 110 ◦C to constant weight,
and weighed. The weight loss of the catalyst was less than 6 wt.%.
These catalysts were analyzed by TOC technique to check if organic
Catalysts containing 5 wt.% of palladium were prepared by
aqueous impregnation of alumina (Fluka, 143 m2/g) and silica
(Sigma–Aldrich, 291 m2/g) from the solution of PdCl2 (POCH,
anhydrous, pure p.a.) which was acidified to pH about 5 with

250
I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
Table 1
Activity and selectivity for hydrodechlorination of 2,4-dichlorophenol over Pd/support and Pd–Fe/support (support = Al2O3, SiO2) catalysts after 1 h of reaction.
Catalyst
Chemisorption
of CO
Dispersion [%]
TOF [h−1
]
X2,4-DCP [%]
SPh [%]
S2-CP [%]
S4-CP [%]
SCHO [%]
[␮mol/gkat
]
5%Pd/Al2O3
109
14
27
13
34
17
13
26
23
3
6
3
7
4
3
6
3
19
10
21
11
17
22
13
94 (95)a
85
52 (54)a
19 (22)a
3
8 (1)a
3
21 (24)a
5%Pd–1%Fe/Al2O3
5%Pd–8%Fe/Al2O3
5%Pd–20%Fe/Al2O3
5%Pd/SiO2
5%Pd–1%Fe/SiO2
5%Pd–8%Fe/SiO2
5%Pd–20%Fe/SiO2
94
97 (98)a
96
–
– –
–
86 (92)a
92
1 (1)a
1
2 (1)a
3
97 (97)a
94
66 (59)a
94
6 (10)a
3
– –
3
28 (31)a
–
91 (92)a
95
98 (100)a
65
1 (0)a
13
1 (0)a
10
– (0)a
12
Activation of catalysts: drying in air at 110 ◦C, 6 h; oxidation in O2 at 500 ◦C, 2 h; reduction in H2 at 300 ◦C, 2 h.
Reaction conditions: T = 20 ◦C, mcat = 0.4 g, V2,4-DCP = 0.4 L, C0 2,4-DCP = 100 mg/L, pH = 7, VH = 2.0 L/min.
2
a
Activity and selectivity to main reaction products for hydrodechlorination of 2,4-dichlorophenol over monometallic catalysts: 5%Pd/Al2O3 and 5%Pd/SiO2 and bimetallic
catalysts: 5%Pd–8%Fe/Al2O3 and 5%Pd–8%Fe/SiO2 after 1.5 h of reaction.
carbon is present, which could indicate the decomposition of HDC
products. The results of the conducted research do not show any
amounts of organic carbon.
Alumina and silica used as a supports in studied mono- and
bimetallic catalysts were inactive in HDC reaction performed in the
same conditions.
reduced in the same conditions in which the catalysts were
prepared. After the reduction the samples were subsequently
cooled to room temperature under He gas stream (30 sccm). The
chemisorbed carbon monoxide was analyzed at room temperature
using the adsorption-backsorption isotherm method.
2.7. Temperature-programmed reduction (TPR-H2)
2.3. X-ray photoelectron spectroscopy (XPS)
TPR measurements were carried out in a flow apparatus, which
is described in Ref. [59]. The samples of fresh catalysts (about 0.3 g)
were flushed with argon at room temperature for 0.5 h prior to the
TPR measurements. After that, temperature programmed reduction
measurements were carried out. TPR runs were performed in the
temperature range 20–300 ◦C with a linear temperature increase
rate of 20 ◦C/min using a hydrogen-argon (5 vol.% of H2) mixture.
The bonding nature at the surface of Pd–Fe/SiO2 catalysts
was elucidated by X-ray photoelectron spectroscopy (XPS). Sam-
ples were prepared by pressing the catalytic powders onto
10 mm × 10 mm pieces of clean, UHV aluminum foil. These were
placed into a Versaprobe 5000 (PHI, USA) spectrometer. Survey and
high-resolution spectra were taken with a focused, monochromatic
Al K-␣ source (E = 1486.6 eV; 100 ␮m spot size). A cold cathode
electron flood gun and low-energy Ar+ ions provided charge neu-
tralization. The operating pressure was 2 × 10−6 Pa for Ar gas and
the system base pressure was 5 × 10−8 Pa. To avoid ion-induced
surface damage, surface sputtering was not used.
2.8. Total organic carbon (TOC)
The total carbon deposited on the catalysts was determined
using a Shimadzu-TOC 5000 instrument with a solid sample mod-
ule, where the carbon deposit is burnt at 900 ◦C in oxygen.
2.4. Powder X-ray diffraction (XRD)
2.9. AAS analysis of the reaction mixture
Room temperature powder X-ray diffraction patterns were col-
lected using a PANalytical X’Pert Pro MPD diffractometer. The X-ray
source was a copper long fine focus X-ray diffraction tube operating
at 40 kV and 30 mA. Data were collected in the range of 20 < 2ꢀ < 90◦,
with an angular step of 0.0167◦ and 20 s of exposure time per step. A
PANalytical X’Celerator detector, based on Real Time Multiple Strip
technology was used to collect and record the diffraction spectra.
Crystalline phases were identified by referencing the ICDD PDF-2
(ver. 2004) database.
