Performance of cobalt titanate towards H2O2 based catalytic oxidation of lignin model compound

Article abstract of DOI:10.1039/c5ra14227j

Mixed metal cobalt titanium oxide (CoTiO₃) prepared by solution phase method has been evaluated for the liquid phase catalytic oxidation of vainlly alcohol to vanillin using H₂O₂ as an oxygen source. The morphology, phase composition and crystal structure of the freshly prepared and reused CoTiO₃ catalyst was studied by SEM, EDX, XRD, XPS and Raman spectroscopy. Vanillyl alcohol conversion was influenced by various experimental conditions such as reaction time, temperature, molar ratio of reactants, catalyst loading, nature of solvent and reaction medium. The design a heterobimetallic oxide catalyst which can efficiently perform the high conversion and selective oxidation of vanillyl alcohol into fine chemicals, such as vanillin and vanillic acid. It has been found that during the 5 h reaction in NaOH, the CoTiO₃ exhibits remarkable conversion of 99% and excellent selectivity of 99.8% to vanillin was achieved in acetic acid and isopropanol solvents, respectively. The oxidation reaction mechanism over the catalyst was postulated based on the observation product from the HPLC analysis. CoTiO₃ catalyst can retain its performance without significant change in the catalytic activity after four consecutive cycles.

Full text of DOI:10.1039/c5ra14227j

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Performance of cobalt titanate towards H2O2 based catalytic oxidation of lignin model
compound
Mariom Shilpy, Muhammad Ali Ehsan, Tammar Hussein Ali*, Sharifah Bee Abd Hamid*, Md.
Eaqub Alia
Nanotechnology and Catalysis Research Center (NANOCAT), University Malaya, Kuala
Lumpur 50603, Malaysia.
Eꢀmail: sharifahbee@um.edu.my, tammar86@gmail.com
Abstract
Mixed metal cobalt titanium oxide (CoTiO3) prepared by solution phase method has been
evaluated for the liquid phase catalytic oxidation of vainly alcohol to vanillin using H2O2 as an
oxygen source. The morphology, phase composition and crystal structure of the freshly prepared
and reused CoTiO3 catalyst was studied by SEM, EDX, XRD, XPS and Raman spectroscopy.
Vanillyl alcohol conversion was influenced by various experimental conditions such as reaction
time, temperature, molar ration of reactants, catalyst loading, nature of solvent and reaction
medium. The design a heterobimetallic oxide catalyst which can efficiently perform the high
conversion and selective oxidation of vanillyl alcohol into fine chemicals, such as vanillin and
vanillic acid. It has been found that during the 5h reaction time in NaOH, the CoTiO3 exhibits
remarkable conversion of 99 % and excellent selectivity of 99.8 % to vanillin was achieved in
acetic acid and isopropnal solvents respectively. The oxidation reaction mechanism over the
catalyst was postulated based on the observation product from the HPLC analysis. CoTiO3
catalyst can retain its performance without significant change in the catalytic activity after four
consecutive cycles.

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1. Introduction
Lignin, one of the three subcomponents of lignocellulosic biomass (along with cellulose and
1,2
hemicellulose), represents more than 20 % of the total mass of the Earth’s biosphere
.
However, essentially due to its complex structure, this renewable polymer derived from biomass
is mainly burned as a source of energy in the pulp and paper industry 1,2. In the current context of
3
sustainable development and green chemistry , lignin valorization represents an important
challenge in the biorefinery area in order to diminish the reliance on oil 4,5. Today, the
valorization of lignin into the production of chemical feedstocks represents a real challenge in
terms of both sustainability and environmental protection. Because of the complexity of lignin,
most of the lignin oxidation studies were performed from model compounds and are very well
documented in literature 6,7,8,9,10. In the past few years, some novel strategies for oxidation of
lignin and lignin compounds have been investigated, such as electrochemistry 11,12, use of
mesoporous materials 8, photocatalysis 13 and use of vanadiumꢀbased catalysis 14.
These studies reveal that some issues need to be resolved, such as the lack of selectivity,
decomposition of the catalyst, low amounts of lignin required and difficult separation of products
after the reactions are completed. These problems can be overcome by designing suitable
heterogeneous catalysts because they offer many advantages over their homogenous counterparts
such as easy handling, separation and reusability. Several noble metalꢀbased heterogeneous
catalysts such as Au/CeO2, Pt/C, Ru/TiO2 etc. have been explored for this purpose and such
reactions are mediated by the use of alkali 15,16, 17. Although noble metal catalysts exhibit high
activity for oxidation reactions, they can be expensive, minimizing their potential for commercial
applications18. Oxides of other transition metals, such as titanium, chromium, manganese, cobalt
and copper are also known to be effective catalysts for oxidation reactions. Among these metals,

