SBA materials as support of iridium catalyst for hydrogenation reactions

Article abstract of DOI:10.1016/j.cattod.2019.03.018

This paper investigates the catalytic properties of SBA-3 and SBA-15 supported iridium catalysts. The produced catalysts (1 wt.% Ir) were tested for their performance in hydrogenation of toluene and the selective nitro group hydrogenation of ortho-chloron

Full text of DOI:10.1016/j.cattod.2019.03.018

Accepted Manuscript
Title: SBA materials as support of iridium catalyst for
hydrogenation reactions
Authors: Angelika Kiderys, Monika Kot, Ewa Janiszewska,
Mariusz Pietrowski, Chia-Min Yang, Michał Zieli n´ ski
PII:
S0920-5861(19)30114-2
DOI:
Reference:
https://doi.org/10.1016/j.cattod.2019.03.018
CATTOD 12040
To appear in:
Catalysis Today
Received date:
Revised date:
Accepted date:
31 October 2018
8 February 2019
8 March 2019
Please cite this article as: Kiderys A, Kot M, Janiszewska E, Pietrowski M, Yang C-Min,
Zieli n´ ski M, SBA materials as support of iridium catalyst for hydrogenation reactions,
Catalysis Today (2019), https://doi.org/10.1016/j.cattod.2019.03.018
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SBA materials as support of iridium catalyst
for hydrogenation reactions
Angelika Kiderys1,2*, Monika Kot , Ewa Janiszewska , Mariusz Pietrowski ,
1,2
1
1
2
1*
Chia-Min Yang , Michał Zieliński
1
Adam Mickiewicz University in Poznań, Faculty of Chemistry, Umultowska 89b, 61-614 Poznań,
Poland
2
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
*Corresponding authors:
Angelika Kiderys - angelika.kiderys@amu.edu.pl,
Michał Zieliński - mardok@amu.edu.pl
Graphical abstract

Research Highlights



New heterogeneous catalytic systems for hydrogenation reactions were developed
SBA materials were employed as a catalyst support and Ir as active phase
Hydrogenation of toluene and o-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-
CAN) were performed


Hydrogenation of o-CNB to o-CAN using in-situ generated hydrogen from the aqueous-
phase reforming (APR) of methanol
Activities of Ir/SBA-3 was higher than iridium supported on SBA-15, SiO
supports
2
or Al
2
O
3

Abstract
This paper investigates the catalytic properties of SBA-3 and SBA-15 supported iridium catalysts. The
produced catalysts (1 wt.% Ir) were tested for their performance in hydrogenation of toluene and the
selective nitro group hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-
CAN) using in-situ generated hydrogen from the aqueous-phase reforming (APR) of methanol. The
obtained results were compared with the hydrogenation performance of iridium catalysts supported on
the most widely used supports such as alumina and silica. The catalysts were characterized by XRD,
BET, TPR-H
2
, H chemisorption, XPS and TEM techniques. The highest activities were observed in
2
the case of the iridium catalysts supported on ordered mesoporous silica, both in hydrogenation of
toluene and o-chloronitrobenzene. The catalytic activity of iridium supported on SBA-3 was much
higher than that of Ir supported on the commonly used supports such as Al
2
O
3
or SiO .
2
Keywords: iridium catalyst, SBA-3, SBA-15, toluene hydrogenation, selective hydrogenation of
chloronitrobenzene, aqueous-phase reforming (APR) of methanol

1
. Introduction
The processes of hydrogenation of aromatic compounds and aromatic nitro compounds play
important role in the chemical industry. The products of selective hydrogenation of chloronitrobenzene
to corresponding chloroanilines have found many applications as an intermediate in the manufacture
of drugs, pesticides, pigments, and dyes [1]. The hydrogenation of aromatic compounds is also
important reaction from the industrially and environmentally point of view. The large amount of
aromatic-free fuels and solvents are produced using processes of hydrogenation of aromatic
hydrocarbons. These reactions have also the significant factor in synthesis of many organic
compounds. The product of benzene hydrogenation, cyclohexane, is a raw material for the production
of caprolactam (a substrate for obtaining nylon) and adipic acid (a substrate for the manufacture of
saturated polyesters and plasticizers) [2].
The performance of catalytic activity in the processes of hydrogenation mainly depends on the
type of the metallic active phase and type of the support. Recently, more attention has been paid to
synthesis and modification of the commonly known supports (Al
2
O
3
, SiO , mesoporous materials)
2
used in these processes [3-5]. The most promising supports are mesoporous silica materials,
particularly SBA types, which represent a unique class of silica-based materials, because of their
outstanding properties like high specific surface area, large pore volume and a uniform pore size
distribution [6]. In the last decade these materials have found a number of nanotechnological
applications, for example, as catalysts, supports, adsorbents, photochemicals, optical and drug
delivery agents [7-11]. From the among of SBA types materials, several catalytic reactions using SBA-
15 as a support for metal active phases were examined and showed promising results [12,13]. In the
literature the applications of SBA-3 as catalyst supports are rare [14-16]. Herein, we report the first
attempt to use SBA-3 and SBA-15 as supports for iridium active phase in the process of
hydrogenation of toluene to methylocyclohexane and selective hydrogenation of o-chloronitrobenzene
to o-chloroaniline. The textural properties of the supports and chemical characters of their surface are
affecting the dispersion and reducibility of the active phase [14-17].
The commonly used active phases in the processes of hydrogenation are platinum group
metals, particularly Pt, Pd, Rh [18-20]. Noble metal-based catalysts are an interesting choice, since
they have high activity for hydrogenation processes, and the reaction can then perform at low
temperatures and pressures. Among the metallic phases the most active and often used in