The amounts of iron and palladium in the reaction mixture
were determined by atomic absorption spectrometry (AAS) on
GBC 923 plus spectrometer with the usage of flame atomiza-
tion (air 10 sccm/min and acetylene 2 sccm/min). The absorption
of reaction and standards solution was set for palladium and
iron at wavelengths of 247.6 nm and 248.3 nm, respectively. The
standard solutions (0.5; 1.0; 1.5; 2.0; 3.0; 4.0 mg/L) were prepared
by the dilutions of Pd and Fe standard samples (CPI Interna-
tional) at 1000 mg/L concentration. The samples of reaction mixture
(V = 5 mL) were mineralized with 5 mL HNO3 (Baker Instra Ana-
lyzed) and 1 mL HCl (Baker Instra Analyzed) in the microwave
reaction system Multiwave 3000 (Anton Paar) at 200 ◦C.
2.5. Time-of-flight secondary mass spectrometry (ToF-SIMS)
The ToF-SIMS IV mass spectrometer was equipped with a Bi liq-
uid metal ion gun and a high mass resolution time-of-flight mass
analyzer. During the measurement, the analyzed area was irradi-
3. Results and discussion
+
ated with pulses of 25 keV Bi3 ions at 10 kHz repetition rate and
an average ion current 0.6 pA. The analysis time was 30 s for both
positive and negative secondary ions giving an ion dose below the
static limit of 1 × 1013 ions/cm2. Secondary ion mass spectra were
recorded from an approximately 100 ␮m × 100 ␮m area of the sur-
face; ion images were obtained for a 500 ␮m × 500 ␮m surface area.
The activity and selectivity of monometallic palladium and
bimetallic Pd–Fe, supported on Al2O3, or SiO2, catalytic systems
in the hydrodechlorination of 2,4-dichlorophenol at room temper-
ature in liquid phase were studied (Table 1). From the presented
results, it can be concluded that supported palladium mono-
and bimetallic catalysts show similar activity in the reaction of
hydrodechlorination of 2,4-dichlorophenol. However, the selectiv-
ity to individual reaction products was completely different for
each system. Monometallic supported catalysts (5%Pd/Al2O3 and
5%Pd/SiO2) showed significantly lower selectivity to phenol. With
2.6. Chemisorption of CO measurements
Carbon monoxide chemisorption analysis was carried out in
a Micromeritics ASAP 2020 apparatus. Samples were previously

I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
251
Table 2
on alumina and silica show that in the case of using alumina as
a support Fe2O3 was the main phase besides Fe3O4 (Table 3),
while in the case of using silica only Fe3O4 phase formation was
observed. Golubina et al. [57] on the basis of XPS investigations
state the presence of Fe2O3 in the surface layer of bimetallic Pd–Fe/C
catalysts even after reduction in H2 at 500 ◦C. Thus, Pd–Fe/C cata-
lysts gain the features of Pd/FexOy/C catalysts. In our studies, we
found the presence of various forms of FexOy on the surface of
palladium–iron catalysts supported on SiO2 and Al2O3, especially
in the 5%Pd–20%Fe/Al2O3 catalysts. That is why strong metal-oxide
interaction becomes possible in such systems, and also spillover
of hydrogen and heat adsorption changes for both substrate and
hydrogen. This may also affect on the dispersion of the active phase,
and consequently influence the selectivity.
Metal particle size of Pd/support and Pd–Fe/support (support = SiO2, Al2O3) catalysts
calculated from CO chemisorption measurements and on the basis of XRD studies
according to the Scherrer equation.
Catalyst
Chemisorption
of CO
Average size of the Pd
crystallites [nm]
[␮mol/gkat
]
CO chemisorption
XRD analysis
5%Pd/Al2O3
109
14
27
5
38
20
39
7
25
18
30
5%Pd–1%Fe/Al2O3
5%Pd–8%Fe/Al2O3
5%Pd–20%Fe/Al2O3
13
5%Pd/SiO2
34
17
13
26
15
31
41
19
8
28
31
10
5%Pd–1%Fe/SiO2
5%Pd–8%Fe/SiO2
5%Pd–20%Fe/SiO2
Before the measurements of activity and selectivity, all the
obtained catalysts were reduced in H2 at temperature 300 ◦C.
Therefore, establishing the phase composition of these systems
was an important issue. Table 3 shows the phase composition of
monometallic palladium and bimetallic Pd–Fe catalysts, supported
on Al2O3 and SiO2. For bimetallic systems with low percent-
age amounts of Fe (1–8 wt.% Fe), maxima ascribed to metallic
phases of Pd and supports (Al2O3 and SiO2) were present in X-
ray diffractograms. For catalysts containing above 8-wt.% of iron,
the phase of metallic Fe was detected by XRD, too. In the case of
5%Pd–20%Fe/Al2O3, 5%Pd–20%Fe/SiO2 catalysts, iron oxides (Fe2O3
and Fe3O4) were additionally observed. The presence of Fe3O4 and
Fe2O3 phases indicates the incomplete reduction of iron oxide dur-
ing activation of the catalysts in an atmosphere of H2 at 300 ◦C.
