Photocatalytic oxidation of aromatic alcohols over silver supported on cobalt oxide nanostructured catalyst

Article abstract of DOI:10.1016/j.jallcom.2018.12.307

In this paper, we report an in-situ synthesis of silver supported on cobalt oxide (Ag/Co₃O₄) nanoparticles (NPs) and studied the catalytic activity of this material as an eco-friendly, simple, recyclable and efficient catalyst for one-pot photocatalytic oxidation of aromatic alcohols. Ag nanoparticles with the sizes of 2–5 nm supported on spherical Co₃O₄ with the radius between 40 and 60 nm were synthesized by homogeneous chemical precipitation followed by hydrothermal heating. The as-synthesized catalyst was thoroughly characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and N₂ adsorption-desorption isotherm (BET) analysis. It was observed that the catalysts with 1 wt% of silver loading shows high activity and selectivity toward the target aldehyde product. The effects of different reaction parameters such as reaction time, oxidant and solvent were investigated and studied in detail. The synergistic effect between the surface Ag NPs and Co₃O₄ nanospheres plays a vital role toward very high catalytic activity.

Full text of DOI:10.1016/j.jallcom.2018.12.307

Accepted Manuscript
Photocatalytic oxidation of aromatic alcohols over silver supported on cobalt oxide
nanostructured catalyst
Xianbing Ji, Yinxia Chen, Bappi Paul, S. Vadivel
PII:
S0925-8388(18)34869-2
DOI:
https://doi.org/10.1016/j.jallcom.2018.12.307
JALCOM 48950
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 24 September 2018
Revised Date: 24 December 2018
Accepted Date: 26 December 2018
Please cite this article as: X. Ji, Y. Chen, B. Paul, S. Vadivel, Photocatalytic oxidation of aromatic
alcohols over silver supported on cobalt oxide nanostructured catalyst, Journal of Alloys and
Compounds (2019), doi: https://doi.org/10.1016/j.jallcom.2018.12.307.
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Graphical abstract

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Photocatalytic oxidation of aromatic alcohols over silver supported on cobalt oxide
nanostructured catalyst
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Xianbing Ji , Yinxia Chen *, Bappi Paul *, S. Vadivel
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Hebei University of Environmental Engineering, Qinhuangdao, Hebei-066102, China
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Department of Chemistry, National Institute of Technology Silchar, Silchar-788010, Assam,
India
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Department of Chemistry, PSG College of Technology, Coimbatore 641004, India
*Corresponding authors. Tel: +91-03842-242915; fax: +91-03842-224797
Email: chyxsd@126.com (Y. Chen); bappipaulnits@gmail.com (B. Paul)
ABSTRACT
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In this paper, we report an in-situ synthesis of silver supported on cobalt oxide (Ag/Co O )
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nanoparticles (NPs) and studied the catalytic activity of this material as an eco-friendly,
simple, recyclable and efficient catalyst for one‐pot photocatalytic oxidation of aromatic
alcohols. Ag nanoparticles with the sizes of 2–5 nm supported on spherical Co O with the
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radius between 40 and 60 nm were synthesized by homogeneous chemical precipitation
followed by hydrothermal heating. The as-synthesized catalyst was thoroughly characterized
by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive
X-ray spectroscopy (EDX), elemental mapping, transmission electron microscopy (TEM), X-
ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR),
thermogravimetric analysis (TGA) and N adsorption-desorption isotherm (BET) analysis. It
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was observed that the catalysts with 1 wt% of silver loading shows high activity and
selectivity toward the target aldehyde product. The effects of different reaction parameters
such as reaction time, oxidant and solvent were investigated and studied in detail. The
synergistic effect between the surface Ag NPs and Co O nanospheres plays a vital role
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toward very high catalytic activity.