hydrogenation reaction is platinum. The interesting metal from this group is iridium that is
characterized by greater resistance to deactivation caused by impurities than other noble metals, but
studies devoted to monometallic Ir catalysts in relation to hydrogenation processes are very rare [21-
2
4]. For example, iridium catalysts have been employed for selective hydrogenation of unsaturated
aldehydes to corresponding unsaturated alcohols [25] and in the selective hydrogenation of furfural to
-methylfuran [26]. On industrial scale it is used for production of acetic acid (Cativa™ process) [27],
2
and in the processes of hydrodesulphurization [28].
The present work compares the activity of iridium particles as the active metal species
supported on the ordered mesoporous silica (SBA-3, SBA-15) and commercial (Al
2
O
3
, SiO ) supports.
2
The aim of this work was to determine the influence of texture of support in the processes of
hydrogenation. The catalysts were tested in hydrogenation of toluene and in the selective nitro group
hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-CAN). The latter reaction
was carried out by flow method using in-situ generated hydrogen from the aqueous-phase reforming
(
APR) of methanol. To the best of our knowledge, no data are available on the use of ordered
mesoporous silica as supports of iridium catalysts in the process of hydrogenation of toluene and o-
chloronitrobenzene.
2. Experimental
2.1.
Preparation of supports and catalysts
The SBA-15 material was synthesized by hydrothermal synthesis performed under acidic
conditions according to the procedures described elsewhere [29]. The support was prepared by the
3
following procedure: 4.0 g of Pluronic P123 (Aldrich) was dissolved in 30 cm of deionized water and
3
1
16 cm of 2M HCl (Polish Chemicals Reagents, Inc., Poland). Reactants were stirred at 35 °C until
3
obtained homogeneous solution, then 9.1 cm of tetraethyl orthosilicate (TEOS - Aldrich) was added
directly into the solution with stirring for 20 h at 35 °C. Then the mixture was aged at 90 °C for 24 h.
The white powder was separated by filtration, washed with distilled water, and dried in the air at room
temperature (RT). Template was removed by calcination at 550 °C for 8 h in air.
The SBA-3 support was prepared by hydrothermal synthesis performed under acidic
conditions according to our own procedure [14]. First, 8.3 g of cetyltrimethylammonium bromide
3
(
CTAB - Aldrich) was dissolved in 165 cm of deionized water followed by an addition of TEOS

3
3
dropwise (23 cm ). After stirring for 15 minutes, 34 cm , 38 vol.% HCl was added with continuous
stirring for next 30 min. After this, the additional portion of hydrochloric acid was added, which resulted
in precipitation of white gel. The mixture was stirred for next 2 h at RT. Then, aging of the gel was
carried out at room temperature for 8 days in static conditions. The resulting material was filtered,
washed, dried in air at RT and then calcined at 550 °C for 8 h in air.
Aluminium oxide was prepared by the reaction of aluminium isopropoxide (98+%, Aldrich) with
the excess of water according to the procedure described elsewhere [30]. The resulting aluminum
hydroxide was washed with isopropyl alcohol (Polish Chemicals Reagents, Inc.) followed by drying at
110 °C for 24 h and calcination at 550 °C for 4 h.
Silica was an amorphous SiO (silica gel, Polish Chemicals Reagents Inc.) that was activated
2
by thermal treatment in air at 550 °C for 4 h.
The Ir/support (support = SBA-3, SBA-15, SiO
2
or Al
2
O
3
) catalysts were prepared by the
IrCl xH O, 99.995%,
O was dissolved in water and this
conventional impregnation method using hexachloroiridium(IV) acid hydrate (H
Aldrich) as a metal precursor. The required quantity of H IrCl xH
2
6
2
2
6
2
solution was added to the evacuated support (the amount of precursor was calculated to achieve
iridium loading of 1 wt.%). Water was removed on a rotary evaporator. Then the impregnated samples
were dried at 100 °C for 24 h and labelled as Ir/SBA-3-D, Ir/SBA-15-D, Ir/SiO
2
-D and Ir/Al
2
O -D.
3
2.2.
Activation of catalysts
Prior to the measurements of hydrogen chemisorption, as well as before the measurements by
transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), X-ray photoelectron
spectroscopy (XPS) and low-temperature nitrogen adsorption-desorption (BET), each precursor-
impregnated support was placed in a fixed-bed flow reactor and reduced in hydrogen flow (99.99%,
3
-1
3
-1
Linde, 50 cm min ). At the beginning, the system was flushed at RT with argon (150 cm min ,
3
-1
9
9.99%, Linde) which was then replaced with hydrogen (150 cm min ). After 15 min, the hydrogen
3
-1
o
-1
flow was reduced to 50 cm min and the temperature ramp (10 Cmin ) started. After reaching the
o
setpoint (400 C), the catalyst precursor reduction was continued for 2 h. Then the catalyst was cooled
down to the room temperature in hydrogen flow. The last step consisted in flushing of the sample with
argon for 15 min. The reduced catalysts were labelled as Ir/SBA-3, Ir/SBA-15, Ir-Al
2
O
3
and Ir/SiO .
2

