D.K. Mishra, et al.
Molecular Catalysis xxx (xxxx) xxxx
MnCo CO shows distinct size of particles and a smooth surface having
less porosity (Fig. S3c and 3d). The size of ruthenium particles as ex-
pected in nano-sizes was further proven by TEM analysis. TEM and HR-
Cu-Kα radiation (40 kV, 30 mA, λ = 1.7902 Å). The morphologies of
samples were obtained by Scanning Electron Microscopy (SEM), JEOL
2
3
(
JSM-6701 F) instrument. Transmission Electron Microscopy (TEM)
and High-Resolution Transmission Electron Microscopy (HRTEM)
images were obtained by a JEOL (JEM-2100 F) instrument equipped
with LaB6 filament and fitted with Energy Dispersive X-ray
Spectrometer for elemental analysis. For TEM, the catalyst samples
were dispersed in 2-propanol under sonication and then deposited on
carbon-coated copper grids. After drying at ambient conditions, it was
TEM images of Ru/MnCo O4 catalyst as represented in Fig. S3 (e) and
(f) could not give any information on the size of Ru-nanoparticles.
Multi-pores can further be seen clearly from a high magnification SEM
2
image of MnCo O which shows that several nanoparticles with a size
2 4,
range of 45−50 nm are aggregated (Fig. S4). Hence, both the size
(∼3.4 nm) and metal dispersion (39.2 %) are confirmed by CO-che-
misorption studies, and the results are summarized in (Table S2). Ele-
mental mapping images acquired during TEM analysis, as shown in Fig.
S5, showed several red spots of ruthenium metal nanoparticles on a
used for TEM analysis. X-Ray Photoelectron Spectroscopy (XPS) spectra
TM+
were acquired by K-Alpha
XPS spectrometer equipped with
monochromatic aluminum (Al)-Kα (1486.6 eV) for X-ray source (for
excitation of samples). X-Ray Photoelectron Spectroscopy (XPS) spectra
black background exhibited from MnCo O4 spinels microspheres. The
2
TM+
were acquired by K-Alpha
XPS spectrometer equipped with
textural properties of MnCo O4 spinels and Ru-based catalysts are
2
monochromatic aluminum (Al)-Kα (1486.6 eV) for X-ray source (for
excitation of samples). The XPS spectra were recorded with the pass-
energy of 200 or 40 eV for the survey or core spectrum measurement,
respectively. For XPS analysis, the samplewas mounted on a stainless
steel sample holder with double adhesive carbon tape. Surface charge
was compensated by a low energy electron flood gun. The peak fitting
of the collected experimental data was done using Gaussian-Lorentzian
functions and Shirley background subtraction and AVANTAGEsoftware
was used.The binding energy (B.E.) scale was referenced by setting the
C (1 s) binding energy (B.E.) of carbon to 284.6 eV. Brunauer-Emmett-
summarized in Table S2. The specific surface area (SA) in the P/P0
range of 0.00-0.45 and the pore volume were obtained from Bru-
nauer–Emmett–Teller (BET) and Barrett-Joyner- Halenda (BJH)
methods, respectively. As the results summarized in Table S2, the
2
specific surface area of MnCo O (Mn: Co = 1: 2) is 151.1 m /g, while
2 4
2
the specific surface area of CoMn O (Mn: Co = 2: 1) is 89.5 m /g. Pore
2
4
volumes of MnCo O (Mn: Co = 1: 2) and CoMn O (Mn: Co = 2: 1)
2
4
2 4
3
3
are 0.2977 cm /g and 0.2978 cm /g, respectively. After the loading of
ruthenium (4.0 % by weight), as expected, the surface area of Ru/
MnCo O catalyst decreased from 151.1 m /g down to 135.4 m /g. Ru/
2
2
2
4
3
Teller (BET) surface area was determined by nitrogen (N
desorption at −196 °C liquid N temperature with a MICROMERITICS
ASAP 2020, Tristar II analyzer. For each measurement, the sample was
degassed at 250 °C for 12 h, then analyzed at −196 °C with N gas at
relative pressures (P/P ) from 0.005 to 1.0 (adsorption) and 1.0 to 0.1
desorption). The quantitative determination of different elements in
2
) adsorption-
2 4
MnCo O catalyst has the pore volume (0.3082 cm /g) which is almost
2
2 4
similar to that of MnCo O (Mn: Co = 1: 2), indicating the pore volume
has little effect on the catalytic performance.
2
X-ray photoelectron spectroscopy (XPS) analysis of Ru/MnCo O
2
4
0
catalyst was further carried out in order to see the valence states of Mn,
Co, O, and Ru metal, and the results are shown in Fig. 1. Mn 2p spec-
trum shows the two pair of doublet peaks, the first pair has a doublet
made of 2p3/2 at 641.4 eV and 2p1/2 652.9 (eV), and another pair has
another doublet made of 2p3/2 at 642.9 eV and 2p1/2 at 653.9 (eV).