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Keywords: Oxide materials; Chemical synthesis; Catalysis; X-ray diffraction
1. Introduction
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During last few decades, preparation and characterization of inorganic materials with
nanosized dimensions and morphological specificity has become highly important and
received a great deal of interest in various science and technology fields [1-7]. Recently,
nanomaterials have attracted much research attention due to their applications in medicine,
biology, electronics and chemical industries [8-11]. Nanostructured materials with low
density and high specific surface area are considered suitable candidates for a variety of
applications. Their significantly enhanced activity can be attributed to their highly accessible
surface area with a large number of active sites [12,13]. It was observed that nanomaterials
doped with another metal boost their catalytic efficiency to great extent due to synergistic
effects [14]. Noble metal nanomaterials such as silver and gold have shown tremendous
potential for applications in various fields including catalysis [15, 16]. Their controlled effect
as dopants on various transition and nontransition metal oxide supports, such as titania,
alumina, and silica, has provided a new aspect to their utility in catalytic science and
technology [17-21]. Several green methods for the synthesis of Ag nanoparticles (NPs) are
known [22]. Synthesis methods for supported transition metal oxide nanomaterials such as
sonochemical methods, microwave irradiation, and vapor deposition have been studied and
they have their own advantages and disadvantages. Despite significant research efforts,
controlled and easy synthesis of Ag-supported Co O nanomaterials in solution is still highly
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challenging. Development of a facile method for the synthesis of Ag-supported Co O4
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nanomaterials with desired size, shape and morphology is still considered a challenging task.
Huang et al has synthesized Ag-decorated Co O nanosheets on nickel foam via a
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hydrothermal method and it was found that the morphology of Co O can be controlled by
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adjusting the hydrothermal time and the concentration of reactants [5]. Herein, we report a
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simple and reproducible preparation method for the synthesis of silver supported on Co O4
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spinel nanoparticles via a hydrothermal synthesis followed by calcination. Silver supported
on Co O nanoparticles was synthesized by an in-situ synthesis procedure and it was found
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that the in-situ synthesis procedure is better than the impregnation method for the
photocatalytic oxidation of alcohol. The added advantage of the synthesis procedure is that it
can be applied on a large scale synthesis (up to 10 g).
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Oxidation of alcohols is one of the most important transformations in synthetic organic
chemistry [23, 24]. The oxidation products are known to be essential intermediates in the
manufacture of agrochemicals, fine chemicals, pharmaceuticals and high-value commodity
chemicals [25, 26]. With a growing concern with economic and environmental acceptability,
researchers across the world are devoting much effort to accomplish such oxidation with
oxygen or hydrogen peroxides [27-30]. Several excellent catalysts have been developed for
environmentally benign oxidation of alcohols to carbonyl compounds [31]. Recently,
photocatalytic oxidation of aromatic alcohols where aldehyde was obtained as a major
product using a nanostructured catalyst has been of interest among researchers [32-35]. In
particular, Jing et al. have reported on the use of Bi MoO spheres for the photocatalytic
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oxidation of benzyl alcohol [36]. Zhang et al. have reported on the photocatalytic oxidation
of benzyl alcohol over TiO nanorods loaded with Au-Pt nanoparticles. They have
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immobilized the Au-Pt nanoparticles on TiO nanorods where photocatalytic activity for
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benzyl alcohol was obtained under visible light irradiation [37]. Perovskite materials were
also studied for the selective photocatalytic oxidation of benzylic alcohols [38]. Ziarati et al
has synthesized graphene highly wrapped yolk@shell TiO2 (G-HW-Y@S-TiO2)
nanomaterials for photocatalytic performance in visible light oxidation of aromatic alcohols
and found that the selectivity of aldehyde was intact even after 12 h of reaction [39]. Ding et
al has reported graphitic C N -based polymers for photocatalytic oxidation of aromatic
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alcohols. The study reveals that vacancy defect in the semiconductors plays an important role
in enhancing the photocatalytic activity of semiconductor photocatalysts [40]. Qiu et al has
studied noble metal nanoparticle-functionalized Zr-metal organic frameworks for aromatic
oxidation of alcohols to aldehydes. It was observed that the photocatalytic oxidation of
aromatic alcohols to aldehydes was enhanced over Au/UiO-66-NH or Au/UiO-66
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photocatalyst, but the activity was suppressed over Pt loading [41]. All the materials have
their own advantage and disadvantage. Moreover all the reported process uses an atom-
economic catalyst system that utilizes available green and clean renewable solar energy
which is favorable from an environmental standpoint. However some suffers from multi-step
catalyst synthesis procedure, long reaction run, low conversion or low selectivity. Therefore,
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we herein report a simple single step procedure for the synthesis of silver supported on Co O4
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spinel nanoparticles and studied its activity for environmentally friendly photocatalytic
oxidation of aromatic alcohols. It was found that the synthesized nanomaterials is highly
active for photocatalytic oxidation of aromatic alcohols and a small loading of silver is
sufficient for high conversion and selectivity towards the target product aldehyde.
