Facile synthesis of highly dispersed and thermally stable copper-based nanoparticles supported on SBA-15 occluded with P123 surfactant for catalytic applications

Article abstract of DOI:10.1016/j.jcat.2016.04.004

Here, we show a strategy to control the dispersion, spatial distribution, and stabilization of copper-based nanoparticles on a micro-mesoporous silica support, as well as their impact on the catalytic activity. In this respect, SBA-15 with P123 occluded mesopores was used as host to load, by impregnation, copper-based nanoparticles, whose dispersion was similar to that of the homologous NPs prepared by precipitation on the SBA-15 with open mesoporosity, while the thermal stability was better. The oxide and reduced forms of the catalysts were rigorously characterized by ICP-OES, low- and high-angle XRD, N₂ physisorption, HRTEM/EDXS, TPR, in situ XRD, and in situ XPS. Due to their high practical impact, both the oxide and metallic forms of the copper-based NPs were evaluated for catalytic activity in CO oxidation and hydrogenation of cinnamaldehyde, respectively. It was shown that the high dispersion of copper-based NPs and the electron-deficient sites, such as M²⁺ with high affinity for the C=O bond, are responsible for the outstanding catalytic performance of the solids. The paper demonstrates that using a simple impregnation method and a functionalized SBA-15 support, high-performance materials can be obtained avoiding the use of precipitating agents and strict control of the synthesis conditions.

Full text of DOI:10.1016/j.jcat.2016.04.004

Journal of Catalysis 339 (2016) 270–283
Contents lists available at ScienceDirect
Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Facile synthesis of highly dispersed and thermally stable copper-based
nanoparticles supported on SBA-15 occluded with P123 surfactant for
catalytic applications
a
Alexandru Chirieac a, Brindusa Dragoi a, , Adrian Ungureanu , Carmen Ciotonea a,b,c, Irina Mazilu a,b
,
⇑
Sebastien Royer b,c, , Anne Sophie Mamede c, Elisabetta Rombi d, Italo Ferino d, Emil Dumitriu a
⇑
a Faculty of Chemical Engineering and Environmental Protection, ‘‘Gheorghe Asachi” Technical University of Iasi, 73 Prof. Dr. Docent Dimitrie Mangeron Street, 700050 Iasi, Romania
b CNRS UMR 7285, Université de Poitiers, IC2MP-TSA 51106-4, rue Michel Brunet, 86073 Poitiers Cedex 9, France
c CNRS UMR 8181, Université de Lille 1, UCCS–Cité Scientifique, 59650 Villeneuve d’Ascq Cedex, France
d Dipartimento di Scienze Chimiche, Universita di Cagliari, Complesso Universitario Monserrato, S.S. 554 Bivio Sestu, 09042 Monserrato, Cagliari, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Here, we show a strategy to control the dispersion, spatial distribution, and stabilization of copper-based
nanoparticles on a micro–mesoporous silica support, as well as their impact on the catalytic activity. In
this respect, SBA-15 with P123 occluded mesopores was used as host to load, by impregnation, copper-
based nanoparticles, whose dispersion was similar to that of the homologous NPs prepared by precipita-
tion on the SBA-15 with open mesoporosity, while the thermal stability was better. The oxide and
reduced forms of the catalysts were rigorously characterized by ICP-OES, low- and high-angle XRD, N2
physisorption, HRTEM/EDXS, TPR, in situ XRD, and in situ XPS. Due to their high practical impact, both
the oxide and metallic forms of the copper-based NPs were evaluated for catalytic activity in CO oxidation
and hydrogenation of cinnamaldehyde, respectively. It was shown that the high dispersion of copper-
based NPs and the electron-deficient sites, such as M2+ with high affinity for the C@O bond, are respon-
sible for the outstanding catalytic performance of the solids. The paper demonstrates that using a simple
impregnation method and a functionalized SBA-15 support, high-performance materials can be obtained
avoiding the use of precipitating agents and strict control of the synthesis conditions.
Received 11 January 2016
Revised 4 April 2016
Accepted 6 April 2016
Keywords:
Copper-based nanoparticles
P123 surfactant
SBA-15
Hydrogenation
Oxidation
Ó 2016 Elsevier Inc. All rights reserved.
1. Introduction
there is a continuous interest in decreasing the size, while improving
the spatial dispersion and thermal stability of NPs. For this purpose,
Intense research efforts are being made nowadays on metal
(oxide) nanoparticles (NPs) synthesis, due to the recognized advan-
tages related to their size, shape, and dispersion, which make them
useful in multiple areas, such as catalysis, chemical and biochemical
sensors, drug delivery, energy storage, and pollution control [1–4].
Usually, their use as catalysts is accompanied by an intrinsic
problem consisting of their low thermal stability, associated with
the sintering phenomenon that occurs during catalytic reactions
performed at temperatures above 400 °C (such as steam reforming,
synthesis gas production, and partial oxidation reactions) and even
during the activation or regeneration processes [5,6]. Therefore,
many strategies have been proposed, such as trapping into organic
agents (e.g., polymers, surfactants, microgels, amines [3], metal core
coating within a mesoporous silica shell [6], deposition on inorganic
supports (e.g., alumina, silica, titania, zirconia, carbon, aluminosili-
cates, and hydrotalcites) [7,8], deposition on organic–inorganic
hybrid supports (e.g., amine-, thiol-, and carboxyl-modified silica
support) [9–11], and addition of metal promoters [12–14]).
In 1998, SBA-15 mesoporous silica synthesis was reported using
triblock copolymer (Pluronic P123, (poly(ethylene oxide)-block-
poly(propylene oxide)-block-poly(ethylene oxide), EO20PO70EO20
)
as structure-directing agent under acidic conditions [15]. This type
of silica, with a defined pore framework consisting of cylindrical
and parallel mesopores in the range size of 5–10 nm (intercon-
nected or not by secondary mesoporosity and/or microporosity
located in the walls), and displaying high surface area and pore vol-
ume, high hydrothermostability [16–18], received much attention
⇑
Corresponding authors. Fax: +40 232 271311 (B. Dragoi); Fax: +33 320436561
(S. Royer).
E-mail addresses: bdragoi@tuiasi.ro (B. Dragoi), Sebastien.Royer@univ-lille1.fr
(S. Royer).
http://dx.doi.org/10.1016/j.jcat.2016.04.004
0021-9517/Ó 2016 Elsevier Inc. All rights reserved.

A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
271
as support for NPs [19–27] or as nanocasts to obtain the corre-
sponding negative replicas [28–31]. The particular organization
of the pores allows improved control of the NPs size, dispersion,
morphology, and distribution in the main or secondary pore sys-
tem [32–35], while the thermal stability is much enhanced in com-
parison with nonsupported NPs or even those supported on
ordinary silica. It should be noticed that SBA-15 with open
porosity, obtained upon removal of P123 surfactant under air
calcination, was usually used as support for NPs. Quite recently,
the as-prepared SBA-15 was used as an organic–inorganic hybrid
host to prepare nanocoatings of ZnO [36], CuO [37], and CeO2
[38] on the internal surfaces of the mesopores. It was stated that
such a hybrid material provide a unique microenvironment that
consists of the confining space created between the organic
template and silica walls, which, besides the high density of sur-
face silanols, can hinder the agglomeration of the NPs into large
aggregates.
So far, impregnation and precipitation have been among the
most frequently used methods to prepare supported NPs. Impreg-
nation involves the wetting of the support with the precursor solu-
tion followed by solvent removal via thermal treatment either at
high temperature overnight, e.g., up to 250 °C [39], or at room tem-
perature for a longer time (incipient wetness impregnation fol-
lowed by mild drying—IWI-MD) [40]. When silica, either ordered
or nonordered, is used as support, the main crystalline phase
resulting from calcination under an oxidizing atmosphere consists
of the corresponding metal oxides, which usually are in low inter-
action with the support surface. In the specific case of bicomponent
NPs, the interaction between these two components is usually
favored and thus NPs with different size, shape, and distribution
of the two components in the same particle can be obtained [40–
42]. However, the major drawback consists of the low loading
degree in metal (ꢀ5 wt.%) that can be achieved, as well as the
agglomeration of the NPs into more or less large bundles during
the multiple thermal treatments (drying, calcination, reduction),
due to limited interaction of precursors with the support surface,
and consequently high mobility of the impregnated phase [40].
These shortcomings were usually overcome using precipitation,
either with urea or with sodium/potassium carbonate [43–45], as
a preparation method. A high loading degree in metals could be
reached, ꢀ60 wt.% or even 80 wt.% [45]. The dispersion of the
metal-based NPs is much improved, while a stronger metal–
support interaction is generated using these methods. Usually,
upon calcination, two types of crystalline phases can be obtained,
metal oxides and (phyllo)silicate (PS)-like phases. Experimental
observation of a phase depends on the thermal history of the pre-
cursors. For example, copper PS-like phases are less thermally
stable than nickel PS-like phases, and therefore, the probability
of generating CuO by the calcination of the copper PS-like phases
is higher than that of the generation of NiO during the calcination
of Ni PS-like phases [46].
oxide phases, which appear heterogeneously distributed on the
support surface, as both large bundles and mesoconfined particles.
Under these circumstances, the improvement of the dispersion and
stabilization of copper in copper-rich bicomponent nanoparticles is
a problem that naturally arises.
In the present study, we show that the dispersion and the ther-
mostability of copper-rich copper–nickel-based NPs (Cu:Ni weight
ratio 4:1) can be enhanced by the rational selection of the support
surface properties when a simple IWI-MD approach is used as
preparation method. In this context, as mentioned above, SBA-15
is a versatile support offering a multitude of properties to be
explored, which are related to the preparation steps. Among these
properties, the chemistry of the surface is indeed very important
for deposition of active metals and can be controlled by different
strategies, one of them consisting of the elimination of P123
organic surfactant before impregnation. On the other hand, the
preparation method plays a decisive role in the physicochemical
properties of the supported NPs. So far, many studies have focused
on the effect of the method of preparation of supported NPs, usu-
ally by comparing impregnation with precipitation, the main
strategies used in industry to load active phases onto a solid sup-
port. Irrespective of the nature of the metal NPs, all of these studies
systematically highlighted the efficiency of precipitation in terms
of dispersion, loading degree, thermochemical stability and cat-
alytic activity of the nanoparticles, in line with the above discus-
sion [24,46–51]. However, although precipitation allows high
loading degrees in metal, it involves corrosive and not environ-
mentally friendly chemicals, as well as strictly controlled condi-
tions for synthesis [43–45]. In addition, precipitation results in
the degradation of the ordered mesoporous structure of the sup-
port. Here, we demonstrate that the use of SBA-15 with triblock
copolymer P123 maintained inside the pores as an organic–inor-
ganic hybrid support for impregnation with metal nitrates is an
effective way to prepare copper-rich NPs whose dispersion and
catalytic activity are higher than those prepared by precipitation.
It is worth mentioning that this comparison between NPs prepared
by impregnation on a partially extracted SBA-15 and by precipita-
tion was imposed by the interactions taking place between the
precursors of the active sites and the support, which are key factors
in the thermal stability of the metal (oxide) NPs and their disper-
sion degrees. We demonstrated that such interaction is stronger
for the IWI-MD/EC sample then for P/C and DP/samples due to
the confinement effect of intrawall pores, which explains the
higher thermostability and smaller size with higher dispersion of
the NPs prepared by IWI-MD on partially extracted SBA-15 in com-
parison with the samples prepared by precipitation. The catalytic
properties of the oxide phases were evaluated for the oxidation
of CO, while metallic phases were evaluated for the hydrogenation
of cinnamaldehyde in the liquid phase. The differences in the cat-
alytic activities and selectivity are discussed in relation to the nat-
ure of metal precursors, metal–support interactions, and size and
dispersion of the metal-based NPs, as well as the promoting effect
of nickel on copper.
Recently, we reported studies of the dispersion and stabilization
of copper in CuNi/SBA-15 (5 wt.% in metal) materials by IWI-MD
[12,42]. Both oxide and metallic NPs manifest enhanced dispersion
as well as high thermostability during the calcination and reduc-
tion processes. Taking advantage of the typical topologies of
ordered supports (monomodal pore size distribution), improved
thermostability was achieved by confining particles in mesospace
to limit mobility of the impregnated phase and particle growth
upon sintering. It was also emphasized that the active phase com-
position has a significant effect on the physicochemical properties
of the copper–nickel-based NPs supported on SBA-15 [12]. The
progressive increase in Cu/Ni weight ratio has a positive effect on
the dispersion and stability of metal-derived NPs, up to a value
close to 1. Further increase in this ratio, in the case of Cu/Ni to
4:1, has a negative impact on the stability and dispersion of metal
2. Experimental
2.1. Chemicals
All chemicals required to prepare the materials were used with-
out any additional purification: tetraethylorthosilicate (Si(OC2H5)4,
TEOS, 98%, Aldrich), nonionic triblock co-polymer Pluronic P123
(poly(ethylene oxide)-block-poly(propylene oxide)-block-poly
(ethylene oxide), EO20PO70EO20, molecular weight 5800, BASF
Corp.), copper nitrate (Cu(NO3)2ꢁ3H2O, 98%, Aldrich), nickel nitrate
(Ni(NO3)2ꢁ6H2O, 98%, Sigma–Aldrich), urea (CH4N2O, SigmaUltra),