2.3.
Catalysts characterization
2.3.1. Determination of surface area, pore volume and pore diameter
The Brunauer-Emmet-Teller (BET) surface areas were determined by N adsorption at -
2
196 °C using a Micromeritics ASAP 2010 sorptometer. Total pore volume and average pore radius
were determined by applying the Barrett-Joyner-Halenda (BJH) method to the desorption branch of
the isotherm. Prior to the measurements of adsorption-desorption isotherms, the samples were
outgassed at 300 °C for 4 h.
2.3.2. Determination of metal content
o
Iridium content in catalysts reduced at 400 C for 2 h was determined by inductively coupled
plasma optical emission spectroscopy (ICP-OES) on a Varian Vista-MPX spectrometer.
The elemental analysis of all the iridium catalysts has indicated practically the same Ir content in
the catalysts (0.99; 1.01; 1.02 and 0.95 wt.% for SBA-3, SBA-15, SiO
2
and Al
2
O , respectively). The
3
o
ICP measurements were carried out for the catalysts reduced for 2 h at 400 C.
2
.3.3. Temperature-programmed reduction with hydrogen – TPR-H
Measurements of temperature-programmed reduction with hydrogen were carried out on
Pulse ChemiSorb 2705 (Micromeritics) instrument. Dried metal precursor-impregnated supports (~50
2
3
-1
mg) were reduced in the flow of 10 vol.%. H
the TPR-H studies, a quartz sand (Aldrich) impregnated with metal precursors (H
used as a reference material. The measurements were conducted in the temperature range from 50 to
2
– Ar (99.999%, Linde) at the flow rate of 30 cm min . In
2
2
IrCl xH O) was
6
2
-
1
9
00 °C at a linear temperature ramp of 10 °Cmin . The TPR-H
catalysts after activation in H at 400 °C for 2 h. All TPR-H profiles, presented in this work, have been
normalized to the same sample weight – 100 mg.
2
analyses were also performed for
2
2
2.3.4. Determination of metal dispersion by hydrogen chemisorption
The measurements of hydrogen chemisorption on supported metal catalysts were conducted
o
by the static method at 35 C on an ASAP 2010C sorptometer.
o
Prior to hydrogen chemisorption, fresh dried catalysts were reduced with H at 400 C for 2 h
2
(
see „Activation of catalysts“) and then the catalyst samples were pretreated in situ to purify their

surfaces from adsorbed gases. The pretreatment consisted in evacuation at room temperature for 15
o
3
-1
min. and then at 350 C for 60 min., followed by reduction in hydrogen flow (40 cm min , 99.999%,
o
o
Linde) at 350 C for 60 min. and evacuation at 350 C for 120 min.
The metallic surface area (S), expressed in m gIr-1, was calculated from the following equation
2
[31]:
v  N na 100
m
A
m
S 
22414m wt
-volume of adsorbed hydrogen expressed in cm , N
- Avogadro’s number (6.0221023 mol-1),
3
where v
m
A
2
n - chemisorption stoichiometry (n=2), a
weight (g), wt (%) - metal loading.
m
- surface area (m ) occupied by one iridium atom, m- sample
The dispersion (D) of iridium was calculated from the formula:
S  M
am  NA
D 
where S is metallic surface area, M is iridium atomic weight, N
surface covered by one iridium atom.
A m
is Avogadro’s number and a is the
2.3.5. Transmission electron microscopy (TEM)
Transmission electron microscope (TEM) images were recorded on a JEOL 2000 microscope
operating at accelerating voltage of 80 kV. The results were used to estimate ordering of the samples
and to estimate the Ir particle size.
2.3.6. X-ray photoelectron spectroscopy (XPS)
X-ray photoelectron spectra (XPS) were recorded on an Ultra High Vacuum (UHV) System
(
(
Specs, Germany). The examined materials were irradiated with a monochromatic Al Kα radiation
1486.6ꢀeV). The operating pressure in the chamber was close to 2ꢀ×ꢀ10−9 mbar. Binding energies
were referenced to the C1s peak from the carbon surface deposit at 284.6 eV.
2.3.7. X-ray diffraction analysis (XRD)
The X-ray powder diffraction was performed on a Bruker AXS D8 Advance diffractometer with
Ni-filtered CuK radiation (λ=1.54056 Å) over the 2Θ ranges of 2-8 and 10-60.