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2. Experimental
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2.1 Catalyst preparation
A spherical Ag/Co O spinel nanoparticles catalyst was prepared by surfactant-
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assisted hydrothermal method through the modification of a synthesis method
previously reported by us [42]. The benefit of this procedure is that the catalyst can be
synthesized on a large scale (up to 10 g) and in a highly reproducible manner. First,
11.96 g of Co(NO ) ꢀ6H O and 0.16 g of AgNO were dissolved separately in a
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minimum volume of distilled water. The resultant solutions were then mixed and
stirred magnetically. Subsequently, 1.8 g CTAB dissolved in a mixture of 50 ml
distilled water and 2 ml ethanol was added to the mixed solution. Through the gradual
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addition of an ammonia solution, the pH of the solution was adjusted to 8 followed by
the addition of 0.1 g of hydrazine and was finally stirred for another 20 min at which
point the mixture turned into a homogeneous solution with a jet black color. Then, the
precursor solution was transferred into a 50 mL autoclave with a Teflon liner and was
held at 180 °C for 12 h. After washing with excess H O and ethanol, the obtained
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sample was dried at 80 °C for 12 h. The as-obtained precursor powder was then
calcined in a quartz reactor inside a tubular resistance furnace for 4 h at 550 °C to
obtain the Ag/Co O spinel nanoparticles catalyst powder. The catalyst was also
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prepared by the impregnation method and the coprecipitation method. The loading of
the silver nanoparticles was confirmed by inductively coupled plasma atomic emission
spectrometer analysis (ICP-AES).
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2.2 Photocatalytic oxidation of alcohol
Liquid phase photocatalytic alcohol oxidation was performed in a 100 mL quartz
reactor equipped with magnetic stirrer with O atmosphere under simulated sunlight
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irradiation. The 20 mg of photocatalyst was suspended in 10 ml acetonitrile, used as a
solvent, followed by the addition of aromatic alcohol (1 mmol). The reaction was
performed under the irradiation of a 300 W Xe lamp without UV and IR cut-off filters.
At regular intervals of the photooxidation reaction, a small portion of the sample was
withdrawn from the reaction mixture for analysis. The conversion and selectivity of
the product were calculated by gas chromatography (GC, Agilent 7890) using
methylbenzene as an external standard.
3. Results and discussion
<Fig. 1>
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The phase purity and crystalline structure of Ag/Co O was investigated using powder
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X-ray-diffraction (PXRD) analysis. The powder XRD patterns of the synthesized
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silver supported by Co O nanoparticles are presented in Fig. 1. The peaks at 2θ of
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19.0°, 31.2°, 36.9°, 44.8°, 55.7°, 59.3°, 65.3°, 74.1° and 77.3° confirmed the formation
of the face-centered cubic structured Co O nanoparticles. The diffraction pattern
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matched the reported Co O patterns well (JCPDS 78-1969). No crystalline phase of
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metallic Ag was detected by XRD for 0.5% and 1% Ag/Co O (Fig. 1(a and b)),
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indicating that the very small Ag-crystallites are highly dispersed over the Co O
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support. Moreover, in addition to the diffraction peaks of Co O , we observed an
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additional peak at 2θ of 38.1° corresponding to the metallic Ag crystal faces of (111)
which coincide well with the literature values (JCPDS File no. 89-3722) for 1.5%
Ag/Co O and the spent catalyst (Figs. 1(c,d)). No impurity peaks were observed,
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indicating the high purity of the nanoparticles. No change in the XRD pattern of the
spent catalyst was observed even after five cycles of reuse (Fig. 1(d)).