Additionally, the surface composition of Pd–Fe/Al2O3 and
Pd–Fe/SiO2 catalysts was studied by ToF-SIMS. On the basis of
the secondary ion mass spectra of Pd–Fe/Al2O3, the ion intensi-
ties of Pd+, Fe+, FeOH+ were estimated (Table 3). Fig. 1 shows the
dependence between the intensities of ions: Pd+, Fe+, FeOH+, and
the composition of the studied Pd–Fe/Al2O3 catalysts. The intensity
of the Pd+ ions emission from the surface of the bimetallic catalysts
did not depend on the amount of Fe introduced into the system. A
proportional increase in the emission of secondary Fe+ and FeOH+
ions was observed with increased iron in the Pd–Fe/support sys-
tems. However, the simultaneous emission of iron and oxygen ions,
confirms the incomplete reduction of Fe in the studied systems. In
addition, ToF-SIMS did not detect the presence of any intermetallic
compounds on the surface of palladium–iron catalysts.
To obtain a better understanding of the surface chemical states
on the bimetallic catalysts, XPS studies were performed. The results
obtained for 5%Pd–1%Fe/SiO2 and 5%Pd–8%Fe/SiO2 catalysts con-
firm the existence of various chemical states of palladium and iron
on the surface of the analyzed systems (Figs. 2 and 3 and Table 4).
The XPS results were fitted with proprietary software (Multipak)
and the results were compared to the NIST database [60] and pre-
viously published data [61–67].
According to the literature, the electron binding energy of the Pd
3d5/2 peak, for metallic palladium, is in the range 334.6–335.6 eV
[60–63]; while for metallic iron supported on SiO2, the characteris-
tic electron binding energy corresponds to the about 711.1 eV [60].
The shift of the peak maximum corresponding to Pd0 toward higher
binding energy, in the 335.3–336.5 eV range [63], indicates the
presence of Pd–Fe intermetallic interactions. The presence of inter-
metallic PdFe alloy in the 5%Pd–8%Fe/SiO2 catalyst is also supported
by the shift in the binding energy of Fe 3d3/2 toward 711 eV [60,68].
On the other hand, it is well known that the binding energy of Fe
2p3/2 is about 709 eV for Fe2+ and 711 eV for Fe3+. The occurrence
of the Fe 2p3/2 peak at 710.7 may indicate that Fe3O4 is formed,
and that both Fe2+ and Fe3+ oxidation states exist. Furthermore, on
the surface of the tested system, the presence of palladium oxides
(PdO and PdOxPd), interaction between Pd and silica (Pd/SiOx/Si),
and palladium chloride (PdCl2) was also revealed [64–67].
these systems, further hydrogenation of phenol to cyclohexanone
was found. Moreover, in the case of monometallic systems, signifi-
cant amounts of 2-chlorophenol and 4-chlorophenol in the reaction
mixture were observed. For bimetallic palladium–iron catalysts
with higher amount of iron (≥20 wt.% Fe), supported on SiO2, the
selectivity to phenol was similar to the phenol selectivity for the
5%Pd/SiO2 system. This behavior may be connected to the sim-
ilar dispersion of the active phase in the 5%Pd–20%Fe/SiO2 and
5%Pd/SiO2 catalysts (Table 1).
On the basis of X-ray diffraction measurements, as well as from
the chemisorption of CO, the average size of Pd crystallites for
mono- and bimetallic systems was estimated (Table 2). It was
observed that the addition of iron into supported palladium cat-
alysts had a significant impact on the size of palladium crystallites
(Fig. 1).
The increase in the average size of Pd crystallites in bimetal-
lic catalysts, seems to cause an improvement in the selectivity
to phenol (Tables 1 and 2). Yet, the 5%Pd–20%Fe/SiO2 catalyst
shows a lower selectivity to phenol when compared to bimetallic
Pd–Fe/SiO2 catalysts with a smaller amount of Fe. For that cata-
lyst, cyclohexanone was detected in the reaction mixture, alongside
phenol, 2-chlorophenol and 4-chlorophenol. The behavior of the
bimetallic 5%Pd–20%Fe/SiO2 catalyst was probably caused by dif-
ferences in the dispersion of the active phase, which is similar to
monometallic Pd/SiO2 catalysts. Another reason for the behavior of
the 5%Pd–20%Fe/SiO2 catalysts, in comparison to other bimetallic
catalysts with smaller amounts of iron, may be the differences in
phase composition. XRD studies of bimetallic catalysts supported
0,7
0,6
0,5
0,4
0,3
0,2
0,1
0
0
1
2
3
4
5
6
7
8
Fe/Pd
Fig. 1. The relative number of counts of secondary ions (♦ – 106Pd+, ꢀ – Fe+, ꢁ –
FeOH+) as a function of the atomic ratio of Fe/Pd in Pd–Fe/Al2O3 (—) and Pd–Fe/SiO2
(- - - -) catalysts.

252
I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
Table 3
Phase composition (XRD) and surface structure (ToF-SIMS) of Pd–Fe/support catalysts dried at 110 ◦C in air (6 h), oxidized at 500 ◦C in O2(4 h) and reduced at 300 ◦C in H2(2 h).