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titanium and cobalt are the most attractive because of their strong capability for dioxygen
activation (through metal–O2 adduct formation) and because these are more cost effective
compared to noble metals. Recently, a mixed metal oxide catalyst of manganese and cobalt
oxide (CoMn2O4) was found to be an active species for oxidation reactions and catalyzed
oxidation of vanillyl alcohol to vanillin 19.
In light of this study, we were attracted and motivated towards the mixedꢀmetal cobalt titanium
oxide system as a focus of our present study. We wish to report the preparation, characterization
and detailed catalytic performance of CoTiO3 for liquid phase oxidation of vanillyl alcohol
mediated with H2O2. The catalytic reaction parameters such as time, mass loading of catalyst,
mole ratio and reusability of the CoTiO3 catalyst have also been systematically carried out during
current study. It has been observed the change of acidic medium to base significantly enhance
the selectivity and conversion of vanillyl alcohol to vanillin. Furthermore, the reusability of
catalyst has been tested for fourth times and no significant change in the catalytic activity is been
observed.

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2. Experimental
2.1. Materials and methods
All Chemicals were purchased from various commercial sources such as: Cobalt (II) acetate tetra
hydrate (Merck 99%), titanium (IV) isoꢀpropoxide (SigmaꢀAldrich 98%), vanilly alcohol
(SigmaꢀAldrich 98%), hydrogen peroxide (SigmaꢀAldrich solution 30% in water), and acetic
acid (Merck 96%). The chemicals were used without further purification.
2.1.1. Synthesis of Catalyst
In a typical synthesis, 1.0 g (4.0 mmol) cobalt (II) acetate tetrahydrate was dissolved in 25 mL
methanol in a 100 mL Schlenk tube fitted with an inert gas/vacuum line adapter and magnetic
stirrer. 1.2 mL titanium (IV) isoꢀpropoxide (4.0 mmol) was added drop by drop via syringe to the
solution. The contents were stirred for 4h to obtain a clear purple solution. The reaction mixture
was evaporated to dryness under vacuum to produce a deep purple solid.
The as synthesized solid was ground to fine powder and calcined in air at the rate of 2 ˚C/min
until 500 ˚C and was kept at this temperature for 6h.
2.2. Characterization
The XRD pattern of the catalysts was recorded on a D8 Advance Xꢀray diffractionꢀBruker AXS
using Cu Kα radiation (d= 1.54Å) at a voltage of 40 kV and current of 40 mA at ambient
temperature. The surface morphology and chemical composition of the catalyst were analysed by
a scanning electron microscope (FEI Quanta 400) equipped with an energy dispersive Xꢀray
spectrometer EDX (INCA Energy 200, Oxford Inst.) operated at an accelerating voltage of
20 kV and a working distance of 9 mm. FTꢀRaman spectra were recorded with a Reinishaw