<Fig. 2>
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The morphology of the as-prepared Ag/ Co O catalysts was determined by scanning
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electron microscopy. The representative SEM images of the fresh catalyst show an almost
spherical shape with the size of 40-60 nm (Figs. (2(a,b). The EDS pattern showed only the
presence of cobalt, silver and oxygen and no impurities could be observed in the spectra (Fig.
2(d)). The dispersion of silver on the nanocrystalline Co O was confirmed by the elemental
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mapping of the catalyst that found a homogenous distribution of Ag on the nanocrystalline
Co O support (Fig. 3). The spent catalyst also showed a homogenous distribution (Fig. S2 in
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ESI).
<Fig. 3>
<Fig. 4>
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High-resolution transmission electron microscopy (HRTEM) analysis was carried out to
examine the particle size and distribution of the silver nanoparticles on nanocrystalline Co O4
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(Fig. 4). The TEM image of Co O nanoparticles showed an almost spherical shape with the
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size of 40-60 nm. The average particle size of silver nanoparticles was observed in the range
of 2–5 nm. The spacing of the lattice fringes was found to be 0.28 nm and 0.23 nm, possibly
due to the (220) plane of Co O and the (111) plane of metallic Ag, respectively.
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Furthermore, the TEM image of the spent catalyst (Fig. S1 in ESI) shows almost the same
shape and size even after five reuses. The corresponding particle size distribution histogram
of the Ag nanoparticles showed a very narrow particle size distribution with the sizes
between 2 and 5 nm which is in good agreement with the values obtained from the XRD data
(Fig. S1 in ESI).
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<Fig. 5>
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The metallic state and the surface composition of the synthesized nanospheres were
investigated by X-ray photoelectron spectroscopy (XPS). As shown in Fig. 5, the XPS
spectrum of the samples reveals the presence of the Ag, Co, and O elements. The Co 2p
spectrum of the fresh catalyst could be fitted to two spin-orbit doublets that are characteristic
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of Co and Co and two shake-up satellites. The two main peaks at 780.1 and 795.2 eV with
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a characteristic peak difference of 15.1 eV can be assigned to the 2p and 2p of Co and
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Co , respectively (Fig. 5(a))[43]. The O 1s spectra of the fresh catalyst could be
deconvoluted to three different oxygen contribution peaks labeled as O , O and Oads at
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the binding energies of 529.8, 531.8, and 533.2 eV, corresponding to the lattice oxygen,
hydroxyl oxygen and physically adsorbed oxygen (O ), respectively (Fig. 5(b)). The high-
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resolution spectrum of the silver nanoparticles contained two prominent Ag 3d and Ag 3d
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peaks at the binding energies of 368.2 eV and 374.1 eV, corresponding to metallic Ag and
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the two small peaks at 368.6 and 374.6 eV are ascribed to the Ag species (Fig. 5(c)) [44].
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<Fig. 6>
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The specific surface area, pore volume and pore diameter play important roles in the
catalytic activity. The textural properties of the synthesized Ag/Co O nanoparticles
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were investigated using nitrogen adsorption and desorption isotherms (Fig. 6). The N2
adsorption–desorption isotherms of the samples show typical IV-type isotherms with
high pore volume and specific surface area. The BET surface areas of the as-
synthesized nanoparticles and the spent catalyst were measured to be 46.23 and 40.74
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m g , respectively (Fig. 6(a)). The Barrett-Joyner-Halenda (BJH) pore size
distribution indicated that most of the pores are in the range from 2 to 15 nm (Fig.
6(b)). Table 1 summarizes the structural and the textural properties such as the surface
area, pore volume and pore size derived from the nitrogen adsorption and desorption
isotherms of the prepared nanomaterials.