272
A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
sodium carbonate (Na2CO3, 99.8%, Merck), distilled water, and
hydrochloric acid. The chemicals used for the hydrogenation
reaction were also used as received: trans-cinnamaldehyde
(C6H5ACH@CHACHO, 98%, Merck) as reagent and isopropanol
(C3H8O, 99%, Sigma–Aldrich) as solvent.
(Ni, Cu, and Si). Before analysis, a known amount of calcined sam-
ple was introduced in a diluted HF–HCl solution and then digested
under microwave radiation. Powder X-ray diffraction (XRD) analysis
was performed on a Bruker AXS D5005 X-ray diffractometer using
Cu Ka radiation (k = 1.54184 Å) as X-ray source. For low-angle
analysis, the data were collected in the 2h range from 0.75° to 5°
with a step of 0.01° (step time 10 s). For high-angle analysis, the
data were collected in the 2h range from 10° to 80° with a step
of 0.05° (step time 8 s). Crystal phase identification was made by
comparison with the ICDD database. Nitrogen physisorption was
carried out on an Autosorb 1-MP automated gas sorption system
(Quantachrome Instruments). Prior to analysis, the samples were
outgassed under high vacuum at 350 °C for 3 h. The adsorption/
desorption isotherms were obtained at ꢂ196 °C, allowing 4 min
for equilibration between each two successive points. Textural
properties were found from the isotherms using the Autosorb 1
software, version 1.55. The BET surface area was determined using
the multipoint algorithm. The t-plot method was applied to quan-
titatively determine the micropore volumes and to assess the
micropore surface areas. The mesopore size distribution was deter-
mined from the desorption branch of the isotherms using a nonlo-
cal density functional theory (NL-DFT). High-resolution transmission
electronic microscopy (HRTEM) coupled with Energy-dispersive X-ray
spectroscopy (EDXS) was used to characterize the pore structure of
the SBA-15 support, the distribution of NPs throughout the pores,
and the microstructure of NPs, as well as their chemical composi-
tion. The micrographs were obtained on a JEOL 2100 instrument
(operated at 200 kV with a LaB6 source and equipped with a Gatan
Ultra scan camera). EDXS was carried out with a Hypernine (Pre-
mium) detector (active area 30 mm2) using the software SM-JED
2300T for data acquisition and treatment. The EDXS analysis zone
is defined on the particle and generally ranges from 5 to 15 nm.
Before analysis, the sample was first included in a resin and then
2.2. Preparation of samples
2.2.1. SBA-15 support
SBA-15 was synthesized according to a classical procedure, as
proposed by Zhao et al. [15], in which 4 g of Pluronic P123 and
1.6 M HCl solution were stirred at 40 °C until the complete dissolu-
tion of the templating agent. Then 8.5 g of TEOS was added drop-
wise and the magnetic stirring was maintained for 24 h. The
resulting gel was transferred into a polypropylene bottle and
heated at 100 °C for 48 h. After filtration and drying, half of the
support was subjected to calcination at 550 °C for 6 h in a muffle
oven (heating ramp of 1.5 °C minꢂ1) to remove the organic tem-
plate, while the other half was subjected to ethanol extraction
for 5 h in order to retain only ꢀ10% of P123 inside the pores (as
confirmed by TG-DSC analysis, Fig. S1).
2.2.2. Catalysts
2.2.2.1. Incipient wetness impregnation followed by mild drying (IWI-
MD). Freshly calcined and partially extracted SBA-15 supports
were impregnated with an aqueous solution of the corresponding
hydrated nitrates to obtain a total metal loading of 5 wt.% with
Cu:Ni weight ratio 4:1. The resulting materials were gently dried
at 25 °C for 5 days. The oxide phases of copper and nickel were
obtained after calcination under stagnant air at 500 °C for 6 h
(heating ramp 1.5 °C minꢂ1). Samples were denoted as IWI-MD/C
and IWI-MD/EC for the calcined and partially extracted support,
respectively.
a
cut of ꢀ100 nm width was realized by ultramicrotomy.
Temperature-programmed reduction (TPR) runs were performed on
an Autochem chemisorption analyzer from Micromeritics,
equipped with TCD to monitor H2 consumption and an MS detector
(Omnistar, Pfeiffer) to follow possible desorption (H2O, O2, CO2)
from the catalyst surface or a possible leak (N2). The calcined sam-
ples were introduced in a U-shape microreactor and activated
under 20 vol.% O2 in N2 flow (30 mL minꢂ1) at 500 °C for 1 h (heat-
ing ramp 5 °C minꢂ1). After cooling to 50 °C, a 3 vol.% H2 in Ar flow
was stabilized (30 mL minꢂ1) and the TPR runs were performed
typically up to 900 °C (heating ramp of 5 °C minꢂ1). In situ powder
XRD patterns at high angle were recorded on a Bruker D8 ADVANCE
X-ray diffractometer equipped with a VANTEC-1 detector, using Cu
2.2.2.2. Precipitation with Na2CO3 (P). The calcined SBA-15 support
was dispersed in a fixed volume of 0.14 M [Cu(NO3)2ꢁ3H2O + Ni
(NO3)2ꢁ6H2O] aqueous solution to obtain a final metal loading of
5 wt.% with Cu:Ni weight ratio 4:1. The reaction was performed
in a double-walled thermostated reactor at a temperature of
60 °C. Then 0.16 M Na2CO3 aqueous solution was added dropwise
and stirred for 2 h. The obtained solid was separated by filtration,
washed with distilled water, dried at 60 °C for 12 h, and calcined
in a muffle oven at 500 °C for 6 h (heating ramp 1.5 °C minꢂ1).
The resulting sample was denoted as P/C.
2.2.2.3. Precipitation with urea (DP). The calcined SBA-15 support
was dispersed in a fixed volume of 0.14 M [Cu(NO3)2ꢁ3H2O + Ni
(NO3)2ꢁ6H2O] aqueous solution to obtain a final metal loading of
5 wt.% with Cu:Ni weight ratio 4:1. The synthesis was performed
in a double-walled thermostated reactor at a temperature of
90 °C. Initially, the pH of the suspension was adjusted to 2 using
a 2 M HNO3 aqueous solution; then 3 M urea aqueous solution
was added dropwise and stirred for 24 h. pH evolution was contin-
uously monitored during the synthesis with a Hanna pH meter.
During the aging step, the measured pH was 7.5 0.1. The obtained
solid was separated by filtration, washed with distilled water, and
dried at 60 °C for 12 h. Then it was calcined in a muffle oven at
500 °C for 6 h (heating ramp 1.5 °C minꢂ1). The resulted sample
was denoted as DP/C.
Ka radiation (k = 1.54184 Å) as X-ray source. The calcined samples
were first placed on a Kanthal filament (FeCrAl) cavity and then
subjected to thermoprogrammed reduction under a 3 vol.% H2 in
He flow (30 mL minꢂ1) from 30 to 550 °C (heating ramp of 5 °-
C minꢂ1). The in situ diffractograms were recorded at definite tem-
peratures in the 2h range from 15° to 70° with a step of 0.05° (step
time 2 s). Crystal phase identification was made by comparison
with the ICDD database. In situ X-ray photoelectron spectroscopy
(XPS) was performed before and after reduction of catalysts at
350 °C for 5 h (heating ramp 5 °C minꢂ1) under 5 vol.% H2/He flow
(30 mL minꢂ1). The spectra were acquired with a VG Escalab220XL
spectrometer from Thermo. The analysis chamber was operated
under ultrahigh vacuum of ꢀ5 ꢃ 10ꢂ9 Torr. X-rays were produced
by a magnesium anode working with Mg Ka (1253.6 eV) radiation.
For the measurements, the binding energy (BE) values were
referred to the Si2p photopeak at 103.8 eV. The surface Cu/Si, Ni/
Si, and Cu/M atomic ratios were calculated by correcting the corre-
sponding peak intensities with theoretical sensitivity factors based
on Scofield cross sections.
2.3. Physicochemical characterization
Inductively coupled plasma optical emission spectrometry
(ICP-OES) was performed on a Perkin sequential scanning spec-
trometer to determine the elemental composition of the catalysts