These two pair of doublet peaks confirm the co-existence of the Mn(II)
and Mn(III). Similarly, the characteristic two pair of doublet peaks, a
doublet of 2p3/2 at 781.6 eV and 2p1/2 at 796.7 (eV) and another
doublet 2p3/2 at ∼779.9 eV and 2p1/2 at 795.1 (eV) are responsible for
the co-existence of Co(II) and Co(III), respectively. The obtained results,
the existence of Mn and Co with oxidation states (III/II), are similar to
previous results reported by Ma and co-workers [43,46]. On the other
hand, O 1s spectrum shows the presence of three different peaks (1s
A–C), indicating the three oxygen groups exist in the spinel lattice
structure of MnCo O . The major 1 s A peak corresponds to the metal
(
solid catalysts and liquid samples (products mixture after oxidative
esterification) was carried by inductively coupled plasma-atomic
emission spectroscopy (ICP-AES, Thermo Scientific iCAP 6500 ICP
spectrometer). Prior to ICP analysis, the samples of solid catalysts were
dissolved in fresh aqua regia solution of hydrochloric acid and nitric
acid (3: 1). The metal contents (amount of Ru loading) in the catalysts
were also determined by Energy-Dispersive X-ray (EDX/EDS)
Spectrometer Quantax 200, Bruker. The surface properties of supports
and corresponding Ru nanoparticles were investigated by temperature-
programmed desorption of ammonia (NH
100 g) was pretreated in a flow-type fixed bed reactor at 300 °C for 3 h
and cooled to 120 °Cin flow of helium (He). At this temperature, suf-
ficient pulse of NH gas was injected until adsorption saturation, fol-
3
-TPD) technique. The sample
(
3
2
4
lowed by purging He-gas with the flow of 30 mL/min for about 2 h. The
temperature was then raised from 120−800 °C at a ramp rate 10 °C/
min to desorb NH . The NH desorbed was collected in a liquid N trap
3 3 2
and oxygen bonds. While two 1 s B and 1 s C could be assigned to the
hydroxyl group and surface adsorbed water molecules, respectively
[47]. While overlapping of 3d3/2 peak and C 1s peak appeared at
around 284.6 eVdid not give clear evidence for the existence of ru-
thenium nanoparticles (in Ru 3d region from 278 to 300 eV). Hence, the
existence of ruthenium nanoparticles was further confirmed from Ru 3p
region (from 455.0–475.0 eV). As shown in the spectrum of Ru 3p, a
characteristic 3p3/2 peak appeared at 463.0 (eV) is due to the metallic
ruthenium.
and detected by on-line gas chromatography.
Results and discussion
Single metal oxides are often associated with distinct weakness such
as low surface area, low acidic strength, and the poor reusability in a
chemical reaction as a catalyst, which hampering their applications as
support materials. To end this, an idea of preparing a solid mixed metal
oxide of cobalt and manganese, was applied to use as a support material
with ruthenium nanoparticles to enhance the acid strength, surface
Temperature programmed reduction (TPR) studies were carried out
to gain an insight into the metal-support interaction and the reduction
of phases in Ru-based catalysts at different temperatures, and the re-
sults are depicted in Fig. S6. Sample of Ru/Co catalyst having a
2
O
3
area, and structural properties. XRD patterns of MnCo
cursor MnCo CO , prepared with a molar ratio of Mn and Co (1: 2) are
represented in Fig. S2. All the diffraction patterns in MnCo are well
in accordance with the MnCo (JCPDS no. 23-1237) [43,45]. The
formation of MnCo is confirmed by the disappearance of peaks from
and the existence of new peaks in pattern of MnCo
and
were investigated by SEM analysis. SEM images of MnCo
2
O
4
and its pre-
predominant phase of cobalt as Co and Co O undergoes pre-
sumably reduction to metallic cobalt in a three-stage process at tem-
peratures ranges 130–190 °C, 200–280 °C, and 280–375 °C. The first
2
O
3
3 4
2
3
2
O
4
2
O
4
peak is attributed to the reduction of Co → Co
2
O
3
3 4
O . In addition, the
2
O
4
second and third peaks are assigned to Co O → CoO and CoO → Co,
3 4
MnCo
(
MnCo
2
CO
3
3
2
O
4
respectively. Ehrhardt et al. reported that when cobalt precursor (cobalt
nitrate) is calcined in an inert atmosphere, it produced different phases
JCPDS 11-692). Moreover, the morphologies of MnCo
2
O
4
2
CO
2
O
4
of cobalt (a mixture of Co
MnO catalyst shows three-stage processes at temperatures ranges
100–160 °C, 165–245 °C, and 248–330 °C. These three peaks are
2 3 3 4
O and Co O ). While the sample of Ru/
showed 2.0–4.0 μm sized particles (spheres like structures) having
multi-porous nature (Fig. S3a, 3b). However, the SEM images of
2
3
Mishra, Dinesh Kumar