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<Table 1>
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<Fig. 7>
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The surface-coordination of the organic surfactant molecules on the uncalcined nanoparticles
was studied by FTIR analysis (Fig. 7). A comparison of the FTIR spectrum of a dried
uncalcined nanoparticles precursor with that of the calcined nanoparticles was performed, not
only confirming the presence of the surfactant molecules but also revealing the nature of the
interaction of the surfactant molecules with the metal oxide surface. For dried uncalcined
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nanoparticles, the O-H group stretching vibration was observed at 3472 cm . The peaks at
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1632 cm were attributed to the C=O stretching vibration and the peaks at 1382 and 1109
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cm were due to the C–N vibrational mode, confirming the presence of CTAB in the
precursor (Fig. 7(a)). After the sample was washed and calcined, the peak intensity of the
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calcined nanoparticle decreased with two additional peaks observed at 674 and 569 cm that
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can be attributed to the characteristic peaks of the metal oxide (Co–O), confirming the
removal of the surfactant during the calcination (Fig. 7(b)).
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<Fig. 8>
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The TGA curve (Fig. 8) shows a two-step decomposition pathway. The weight loss of 4.04%
in the first step (30-200°C) is due to the removal of the physically adsorbed moisture in the
precursor. The weight loss of 32.16% in the second step (200-520°C) indicated the
combustion of CTAB from the surface and the subsequent conversion of Ag/Co(OH) to
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Ag/Co O .
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The UV-visible light absorption properties of the composites were measured by UV-Vis DRS
spectroscopy (Fig. S3(a) in ESI). The Ag/Co O composites shows a wide absorption range
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over the visible light region. Band gaps were calculated using the Tauc plot and the band gap
of Ag/Co O was found to be 1.47 eV (Fig. S3(b) in ESI). Photoluminescence (PL) was also
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investigated at room temperature, and the Ag/Co O composites were excited at the
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wavelength of 310 nm and the characteristic green emission peak was observed at 492 nm
(Fig. S3(c) in ESI).
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3.2 Catalytic activity
We have explored the catalytic activity of the synthesized nanomaterial for photocatalytic
alcohol oxidation. Various reaction parameters such as the solvent, time and catalyst weight,
were optimized in order to obtain the best result, with benzyl alcohols chosen as the standard
substrate. The photocatalytic oxidation experiment was conducted under different solvents
viz. acetonitrile, dimethyl carbonate, trifluorotoluene, tributyl phosphate and water. It was
apparent from the optimization experiments that acetonitrile was the best and most suitable
solvent for the present photocatalytic reaction (Table 2). Table 3 summarizes the optimized
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parameters of various catalyst for the photocatalytic alcohol oxidation where aldehyde was
detected as the major product with benzoic acid as a minor product.
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<Table 2>
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To explore the individual role of the oxide, we have performed the catalytic activity
measurements in the presence of commercially available Ag and Co O and found a
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negligible amount of activity. By contrast, when the reaction was performed with the
commercially available Ag/Co O catalyst, we find an increase in the conversion of the
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alcohol but the activity of the reported synthesized silver supported on Co O is still not
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comparable. This can be attributed to the small particular size and high surface area which
leads to a high dispersion of catalyst compared to the commercial catalyst, which has an
irregular shape and large particle size, leading to the limited accessibility of the catalyst for
the catalytic reaction. By contrast, the synthesized nanocatalyst consists of highly dispersed
nanospheres, leading to more exposed active surface sites for the catalytic reaction to occur.
Again, when the reaction was performed in absence of the catalyst and in the presence of the
oxidant, we observed a negligible conversion amount, underscoring the vital role of the
catalyst in the photocatalytic oxidation reaction of alcohol and for the selectivity to
benzaldehyde.
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<Table 3>
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Taking into account this optimized parameter, we explored the scope of the reaction for
various substituted alcohols. It was observed that the substituted electron-donating group
facilitates the oxidation reaction, whereas the electron-withdrawing group retards the
formation of the aldehyde (Table 4). When the substrate is an electron-donating group such
as -CH and -OCH , it facilitates the oxidation reaction with the reaction completed in a short
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time with a somewhat high conversion. Whereas when the substrate is an electron-
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withdrawing group such as Br and F. aldehyde formation is hampered, so that the reaction
requires a long time to complete. The conversion and selectivity are not so much affected,
however, we have drawn the conclusion with respect to time. Based on the results and
previously reported methods, we proposed a possible mechanism as shown in Scheme 1.