2.4.
Catalytic tests
2.4.1. Hydrogenation of toluene to methylcyclohexane
Toluene hydrogenation was performed at atmospheric pressure using a fixed-bed flow reactor
and H
2
as a carrier gas. Fresh dried catalyst (25 mg) was placed into the reactor and reduced in situ
3
−1
with hydrogen (100 cm ⋅min , 99.99 %, Linde) at 400 °C for 2 h. After that time, the reactor
3
−1
temperature was lowered to a desired level and hydrogen flow (50 cm ⋅min ), that passed through a
saturator filled with toluene and equilibrated at 10 °C (99.8 %, Aldrich), was directed to the reactor.
Inner diameter of the reactor was 8.0 mm, and the volume of catalyst bed was from 0.15 to 0.25 cm3
depending on the density of tested catalyst. The concentration of toluene in the hydrogen feed was
−
3
−1
stable and equal to 0.75 μmol⋅cm . The catalysts were heated at the rate of 10 °C∙min until reaching
the temperature of the catalytic test (75-250 °C). The reaction products were analyzed on a gas
chromatograph equipped with a capillary column RESTEK-MXT-1. The catalytic activity was presented
as apparent rate calculated by following equation:
FYC  mol

Tl
rt 



N
mol min
Ir

where F - total flow rate of feed (cm ⋅min− 1); Y - fractional conversion; C - concentration of toluene in
3
3
−1
the feed (molTl⋅cm ) and N - iridium content (molIr) in the sample. Turnover frequency (TOF, min ) was
calculated by dividing the number of molecules converted per second by the number of active iridium
atoms measured by H chemisorption.
2
2.4.2. Hydrogenation of ortho-chloronitrobenzene to ortho-chloroaniline with hydrogen generated in
situ in APR of methanol
Hydrogenation of o-CNB to o-CAN with in situ generated hydrogen from aqueous-reforming of
®
methanol was conducted in an X-Cube reactor (ThalesNano, Inc.). The reaction was carried out in
o
continuous-flow mode in an isothermal fixed-bed reactor at 225 and 275 C. Both reactions, i.e.
aqueous-phase reforming of methanol (that is the source of hydrogen) and hydrogenation of
chloronitrobenzene proceed at the same time in the same reactor and in the presence of the same
catalyst. Flow rate of the reaction mixture (0.05 M o-CNB in the mixture of methanol : water = 2:1 by
3
-1
volume) was 0.2 cm min , catalyst weight 50 mg, and liquid pressure 5 MPa. Inner diameter of the
3
reactor was 3.8 mm and the volume of catalyst bed was 0.08 cm . At the above parameters, liquid

hourly space velocity (LHSV) was 150 h-1 and space time (ST = volume of catalyst bed/volume flow
rate) was ~24 s. The reaction products were collected in a receiver and analyzed in 30-minute
intervals on a gas chromatograph equipped with a capillary column DB-1 and FID detector. A blind test
carried out in the absence of catalyst proved that no conversion of o-CNB occurred under used
−
1
conditions. Turnover frequency (TOF, min ) was calculated by dividing the number of molecules
converted per second by the number of active iridium atoms measured by H chemisorption.
2
Since the subject of this study was hydrogenation of o-CNB using APR of methanol as a
source of hydrogen, a quantitative analysis of gaseous products was not carried out. Qualitative
analysis has shown the presence of H
reaction of methanol reforming.
2
, CO
2
, CH and trace amounts of CO originating from the
4

3. Results and discussion
Very important parameters characterizing supports and catalysts are their surface area and
o
porosity. The textures of supports after calcination at 550 C (Table 1, Figure 1) and iridium catalysts
o
after reduction at 400 C (Table 2) were characterized by the low-temperature nitrogen adsorption-
desorption measurements. All isotherms of the supports (Figure 1a) are typical for SBA-3, SBA-15,
SiO
2
and Al
The SBA-3 support shows nitrogen adsorption/desorption isotherms of type IV(b)
characteristic for mesoporous materials (Fig. 1a) [34]. As the relative pressure increases isotherms of
the support show a sharp step, in the range of p/p = 0.15-0.30, characteristic of capillary
condensation of nitrogen within uniform mesopores. This step for SBA-3 is less prominent and shifted
to lower p/p in comparison to the other supports. It indicates that silica SBA-3 possesses smaller
mesopores [35]. Other supports (SBA-15, SiO and Al ) were characterized by type IV(a) isotherms
according to the IUPAC classification) with a clearly marked hysteresis loop (H1 for SBA-15, H2(b) for
SiO , and H4 for Al ), that testifies to their mesoporosity [34]. The loop of type H1 is found in
2
O
3
materials presented in the literature [14,32,33].
0
0
2
2
O
3
(
2
2
O
3
materials which exhibit a narrow range of uniform mesopores, as for instance in templated silicas (e.g.,
MCM-41, MCM-48, SBA-15). Usually, network effects are minimal and the steep, narrow loop is a
clear sign of delayed condensation on the adsorption branch. The shape of the hysteresis loop (type
H2(b)) indicates that the SiO
isotherm adsorption and desorption branches in the range of p/p
hysteresis loop closes at p/p =0.4 indicates that small cone-shaped pores are present as well. The
average pore size of SiO support, calculated by the BJH method on the basis of the isotherm
desorption branch, is 7.1 nm. The hysteresis loop recorded for Al can be classified as H4, that is
2
has mainly cylindrical pores as results from the parallel course of the
0
=0.7 - 0.9. The fact that the
0
2
2
O
3
often found for materials with aggregated crystals [34]. The pore size distribution covers the range
from 2 to 10 nm, with two maxima at 4 and 8 nm (Figure 1b). The average pore size calculated by the
BJH method is 7.5 nm (Table 1).
The low-temperature nitrogen adsorption/desorption isotherms were used to calculate surface
area, average pore diameter and average pore volume of iridium catalysts - Table 2. The impregnation
with iridium precursor does not change the texture of the supports. The BET surface area, pore
volume and average pore size (Table 2) remain close to the values obtained for the supports before
impregnation (Table 1). Only in the case of Ir/Al
2
O , introduction of iridium leads to decrease of surface
3