A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
273
2.4. Catalytic tests
2.4.1. Hydrogenation of cinnamaldehyde
For each test, the calcined catalysts were reduced under hydro-
gen flow (1 L hꢂ1) at 350 °C for 10 h (heating rate of 6 °C minꢂ1 up
to the reduction temperature). The corresponding samples are
denoted as IWI-MD/R, IWI-MD/ER, P/R, and DP/R. The catalytic
tests were carried out in a high-pressure Parr reactor under the fol-
lowing conditions: 1 mL aldehyde, 40 mL isopropanol, 0.265 g cat-
alyst, hydrogen pressure of 10 bar, and reaction temperature of
130 °C. Samples were periodically taken off and analyzed by GC
with an HP 5890 series gas chromatograph, which is equipped with
a DB-5 capillary column and a flame ionization detector. The iden-
tification of the reaction products was achieved from the retention
times of pure compounds and occasionally by GC–MS (an Agilent
6890 N system equipped with an Agilent 5973 MSD detector and
a DB-5-ms column). The conversion of cinnamaldehyde and the
selectivity in the different hydrogenation products were calculated
by taking into account the FID response factors for each
compounds.
2.4.2. Oxidation of CO
CO oxidation was carried out under atmospheric pressure in a
quartz-glass fixed-bed continuous-flow microreactor in the tem-
perature range 80–200 °C. Prior to the reaction, the catalysts were
pretreated at 350 °C under H2 (15 mL minꢂ1) for 2 h, and then in air
(15 mL minꢂ1) for 1 h. The corresponding samples are denoted as
IWI-MD, IWI-MD/E, P, and DP. The catalyst (0.1 g) was contacted
with a CO/O2 mixture (total flow 55 cm3 minꢂ1; composition
1.5 vol.% CO, 1.5 vol.% O2, balance He). Analyses of the reaction
mixture were performed on line with a HP 6890 GC equipped with
a HP Poraplot Q capillary column and both a TCD and a FID (cou-
pled with a methanator) detector. At each reaction temperature,
conversions are evaluated after 30 min on stream to allow the
attainment of steady-state conditions.
Fig. 1. X-ray diffractograms at low angle for calcined Cu4Ni1/SBA-15 prepared
materials: (a) SBA-15; (b) IWI-MD/C; (c) IWI-MD/EC; (d) P/C; (e) DP/C.
2D hexagonal arrangement of pores and revealing long-range
mesopore ordering [15,18]. Additionally, the presence of (210)
and (300) planes is an indication of the excellent textural unifor-
mity of the original SBA-15 as well as of Cu4Ni1/SBA-15 samples
prepared by IWI-MD. No significant differences were observed
for the intensities and 2h positions of the diffraction peaks for
SBA-15, IWI-MD/C, IWI-MD/EC, and P/C samples, which reveal
similar orderings of the primary mesopores with comparable
structural parameters. For the P/C sample, only a small attenuation
of the (210) and (300) reflections is observed, suggesting a partial
loss of the long-range order in the final material.
3. Results and discussion
3.1. Structural and textural properties of samples
The calculated values for the elemental composition of calcined
copper–nickel-based samples are summarized in Table 1. It can be
observed that the Cu/Ni ratios are slightly higher than those
selected for preparation, indicating a small copper enrichment of
the samples.
XRD patterns collected in the low-angle range for the calcined
SBA-15 and copper–nickel-based materials are shown in Fig. 1.
On the basis of these diffractograms, the corresponding d-spacing
of the (100) plane and ao parameters were calculated and listed
in Table 1.
For the DP/C sample, these two reflections can no longer be
observed. In addition, the intensity of the (100) reflection
decreases, while the corresponding 2h position is shifted to lower
values, indicating larger mesopores and higher d-spacing and cell
parameter. Additionally, the intensity of the diffraction peaks at
higher 2h is also decreased up to disappearance. Consequently,
the precipitation with urea induces significant changes in the
structural characteristics of the support. A partial collapse of the
ordered mesoporous structure of the SBA-15 support, due to
the partial dissolution of the silica walls, can be proposed to be the
origin of these results. Similar behavior was previously observed
for cobalt deposition on SBA-15 by precipitation with urea,
confirming that harsh conditions such as pH and temperature
can partially damage the mesostructure of the support [46].
XRD patterns recorded for the calcined materials from 20° to
80° 2h are depicted in Fig. 2. The X-ray diffractogram for the IWI-
MD/C sample shows small diffraction peaks characteristic of cubic
NiO (ICDD 047-1049) and sharper diffraction peaks characteristic
of monoclinic CuO (ICDD 048-1548), indicating smaller crystallites
of NiO than those of CuO. The average sizes of metal oxide crystal-
lites, dNiO and dCuO, estimated from peak broadenings, are 29.5 and
14.5 nm, respectively. This result suggests that an important part
of the metal oxide precursors are transported outside the pores
of SBA-15 during thermal activation. It is interesting to note that
for the IWI-MD/EC sample, prepared by IWI-MD on partially
As a first observation, all patterns show the three diffraction
peaks indexed as (100), (110), and (200) peaks, characteristic of
Table 1
Chemical composition and structural properties of the calcined support and Cu4Ni1/
SBA-15 samples.
a
b
c
Sample
Cu–Ni (wt.%)
d100 (nm)
a0 (nm)
SBA-15
IWI-MD/C
IWI-MD/EC
P/C
–
9.1
9.1
9.1
9.1
9.8
10.5
10.5
10.5
10.5
11.3
5.1–1.1
4.3–0.9
4.5–0.9
4.9–1.1
DP/C
a
b
c
Metal content by ICP-OES.
d100 = lattice spacing obtained by low-angle XRD.
a0 = unit cell parameter calculated using the equation a0 ¼ 2d100
p
= 3.

274
A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
These assumptions appear to be reasonable, since the corre-
sponding XRD patterns do not display reflections of any crystalline
phase, suggesting a high distribution of the oxide phase through-
out the silica porosity. Interestingly, this level of metal oxide distri-
bution is very similar to those obtained by the precipitation of the
metallic cations from the corresponding nitrate salts either with
sodium carbonate (P/C sample) or urea (DP/C sample) (Fig. 2).
However, for the DP/C sample, very large diffraction peaks can be
distinguished at 2h ꢀ 35° and 60°. These reflections are attributed
to (phyllo)silicate-like phases, as generally reported by precipita-
tion with urea on silica [43,44]. Taking into account the weight
ratio between copper and nickel (4:1), these reflections could
eventually be associated with a residual highly dispersed copper
(phyllo)silicate-like phase (Cu-PS). Ni-PS-like phases could also
form, but they are difficult to observe by XRD due to the small
amount of nickel (Table 1). It is worth mentioning that, irrespective
of the preparation method, after calcination, bicomponent metal
oxide nanoparticles with size below the XRD sensitivity and very
well distributed in the solid support are obtained, except for the
IWI-MD/C sample.
Textural properties of the calcined SBA-15 and copper–nickel-
based materials were assessed by nitrogen physisorption. The cor-
responding adsorption/desorption isotherms, as well as the pore
size distribution curves, are illustrated in Fig. 3. It can be noticed
that the isotherms of the original SBA-15 and copper–nickel-
based materials prepared by IWI-MD, either on calcined or on par-
tially extracted support, are very similar. They are of type IV with
hysteresis loop of type H1, which are characteristic, of mesoporous
materials with cylindrical and parallel pores [15,18].
Fig. 2. X-ray diffractograms at high angle for calcined Cu4Ni1/SBA-15: (a) IWI-MD/
C; (b) IWI-MD/EC; (c) P/C; (d) DP/C.
extracted SBA-15, the XRD pattern does not show diffraction peaks
associated with either Ni oxide or Cu oxide, clearly indicating (i) an
excellent dispersion of the crystalline phases, with size below the
XRD detection limit (ꢀ3 nm) and (ii) a crucial role of residual
organics from P123 in the dispersion of metal precursors. So far,
different strategies have been proposed for preparing finely dis-
persed NPs, but they are usually complicated and involve several
steps, among them the functionalization of the surface with hydro-
philic or hydrophobic organic groups, as well as the use of toxic
organic solvents or even organometallic precursors, making them
unsustainable [32,33,52–55]. The approach consists in the modifi-
cation of support surface properties, grafting/encapsulating func-
tions having more affinity with the ionic species in solution. In
strong interaction with the support surface, surface species mobil-
ity is reduced during thermal treatment, and consequently,
increased dispersion of the active phases can be achieved. In this
context, the use of SBA-15 silica containing mesopores occluded
with residual P123 triblock copolymer as a functional support is
highlighted as an efficient preparation method to improve the dis-
persion of transition metal (oxide) NPs.
It is evident that the impregnation of SBA-15 solids followed by
drying and calcination did not change the mesostructure of the
support. Moreover, the parallel hysteresis branches indicate the
absence of pore plugging by oxide NPs, usually evidenced by a
new maximum in the pore size distribution curves [59]. The curves
drawn in Fig. 3 for these three samples display only the maximum
corresponding to the size of the main mesopores (i.e., 8.4 nm) of
the initial SBA-15 support. The sample obtained by carbonate pre-
cipitation exhibits an isotherm of type IV, but the hysteresis loop
changes from H1 to H2 type. Moreover, the relative pressure asso-
ciated with the capillary condensation in mesopores shifted to
lower values (0.5–0.8) in comparison with the support (0.65–
0.8). These results indicate the modification of the topology of
the mesopores, as well as a slight broadening of the pore size dis-
tribution. H2-type hysteresis observed for the P/C sample could be
explained by a local structural disorder of the mesoporosity as a
result of the very slight acidic pH of the synthesis mixture
(ꢀ6.5). However, this result, besides XRD at high angle, indicates
high dispersion of Cu and Ni metal precursors, since the hysteresis
shape does not indicate any constriction in the pores. An isotherm
of type IV, typical of mesostructured materials, is also obtained for
the DP/C sample. However, the significant changes in either the
isotherm or hysteresis shape and position indicate a significant
alteration of the ordered mesopore structure at long range, con-
firming XRD results at low angle [47,60]. The isotherm revealed
two distinct stages of capillary condensation at relative pressures
(p/p0) ꢀ 0.6–0.8 and ꢀ0.8–0.95, respectively, suggesting a bimodal
pore size distribution in the material. Indeed, the corresponding
pore size distribution (PSD) curve shows a very wide pore size dis-
tribution with two visible maxima, at 8.1 and ꢀ15 nm, respec-
Improvement of the dispersion of NPs deposited on partially
extracted SBA-15 can be explained by taking into consideration
two aspects:
– First, by using the support without calcination, the framework
contraction due to the surface dehydroxylation and formation
of siloxane bond is avoided, while the concentration of surface
silanols is maintained at high levels („SiAOH, 4.7 mmol gꢂ1
)
[56,57].
– Second, the presence of the organic surfactant having hydrophi-
lic PEO groups embedded in the walls creates a confining space
between the template and the silica walls that limits the mobil-
ity and growth of the metal precursors within the mesopores
during thermal steps [37,58]. Therefore, a tandem effect of (i)
the silanols, which stabilize the inorganic precursor of the
metal, and (ii) the confining space within the mesopores, allow-
ing the high dispersion of the very small metal (oxide) NPs,
could be assumed.
tively. The first appears to be
a remnant of the primary
mesopores of the parent SBA-15, while the second originates from
much larger pores generated by a dissolution–reprecipitation pro-
cess in a slightly alkaline medium (pH ꢀ7.5) and a high tempera-
ture of synthesis (90 °C) applied for the precipitation step. On the
basis of the isotherms in Fig. 4 and applying specific algorithms,