Catalyst
XRD analysisa
ToF-SIMS analysisb
Pd
Fe
Fe3O4
Fe2O3
Al2O3
SiO2
Fe+
FeOH+
106Pd+
108Pd+
5%Pd/Al2O3
+
+
+
+
−
−
+
−
−
−
+
−
−
−
+
+
+
+
+
−
−
0.11
0.05
0.05
0.06
0.11
0.05
0.05
0.06
5%Pd–1%Fe/Al2O3
5%Pd–8%Fe/Al2O3
5%Pd–20%Fe/Al2O3
0.13
0.45
0.57
0.04
0.15
0.20
+
5%Pd/SiO2
+
+
+
+
−
−
+
−
−
−
+
−
−
−
−
+
+
+
+
−
−
0.09
0.04
0.05
0.08
0.09
0.04
0.05
0.08
5%Pd–1%Fe/SiO2
5%Pd–8%Fe/SiO2
5%Pd–20%Fe/SiO2
0.17
0.52
0.64
0.06
0.18
0.20
+
a
Patterns obtained with CuK␣ radiation, step scanned 20 s per step of 0.0167◦ of 2ꢀ. Crystalline phases were identified by references to ICDD PDF-2 (ver.2004) database.
b
Ion counts relative to the Al+(Si+) number of counts.
The catalytic samples, which underwent preliminary calcina-
This observation is consistent with previous studies made by Lietz
et al. [70] and from our research on the catalytic properties of sup-
ported palladium systems promoted with Ag [71], Bi [46,47], In
[72], Te [73] and Tl [74].
tions in O2 at 500 ◦C, were treated with hydrogen in a TPR-H2(1)
process (Fig. 4A). The calcined sample of the system containing
5%Pd/SiO2 showed two low-temperature peaks located in the tem-
perature range of 50–150 ◦C; first negative peak connected with
hydrogen desorption from the ␤-hydride of palladium formed dur-
ing the reduction of weakly bonded palladium oxide, and the
second positive peak connected with the reduction of palladium
oxide is more strongly bounded with the carrier. An addition of
a small amount of iron (5%Pd–1%Fe/SiO2) modified the intensity
of the hydrogen evolution peak and the negative peak disappears,
which suggests that ␤-PdH formation was inhibited. Lingaiah et al.
[69] proved that the introduction of iron inhibits the formation of
␤-PdH phase that occurs in the monometallic palladium catalysts.
For the monometallic 8%Fe/SiO2 system, a wide peak of hydro-
gen adsorption in the temperature range of 300–500 ◦C was
observed. This is quite a natural situation considering that iron
oxides do not easily reduce. Also, iron could create different forms of
oxides in the first stages of contact between the sample and oxygen.
For the bimetallic 5%Pd–x%Fe/SiO2 (x = 1; 8; 20%-wt.% Fe) cata-
lysts the reduction process started practically at room temperature.
The first maximum of the reduction rate at about 100 ◦C could
probably be attributed to the reduction of palladium oxide. How-
ever, the slight shift of the H2 adsorption maximum to a higher
Fig. 2. Experimental spectra of 5%Pd–1%Fe/SiO2 and 5%Pd–8%Fe/SiO2 catalysts obtained for catalyst samples after oxidation at 500 ◦C in air and reduction at 300 ◦C in H2
atmosphere.

I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
253
Fig. 3. Experimental Pd 3d3/2 and Si 2p3/2 spectra of (a) 5%Pd–1%Fe/SiO2 and (b) 5%Pd–8%Fe/SiO2 catalysts after oxidation at 500 ◦C in air and reduction at 300 ◦C in H2
atmosphere.
temperature, in comparison to the 5%Pd/SiO2 profile, could be
attributed to the reduction of PdxFeyO, which formed during the
first contact of the bimetallic catalysts with oxygen, when the sur-
face of catalyst is not totally stabilized. The presence of palladium
on the surface of bimetallic Pd–Fe/SiO2 catalysts probably facili-
tates the reduction of oxidized forms of iron. The next maxima
in the reduction rate (present in the termograms) of bimetallic
systems indicated the reduction of different iron oxides. The XRD
studies revealed the presence of two different iron oxides (Fe2O3
and Fe3O4) in the catalytic systems with higher amount of iron
(>8 wt.% Fe) under reduction in hydrogen atmosphere at 300 ◦C; this
is in good agreement with TPR-H2 measurements. Golubina et al.
[57], demonstrated on the basis of XPS data the presence of Fe2O3
in the surface layer of supported bimetallic Pd–Fe catalysts, even
after reduction by H2 at 500 ◦C. This result is in accordance with
other data [75] demonstrating that Fe3+ does not reduce in oxide-
supported catalysts in the presence of noble metal even during
H2 treatment at about 500 ◦C. Because of the incomplete reduc-
tion of FexOy even at 500 ◦C, we decided to reduce our catalysts in
lower temperature (at 300 ◦C) to avoid sintering of palladium on
the surface.
Table 4
XPS data of Pd–Fe/SiO2 catalysts after oxidation at 500 ◦C in air and reduction at
300 ◦C in H2 atmosphere. Analysis of the spectra was performed based on the NIST
[60] database and literature data [61–67].