Under the irradiation of visible light, the photogenerated carriers were produced, the excited
electrons migrated from the valence band (VB) of Co O to the conduction band (CB). At the
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same time, the electrons from the conduction band of Co O migrated to the Ag nanoparticles
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where the surface plasmon resonance (SPR) activity of Ag also plays a vital role; the Ag
nanoparticle also absorbs photons producing electron-hole pairs due to SPR, leading to the
prevention of the electron-hole pair recombination and an excellent photocatalytic activity.
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The CB energy level of 0.50 V is more positive than the potential of O / O which is -0.046
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V so that the electrons transfers to Ag when the O is reduced to O which in turns produces
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the superoxide radical ( OOH). The superoxide radical converts the activated alcohol cation
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radicals produced by the action of h holes in the VB of Co O on the alcohol to aldehyde
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[40,45]. A comparison between the present catalyst and some of the previously reported
catalytic methods for the photocatalytic oxidation of benzyl alcohol to benzaldehyde are
summarized in table S1 in ESI.
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<Table 4>
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After each catalytic run and completion of the reaction, the solid catalyst was filtered from
the reaction mixture and washed with ethanol, and reused for multiple cycles to check the
stability of the catalyst (Fig. 9). Negligible change in the activity of the recovered catalyst
after 5 consecutive cycle was observed, indicating the true heterogeneity of the catalyst
(Table 2, entry 7). The SEM image of the spent catalyst showed almost similar sizes and
shapes to that of the fresh catalyst (Fig. 2(c)). Moreover, a negligible amount of leaching of
the metal was detected during the reaction (concentrations of both metals were <2 ppb).
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<Fig. 9>
4. Conclusions
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In summary, we have presented a facile and simple surfactant-assisted synthesis of silver
nanoparticles supported on the Co O nanoparticles via hydrothermal heating followed by
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calcination. The methodology adopted for the synthesis of the supported nanoparticle is
simple and can be readily utilized for large-scale synthesis. Initial characterization shows that
the nanoparticle is spherical in shape with the size of 40-60 nm. The synthesized nanoparticle
was evaluated as a catalyst for one-pot photocatalytic oxidation of alcohol to aldehyde. The
catalyst with 1% Ag loading was found to have the optimum loading for the photocatalytic
alcohol oxidation to aldehyde with the high conversion of 76% and aldehyde selectivity of
>99% within 8 h of reaction time.
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Acknowledgements
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The author like to thank the prominent talent project, Hebei university of environmental
engineering (BJRC201701), the project of natural science foundation of the Hebei province
(E2016415004), the project of science and technology department of the Hebei Province
(15213629) and the scientific research project item of the Hebei province education office
(QN2016032). We also acknowledge the Qinhuangdao key laboratory of environment
functional materials.
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Figures and captions
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
1
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Fig. 1. XRD patterns of (a) 0.5% Ag/Co O , (b) 1% Ag/Co O , (c) 1.5% Ag/Co O , (e) 1
3
4
3
4
3
4
% Ag/Co O (spent catalyst).(*-Ag(111)).
3
4
Fig. 2. SEM images of the (a,b) fresh (c) spent and (d) SEM-EDS mapping of 1% Ag/Co O4
3
nanoparticles.
Fig. 3. Elemental mapping of 1% Ag/Co O catalyst (a) Ag, (b) Co and (c) O.
3
4
Fig. 4. (a, b) TEM images, (c) HRTEM image (lattice fringes) and (d) ED pattern of 1%
Ag/Co O nanoparticles.
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4
Fig. 5. XPS spectra of (a) Co 2p, (b) O 1s, and (c) Ag 3d spectrum of 1% Ag/Co O
3
4
catalyst.
Fig. 6. (a) N adsorption-desorption isotherm and (b) pore size distribution curve of 1%
2
Ag/Co O nanoparticles with different loading.
3
4
Fig. 7. FTIR diagram of (a) uncalcined and (c) calcined 1% Ag/Co O nanoparticles.
3
4
Fig. 8. TGA/DTA analyses of the uncalcined 1% Ag/Co O nanoparticles.
3
4
Fig. 9. Recyclability test of 1% Ag/Co O nanoparticles.
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4
Scheme 1. The possible mechanism for photocatalytic oxidation of aromatic alcohols.