A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
275
Fig. 3. N2 physisorption isotherms of calcined Cu4Ni1/SBA-15: (a) SBA-15; (b) IWI-MD/C; (c) IWI-MD/EC; (d) P/C; (e) DP/C.
the textural properties of the investigated materials were evalu-
ated and they are summarized in Table 2. When compared with
SBA-15 support, all copper–nickel-based samples show lower val-
ues of the main textural properties, these changes having different
reasons, as explained further. For P/C and DP/C samples, the
decrease of the calculated values is also correlated with the partial
disordering of the mesostructure, which obviously depends on the
pH value. As a consequence, the DP/C sample manifests a much
greater decline of the mesostructure due to the harsher conditions
applied, as already mentioned. For the samples prepared by
impregnation (i.e., IWI-MD/C and IWI-MD/EC), the decrease of
the values of the textural properties is attributed to the deposition
of the metal oxide phase inside the mesopores (IWI-MD/EC) or at
the pore opening (IWI-MD/C).
The additional decrease of the micropore-related textural val-
ues (surface and volume) could suggest their blocking with metal
precursors homogeneously distributed in mesopores and/or depo-
sition of precursors even in intrawall pores. For the samples pre-
pared by precipitation methods, the decline of the microporosity
could also be a consequence of structural order loss, as identified
by XRD at low angle. The results obtained by nitrogen physisorp-
tion, which are basically in good agreement with the XRD results
at low angle, besides those provided by XRD at high angle, indicate
that IWI-MD is an effective method of preparing (bi)metallic NPs
supported on SBA-15 silica occluded with P123, with excellent tex-
tural uniformity and dispersion of the metal precursors similar to
that obtained by precipitation. In light of these results, it can be
stated that the precipitation methods, especially DP, are less effec-
tive because they lead to mesostructure alteration.
an excellent long-range order of the cylindrical mesopores. Second,
three kinds of metal oxide NPs can be observed.
Therefore, part of the metal oxide phase forms very large aggre-
gates ꢀ80 nm in size, stabilized at the mesopore openings. Another
part forms aggregates 80–100 nm in size on the external surface of
the SBA-15 grains. A small part of the metal oxide phase is confined
within the mesopores and generates nanobundles as a result of
mass transfer through the micropores interconnecting the adjacent
mesopores (Fig. 4A). As a general trend, the high proportion of cop-
per (Cu:Ni = 4:1) has a negative effect on the size and dispersion of
the metal oxide phases when calcined SBA-15 silica is used as sup-
port. Similar results were previously discussed in a study focusing
on the effect of chemical composition on the morphostructural
properties of copper-containing NPs confined and stabilized within
the channels of ordered SBA-15 silica by the IWI-MD approach [12].
From XRD and N2-physisorption results, partially extracted
SBA-15 silica is more appropriate as a support, providing a more
favorable microenvironment for impregnation, consisting of a
higher density in surface silanol and a confined space inside the
mesopores. Indeed, TEM images collected for this sample
(Fig. 4B) confirm these results. The hexagonal arrangement of
mesopores is well observed, while no external NPs can be detected
throughout the observed zones. Apparently, the mesopores are
empty of particles. However, at high resolution, very small
(ꢀ2 nm) and darker spots (such as those indicated by arrows)
appear highly dispersed along the mesochannels. These particles
cannot be detected by XRD due to their small size, while the
obstruction of the primary mesopores is circumvented (due to
the absence of aggregation). Punctual EDX microanalysis (either
with a large analysis zone over silica grains or a focalized
5–10 nm zone) evidenced copper and nickel in a ratio close to that
assessed by ICP, indicating a homogeneous dispersion of the two
elements inside the support.
The morphology and size of nanoparticles, as well as their loca-
tion with respect to the mesopores, were further analyzed by TEM
at low and high magnification. Representative TEM images of cal-
cined materials prepared by IWI-MD, P, and DP are shown in Fig. 4.
In total agreement with XRD and N2 physisorption, different
qualities of mesostructures can be observed depending on the
preparation method.
TEM images recorded for the P/C sample (Fig. 4C) reveal a mate-
rial that consists of mesochannels with local discontinuities, as
suggested by XRD at small angle and N2 physisorption. The diam-
eter of the mesopores determined by TEM (ꢀ7–8 nm) is in full
agreement with the average pore diameter determined by N2
First, TEM images corresponding to the IWI-MD/C sample
(Fig. 4A) show the typical mesoporous structure of SBA-15 with

276
A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
Fig. 4. TEM images at low and high resolution for calcined Cu4Ni1/SBA-15: (A) IWI-MD/C; (B) IWI-MD/EC; (C) P/C; (D) DP/C.
physisorption and NL-DFT calculation (predominantly 8.4 nm,
minor 7.4 nm). Concerning the metal-based NPs, finely dispersed
metal precursors (area marked with rectangle) can be observed
toward the external surface, most likely in the form of Cu and Ni
oxide phases generated by calcination. Indeed, according to EDX
microanalysis, these phases are characterized by a (Cu + Ni)/Si
atomic ratio almost four times higher than that corresponding to
the bulk composition determined by ICP (0.53 vs. 0.15), showing
an enrichment in the active phase in these areas. In addition, the
Cu/(Cu + Ni) atomic ratio, determined by EDX, is nearly identical
to that determined by ICP (0.85 vs. 0.82), indicating homogeneous
dispersion of the two metal precursors in these areas. However, by
analyzing several TEM images, it can be concluded that, although
observed, these external oxide phases do not represent a major
phase. The phases containing the metal precursors are mainly
located inside the pores of SBA-15, while the emerged NPs are
too small to be easily observed in the collected images. Copper
and nickel were detected only by EDX microanalysis performed
on different areas of the sample (Fig. S2).
In agreement with XRD at low angle and N2 physisorption
results, TEM images recorded for the DP/C sample (Fig. 4D) confirm
the significant alteration of the SBA-15 mesostructure, with cre-
ation of bimodal porosity (formation of large pores created by a dis
solution–reprecipitation process occurring during synthesis). Addi-
tionally, neither metal precursor phases on the external surface nor
crystalline phases of large size are observed, indicating high dis-
persion of metal phases. Even at high resolution, the detection of
the transition metals containing particles is difficult. Hence, the
presence of the two elements in the silica grains was proved by
EDX microanalysis in multiple areas, confirming the excellent