3
-1
area (~20%), pore volume of the catalyst (from 0.34 to 0.22 cm g ) and average pore diameter from
7.5 to 5.9. These diminishments are related to incorporation of iridium active phase into the porous
structure and blocking its surface [21].
An important parameter characterizing metallic catalysts is the dispersion of the metal. The
Ir/SBA-3 and Ir/SBA-15 catalysts prepared from hexachloroiridium(IV) acid as a metal precursor show
very high dispersion (Table 2). From among the reduced catalysts the highest dispersion calculated
from irreversibly adsorbed hydrogen was observed for Ir/SBA-15 catalyst. This catalyst exhibits slightly
higher dispersion (~80%) and lower particle size (1.4 nm) when compared to iridium catalyst
supported on SBA-3 (D~75%). Using the SBA supports with unique mesoporous structure provides
higher dispersion and lower particles size compared to iridium catalysts supported on commercial
Al
2
O
3
and SiO
2
supports, where dispersion was ~38 and ~57%, respectively. It indicates that the pore
chemisorption
structure and large surface area of the supports can affect the metal dispersion. The H
2
analysis showed particles size of iridium smaller than 3 nm for all catalysts. These results were
confirmed by TEM analysis - Figure 2. As results from Fig. 2, the TEM micrographs of the catalysts
indicate the particles size below 3 nm and a homogeneous dispersion of the nanoparticles on the
surface of supports. The TEM analysis confirmed also the well-ordered hexagonal pore system of SBA
catalysts. The pore ordering of the samples was also confirmed by low angle XRD analysis (Fig.3A,
3B). Both ordered mesoporous supports and iridium catalysts (Ir/SBA-3 and Ir/SBA-15) showed the
typical characteristic patterns of the SBA structures, matching well those reported in the literature [6].
In the case of Ir/ SBA-15 some decrease in intensity and broadening after Ir deposition on SBA-15
was observed. It suggested some loss of the ordering of the pore structure, especially for used
catalyst. It may be related to the lower hydrothermal stability of SBA-15 material in comparison to
stability of SBA-3 due to its lower contribution of micropores [36]. XRD patterns in the wide angle
range show only reflection attributed to the amorphous silica and Al
2
3
O (Figure 3). No metallic iridium
(
Ir0) was observed by XRD (absence of reflections at 40.6° and 47.3°), suggesting the presence of
very small, well dispersed metal crystallites (under 3 nm) [14,37]. These results are consistent with
TEM as well as with hydrogen chemisorption data.
The SBA materials reveals stronger interactions of the adsorbed iridium species with the
support surface compared to the other presented supports, which favours high dispersion of the active
phase. The interactions of iridium particles with the support were confirmed by TPR-H studies, Figure
2

4
. Measurements of temperature-programmed reduction with hydrogen (TPR-H
about reducibility of chemical compounds present in a sample and about their interactions with
support. TPR studies were carried out on dried samples. No reduction signals were seen in TPR-H
profiles of the supports (data not shown), which proves that the supports were irreducible. For the
2
) provide information
2
o
o
fresh catalysts (Figure 4) two maxima were observed at 130-190 C and 350-530 C ranges, and the
o
peak intensities depended on the type of used support. The peak at ~200 C assigned to the reduction
of highly dispersed iridium species originate from the precursor or to the reduction of IrO
x
to metallic
iridium [38-40]. Only this peak is observed in H IrCl sample, which means that the iridium precursor is
2
6
o
fully-reduced at this temperature [38]. The signals at 350-530 C range are assigned to iridium
stronger bonded to the support surface [21]. This peak is more intensive and slightly shifted to the
higher temperature for iridium catalysts based on SBA type supports than those for Ir/SiO
2
-D and
Ir/Al -D samples. The fact that the reduction of catalysts takes place mainly at higher temperatures
2
O
3
for Ir/SBA materials indicates that interaction between iridium species and these supports is stronger
making their reduction process more difficult. These results are confirmed by chemisorption study, the
Ir/SBA-3 and Ir/SBA-15 samples are characterized by higher dispersion and smaller size of iridium
particles compared to those for Ir/SiO
2
and Ir/Al
2
O . The total degree of reduction of the supported
3
iridium precursor calculated on the basis of hydrogen consumption at the temperature range RT-600
oC was over 90% for Ir/SiO
2
(93.9%), Ir/SBA-15 (94.6%) and Ir/SBA-3 (99.2%) catalysts, which
indicates an almost complete reduction of the active phase and presence of iridium in the catalyst at
zero oxidation state. The lower intensity of the TPR-H profile for Ir/Al is a result of lower reduction
degree (85.9%) in comparison to the reduction of iridium phase on silica supports. It may also result
from the smaller amount of iridium introduced during the impregnation of the Al support, as was
indicated by ICP analysis. The TPR-H profiles of catalysts after activation (H reduction, 400 °C, 2 h)
2
2
O
3
2
O
3
2
2
showed no reduction signals (data not shown) that proved the metallic state of iridium in the
investigated catalysts.
Figure 5 displays the XPS Ir 4f spectra for the reduced Ir/SBA-3 and Ir/SBA-15 catalysts. The
peak corresponding to Ir 4f7/2 has been analyzed. Its deconvolution indicates the presence of two
iridium species with binding energies at 60.7 eV related to metallic iridium and at ca. 62 eV assigned
δ+
to Ir-O (Ir ) [41-43]. The latter is a result of interaction of Ir atoms with the oxide support, giving rise to
an oxidic state denoted as Ir . The presence of Irδ+ can be also caused by oxidation of Ir as a result
δ+
0