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inVia Raman microscope, using the 514 nm excitation source of Ar+1 laser with a 0.01 mw
output power. Xꢀray photoelectron spectroscopy was studied using an ULVACꢀPHI Quantera II
with a 32ꢀchannel Spherical Capacitor Energy Analyzer under vacuum (1 x 10ꢀ6 Pa) using
Monochromated Al Kα radiation (1486.8eV) and natural energy width of 680meV. The
carbonaceous C 1s line (284.6 eV) was used as a reference to calibrate the binding energies.
2.3. Typical method for the oxidation of vanillyl alcohol
The oxidation reaction was carried out in a 50 mL twoꢀnecked round bottom flask fitted with a
waterꢀcooled reflux condenser. In a typical oxidation reaction, the calculated quantities of
vanillyl alcohol (0.15 g, 1.0 mmol) and acetonitrile (25 mL) were added to round bottom flask
and kept on magnetic stirrer with oil bath at 358 K. After the desired temperature was attained,
the amount of catalyst was added while stirring (850 rpm) followed by H2O2 (0.2 mL, 2.0 mmol).
About 0.5 cm3 of reaction mixtures withdrawn periodically by means of a syringe and filtered.
The progress of the reaction was monitored by analyzing the filtrate into Agilent HPLC 1100
series liquid chromatography equipped with an ultraviolet detector was used for the analysis.
HPLC analysis was performed on a 25 cm RPꢀ18 column. The products and reactant were
detected using a UV detector at λmax = 270 nm. Aqueous acetonitrile (15%) with (1%) acetic acid
was used as a mobile phase at a column temperature of 28°C and a flow rate of 1.0 ml minꢀ1.

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3. Results and discussion
3.1. Structural and morphological characterization
The phase composition and chemical formula of the asꢀsynthesized CoꢀTi oxide catalyst was
determined from XRD and the resultant Xꢀray pattern is presented in Fig. 1 (blue line). A careful
matching of the fresh CoꢀTi oxide XRD pattern with the standard inorganic crystal structure
database available in PANalytical X’Pert HighScore Plus” software identifies the formation of
CoTiO3 as a catalyst product. The cobalt titanium oxide (CoTiO3)crystallizes in the
rhombohedral crystal system with cell parameters a = b = 5.0440, c = 13.9610 A˚; α = β =
90oand γ = 120˚and is identified by its peaks at 2θ = 24.0, 32.9, 35.4, 40.6, 49.2, 53.5, 60.3, 63.7,
71.4, 75.3, 84.1 and87.9 produced by their Miller indices (012), (104), (110), (113), (024), (116),
(214), (300), (119), (220), (134) and (226) correspondingly. All peaks in XRD pattern show
excellent matching with standard pattern (ICSD = 00ꢀ001ꢀ1040) in terms of their peak position,
2θ value and dꢀspacing. No possible crystalline impurities such as Co2O3, Co3O4 and TiO2 were
detected from XRD pattern. This clearly indicates the formation of pure crystalline CoTiO3 at
500 ˚C.
After performing the catalytic oxidation reaction, the reused catalyst was again characterized by
XRD (Fig. 1, green line) in order to observe any change in its phase composition and chemical
identity. It is worth noticing that no significant change in the composition and phase has been
detected and finger prints of reused catalyst are similar to the fresh CoTiO3in terms of its peak
position and 2θ values. Both the XRD patterns are dominated by the peak at 2θ = 32.9˚ also
reveals that CoTiO3 product is well crystallized. However the crystallinity of the reused catalyst
has been reduced as compared to the freshly prepared CoTiO3.

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Recent literature implies that attempts to synthesize pure CoTiO3 generally require higher
temperatures exceeding 600 °C and often produce TiO2 and Co2TiO4as impurity phases.20,21,22
.
Furthermore, it needs prolonged annealing at higher temperature of 700 °C to enhance the
crystallinity of the material. On the other hand, in the present case, solution method at a
relatively low temperature of 500 °C to furnish a high crystalline CoTiO3 product free from all
other titania and cobalt oxide phases.
[Insert Figure 1 about here]
The cobalt titanate phase that was identified from the XRD pattern was further confirmed by
Raman spectroscopy as is shown in Fig.2.
The Raman scattering vibration modes detected at 193, 208, 237, 267, 335, 383, 480, 521 and
689 cmꢀ1 are characteristic of ilmenite CoTiO3. The Raman spectroscopy results are in good
agreement with our XRD pattern and also matched well with the previously reported Raman data
for the CoTiO3materials 20.
[Insert Figure 2 about here]
The change in surface morphology of the asꢀsynthesized CoTiO3 catalyst before and after
vanillyl alcohol oxidation reaction has been studied by scanning electron microscopy and images
are shown in Fig. 3. Before carrying out the catalytic reaction, CoTiO3catalyst is comprised of
large size crystallites (Fig. 3a) and high resolution image reveals the rough and stony surface of
the catalyst (Fig. 3b).It is generally believed that the rough surface of the catalyst because of its
high surface area can better perform the catalytic action as compared to smooth and plane
surface which has less surface area. After execution of the oxidation reaction the morphology of