A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
277
Table 2
but also with nickel. A small peak with Tmax ꢀ 540 °C can be asso-
ciated with the reduction of Ni2+ (NiO phase). Since the reduction
of bulky NiO takes place at temperatures below 420 °C [63], it is
assumed that a reduction at 540 °C corresponds to NiO confined
to mesopores and/or in interaction with the support. According
to the TEM analysis for this sample, a small part of the formed
metal oxides are confined within the mesopores of SBA-15 silica
and could explain this reduction at high temperature. Additionally,
two shoulders can be observed at 240 and 350 °C. The first could be
attributed to the reduction of Cu2+ (from CuO) with relatively high
dispersion, probably CuO involved in the confined nanoparticles
observed in TEM images. The second could be attributed to the
reduction of both cations, Cu2+ and Ni2+, in CuO and NiO in interac-
tion with each other. This complex TPR profile, displaying different
reduction temperatures, reveals a heterogeneous distribution of
the oxides in this material, thus sustaining TEM analysis results
that showed different distributions of the metal oxides after
impregnation of the calcined SBA-15, drying, and calcination.
The TPR profile for IWI-MD/EC is less complex, showing a single
reduction peak, i.e., Tmax = 280 °C. Although this reduction temper-
ature would indicate a bulk copper oxide, this is unlikely, since a
very high dispersion for the copper phase is clearly shown by the
other analyses (i.e., XRD, TEM). The peak is narrower in comparison
with that obtained for the IWI-MD/C sample, indicating much
improved dispersion of the bicomponent copper-rich nanoparti-
cles, which are smaller and with enhanced homogeneity over their
size [62]. Since the reducing cations are included in bicomponent
NPs, a strong metal–metal interaction could be considered, as well.
For the samples prepared by precipitation methods (i.e., P/C and
DP/C), TPR profiles are different from those recorded for the sam-
ples obtained by impregnation. Two maxima for the consumption
of hydrogen are observed. The first maximum is located at 230 and
210 °C for P/C and DP/C, respectively. This hydrogen consumption
is associated with the reduction of Cu2+ to Cu0 in the CuO phase
generated by the decomposition, during calcination at 500 °C, of
(phyllo)silicates-like phases formed due to the synthesis process.
As noticed, these maxima are shifted toward much lower temper-
atures in comparison to IWI-MD samples, due to the high disper-
sion of the generated phases [64–67]. The second peaks are
located at 520 and 570 °C for P/C and DP/C, respectively, the peak
corresponding to the DP/C sample being much larger than that for
the P/C sample. These temperatures are usually associated with the
reduction of nickel in strong interaction with the support, as in
(phyllo)silicates-like phases [46–68]. Additionally, a two-steps
reduction of copper in residual PS-like phases [PS ? Cu+
(>200 °C) and Cu+ ? Cu0 (>600 °C)] could be also considered for
the DP/C sample [64].
Textural properties of the calcined supports and Cu4Ni1/SBA-15 samples.
Sample
SBET
Smicro
Vpore
Vmicro
Dp
(m2/g)a
(m2/g)b
(cm3/g)c
(cm3/g)d
(nm)e
SBA-15
IWI-MD/C
IWI-MD/EC
P/C
816
717
699
458
323
183
142
156
25
1.19
1.06
1.01
0.87
0.84
0.082
0.063
0.069
0.009
0.003
8.4
8.4
8.4
7.4; 8.4
8.4, 15.0
DP/C
11
a
b
c
SBET = total specific surface area obtained by BET equation.
Smicro = micropore surface area obtained by t-plot method.
Vtotal = total pore volume measured at p/p0 = 0.97.
Vmicro = micropore volume obtained by t-plot method.
Dp = pore size determined by NL-DFT algorithm.
d
e
homogeneity of the cation dispersion into support mesoporosity,
with a measured (Cu/(Cu + Ni)) atomic ratio in agreement with
that determined by ICP (0.85–0.88 vs. 0.80).
3.2. Reducibility and evolution of crystal phases upon reduction under
hydrogen
The reducibility and nature of the generated metallic phases
upon synthesis and calcination, as well as the metal–metal and
metal–support interactions, were investigated by TPR. The
recorded reduction profiles are displayed in Fig. 5.
The TPR profile for the IWI-MD/C sample shows a maximum at
325 °C. Usually, the reduction of bulk CuO takes place in the range
from 250 to 325 °C, with a maximum at ꢀ280 °C [61]. The slight
shift of the reduction temperature toward higher values, as well
as the breadth of the corresponding peak in Fig. 5a suggest a large
distribution of particle sizes [62] that are probably involved in dif-
ferent interactions with silica (i.e., from no to weak interactions),
As a conclusion for TPR investigation, it can be pointed out that
the samples prepared by impregnation show mainly metal–metal
interactions, while those prepared by precipitation methods are
mostly characterized by metal–support interactions, both kinds
of interactions directly affecting the metal precursor size, disper-
sion, and reducibility.
In order to clarify the intermediate crystalline phases formed
during the reduction process, as well as their thermal stability,
the calcined IWI-MD/EC, P/C, and DP/C samples were reduced at
different temperatures under hydrogen and monitored in situ by
XRD. The corresponding XRD patterns are illustrated in Fig. 6. Note
that IWI-MD/C was not investigated by this technique due to the
poor homogeneity of the oxide phase in the final solid.
For IWI-MD/EC and P/C samples, and irrespective of the reduc-
tion temperature, XRD patterns show diffraction lines attributed
only to the Kanthal holder. No significant sintering of the phase
can be detected until 550 °C, and formed phases remain very small.
For the DP/C sample, XRD performed after reduction at 30 °C
displays the same phase as detected by ex situ XRD analysis, that
Fig. 5. TPR profiles for calcined Cu4Ni1/SBA-15: (a) IWI-MD/C; (b) IWI-MD/EC;
(c) P/C; (d) DP/C.

278
A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
Fig. 6. In situ XRD patterns for (A) IWI-MD/EC, (B) P/C, and (C) DP/C after reduction under hydrogen at different temperatures: (a) 30 °C, (b) 150 °C, (c) 250 °C, (d) 350 °C, (e)
450 °C, (f) 550 °C, (g) 30 °C.
is, a residual Cu-PS-like phase. As the temperature increases, the
corresponding diffraction peaks become smaller; after reduction
at 350 °C, they are very difficult to distinguish. When the temper-
ature is further raised to 450 °C, these peaks disappear, indicating
their complete reduction to the metallic phase and their low ther-
mostability, as already discussed in the TPR section. A very broad
and small peak can be observed at 2h ꢀ 43.4° due to the diffraction
of the (111) plane of metallic Cu0 (JCPDS 04-0836) when the
reduction temperature exceeds 350 °C. It became sharper as the
temperature increases, suggesting minor sintering of the metallic
copper. However, even after reduction at 550 °C, this peak,
although more outlined in comparison to reduction at 350 °C, is
still broad and small, making difficult the estimation of the average
crystal size by the Scherrer equation. Interestingly, when these
XRD patterns are compared with those collected for the IWI-MD/
EC sample, no traces of metallic copper can be distinguished in
the XRD patterns for the last sample, even after reduction at
550 °C. Hence, the high dispersion of the oxide NPs obtained from
the partially extracted SBA-15 support not only was confirmed, but
also results show that NPs’ thermostability exceeds that mani-
fested by the DP-derived material. Thus, (i) the role of P123 in
NPs stabilization and (ii) the advantage brought by the IWI-MD
method when a suitable support is used to prepare highly dis-
persed and thermostable supported NPs were validated. Conse-
quently, the microenvironment generated at the interface
between the silanol-rich inorganic surface and the pore-occluded
residual template impact positively not only the dispersion but
also the thermostability of NPs.
resolution, the presence of transition metal in the particles being
confirmed by EDX spectroscopy. However, the oxide nanoparticles
can easily be observed on the wall surface of the primary
mesochannels (Fig. 4B and related discussion). Since no visible
deterioration of the mesopores can be noticed for the reduced
materials, a mass transfer from the main mesopores to intrawall
pores located nearby can be proposed to explain the migration of
the precursor and the lack of metallic particle formation at the pri-
mary mesopore surface after reduction. Because NPs are very diffi-
cult to see under these conditions, this sample was exposed to a
strong electron beam in the microscope for a period long enough
to destroy the porous network of SBA-15, while increasing the con-
trast between silica and NPs. This interesting method was previ-
ously proposed to detect small NPs that are particularly confined
in intrawall pores of SBA-15 [32]. Representative images are
depicted in Fig. 8.
In the first image, the pores appear empty of particles, while
some gray spots can hardly be distinguished in the walls. After
exposure to an electron beam for 3 min (Fig. 9B), the ordered
mesostructure appears partially damaged, while the nanoparticles
are still not very clearly seen. Only after 6 min of exposure (Fig. 9C)
does the ordered pore structure appear completely destroyed, and
uniform nanosized particles emerge in the TEM images. The parti-
cle size was possible thereafter to measure from such images (the
corresponding histogram is provided in Fig. 7A). An average size of
1.33 0.64 nm was obtained for this sample. It should be men-
tioned that a slight overestimation of the particle size could not
be excluded as a result of the bombardment, which is known to
result in particle sintering. This observation strongly supports the
idea that using a simple method such as impregnation over par-
tially extracted SBA-15, without a support surface postfunctional-
ization step, the copper-based nanoparticles can be selectively
located in the intrawall porosity of the SBA-15.
Due to the fact that the identification of the metallic NPs was
difficult to perform by XRD, TEM analysis was also carried out for
the three samples after reduction at 550 °C. Representative images
are depicted in Fig. 7.
For the samples prepared by precipitation (P/C and DP/C), dark
spots can be observed along the mesochannels or even in the walls
(indicated by white arrows in Fig. 7B and C). The very small size of
the particles, in addition to the low contrast with silica, makes the
measurement of particles difficult. Even under these conditions,
the size distribution was estimated for 70 particles from different
images taken at high resolution. Even if it is below the recom-
mended confidence particle number (200 particles), this distribu-
tion reflects the size of visible particles by TEM. Values of 2.99
and 2.29 nm were calculated for the average sizes of the nanopar-
ticles in P/C and DP/C samples, respectively, consistent with data
obtained by in situ XRD. Interestingly, for the IWI-MD/EC sample,
the emerged metallic NPs are not directly observed, even at high
3.3. Surface chemical states of samples
The surface composition and chemical states of copper and
nickel for the calcined and reduced samples were investigated by
XPS analysis. The binding energies (BE) and the atomic ratios at
the sample surfaces are listed in Table 3. The corresponding spectra
are provided in Figs. S3–S6.
For the IWI-MD/C sample, two BE at 933.6 and 855.7 eV attrib-
uted to the oxidation states of Cu2+ and Ni2+ in CuO and NiO
phases, respectively, were identified in the XPS spectra. These val-
ues are close to that reported for the corresponding bulk CuO

A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
279
Fig. 7. TEM images for (A) IWI-MD/EC, (B) P/C, and (C) DP/C after reduction under hydrogen at 550 °C and the corresponding particle size distributions.
Fig. 8. HRTEM images of IWI-MD/EC sample before (A) and after exposure to strong electron beam for 3 min (B) and 6 min (C).

