T.M. Bustamante, et al.
Molecular Catalysis xxx (xxxx) xxxx
electronic and geometric structures to enhance the catalytic perfor-
mance including activity, selectivity, and the operational stability of
of 0, 0.05, 0.1, 0.3, and 0.5% were synthesized using the methodology
reported by Morales et al. [47]. The calcined material was subjected to
catalyst system for the hydrogenation of the -NO
2
group [37–40].
an ex situ reduction treatment at 500 °C using H
for 3 h. Subsequently, the catalyst was transferred to the reactor and
quickly immersed in ethanol that had been previously degassed with N
to prevent its oxidation. The reduction temperature was chosen based
on the H -TPR results.
2
as the reducing agent
This study reports the use of bimetallic Co-Pd catalysts containing a
small amount of Pd as a dopant to promote their catalytic activity and
chemoselectivity. The preparation of catalysts via the controlled re-
2
duction of a cobalt titanate precursor (Pd
x
Co1-xTiO
3
) that includes a
2
small amount of Pd as a promoter metal is reported for the first time.
The resulting Pd-Co bimetallic catalysts are supported on the mixed
2.4. Characterization
3 2
oxides CoTiO -CoO-TiO (CTO). The catalysts were designed to obtain
systems of the type (y)Pd-Co/CTO (y = 0, 0.05, 0.1, 0.3, and 0.5% in
Pd) to study the effects of the Pd content on their physicochemical
properties and catalytic activity in the hydrogenation of liquid-phase
halonitroarenes; 4-chloronitrobenzene (CNB) was used as a substrate
for the production of 4-chloroaniline (CAN). The best catalytic system
was evaluated in the hydrogenation of several halonitroarenes of
pharmaceutical interest, namely, the 4-(2-fluoro-4-nitrophenyl) mor-
pholine precursor of the antibacterial drug linezolid [41], the 1-(4-
chlorophenoxy)-2-nitrobenzene precursor of the antipsychotic drug
loxapine [42], the 2-chloro-1-((3-fluorobenzyl)oxy)-4-nitrobenzene
precursor of the antineoplastic drug lapatinib, which is used in the
treatment of breast cancer [43], methyl 2-chloro-5-nitrobenzoate, an
intermediate in the synthesis of 3,4-dihydroquinolin-2(1 H)-ones used
in the treatment of type 2 diabetes [44], and the 1-chloro-4-nitro-2-
Chemical analysis was conducted via atomic absorption spectro-
metry (AAS) using a Perkin Elmer 3100 instrument. The samples were
first evaluated in triplicate by digesting 0.05 g of the calcined Pd Co
x
1-
x
TiO precursor or reduced (y)Pd-Co/CTO catalyst in 10 mL of a con-
3
centrated nitric/hydrochloric (1:3) acid solution via microwave-as-
sisted digestion. After the reduction process, the Co and Pd metal
loadings were measured using AAS.
Temperature programmed reduction (TPR) was performed using a
TPR/TPD 2900 Micromeritics system with a thermal conductivity de-
tector (TCD). Two reduction measurement profiles were recorded. In
the first (H -TPR1), TPR data was recorded for 0.050 g samples of the
2
calcined Pd Co1-xTiO3 precursors using a 5% H /Ar flow of 40 mL
x
2
−1
−1
min
and a heating rate of 10 °C min
from room temperature to
800 °C. In the second (H -TPR2), 0.050 g samples of the calcined
2
(
trifluoromethyl) benzene precursor of the antineoplastic drug sor-
x
Pd Co1-xTiO3 precursors were first thermally reduced in the TPR-
afenib, which is used in the treatment of kidney cancer [45]. Finally,
the best catalytic system was subjected to operational stability tests to
evaluate its durability in continuous operation cycles.
equipment using the same experimental conditions as in the prepara-
tion of the (y)Pd-Co/CTO materials (pure H flux of 30 ml/min, heating
2
from room temperature to 500 °C at 10 °C/min). After the reducing
treatment, the samples were cleaned at 100 °C under an Ar flow for 2 h,
2. Experimental
and TPR data from a second run using the H -TPR1 conditions was
2
2
recorded. Thus, the H -TPR1 data represented the complete reduction
2.1. Materials
of the Co species in the precursor materials, and the H -TPR2 data re-
2
presented Co reduction in the prepared (y)-Pd-Co/CTO catalysts. The
Cobalt(II) acetate (Co(CH
3
CO
2
)
2
), titanium butoxide (Ti
reducibility was calculated from the H -TPR data as follows:
2
(
5
3
3 2 2 2 4
CH CH CH CH O) ), 4-chloronitrobenzene, 4-chloroaniline, 2-chloro-
-nitrobenzotrifluoride, methyl 2-chloro-5-nitrobenzoate, and 4-chloro-
-(trifluoromethyl)aniline were obtained from Sigma-Aldrich.