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CoTiO3 changes to oval shaped crystallites which exhibit smooth and plane surface (Fig. 3c and
d).
[Insert Figure 3 about here]
The stoichiometric composition of the catalyst before and after the catalytic oxidation reaction
was established from energy dispersive Xꢀray analysis and EDX spectra are shown in Fig. 4. It
has been erudite that the elemental composition of the catalyst before and after catalytic
oxidation reaction remains unchanged and EDX spectra show the expected stoichiometric ratio
indicating that the composition of the catalyst before and after oxidation reaction is in fact
CoTiO3. The molar ratio of Co/Ti obtained from different peak areas of the EDX spectra is thus
close to the expected 1:1 ratio of CoTiO3.
[Insert Figure 4 about here]
Figure 5 indicates the EDX mapping of CoTiO3 catalyst before and after the catalytic oxidation
reaction and reveals that Co, Ti and O atoms are homogeneously distributed throughout the
catalyst’s surface.
[Insert Figure 5 about here]
The XPS survey san plot (Fig. 6a) indicates the presence of the major cobalt, titanium, and
oxygen components in on the surface of the catalyst. Figure 6 (b, c and d) shows the high
resolution XPS spectra in the Co 2p and Ti 2p and O1s region for the catalyst powder. Fig. 4
shows that the binding energies of Co 2p3/2 and Co2p1/2 are 780.0~780.8 eV, and
796.2~796.4eV, respectively. These values are comparable to the 780.7 (2p3/2) And 796.3 eV
23
(2p) that was found in Co3O4 . The binding energies of Ti 2p3/2 (457.2~458.6 eV) and Ti 2p
(463.0~ 464.2 eV) are agreeable with that of the TiO powder (458.5 eV for Ti 2p3/2)24 and the

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binding energy of O 1s is between 529.2~530.2 eV. Overall the XPS spectra is in good
agreement with the previously reported CoTiO3 prepared by a modified solꢀgel method25.
[Insert Figure 6 about here]
3.2.
Liquid phase oxidation of vanillyl alcohol
To determine the optimum reaction condition of vanillyl alcohol oxidation various reaction
parameters were studies such as effect of time, catalyst amount, molar ratio of vanillyl alcohol:
H2O2, reaction temperature, solvent type and the effect of alkaline medium on the reaction.
Under the optimum reaction condition, the oxidation of vanillyl alcohol without catalyst did not
show any activity and the reusability analyses were also investigated. Moreover, the reactions
also were performed under optimum reaction conditions in alkaline medium. The idea behind
using base is probably to deprotonate the phenolicꢀOH to form the phenoxy anion, which is more
reactive and easier, favours coordinate to CoTiO3 and resulting more selectivity to vanillin and
increasing the activity26. The equation for the oxidation of vanillyl alcohol is shown in Scheme
1.
Scheme1: liquid phase oxidation of vanillyl alcohol products in CoTiO3 catalyst.
3.2.1 Influence of reaction time
The effect of reaction time on vanillyl alcohol conversion and selectivity to vanillic acid and
vanillin were studied for CoTiO3 and the results are shown in Fig. 7. The conversion increased

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slowly from 28 % to 67 % when the time increased from 30 min. to 5 h. Further extending the
reaction time to 6 h. did not improve the oxidation. Based on the highest conversion, the 5 h
reaction time was selected as an optimum time for this catalytic system. However, the selectivity
of vanillic acid was found to be decreased from 87 % to 77 % within time increase, this decrease
is consistent with the increased selectivity of vanillin from 10 % to 19 % in reaction time 30 min.
to 5 h.
[Insert Figure 7 about here]
3.2.2 Catalytic activity with different mass of catalyst:
The prepared catalyst was tested in liquid phased oxidation of vanillyl alcohol. As illustrated in
Fig. 8, as the mass of the catalyst increased the conversion of vanillyl alcohol to corresponding
product was found to be increased sharply from 24 %, to 67 % when the catalyst mass used was
increased from 25 to 100 mg. The selectivity of acid formatting was found to slightly decrease as
the catalyst mass was increased. However, further increase in the catalyst mass to 125 mg
resulted in a decrease in vanillyl alcohol conversion to 59 %. The reason behind that could be
due to the rapid decomposition of H2O2 over the large surface area available with a higher mass
catalyst 27,28. As a result, the selectivity of vanillin was observed slightly increased associated
with decreased formation of vanillic acid. On the other hand, the absence of the catalyst leads to
maximum value of 3% vanillyl alcohol conversion to vanllic acid.
[Insert Figure 8 about here]