of contact with air during transferring the samples to XPS cell. The contribution of partially oxidized
δ+
0
iridium (Ir ) is higher for Ir/SBA-15 catalyst due to larger influence of the support on Ir that is usually
observed for smaller Ir nanoparticles [42]. The results of XPS are in agreement with TPR-H
confirming the interaction of iridium species with oxide supports.
2
data
Catalytic activity of the investigated materials has been studied in hydrogenation of toluene
and in the reaction of selective hydrogenation of o-chloronitrobenzene (o-CNB) to o-chloroaniline (o-
CAN). The last reaction was carried out using flow method in conditions of in-situ hydrogen generation
from alcohol (methanol) and water by aqueous phase reforming without using compressed hydrogen.
The results of the hydrogenation of toluene performed at several temperatures are presented
in Fig. 6. The catalytic measurements carried out on the supports alone, i.e. SBA-3, SBA-15, SiO
2
and
Al , proved their inactivity in the hydrogenation of toluene, while the reduced Ir-catalysts showed a
2
O
3
considerable activity in this reaction. Methylcyclohexane was the only reaction product obtained over
the catalysts tested. The activity of the iridium catalysts supported on SBA-3 material for toluene
hydrogenation, expressed as the apparent rate (r
t
) of reaction (Fig. 6) as well as the turnover
frequency (TOF, min-1 - Table 2) was higher than that obtained over the catalyst supported on
commonly used SiO
2
or Al
2
3
O . The activity increased with the rise in the reaction temperature reaching
o
a maximum at 125-150 C for catalyst supported on SBA-3. In the case of Ir/SBA-15 the maximum of
activity was recorded at 150 oC while for Ir/SiO
it was 125 oC. Only for Ir/Al
catalyst the
2
2
O
3
o
hydrogenation activity increase with temperature of reaction reached the maximum at 175 C. For all
catalysts, a further increase in temperature caused a decrease in the activity. The decline in the
catalytic activity at higher temperatures is explained in the literature by the occurrence of
dehydrogenation [44], cracking of methylcyclohexane formed in the reaction studied [45]. The drop of
catalytic activity could also results from a loss of catalytically active sites caused by poisoning of the
catalyst surface by carbon produced in cracking of reactants [46]. However, we did not observe any
cracking products and, as was already mentioned, the only detected product was methylcyclohexane.
This permits to conclude that the only possible reason for the decrease in the catalytic activity at
higher temperatures was the reaction proceeding in the opposite direction, i.e. dehydrogenation of
-
1
methylcyclohexane. Calculations of TOF (min ) – Table 2, performed using the values of metal
dispersion, have shown that the most active catalyst was Ir/SBA-3, whose activity was almost 25%
higher than that of Ir/SBA-15 or Ir/SiO
2
. The activity of Ir/Al
2
O was comparable with the activity of
3

Ir/SBA-15 and Ir/SiO
2
due to its twice lower iridium dispersion. The lower dispersion of Ir/Al
2
O is
3
probably related to its twice lower BET surface area in comparison to SiO
2
and four times lower than
for SBA-15 support. To check the stability, the most active catalysts Ir/SBA-3 and Ir/SBA-15 were
tested at 150C for 25 hours and the results are presented in Figure 7. In the evaluated period of time
all catalysts showed a stable work. The activity of Ir/SBA-3 catalyst increased for the first 40 minutes
-
1
-1
of the reaction to the level of ~27 molTlmolIr min , then it gradually decreased and stabilized after few
hours. Similarly, the activity of Ir/SBA-15 catalyst diminished during the first 6-7h and then stabilized.
The activity of Ir/SBA-3 in 25 h test decreased by less than 24%, while the activity of Ir/SBA-15 fell
down by 30%. The characterisation of the used catalysts by means of XRD indicates the decrease of
ordering of the Ir/SBA-15 catalyst (Fig. 3) whereas the ordering of Ir catalyst supported on SBA-3 is
unchanged as was mentioned above. The textural properties of the catalysts after reaction are almost
2
unchanged. For both catalysts, the decrease of surface area about 14% (Ir/SBA-3 – 1108 m /g,
2
Ir/SBA-15 – 582 m /g) and slightly decrease of pore volume are observed. The average pore size of
the fresh and used Ir/SBA-3 catalysts are similar whereas it is higher for the used Ir/SBA-15 catalyst in
comparison to the fresh Ir/SBA-15 catalyst. The H
hydrogen volume adsorbed about 10% for both catalysts.
A comparison of the apparent rate and TOF values obtained for the best Ir/SBA-3 catalyst
2
chemisorption analysis showed decrease of
-
1
-1
-1
o
(r =28.7 molTlmolIr min ; TOF=38.1 min at 150 C) with the results reported in the literature for
t
iridium supported on modified acidic silica [33], magnesium fluoride and alumina [21], as well as
magnesium oxo-fluoride [24], shows that the iridium catalyst supported on SBA-3 is more promising
o
o
catalyst. Hydrogenation activities of Ir/MgF
2
-MgO catalysts at 125 C, after reduction at 500 C, were
r
t
=8.5 molTlmolIr-1min-1 and TOF=~12 min-1 [24] whereas the apparent rate on Ir supported on SiO
2
modified with NH
Cl reduced at 400 C was below 23 molTlmolIr-1min-1 at 150 C [33]. Based on the
o
o
4
paper [47], presenting the influence of different active phase (Pt, Ir, Ru) on catalytic activity for toluene
hydrogenation, it can be concluded that iridium may have a great potential for hydrogenation of
aromatic compounds.
The second reaction, in which the catalysts were tested, was selective nitro group
hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-CAN) in a flow reactor in
aqueous phase reforming (APR) conditions in the absence of external hydrogen. In the APR, reaction
proceeds between an organic compound (methanol) and water, which yield mainly hydrogen of high