The catalyst samples which underwent preliminary calcina-
tions in O2 at 500 ◦C and were treated with hydrogen in TPR-H2(1)
process, were reoxidized at 500 ◦C for 2 h. Finally, TPR-H2(2) mea-
surements were taken and their results are presented in Fig. 4B.
The similar behavior of 5%Pd/SiO2 and 8%Fe/SiO2 catalysts in the
TPR-H2(1) and TPR-H2(2) processes reveals the stationary state of
the catalysts’ surface composition under the activation step. After
the catalyst reached the stationary state, its surface and texture did
not change. This is probably why the obtained profiles in TPR-H2(2)
are repeatable over successive cycles.
In the case of bimetallic Pd–Fe/SiO2 catalysts, an additional
maximum in the reduction curve at around 130 ◦C was built into
the thermograms. Due to the lack of high-temperature maxima
attributed to iron oxides reduction, it can be concluded that the
surface of reoxidized bimetallic catalysts consists of PdxFeyO phase,
Catalyst
5%Pd–1%Fe/SiO2
5%Pd–8%Fe/SiO2
Chemical state
on the surface
Metal
Binding energy
[eV]
334.5
335.5
336.3
337.1
–
–
Pd
Pd, PdFe
PdO
PdO
PdCl2
PdOxPd
335.3
336.8
337.1
338.2
340.0
Pd 3d5/2
–
Fe2+/Fe3+
Fe/SiO2, PdFe
–
Fe 2p3/2
Si 2p3/2
710.7
102.3
103.7
–
–
–
Pd/SiOx/Si
SiO2, Fe/SiO2
SiO2
104.0

254
I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
Fig. 4. Temperature programmed reduction (A) TPR-H2(1); (B) TPR-H2(2) of (1) 8%Fe/SiO2; (2) 5%Pd/SiO2; (3) 5%Pd–1%Fe/SiO2; (4) 5%Pd–8%Fe/SiO2; (5) 5%Pd–20%Fe/SiO2
catalysts after drying in air at 110 ◦C, 6 h and oxidizing in O2 at 500 ◦C, 4 h.
which is readily reduced with hydrogen at low temperature. How-
ever, it is also possible that the reduction of iron oxides catalyzed
by palladium may also contribute to the formation of an additional
low-temperature peak during temperature-programmed reduc-
tion of the reoxidized bimetallic Pd–Fe catalysts.
XRD and ToF-SIMS studies did not show the occurrence of strong
interactions between Pd and Fe on the surface of Pd–Fe/SiO2 and
Pd–Fe/Al2O3 systems. However, XPS spectra and TPR-H2 termo-
grams may suggest some interactions between palladium and iron
on the surface of silica, which most strongly occurred in systems
with higher amounts of iron (>8 wt.% Fe).
Supported Pd and Pd–Fe catalysts are characterized by satis-
factory stability in the studied reaction, which is an important
property of the systems used in industrial practice. Table 5 shows
the changes in the activity of 5%Pd/Al2O3, 5%Pd–8%Fe/Al2O3 and
5%Pd–8%Fe/SiO2 catalysts after subsequent ten 1.5-h measuring
cycles. In the course of overall process, including particular catalytic
cycles, the catalysts were not removed from the reaction mixture.
In the case of the monometallic 5%Pd/Al2O3 catalyst, a gradual
but systematic decrease in the activity, as well as in the selectivity
to phenol and cyclohexanone, was observed in succeeding mea-
suring cycles. On the other hand, after the tenth reaction cycle,
the selectivity to 2-chlorophenol, when compared to the initial
value, doubled. Thus, we can conclude that the hydrodechlorination
of 2,4-dichlorophenol over the 5%Pd/Al2O3 catalyst in subsequent
measuring cycles was retained on the first step of dechlori-
nation, and 2-chlorophenol became the main product of the
reaction.
to the palladium–iron system deposited on SiO2. The conver-
sion of 2,4-DCP over the 5%Pd–8%Fe/Al2O3 catalyst after 15 h of
work was approximately 70%. Better results were obtained for the
5%Pd–8%Fe/SiO2 catalyst, which showed a high activity even after
tenth reaction cycle. 5%Pd–8%Fe/Al2O3 and 5%Pd–8%Fe/SiO2 cata-
lysts showed a gradual but systematic decrease in the selectivity to
phenol in the succeeding measuring cycles. The decrease in selec-
tivity was greater for palladium–iron systems deposited on SiO2.
The comparison of catalytic properties of 5%Pd–8%Fe/Al2O3 and
5%Pd/Al2O3 systems leads to the conclusion that in both cases the
increase of concentration of 2-chlorophenol and 4-chlorophenol
after subsequent measurement cycles can be observed. It might be
also noticed that the concentration of 2-chlorophenol in the reac-
tion mixture, in case of 5%Pd/Al2O3 catalyst, is high at the beginning
of the reaction and that is goes up after subsequent measurement
cycles. For 5%Pd–8%Fe/Al2O3 system, during first measurement
cycles, the concentration of 2-chlorophenol is low and reaches a
significant value, comparable with the monometallic system, only
after the tenth measurement cycle. A similar dependence has been
observed for 5%Pd–8%Fe/SiO2 system. Consequently, it seems that
such changes of properties may be caused by leaching of iron into
the reaction mixture.