Total normalizated area of H2 − TPR2
Total normalizated area of H2 − TPR1
reducibility (%) =
∙100
(1)
Palladium(II) acetate (Pd(CH
and ethylene glycol were purchased from Merck. All the purchased
reagents were used without further purification. The gases
99.99%), He (99.99%), synthetic air, and nitrogen were provided by
3
CO
2
)
2
), isopropanol, absolute ethanol,
In this expression, the peak areas were normalized by the total ex-
perimental Co content determined using AAS characterization.
The specific areas were calculated using the BET method from N2
H
2
(
adsorption-desorption isotherms obtained at −196 °C using
a
Linde Chile. The drug precursors 4-(2-fluoro-4-nitrophenyl) morpho-
line, 1-(4-chlorophenoxy)-2-nitrobenzene and 2-chloro-1-((3-fluor-
obenzyl)oxy)-4-nitrobenzene could not be sourced from commercial
suppliers, so they were synthesized and characterized as detailed in the
Supplementary material.
Micromeritics TriStar II 3020. X-ray powder diffraction (XRD) patterns
of the as-synthesized powder samples were obtained with nickel-fil-
tered CuKα1 radiation (λ =1.5418 Å) using a Rigaku diffractometer,
and were collected over the 2θ range 20-90°. The reduced (y)Pd-Co/
CTO catalyst samples were subjected to a passivation treatment prior to
XRD to avoid continued oxidation during the XRD measurement. The
details of the passivation treatment have been described in our previous
reports [47].
x 3
2.2. Synthesis of the Pd Co1-xTiO precursors
The synthesis of the precursors with the formula Pd
carried out using the methodology reported by Qu et al. with some
modifications [46]. In general, the amounts of Co(CH COO) , Pd
CH COO) , and Ti(CH CH CH CH O) required to achieve a molar
x
Co1-xTiO
3
was
Transmission electron microscopy (TEM) micrographs were ob-
tained using a JEOL model JEM-1200 EX II microscope; the materials
were dispersed on a carbon grid. The reduced (y)Pd-Co/CTO catalysts
were subjected to the passivation treatment prior to TEM character-
ization.
3
2
(
3
2
3
2
2
2
4
ratio of (Co + Pd)/Ti = 1 were dissolved in an ethylene glycol/iso-
propanol (50/50) mixture. The nominal contents of Pd used corre-
sponded to x = 0, 0.0008, 0.0015, 0.0045, and 0.0075. The above
mixture was stirred for 24 h until a pinkish milky dispersion was ob-
tained. Finally, the dispersion was stirred for 10 min and washed with
absolute ethanol (×3) to remove excess ethylene glycol. The recovered
solid was dried in an oven at 100 °C for 12 h and calcined in a static air
atmosphere from room temperature to 700 °C at a heating ramp rate of
X-ray photoelectron spectroscopy (XPS) was performed using a VG
Escalab 200R electron spectrometer equipped with a hemispherical
electron analyzer and a Mg Kα (1253.6 eV) X-ray source. The calcined
x 3
Pd Co1-xTiO precursor samples were measured without prior reducing
treatment. The reduced (y)Pd-Co/CTO catalysts were reduced in situ in
the XPS pre-chamber prior to analysis. Finally, magnetic characteriza-
tion of the nanomaterials was carried out using a Quantum Design
Dynacool Physical Properties Measurement System (PPMS) equipped
with a vibrating sample magnetometer (VSM). Magnetization curves
were only obtained for the (y)Pd-Co/CTO reduced catalysts, which
were passivated prior to analysis, at 27 °C. Data is reported in emu per
−
1
5° min
.
2.3. Synthesis of the (y)Pd-Co/CTO catalysts
The (y)Pd-Co/CTO catalysts with nominal Pd mass percentages (y)
S
gram of Co. M was evaluated by extrapolating the experimental results
3