purity [48,49]. According to literature reports [49], this hydrogen can be utilized in a simultaneous
reaction of hydrogenation, if a reducible compound (for example ortho-chloronitrobenzene) is present
in the reaction medium.
®
o
The reaction was carried out in an X-Cube flow, pressurized reactor at 225 and 275 C (such
a high temperature is necessary to start the APR reaction) under pressure of 5 MPa, using o-CNB
dissolved in the mixture of methanol : water (2:1 by vol.) as reactants. Results of catalytic activity
-
1
measurements, expressed as TOF min , are presented in Table 2. The most active catalyst at both
tested temperatures was Ir/SBA-3. The high activity, but almost ~40% lower than for Ir/SBA-3 catalyst,
was also shown for Ir/SBA-15, whereas other catalysts were poorly active. It is worth notice that during
hydrogenation of o-CNB in APR conditions the selectivity to o-CAN was always 100%, irrespective of
catalyst employed and conversion obtained. The research has shown that the method based on
hydrogen obtained in-situ from aqueous phase reforming of methanol, is promising method from the
viewpoint of utilization of reactants. The above method admittedly requires a higher temperature,
however, the advantage of the method is its 100% selectivity.
The highest activity in both investigated reactions showed iridium catalyst supported on SBA-3
material. This material has already been presented as the best support in comparison to the other
mesoporous ordered silica supports [50]. The authors considered the advantage of this support as a
result of its structure feature such as small pore diameter. Appropriate pore diameter generates the
required intimate contact between potentially active sites and reactant molecules allowing their
reaction. Such observation was done also by Pérez-Ramírez et al. [51]. Perhaps in the case of our
catalysts on supports with larger pores (SBA-15, SiO
2
, Al
2
O ) their lower activity compared to the
3
narrower SBA-3 also results from insufficient opportunity for contact of reagents with iridium active
sites resulting in lower activity of these catalysts.
Conclusion
The use of iridium active phase and SBA materials as supports has allowed to obtain new
catalysts with high activities in the hydrogenation of toluene and the selective hydrogenation of ortho-
chloronitrobenzene to ortho-chloroaniline, greater than that of the iridium system supported on Al
or SiO . The Ir/support catalysts prepared from H IrCl xH O precursor are characterised by different
dispersion of metallic phase. The dispersion has particularly significant effect on the activity of
2
O
3
2
2
6
2

catalysts. The catalysts with the greatest dispersion showed the highest activities in hydrogenation
reactions. Exceptionally high activity of the iridium phase supported on SBA-3 proves that this support
allows to obtain an active and selective catalysts of hydrogenation of aromatic hydrocarbons and nitro
group present in o-CNB. High activity of the latter can also be a result of its textural parameters such
as appropriate pore size allowing for sufficient contact time between reagents and the active sites.
Acknowledgements
This research has been carried out with the support of Advanced Education European- Asiatic
Exchange Programme in Materials Science and Catalysis - EURASIACAT Erasmus Mundus
Programme.
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o
Table 1. Characterization of supports calcined at 550 C.
Physical characterization of supports
Sample code a)
Total
pore Average
diameter,
nm
pore
Surface
m g
areab),
Method of activation
volume,
2
-1
3
-1
cm g
SBA-3
1292
641
381
184
0.72
0.72
0.68
0.34
2.2
4.5
7.1
7.5
SBA-15
calcination
air, 8 h, 550 C)
o
(
SiO
2
Al
2 3
O
a)
b)
For code explanation, see Experimental section.
The Brunauer-Emmet-Teller surface areas were determined by N adsorption at -196 C using a Micromeritics ASAP2010
2
o
sorptometer. Total pore volume and average pore size were determined by the Barrett-Joyner-Halenda (BJH) method.