280
A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
Fig. 9. CNA conversion vs. reaction time (A) and selectivity to CNOL vs. CNA conversion (B) for Cu4Ni1/SBA-15. Test conditions: Treduction = 350 °C; Treaction = 130 °C; 0.265 g
catalyst; 1 mL of CNA; 40 mL isopropanol as solvent; 10 bar H2; stirring rate 900 rpm.
Table 3
XPS results for calcined and reduced Cu4Ni1/SBA-15 samples.
Sample
Cu2p3/2 (eV)
Ni2p3/2 (eV)
Cu/Sia
Ni/Sia
Cu/Ma
Calcined materials
IWI-MD/C
IWI-MD/EC
P/C
933.6
855.7
857.2
857.0
856.9
0.011 (0.051)
0.030 (0.045)
0.039 (0.048)
0.102 (0.052)
0.014 (0.012)
0.010 (0.010)
0.015 (0.010)
0.033 (0.013)
0.441 (0.810)
0.744 (0.818)
0.716 (0.820)
0.753 (0.800)
933.6; 936.0
933.6; 936.0
933.9; 936.0
DP/C
Cu2p3/2 (eV)
Cu0
Reduced materials at 350 °C
Ni2p3/2 (eV)
Ni2+
Ni0
IWI-MD/R
IWI-MD/ER
P/R
933.2
855.7
857.1
857.2
857.0
852.4
853.0
852.6
852.4
0.005 (0.051)
0.023 (0.045)
0.026 (0.048)
0.053 (0.052)
0.006 (0.012)
0.008 (0.010)
0.014 (0.010)
0.030 (0.013)
0.462 (0.810)
0.740 (0.818)
0.654 (0.820)
0.637 (0.800)
932.8
933.0
932.8
DP/R
a
Surface atomic ratios and bulk atomic ratios (in parentheses); M = Cu + Ni.
(ꢀ933.5 eV [69]) and greater than that of bulk NiO (ꢀ854.9 eV
[70]). Accordingly, copper is poorly dispersed and in weak interac-
tion with silica, while nickel is better dispersed and in strong inter-
action with silica. The value of BE for nickel is very close to that
usually reported for Ni2+ in phyllosilicate-type phases [71,72] sup-
porting the formation of such phases even for IWI-MD/C material,
although these phases were not detected by the other investigation
techniques. This result is, however, not very surprising, since our
previous studies on copper–nickel bimetallic NPs supported on
SBA-15 clearly showed the formation of Ni PS-like [12,40].
Additionally, changes in Ni2p3/2 BE can also be correlated with
the d–d band interactions between nickel and copper atoms in
close vicinity to each other [70].
For the other three samples, two binding energies were identi-
fied for Cu2+ after curve fitting. The first (933.6/933.9 eV) makes an
insignificant contribution and corresponds to that of CuO in weak
interaction with silica. This is likely to occur due to (i) the larger
amount of copper than nickel in all these samples and (ii) the
mobility of the copper species, which makes difficult to stabilize
them with strong interaction with support surface [60]. The second
(936.0 eV) represents the major contribution to the Cu2+ signal.
The position suggests either a high dispersion of the copper phase
(IWI-MD/EC) [73–77] and/or a strong copper–silica interaction as
in (phyllo)silicate phases (P/C and DP/C), in line with the TPR data
[78]. For Ni2+, the evaluated BEs are higher than that of Ni2+ in the
IWI-MD/C sample, indicating a higher dispersion of nickel phases
as well as stronger nickel–silica interactions [79–82].
The XPS quantitative data are listed in Table 3. For the IWI-MD/C
sample, a large decrease of the Cu/Si ratio at the surface, in com-
parison with the bulk composition, was observed, which is in line
with the observed heterogeneous distribution of the metal oxide
NPs in the sample. For the IWI-MD/EC and P/C samples, the Cu/
Si ratio is closer to the bulk ratio, suggesting a more homogeneous
distribution of copper in these two samples, while for DP/C sample
this ratio is higher than the bulk ratio value, indicating a slight
enrichment in copper at the sample surface. As concerns the Ni
distribution in the IWI-MD/C sample, an enhanced Ni proportion
on the surface is assumed on the basis of the higher value for
Ni/Si measured by XPS than by ICP. For the IWI-MD/EC sample,
Ni/Si ratios on the surface and in the bulk are identical, proving
the homogeneous distribution of this element on the sample sur-
face. For samples prepared by precipitation methods, an increase
of Ni/Si calculated by XPS can be observed as a result of the surface
enrichment in Ni.

A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
281
Cu/M ratios calculated by XPS show that most of the Ni is
located in the near-surface region of IWI-MD/C, while for the other
three samples, the Cu/M ratio on the surface is slightly lower than
the bulk value, indicating a slight enrichment in nickel at the sur-
face. Therefore, according to ICP, XPS, and TEM, different distribu-
tions of the two elements (Cu and Ni) in the four samples, related
to the preparation method, the nature of the support (calcined or
partially extracted), and metal–support and metal–metal interac-
tions, can be recognized.
SBA-15 (IWI-MD/ER) and by deposition–precipitation (DP/R) are
the most active (CNA conversion of 100% in 120 min of reaction).
This significant increase in catalytic activity can be attributed to
a large number of accessible active sites, characterized by a higher
dispersion of Cu0 and Ni0 [13,84,85]. Regarding the catalytic activ-
ity of samples prepared by precipitation with Na2CO3 (P/R), lower
activity than for DP/R is measured. This is in line with XPS data (see
the Cu/Si and Ni/Si surface atomic ratios in Table 3), which show a
smaller amount of metallic active phases on the P/R surface in
comparison with the surface of DP/R.
After reduction at 350 °C, the binding energies for copper are
shifted to lower values due to the reduction of Cu2+ to Cu0
[70,83]. Interestingly, almost similar values are obtained for IWI-
MD/R and P/R, i.e., 933.2 and 933.0 eV, respectively, while for
IWI-MD/ER and DP/R the same value was assessed for both of
them, 932.8 eV. As noticed, for the last two samples, the binding
energies are lower than for the first two samples, indicating elec-
tron transfer between nickel and copper, which are in strong inter-
action [83]. For nickel, two binding energies were identified in the
spectra collected for all samples. The first is almost similar to that
obtained for the calcined samples, meaning that there is incom-
plete reduction of surface nickel at this temperature, a result sup-
ported by TPR. The second binding energy value (852.6–853.0 eV)
is lower than the first one and is characteristic of metallic Ni0
[70,83]. As a general trend, the M/Si and Cu/M ratios are main-
tained at values almost similar to those for the calcined samples,
suggesting that the distribution of elements is not significantly
changed after reduction, and thus confirming the good stability
of NPs toward thermal sintering.
Fig. 9B shows the selectivity of Cu4Ni1/SBA-15 materials to
CNOL as a function of the conversion of CNA. Both samples pre-
pared by IWI-MD, irrespective of the nature of support (calcined
on partially extracted), manifest the same selectivity to the unsat-
urated alcohol. The main values are in the range 5–10% for a con-
version range of 20–90%. Accordingly, it can be claimed that the
chemical nature of the active sites is similar for both samples,
the main difference between these two materials consisting in dif-
ferent dispersion degrees (as already shown by the physicochemi-
cal characterization discussed above). For the samples prepared by
precipitation methods, the nature of the active sites is significantly
modified, since improved selectivity in CNOL is obtained. Conse-
quently, modifications in the adsorption of cinnamaldehyde are
assumed to be responsible for the improved selectivity. This state-
ment is supported by the catalytic behavior of the IWI-MD/ER sam-
ple, whose dispersion is higher than for the samples prepared by
precipitation, but whose selectivity to CNOL is low. It is obvious
that the C@O bond is more easily activated on the catalytic sites
generated from (phyllo)silicate-like phases as metallic precursors.
It is worth recalling that the major advantage of this reaction con-
sists of its high sensitivity to the electronic and geometric proper-
ties of the NPs supported on a catalytic support [84,86]. The surface
structure of NPs is significantly changed in the 1–5 nm size range,
since the number of corner, edge, and terrace atoms changes,
affecting the surface electronic properties and thus the adsorption
properties of the reactant molecule [4]. Additionally, the chemical
nature of the support is also an important parameter for the
adsorption of the reactant molecule [87]. Taking into account these
two hypotheses, and on the basis of the TPR and XPS showing that
part of the metallic precursors are not reduced at this temperature,
it can be assumed that the unreduced phases are electron-deficient
and thus affect the route of adsorption of CNA. The intimate con-
tact between the surface metallic active sites and these electron-
deficient sites is expected to promote the dissociation of hydrogen
on the metallic sites, in parallel with the coordination of the oxy-
gen of C@O bond on the neighboring electron-deficient site. As a
result, this bond is polarized and finally hydrogenated to produce
the unsaturated alcohol.
3.4. Catalytic properties of oxide and metallic materials
3.4.1. Hydrogenation of CNA, metal phase accessibility, and metal–
metal/metal–support interaction
After reduction at 350 °C under H2 flow, the catalytic perfor-
mances of Cu4Ni1/SBA-15 materials were evaluated for the hydro-
genation of cinnamaldehyde (CNA) in liquid phase at 130 °C under
10 bar of H2. The hydrogenation of CNA takes place in two steps
(Scheme 1).
First, the partially hydrogenated products, cinnamyl alcohol
(CNOL) and hydrocinnamaldehyde (HCNA), are produced. These
two compounds are hydrogenated further to the saturated alcohol,
hydrocinnamyl alcohol (HCNOL).
Fig. 9A shows the variation of the total conversion of CNA
depending on the reaction times for all catalysts. As a first observa-
tion, the sample prepared by IWI-MD on calcined SBA-15 (IWI-MD/
R) is less active (CNA conversion of 90% in 360 min of reaction),
while the samples prepared by IWI-MD on partially extracted
The possible presence of Cu+ species, generated by the reduc-
tion of a residual Cu-PS-like phase (over precipitation-derived
materials, as stated on TPR section), can also act positively on the
selectivity. Indeed, it was previously reported that the presence
of Cu+, in strong interaction with an alumina surface, could explain
enhanced selectivity to CNOL [85].
3.4.2. Oxidation of CO
Monocomponent CuO and NiO supported on SBA-15 and pre-
pared by the IWI-MD method were used as reference materials
to stress the catalytic performance of the bicomponent copper–
nickel phases. The conversion curves are depicted in Fig. 10.
When monometallic nickel is used as a catalyst, the activity,
expressed as CO conversion, is practically zero irrespective of the
reaction temperature. This behavior confirms some references
showing that nickel oxide does not seem to exhibit good perfor-
mance in CO oxidation [88] but disaffirms others that report nickel
as a reactive metal oxide catalyst for CO oxidation by O2 [89]. A
Scheme 1. Reaction pathways for the hydrogenation of can.