Table 1. Textural properties of 1% Ag/Co O .
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4
Table 2. Optimization table for photocatalytic oxidation of benzyl alcohol in presence
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1
2
3
4
of 1% Ag/Co O catalyst .
3 4
Table 3. Activities of the different catalysts for photocatalytic oxidation of benzyl alcohols.
Table 4. Activities of 1% Ag/Co O nanostructure catalyst for photocatalytic oxidation of
3
4
substituted alcohols.
5
6
<Fig. 1>
1
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2
<Fig. 2>
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4
<Fig. 3>
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0

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2
<Fig. 4>
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<Fig. 5>
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1

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2
<Fig. 6>
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<Fig. 7>
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2

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2
<Fig. 8>
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<Fig. 9>
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3

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2
<Scheme 1>
3
4
5
Table 1
a
b
Catalyst (Ag/Co O ) Ag
BET specific surface
Pore Volume
Pore size
(nm)
3
4
2
3
loading
area (m /g)
46.23
(cm /g)
Fresh catalyst
Spent catalyst
0.9
0.8
0.13
0.11
14.1
40.74
14.6
a
b
Total pore volume. Average pore diameter
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Table 2
Entry
Catalyst
Time (h)
Solvent
Conversion (%) Selectivity (%)
(
mg)
10
15
20
20
20
30
20
20
1
2
3
4
5
6
7
8
12
12
8
4
12
8
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
trifluorotoluene
dimethyl
60
74
76
58
78
79
49
76
99
99
>99
>99
99
>99
>99
97
8
12
carbonate
9
20
8
tributyl phosphate
94
32
1
1
0
1
20
-
8
8
Water
Acetonitrile
28
8
16
-
2
3
Table 3
Entry
Catalyst
Conversion (%) Selectivity (%) Yield (%)
com
Ag
23
34
27
42
46
76
74
54
78
8
96
94
96
95
96
>99
>99
>99
98
22
32
26
40
44
75
73
53
76
-
com
us
2
3
4
5
6
7
8
9
Co O
Ag
3
us
4
Co O4
3
imp
Ag/Co O4
1% Ag/Co O nano catalyst
1% Ag/Co O nano catalyst
0.5% Ag/Co O4
1.5% Ag/Co O4
No Catalyst
3
e
f
3
4
3
4
3
3
10
-
Conversion of benzyl alcohol based upon the FID-GC results = [moles of benzyl alcohol
reacted/initial moles of benzyl alcohol used] × 100. Selectivity of the product calculated by
total moles of the product formed/total moles of benzyl alcohol converted; Yield of aldehyde
e
f
=
conversion × selectivity/100;. Fresh catalyst. Spent Catalyst; com = commercial; us =
bare Ag and Co O prepared by our method; imp = impregnation method.
3
4
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5
6
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5

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1
Table 4
Entry Substrate
Product
Time
h)
Conversion Selectivity
(%) (%)
(
O
H
1
2
OH
8
76
>99
O
OH
6
76
>99
H
H C
3
H C
3
O
3
4
OH
9
6
75
78
>98
>99
H
O
Cl
Cl
OH
H
O N
2
O N
2
O
5
6
OH
10
8
74
76
>99
>99
H
HO
HO
O
OH
OH
H C
3
H
N
CH3
H C
3
N
CH3
O
7
4
78
>98
H
H CO
3
H CO
3
O
8
9
1
OH
9
75
72
78
>98
>98
>99
H
F
F
O
OH
12
8
H
Br
Br
O
0
1
2
3
OH
H
CH3
Br
CH3
O
O
1
1
1
OH
OH
10
6
76
79
75
>99
>99
>99
H
H
H
Br
NO2
NO2
O
8
OH
Cl
Cl
2
2
6

ACCEPTED MANUSCRIPT
Highlights
ꢀ
ꢀ
ꢀ
ꢀ
One-pot hydrothermal synthesis of silver supported cobalt oxide.
2–5 nm Ag-nanoparticles supported on 40–60 nm Co O nanosphere.
Room temperature photocatalytic oxidation of alcohol to aldehyde.
Alcohol conversion of 76% with 99% selectivity of aldehyde.
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