In order to check the stability of Pd–Fe/support catalysts in the
process of HDC, AAS analysis of the reaction mixture for the pres-
ence of palladium and iron was conducted. Trace amounts of Pd
were observed systematically in the reaction mixture; iron was
not observed in the first cycle, but in subsequent cycles of reac-
tion there were trace amounts present. The amount of both metals
in the reaction mixture was very low, which confirmed the stability
of the catalysts.
For the bimetallic catalysts, the 5%Pd–8%Fe/Al2O3 showed a
lower stability in the process of HDC of 2,4-DCP in comparison

I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
255
Table 5
Conversion and selectivity to main reaction products for hydrodechlorination of 2,4-DCP over 5%Pd/Al2O3, 5%Pd–8%Fe/Al2O3 and 5%Pd–8%Fe/SiO2 catalysts after the following
1.5 h cycles of reaction.
Catalysts
Cycle of reaction
X [%]
SPh [%]
S2-CP [%]
S4-CP [%]
SCHO [%]
AAS analysis of reaction mixture
Pd [mg/dm3] (247.6 nm)
0.04
Fe [mg/dm3] (248.3 nm)
1
2
3
5
7
95.4
92.6
92.0
91.2
89.5
88.8
53.6
50.1
47.4
46.0
43.2
42.7
21.7
23.8
30.8
33.2
37.4
39.1
0.6
1.8
2.5
1.6
2.0
3.2
24.1
24.3
19.3
19.2
17.4
15.0
–
–
–
–
–
–
5%Pd/Al2O3
0.02
0.01
10
1
2
3
5
7
92.6
88.3
87.1
83.1
75.4
69.4
98.0
90.0
88.1
82.7
71.7
62.0
0.8
8.5
10.1
14.9
26.3
33.0
1.2
1.5
1.8
2.4
2.0
5.0
–
–
–
–
–
–
0.05
–
–
0.04
–
0.02
b.d.l.
–
–
0.01
–
0.05
5%Pd–8%Fe/Al2O3
5%Pd–8%Fe/SiO2
10
1
2
3
5
7
92.4
91.9
89.9
88.2
87.1
81.8
99.3
71.8
56.1
50.6
46.8
40.8
0.2
26.8
42.2
47.8
51.5
55.0
0.5
1.4
1.7
1.6
1.7
4.2
–
–
–
–
–
–
0.03
–
–
0.04
–
0.01
b.d.l.
–
–
b.d.l.
–
0.08
10
AAS measurments of reaction mixture after following reaction cycles over the same samples of catalysts (test of stability). b.d.l. – below detection limit; detection limits for:
Pd – 0.01 mg/L, Fe – 0.005 mg/L.
Fresh as well as used 5%Pd–8%Fe/Al2O3 and 5%Pd–8%Fe/SiO2
catalysts applied in the stability tests were analyzed to check if
organic carbon is present, which could indicate the decomposition
of HDC products. The results of the conducted research do not show
any amounts of organic carbon, which further indicates the stability
of catalysts in the studied reaction.
In the light of this research it might be assumed that due to a
long contact of supported Pd–Fe catalysts with HCl, as a reaction
product of HDC of 2,4-DCP in liquid phase, iron chloride is formed
and the systems behave in a similar way to monometallic palla-
dium systems. The confirmation of this hypothesis requires further
research on the structure and it will be described in a further article.
catalysts. It can be assumed, that the addition of iron into sup-
ported palladium systems prevented further reduction of phenol
into cyclohexanone which occurred on the surface of monometal-
lic palladium catalysts. The reason for this behavior of Pd–Fe/SiO2
and Pd–Fe/Al2O3 catalysts in the HDC of 2,4-DCP is probably con-
nected to bimetallic interactions on the surface of carriers. XPS and
TPR-H2 results indicate that some interactions between palladium
and iron on the surface of tested catalysts do occur. However, XRD
and ToF-SIMS studies of those bimetallic systems did not reveal the
presence of intermetallic PdxFey phases.
It has been previously demonstrated [47,48,57] that the HDC
of 2,4-DCP reaction over supported Pd catalysts is structurally
sensitive. Activity, and especially selectivity to phenol, strongly
depends on the dispersion of the active phase. Systems with low
dispersion of palladium are more selective to phenol and cyclohex-
anone.
4. Conclusions
Hydrodechlorination of 2,4-dichlorophenol process over palla-
dium supported catalysts may occur according to the scheme:
The introduction of iron into palladium catalysts causes an
increase in selectivity to phenol. Only phenol and small amounts of
side products (2-chlorophenol and 4-chlorophenol) were detected
in reaction mixture after the HDC of 2,4-DCP over Pd–Fe/support
In conclusion, this investigation provides strong evidence of the
efficiency of Pd–Fe/supported catalysts in the HDC of 2,4-DCP. Espe-
cially, bimetallic palladium–iron catalysts, containing up to 8 wt.%

256
I.A. Witon´ska et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 248–256
of iron, supported on SiO2 and Al2O3 seem to be interesting from
practical point of view. However, it is still difficult to provide a clear
explanation of the improved activity and selectivity of Pd–Fe over
monometallic catalysts. This is due to the overlapping effects of
active phase dispersion, surface structure, and chemical composi-
tion.