282
A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
For the bimetallic Cu4Ni1/SBA-15 catalyst prepared by IWI-MD/
C, a significant increase in catalytic activity, shown by a shift of the
conversion curve toward the lower temperatures, is noticed
(T50_2 = 180 °C). This sample shows a CO conversion of 50% at
180 °C (T50), which is three times higher than the conversion mea-
sured for CuO/SBA-15 (14.2%). A similar promotion effect was also
observed over Au–Cu bimetallic phases [93], NiOACuO bulk sys-
tems (equimolar transition metal oxide contents [89], and
nickel–copper supported on cordierite-Mg2Al4Si5O18 with 10–
20 wt.% of each oxide [90]. For AuACu based catalysts the higher
activity was explained by a synergistic effect between gold and
copper, while for the copper–nickel systems, the improved activity
was mainly attributed to the formation of an NiCuO2 phase. Usu-
ally, the synergistic effect can be the result of an electron transfer
from a component to another. Indeed, TPR and XPS results have
shown such an interaction between nickel and copper for this sam-
ple based on the promoting effect of the electron transfer from
nickel to copper, resulting in the increase of the surface electron
density of copper. Thus, the adsorption of CO is more favorable
on these sites as a result of the activation of the CAO bond. As
shown by TPR and XPS, the strength of such metal–metal interac-
tions is higher for the sample prepared by IWI-MD on the partially
extracted support, which should undergo additional improved
activity for CO oxidation. Accordingly, the CO conversion curve
shows T50_1 = 170 °C for this sample, and thus a temperature
10 °C lower than for the sample prepared on the calcined support.
For the samples prepared by precipitation methods, additional
improvement in the CO conversion can be noticed, 50% CO conver-
sion being observed at 160 °C (T50_1 = 160 °C). For these two sam-
ples, the higher activity is explained in a manner similar to that
for the selectivity to CNOL, i.e., by the existence of the surface
electron-deficient sites with improved affinity for the CAO bond.
Fig. 10. CO conversion vs. reaction temperature for Cu4Ni1/SBA-15 after reduction–
oxidation cycle. Test conditions: 100 mg of the catalyst activated under H2
(15 mL minꢂ1) for 2 h at 350 °C and then air (15 mL minꢂ1) at 350 °C for 1 h.
Reaction flow: 1:1 vol.% of CO and O2.
possible explanation for the results reported in Fig. 10 could be the
oxidation state of Ni after the reduction–oxidation processes per-
formed at 350 °C before the catalytic test. The metallic nickel gen-
erated during the reduction step did not reoxidize to NiO during
the reoxidation step, and thus the material manifests no activity
for CO oxidation. Additionally, the calcination temperature
(500 °C) of the solid after impregnation and drying could also be
an explanation for this poor activity, taking into account previous
studies that assigned the low activity of monometallic nickel to
the high calcination temperature, >350 °C [90]. For CuO/SBA-15
catalyst, a CO conversion of 35% is reached at 200 °C (Fig. 10). It
was reported that the activity of copper catalysts in CO oxidation
depends on the support, oxidation atmosphere, and preparation
method [91]. Copper NPs (30–40 nm) supported on Al2O3 surface
and molecular sieve-type supports present activity in CO oxidation
at temperatures above 200 °C for oxygen-lean conditions (2.6% O2
and 3.8% CO), while under oxygen-rich conditions (28.6% O2 and
3.8% CO), 50% CO conversion was reached at temperatures as low
as 150 °C. The use of rare-earth metals (e.g., cerium) as activators,
dispersants, and stabilizers was also a strategy to enhance the cat-
alytic activity of the copper-based active phase.
When CO and O2 were in almost equal volume proportions
(4.0% O2 and 4.6% CO), the activity of copper supported on Al2O3
was much improved in comparison with that of Pd/Al2O3. How-
ever, these copper-based catalysts were active for temperatures
above 160 °C [91]. Likewise, Cao et al. [92] investigated CuO sup-
ported on meso–macroporous titania for CO oxidation and they
established that the nature of the support, the metal oxide loading,
the particle size, and the precalcination temperature are crucial for
the catalytic performance of the resulted materials. However, a
SMSI effect between copper and titania support also has to be
taken into consideration for their studies, knowing that for these
kinds of support (titania, ceria, vanadia), the affinity for the CAO
bond is much stronger due to their oxygen surface deficiency in
comparison to silica and alumina. In light of these reports, and also
considering the satisfying tolerance to SO2 of the supported CuO
[88], a CO conversion of 35% at 200 °C over CuO supported on
SBA-15 silica could indicate that this material is a good catalyst
for low-temperature oxidation reactions.
4. Conclusions
Copper–nickel metal (oxide) NPs (5 wt.% metal, and Cu:Ni
weight ratio 4:1) were prepared by loading the corresponding pre-
cursors on the SBA-15 silica surface by IWI-MD, P, and DP
approaches. For IWI-MD, calcined and partially extracted SBA-15
were used as supports. The use of SBA-15 occluded with P123 tem-
plate was evidenced to be a good strategy to obtain highly dis-
persed copper-rich copper–nickel based NPs on the internal
surface of SBA-15. The degree of dispersion, using this approach,
is higher than that obtained for NPs prepared by precipitation
(either with Na2CO3 or urea), while the textural properties of the
sample did not suffer from any change. Moreover, according to
in situ XRD after thermoprogrammed reduction, the copper–nickel
NPs manifest improved thermostability in comparison with NPs
prepared by precipitation.
Additionally, different metal–metal and metal–support interac-
tions were noticed depending on the preparation method, bicom-
ponent NPs prepared by IWI-MD being mainly characterized by
metal–metal interactions, while for those prepared by precipita-
tion, the metal–support interactions were more evident. The sup-
ported metal (oxide) NPs were used for the hydrogenation of
cinnamaldehyde and CO oxidation reactions. For the cinnamalde-
hyde hydrogenation, the highest activity (conversion of 100% in
120 min of reaction) was measured for the samples prepared by
impregnation on the partially extracted SBA-15 and by precipita-
tion with urea. The improved activities are associated with the
high dispersion of the metallic active phases in these materials.
Enhanced selectivity to unsaturated alcohol was noticed for the
samples prepared by precipitation and related to the formation
of dual-metal electron-deficient sites. For CO oxidation, the sam-
ples prepared by precipitation were more active than the samples