o
Table 2. Characterization of iridium catalysts reduced at 400 C.
Hydrogenation
of ortho-chloronitrobenzene
c)
e)
Physical characterization of iridium catalysts
Hydrogen chemisorption data for Ir/support catalysts
Toluene hydrogenation
e)
Sample
codel
Volume
cm ·g
adsorbed, Dispersion,
%
o
o
o
Average
pore
diameter,
nm
Ir
Mean
150 C
225 C
275 C
a)
3
-1
Surface
Total pore
volume,
cm g
Method of
activation
b)
surface
area
m gIr
size of
area ,
d)
d)
Ir ,
2
-1
3
-1
m g
2
-1
-
1
-1
-1
Ht
Hirr
Hr
Dirr
nm
TOF, min
TOF, min
TOF, min
Ir/SBA-3
1290
675
379
150
0.68
0.70
0.66
0.22
2.1
4.2
7.0
5.9
0.71
0.94
0.66
0.39
0.44
0.46
0.33
0.22
0.27
0.48
0.33
0.17
75.4
79.8
56.9
37.4
181.7
190.0
136.3
90.9
1.5
1.4
2.0
2.9
38.1
25.3
29.4
28.3
0.79
0.48
0.13
0
0.91
0.59
0.26
0.15
Ir/SBA-15
reduction
(H ,
2
2h,
o
400 C)
Ir/SiO
2
2 3
Ir/Al O
a)
For code explanation, see Experimental section.
b)
o
The Brunauer-Emmet-Teller surface areas were determined by N
Joyner-Halenda (BJH) method.
2
adsorption at -196 C using a Micromeritics ASAP2010 sorptometer. Total pore volume and average pore size were determined by the Barrett-
c)
Dispersion and mean size of Ir particles (in nm) were determined by H
2
chemisorption using a Micromeritics ASAP2010C sorptometer. Prior to hydrogen chemisorption, fresh samples were reduced with H
00 C for 2 h. Chemisorption of hydrogen was carried out at 35 C, and the isotherms were determined using five different pressures in the range of 12-40 kPa (H - total adsorbed hydrogen). Then the catalyst was
) and the same procedure was repeated. The difference between adsorbed hydrogen extrapolated to zero pressure value for two isotherms
2
at
o
o
4
t
o
evacuated at 35 C for 30 min. to remove reversibly adsorbed hydrogen (H
r
equals to the amount of hydrogen irreversibly bound (Hirr). Dirr – dispersion calculated from irreversibly adsorbed hydrogen.
d )
Ir surface area and mean size of metal particles calculated from the amount of irreversibly chemisorbed hydrogen.
Catalytic activity was expressed as turnover number (TOF, min ) in moles of toluene or ortho-chloronitrobenzene reacted per surface metal atoms (determined by hydrogen chemisorption).
e)
-1

4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
SBA-3
SBA-3
SiO2
SBA-15
SBA-15
SiO2
Al O
2
3
Al O
0.0
0.5
2
3
-
0
.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
1
10
100
Pore diameter, nm
Relative pressure, p/p0
Figure 1. Nitrogen physisorption isotherms (the curves shifted along Y axis for clarity) and pore size
o
distribution for samples calcined in air at 550 C.

Ir/SBA-3
Ir/SBA-15
2
Ir/Al O
3
Ir/SiO
2
o
Figure 2. TEM images of iridium catalysts after reduction at 400 C.

A
B
4000
Ir/SBA-15
50000
after reaction
Ir/SBA-3
after reaction
Ir/SBA-15
Ir/SBA-3
SBA-3
SBA-15
2
3
4
5
1
2
3
4
5
2
theta, degree
2 theta, degree
C
1000
Ir/SBA-3
Ir/SBA-15
Ir/SiO2
Ir/Al O
2
3
10
20
30
40
50
2
theta, degree
Figure 3. Low- (A and B) and wide- (C) angle XRD patterns of supports and catalysts.

130-290
350-530
Ir/SBA-3-D
Ir/SBA-15-D
Ir/SiO -D
2
Ir/Al O -D
2
3
Ir-precursor
600 700 800
100
200
300
400
500
o
Temperature, C
Figure 4. TPR-H
2
profiles of the dried Ir catalysts and iridium precursor - H
2
IrCl (signal intensity for
6
catalysts has been normalized to 100 mg).

A
4f 7/2
B
4f 5/2
4
f 7/2
4f 5/2
67
66
65
64
63
62
61
60
59
69 68 67 66 65 64 63 62 61 60 59
Binding energy, eV
Binding energy, eV
Figure 5. X-ray photoelectron spectra (Ir 4f core levels) for Ir/SBA-3 (A) and Ir/SBA-15 (B) samples.

30
25
20
15
10
5
0
Ir/SBA-3
Ir/SBA-15
Ir/SiO2

Ir/Al O3
2
50
75
100 125 150 175 200 225
o
Temperature, C
Figure 6. The effect of support on the apparent rate (calculated on total iridium) of hydrogenation of
toluene as a function of temperature.
o
3
-1
Activation of catalyst: 400 C, H
2
=100 cm min , 2 h;
-
3
3
-1
Reaction: cTl=0.75 molcm , H
2
= 50 cm min , activity after 20 min.

35
30
25
20
15
10
5
0
Ir/SBA-3
Ir/SBA-15
0
1
2
3
4
5
22 23 24 25
time, h
Figure 7. Changes in the activity of Ir/SBA-3 and Ir-SBA-15 catalysts in toluene hydrogenation as a
function
of
of
the
reaction
time
at
150C.
3
-1
Activation
catalyst:
400C,
H
2
=100
cm min ,
2h;
-
3
3
-1
Reaction: cTl=0.75 molcm , H =50 cm min .
2