[33] T. Zhou, Y. Li, T.-T. Lim, Sep. Purif. Technol. 76 (2010) 206–214.
[34] Agency for Toxic Substances and Disease Registry (ATSDR), Toxicological Pro-
file for Phenol (Update), Public Health Service, U.S. Department of Health and
Human Services, Atlanta, GA, 1998.
[35] G. Yuan, M.A. Keane, Appl. Catal. B 52 (2004) 301–314.
[36] G. Yuan, M.A. Keane, J. Catal. 225 (2004) 510–522.
[37] G. Yuan, M.A. Keane, Catal. Today 88 (2003) 27–36.
[38] C.B. Molina, L. Calvo, M.A. Gilarranz, J.A. Casas, J.J. Rodriguez, Appl. Clay Sci. 45
(2009) 206–212.
[39] E. Díaz, J.A. Casas, Á.F. Mohedano, L. Calvo, M.A. Gilarranz, J.J. Rodríguez, Ind.
Eng. Chem. Res. 47 (2008) 3840–3846.
References
[40] I. Hannus, S. Mészáros, M. Búza, J. Halász, React. Kinet. Catal. Lett. 96 (2009)
405–411.
[1] W. Zhang, Ch.B. Wang, H.L. Lie, Catal. Today 40 (1998) 387–395.
[2] M. Czaplicka, Sci. Total Environ. 322 (2004) 21–39.
[3] S. Ramamoorthy, S. Ramamoorthy, Chlorinated Organic Compounds in the
Environment, CRC Press, Boca Raton, 1997.
[4] R.K. Juhler, S.R. Sorensen, L. Larsen, Water Res. 35 (2001) 1371–1378.
[5] USEPA, EPA/600/P-98/002Aa, 1998.
[41] J.L. Benítez, G.D. Angel, Ind. Eng. Chem. Res. 50 (2011) 2678–2682.
[42] P.D. Vaidya, V.V. Mahajani, Appl. Catal. B 51 (2004) 21–31.
[43] G.S. Pozan, I. Boz, Environ. Eng. Sci. 25 (2008) 1197–1202.
[44] T.T. Bovkun, Y. Sasson, J. Blum, J. Mol. Catal. A: Chem. 242 (2005) 68–73.
[45] G.S. Pozan, I. Boz, J. Hazard. Mater. 136 (2006) 917–921.
[46] I. Witon´ ska, A. Królak, S. Karski, J. Mol. Catal. A: Chem. 331 (2010) 21–28.
[47] I. Witon´ ska, A. Królak, Przem. Chem. 90 (2011) 636–640.
[48] S. Gomez-Quero, F. Caı´rdenas-Lizana, M.A. Keane, Ind. Eng. Chem. Res. 47 (2008)
6841–6853.
[49] E.-J. Shin, M.A. Keane, React. Kinet. Catal. Lett. 69 (2000) 3–8.
[50] Z. Jin, C. Yu, X. Wang, Y. Wan, D. Li, G. Lu, J. Hazard. Mater. 186 (2011) 1726–1732.
[51] B. Coq, F. Figueras, J. Mol. Catal. A: Chem. 173 (2001) 117–134.
[52] Z. Zhang, Q. Shen, N. Cissoko, J. Wo, X. Xu, J. Hazard. Mater. 182 (2010) 252–258.
[53] Ch. Xia, Y. Liu, S. Zhou, C. Yang, S. Liu, S. Guo, Q. Liu, J. Yu, J. Chen, Catal. Commun.
10 (2009) 1443–1445.
[6] USEPA, 8EHQ-14302, 2001.
[7] G. Yuan, M.A. Keane, Catal. Commun. 4 (2003) 195–201.
[8] N. Graham, W. Chu, C. Lau, Chemosphere 51 (2003) 237–243.
[9] W. Chu, C.K. Law, Water Res. 37 (2003) 2339–2346.
[10] M.S. Ureta-Zanartu, P. Bustos, C. Berrios, M.C. Diez, M.L. Mora, C. Gutierrez,
Electrochim. Acta 47 (2002) 2399–2406.
[11] H. Cheng, K. Scott, P.A. Christensen, J. Electrochem. Soc. 150 (2003) D17–D24.
[12] S.G. Poulopoulos, M. Nikolaki, D. Karampetsos, C.J. Philippopoulos, J. Hazard.
Mater. 153 (2008) 582–587.
[13] G. Waldner, M. Pourmodjib, R. Bauer, M. Neumann-Spallart, Chemosphere 50
(2003) 989–998.
[14] S.K. Banerji, R.K. Bajpai, J. Hazard. Mater. 39 (1994) 19–31.
[15] C.M. Kao, C.T. Chai, J.K. Liu, T.Y. Yeh, K.F. Chen, S.C. Chen, Water Res. 38 (2004)
663–672.
[54] Y. Shih, M.-Y. Chen, Y.-F. Su, Appl. Catal. B 105 (2011) 24–29.
[55] F. He, D. Zhao, Appl. Catal. B 84 (2008) 533–540.
[56] M. Munoz, Z.M. de Pedro, J.A. Casas, J.J. Rodriguez, Water Res. 47 (2013)
3070–3080.