A. Chirieac et al. / Journal of Catalysis 339 (2016) 270–283
283
[35] I. Yuranov, P. Moeckli, E. Suvorova, P. Buffat, L. Kiwi-Minsker, A. Renken, J. Mol.
Catal. A: Chem. 192 (2003) 239.
[36] Q. Jiang, Z.Y. Wu, Y.M. Wang, Y. Cao, C.F. Zhou, J.H. Zhu, J. Mater. Chem. 16
(2006) 1536.
prepared by impregnation, also because of these electron-deficient
sites with high affinity with the CAO bond.
[37] W.-H. Tian, L.-B. Sun, X.-L. Song, X.-Q. Liu, Y. Yinand, G.-S. He, Langmuir 26
(2010) 17398.
Acknowledgments
[38] Y. Yin, D.-M. Xue, X.-Q. Liu, G. Xu, P. Ye, M.-Y. Wu, L.-B. Sun, Chem. Commun.
48 (2012) 9495.
[39] A. Lekhal, J. Benjamin Glasser, G. Johannes Khinast, in: J.R. Regalbuto (Ed.),
Catalyst Preparation, Science and Engineering, CRC Press, Taylor & Francis
Group, 2007. pp 379.
This work was partially supported by two grants of the Romanian
National Authority for Scientific Research, CNCS-UEFISCDI (Projects
PN-II-RU-TE-2012-3-0403 and PN-II-ID-PCE-2011-3-0868).
[40] A. Ungureanu, B. Dragoi, A. Chirieac, S. Royer, D. Duprez, E. Dumitriu, J. Mater.
Chem. 21 (2011) 12529.
[41] B.R. Cuenya, Thin Solid Films 518 (2010) 3127.
Appendix A. Supplementary material
[42] R. Ferrando, J. Jellinek, R.L. Johnston, Chem. Rev. 108 (2008) 845.
[43] K.P. de Jong, in: K.P. de Jong (Ed.), Synthesis of Solid Catalysts, Wiley-VCH
Verlag GmbH & Co. KGaA, Weinheim, 2009. pp 111.
[44] C. Louis, in: J.R. Regalbuto (Ed.), Catalyst Preparation, Science and Engineering,
CRC Press, Taylor & Francis Group, 2007. pp. 319.
[45] M. Lok, in: K.P. de Jong (Ed.), Synthesis of Solid Catalysts, Wiley-VCH Verlag
GmbH & Co. KGaA, Weinheim, 2009. pp 135.
[46] C. Ciotonea, B. Dragoi, A. Ungureanu, A. Chirieac, S. Petit, S. Royer, E. Dumitriu,
Chem. Commun. 49 (2013) 7665.
[47] H. Liu, H. Wang, J. Shen, Y. Sun, Z. Liu, Appl. Catal., A 337 (2008) 138.
[48] S.F.H. Tasfy, N.A.M. Zabidi, D. Subbarao, J. Appl. Sci. 11 (2011) 1150.
[49] Q. Wu, W.L. Eriksen, L.D.L. Duchstein, J.M. Christensen, C.D. Damsgaard, J.B.
Wagner, B. Temel, J.-D. Grunwaldt, A.D. Jensen, Catal. Sci. Technol. 4 (2014) 378.
[50] S. Wang, W. Guo, H. Wang, L. Zhu, S. Yin, K. Qiu, New J. Chem. 38 (2014) 2792.
[51] P. Munnik, P.E. de Jongh, K.P. de Jong, Chem. Rev. 115 (2015) 6687.
[52] H.-A. Lin, C.-H. Liu, W.-C. Huang, S.-C. Liou, M.-W. Chu, C.-H. Chen, J.-F. Lee, C.-
M. Yang, Chem. Mater. 20 (2008) 6617.
[53] C.H. Liu, Y. Guan, E.J.M. Hensen, J.F. Lee, C.M. Yang, J. Catal. 282 (2011) 94.
[54] C.H. Liu, N.C. Lai, S.C. Liou, M.W. Chu, C.H. Chen, C.M. Yang, Microporous
Mesoporous Mater. 179 (2013) 40.
[55] E. Besson, A. Mehdi, C. Reye, R.J.P. Corriu, J. Mater. Chem. 19 (2009) 4746.
[56] C. Setzer, G. van Essche, N. Pryor, in: F. Schüth, K. Sing, J. Weitkamp (Eds.),
Handbook of Porous Solids, vol. 1, Springer, Weinheim, 2002. p. 1551.
[57] W. Lifeng, R.T. Yang, J. Phys. Chem. C 115 (2011) 21264.
[58] A. Galarneau, H. Cambon, F. Di Renzo, F. Fajula, Langmuir 17 (2001) 8328.
[59] J.R.A. Sietsma, J.D. Meeldijk, M. Versluijs-Helder, A. Broersma, A.J. van Dillen, P.
E. de Jongh, K.P. de Jong, Chem. Mater. 20 (2008) 2921.
[60] A. Carrero, J.A. Calles, A.J. Vizcaino, Appl. Catal., A 327 (2007) 82.
[61] G. Aguila, F. Gracia, P. Araya, Appl. Catal., A 343 (2008) 16.
[62] S.M. Ciocilteu, M. Salou, Y. Kiyozumi, S.-I. Niwa, F. Mizukamia, M. Haneda, J.
Mater. Chem. 13 (2003) 602.
[63] R. Brown, M.E. Cooper, D.A. Whan, Appl. Catal. 3 (1982) 177.
[64] S. Zhu, X. Gao, Y. Zhu, W. Fan, J. Wang, Y. Li, Catal. Sci. Technol. 5 (2015) 1169.
[65] X.C. Zheng, S.H. Wu, S.P. Wang, S.R. Wang, S.M. Zhang, W.P. Huang, Appl. Catal.,
A 283 (2005) 217.
[66] Z. Liu, M.D. Amiridis, Y. Chen, J. Phys. Chem. B 109 (2005) 1251.
[67] C.-H. Tu, A.-Q. Wang, M.-Y. Zheng, X.-D. Wang, T. Zhang, Appl. Catal., A 297
(2006) 40.
[68] P.C.M. van Stiphout, D.E. Stobbe, F.T.V.D. Scheur, J.W. Geus, Appl. Catal. 40
(1988) 219.
[69] A. Gervasini, M. Manzoli, G. Martra, A. Ponti, N. Ravasio, L. Sordelli, F.
Zaccheria, J. Phys. Chem. B 110 (2006) 7851.
[70] A.R. Naghash, T.H. Etsell, S. Xu, Chem. Mater. 18 (2006) 2480.
[71] J.C. Vedrine, G. Hollinger, T.M. Duc, J. Phys. Chem. 82 (1978) 1515.
[72] T. Lehmann, T. Wolff, C. Hamel, P. Veit, B. Garke, A. Seidel-Morgenstern,
Microporous Mesoporous Mater. 151 (2012) 113.
[73] M.-J. Suh, S.-K. Ihm, Top. Catal. 53 (2010) 447.
[74] L. Xiaowei, S. Mingmin, H. Xi, Z. Haiyang, G. Fei, K. Yan, D. Lin, C. Yi, J. Phys.
Chem. B 109 (2005) 3949.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2016.04.004.
TG-DSC curves of as-made and partially extracted SBA-15 sup-
port; TEM images collected at different magnifications besides
EDX spectra collected in different areas the for P/C sample; and
XPS spectra for all four samples are available free of charge via
the Internet.
References
[1] A.H. Faraji, P. Wipf, Bioorg. Med. Chem. 17 (2009) 2950.
[2] A. Cao, C. Veser, Nat. Mater. 9 (2010) 75.
[3] L. Starkey Ott, R.G. Finke, Coord. Chem. Rev. 251 (2007) 1075.
[4] R.M. Rioux, H. Songa, M. Grass, S. Habas, K. Niesz, J.D. Hoefelmeyer, P. Yang, G.
A. Somorjai, Top. Catal. 39 (2006) 167.
[5] J.G. Speight, B. Ozum, Petroleum Refining Processes, Marcel Dekker, New York,
2002. pp 294.
[6] S.H. Joo, J.Y. Park, C.-K. Tsung, Y. Yamada, P. Yang, G.A. Somorjai, Nat. Mater. 8
(2009) 126.
[7] D. Astruc, in: D. Astruc (Ed.), Nanoparticles and Catalysis, vol. 1, Wiley-VCH
Verlag GmbH & Co. KGaA, Weinheim, 2008. pp 24.
[8] C.N. Satterfield, Heterogeneous Catalysis in Industrial Practice, second ed.,
Krieger Publishing Company, Malabar, Florida, 1991. pp 112.
[9] V. La Parola, B. Dragoi, A. Ungureanu, E. Dumitriu, A.M. Venezia, Appl. Catal., A
386 (2010) 43.
[10] C.S. Chen, Y.T. Lai, T.W. Lai, J.H. Wu, C.H. Chen, J.F. Lee, H.M. Kao, ACS Catal. 3
(2013) 667.
[11] R.P. Jumde, C. Evangelisti, A. Mandoli, N. Scotti, R. Psaro, J. Catal. 324 (2015) 25.
[12] A. Ungureanu, B. Dragoi, A. Chirieac, C. Ciotonea, S. Royer, D. Duprez, A.S.
Mamede, E. Dumitriu, ACS Appl. Mater. Interfaces 5 (2013) 3010.
[13] B. Dragoi, A. Ungureanu, A. Chirieac, V. Hulea, S. Royer, E. Dumitriu, Catal. Sci.
Technol. 3 (2013) 2319.
}
[14] C. Papadopoulou, H. Matralis, X. Verykios, in: L. Guczi, A. Erdohelyi (Eds.),
Catalysis for Alternative Energy Generation, Springer, New York, 2012. pp 112.
[15] D. Zhao, J. Feng, Q. Huo, N. Melosh, G.H. Fredrickson, B.F. Chmelka, G.D. Stucky,
Science 279 (1998) 548.
[16] G.J. de A.A. Soler-Illia, E.L. Crepaldi, D. Grosso, C. Sanchez, Curr. Opin. Colloid
Interface Sci. 8 (2003) 109.
[17] C.-M. Yang, B. Zibrowius, W. Schmidt, F. Schuth, Chem. Mater. 15 (2003) 3739.
[18] S.H. Joo, R. Ryoo, M. Kruk, M. Jaroniec, J. Phys. Chem. B 106 (2002) 4640.
[19] J. Sun, D. Ma, H. Zhang, X. Liu, X. Han, X. Bao, G. Weinberg, N. Pfänder, D. Su, J.
Am. Chem. Soc. 128 (2006) 15756.
[20] Z.-J. Wang, X. Yongbing, L. Chang-Jun, J. Phys. Chem. C 112 (2008) 19818.
[21] J. Zhu, W. Tao, X. Xuelian, X. Ping, L. Jinlin, Appl. Catal., B 130–131 (2013) 197.
[22] P. Munnik, M. Wolters, A. Gabrielsson, S.D. Pollington, G. Headdock, J.H. Bitter,
P.E. de Jongh, K.P. de Jong, J. Phys. Chem. C 115 (2011) 14698.
[23] T. Tsoncheva, V. Dal Santo, A. Gallo, N. Scotti, M. Dimitrov, D. Kovacheva, Appl.
Catal., A 406 (2011) 13.
[24] L.-F. Chen, P.-J. Guo, L.-J. Zhu, M.-H. Qiao, W. Shen, H.-L. Xu, K.-N. Fan, Appl.
Catal., A 356 (2009) 129.
[25] F. Boubekr, A. Davidson, S. Casale, P. Massiani, Microporous Mesoporous
Mater. 141 (2011) 157.
[26] J. Taghavimoghaddam, G.P. Knowles, A.L. Chaffee, J. Mol. Catal. A: Chem. 358
(2012) 79.
[27] H. Friedrich, J.R.A. Sietsma, P.E. de Jongh, A.J. Verkleij, K.P. de Jong, J. Am. Chem.
Soc. 129 (2007) 10249.
[75] H. Zhu, Y. Wu, X. Zhao, H. Wan, L. Yang, J. Hong, Q. Yu, L. Dong, Y. Chen, C. Jian,
J. Wei, P. Xu, J. Mol. Catal. A: Chem. 243 (2006) 24.
[76] A. Kaddouri, N. Dupont, P. Gelin, P. Delichere, Catal. Lett. 141 (2011) 1581.
[77] K. Yoshida, C. Gonzalez-Arellano, R. Luque, P.L. Gai, Appl. Catal., A 379 (2010) 38.
[78] I. Nakai, Y. Sugitani, K. Nagashima, Y. Niwa, J. Inorg. Nucl. Chem. 40 (1978) 789.
[79] P. Burattin, M. Che, C. Louis, J. Phys. Chem. B 102 (1998) 2722.
[80] P. Burattin, M. Che, C. Louis, J. Phys. Chem. B 103 (1999) 6171.
[81] C.J.G. van der Grift, P.A. Elberse, A. Mulder, J.W. Geus, Appl. Catal., A 59 (1990)
275.
[82] C. Svatopluk, W.R. Glomm, E.A. Blekkan, Catal. Today 147 (2009) 217.
[83] A. Yin, C. Wen, X. Guo, W.L. Dai, K. Fan, J. Catal. 280 (2011) 77.
[84] P. Maki-Arvela, J. Hajek, T. Salmi, D.Y. Murzin, Appl. Catal., A 292 (2005) 1.
[85] S. Valange, A. Derouault, J. Barrault, Z. Gabelica, J. Mol. Catal. A: Chem. 228
(2005) 255.
[28] A. Rumplecker, F. Kleitz, E.-L. Salabas, F. Schuth, Chem. Mater. 19 (2007) 485.
[29] W. Yue, W. Zhou, Chem. Mater. 19 (2007) 2359.
[86] Y. Yuan, S. Yao, M. Wang, S. Lou, N. Yan, Curr. Org. Chem. 17 (2013) 400.
[87] K.J.A. Raj, M.G. Prakash, T. Elangovan, B. Viswanathan, Catal. Lett. 142 (2012) 87.
[88] S. Royer, D. Duprez, ChemCatChem 3 (2011) 24.
[30] M.A. Wahab, F. Darain, Nanotechnology 25 (2014) 165701.
[31] A.-H. Lu, D. Zhao, Y. Wan (Eds.), Nanocasting, A Versatile Strategy for Creating
Nanostructured Porous Materials, RSC Publishing, Cambridge, UK, 2010. pp. 1.
[32] C.M. Yang, H.A. Lin, B. Zibrowius, B. Spliethoff, F. Schüth, S.C. Liou, M.W. Chu, C.
H. Chen, Chem. Mater. 19 (2007) 3205.
[33] S. Valange, R. Palacio, A. Charmot, J. Barrault, A. Louati, Z. Gabelica, J. Mol. Catal.
A: Chem. 305 (2009) 24.
[34] X. Zhong, J. Barbier Jr., D. Duprez, H. Zhang, S. Royer, Appl. Catal., B 121 (2012)
123.
[89] H.G. El-Shobaky, Appl. Catal., A 278 (2004) 1.
[90] H.G. El-Shobaky, Y.M. Fahmy, Appl. Catal., B 63 (2006) 168.
[91] F.-L. Du, Z.-L. Cui, Z.-K. Zhang, S.-Y. Chem, J. Nat. Gas Chem. 6 (1997) 135.
[92] J.-L. Cao, G.-S. Shao, T.-Y. Ma, Y. Wang, T.-Z. Ren, S.-H. Wu, Z.-Y. Yuan, J. Mater.
Sci. 44 (2009) 6717.
[93] X. Liu, A. Wang, L. Li, T. Zhang, C.-Y. Mou, J.-F. Lee, J. Catal. 278 (2011) 288.