[57] E.V. Golubina, E.S. Lokteva, V.V. Lunin, N.S. Telegina, A.Yu. Stakheev, P. Tundo,
Appl. Catal. A 302 (2006) 32–41.
[16] B.-V. Chang, C.-W. Chiang, S.-Y. Yuan, Chemosphere 36 (1998) 537–545.
[17] D.-S. Shen, X.-W. Liu, H.-J. Feng, J. Hazard. Mater. B119 (2005) 239–243.
[18] E.J. Shin, M.A. Keane, Chem. Eng. Sci. 54 (1999) 1109–1120.
[19] Z. Jin, Ch. Yu, X. Wang, Y. Wan, D. Li, G. Lu, J. Hazard. Mater. 186 (2011)
1726–1732.
[20] V.I. Simagina, O.V. Netskina, E.S. Tayban, O.V. Komova, E.D. Grayfer, A.V.
Ischenko, E.M. Pazhetnov, Appl. Catal. A 379 (2010) 87–94.
[21] Z.M. de Pedro, E. Diaz, A.F. Mohedano, J.A. Casas, J.J. Rodriguez, Appl. Catal. B
103 (2011) 128–135.
[58] P. Albers, J. Pietsch, S.F. Parker, J. Mol. Catal. A: Chem. 173 (2001) 275–286.
[59] T. Paryjczak, J. Rynkowski, S. Karski, J. Chromatogr. A 188 (1980) 254–256.
[60] NIST Standard Reference Database 20, Version 3.5.
[61] K.S. Kim, A.F. Gossmann, N. Winograd, Anal. Chem. 46 (1974) 197–200.
[62] G. Kumar, J.R. Blackburn, R.G. Albridge, W.E. Moddeman, M.M. Jones, Inorg.
Chem. 11 (1972) 296–300.
[63] S.-L. Chang, J.W. Anderegg, P.A. Thiel, J. Non-Cryst. Solids 195 (1996) 95–99.
[64] H. Bender, W. Chen, J. Portillo, L. Van den Hove, W. Wandervorst, Appl. Surf.
Sci. 38 (1989) 37–47.
[22] P.N. Rylander, Catalytic Hydrogenation over Platinum Metals, Academic Press,
New York, 1967.
[65] E. Paparazzo, J. Phys. D: Appl. Phys. 20 (1987) 1091–1097.
[66] B. Schleich, D. Schmeisser, W. Gopel, Surf. Sci. 191 (1987) 357–384.
[67] J.A. Taylor, G.M. Lancaster, A. Ignatiev, J.W. Rabalais, J. Chem. Phys. 68 (1978)
1776–1784.
[68] P. Li, E.Y. Jiang, H.L. Bai, J. Phys. D: Appl. Phys. 44 (2011) 075003–0750011.
[69] N. Lingaiah, P.S. Sai Prasad, P. Kanta Rao, F.J. Berry, L.E. Smart, Catal. Commun.
3 (2002) 391–397.
[70] G. Lietz, M. Nimz, J. Volter, K. Lazar, L. Guczi, Appl. Catal. 45 (1988) 71–83.
[71] S. Karski, I. Witon´ ska, J. Rogowski, J. Gołuchowska, J. Mol. Catal. A: Chem. 240
(1–2) (2005) 155–163.
[23] J.B. Hoke, G.A. Gramiccioni, E.N. Balko, Appl. Catal. B 1 (1992) 285–296.
[24] V. Felis, P. Fouilloux, C.D. Bellefon, D. Schweich, Rec. Prog. Gen. Proc. 13 (1999)
303–309.
[25] F.J. Urbano, J.M. Marinas, J. Mol. Catal. A: Chem. 173 (2001) 329–345.
[26] F.J. Berry, L.E. Smart, P.S. Sai Prasad, N. Lingaiah, P. Kanta Rao, Appl. Catal. A 204
(2000) 191–201.
[27] A. Gampine, D.P. Eyman, J. Catal. 179 (1998) 315–325.
[28] B.F. Hagh, D.T. Allen, Chem. Eng. Sci. 45 (1990) 2695–2701.
[29] C. Menini, C. Park, E.-J. Shin, G. Tavoularis, M.A. Keane, Catal. Today 62 (2000)
355–366.
[72] I. Witon´ ska, S. Karski, J. Rogowski, N. Krawczyk, J. Mol. Catal. A: Chem. 287
[30] S. Gómez-Quero, F. Cárdenas-Lizana, M.A. Keane, J. Chem. Eng. 166 (2011)
1044–1051.
(2008) 87–94.
[73] I. Witon´ ska, M. Frajtak, S. Karski, Appl. Catal. A 401 (2011) 73–82.
[74] S. Karski, I. Witon´ ska, J. Gołuchowska, J. Mol. Catal. A: Chem. 245 (2006)
225–230.
[31] Y. Shao, Z. Xu, H. Wan, Y. Wan, H. Chen, S. Zheng, D. Zhu, Catal. Commun. 12
(2011) 1405–1409.
[32] C.B. Molina, A.H. Pizarro, M.A. Gilarranz, J.A. Casas, J.J. Rodriguez, Chem. Eng. J.
160 (2010) 578–585.
[75] V.I. Kovalchuk, B.N. Kuznetsov, J. Mol. Catal. A: Chem. 102 (1995) 103–110.