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3.2.3 Influence of Temperature
The reaction temperature was found to have a great influence on the conversion of the reaction.
Thus, in the oxidation of vanillyl alcohol the effect of temperature on the reaction was studied in
the range of 338ꢀ363 K (Fig. 9). The reaction was conducted at a fixed parameter (vanillyl
alcohol: H2O2 molar ration 1:2 and a catalyst amount of 100 mg in 25 ml acetonitrile). The
conversion was found to increase from 51 % at 338 K to 72 % at 363 K. The plausible
explanation for this observation could be due to the enhanced decomposition of H2O2 at high
temperature 27. However, there is no significant change in the selectivity of vanillic acid and
vanillin at different temperature. Therefore, 358 K was preferred as suitable reaction temperature
for the subsequent optimization studies, since there are moderate conversion and rapid
decomposition of H2O2.
[Insert Figure 9 about here]
3.2.4 Influence of H2O2 mole ratio
To determine the optimum ratio of H2O2 needed for this oxidation of vanillyl alcohol reactions,
four different ratio were studied. The results obtained from the reactions are shown graphically
in Fig. 10. The conversion was ranging from 51ꢀ67 % for 1 to 4 H2O2 molar ratio. However, the
results clearly show that when H2O2 is taken in more than equimolar ratio (vanillyl alcohol:
H2O2:ꢀ1:2, 1:3) the conversion significant increased (67 %). Generally, the decomposed of H2O2
29
produced water as byꢀproduct , and that might poison the catalyst by adsorbing strongly to the
catalyst CoTiO3 and blocked the active site, thus inhibiting the conversion of vanillyl alcohol to
further products. Furthermore, decomposition of H2O2 increased the formation of vanillic acid,
on the contrary, the formed of guaiacol which was decreased with increasing of H2O2 ratio, while

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the formed of vanillin did not significantly change. Unlike, it can be seen from Fig. 10, which
indicates that an increase in H2O2 more than 2 equimolar ratio no significant change in the
performance of the catalyst.
[Insert Figure 10 about here]
3.2.5 Reusability of the catalyst
In order to study the stability of CoTiO3heterogeneous catalyst the regenerating test carried out.
After observing the completion of the reaction over a fresh catalyst which was carried out as
mention in typical method for the oxidation of vanillyl alcohol, the liquid contents were removed
from the flask and CoTiO3catalyst washed several times with acetone. Then, dried under vacuum
at 100 °C for 2 h. This dried catalyst was reused in a second cycle for the oxidation of vanillyl
alcohol and a similar procedure was followed for four subsequent oxidation cycles, the result is
depicted in Fig.11. It can be observed that the vanillyl alcohol conversion decreased ca. 15 %
and 20 % after the third and fourth reuse, respectively. However, the selectivity of the vanillic
acid and vanillin was found with slight changes after third recycle. To further confirm the
catalyst nature of CoTiO3 after the fifth reused, the XRD, SEM and Raman were analysed and
was described in section 3.1.
[Insert Figure 11 about here]
3.2.6 Influence of solvent
Since the catalytic activity is strongly dependent on the basic character of the solvent, the
influence of nature solvent on the oxidation of vanillyl alcohol and vanillin selectivity were
investigated over sixth different solvent system with 100 mg catalyst mass and 1:2 vanillyl

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alcohol: H2O2 molar ratio, the result is represented in Fig. 12. Based on the experiment, highest
conversion was achieved in acetic acid (91 %) followed by ethyl alcohol (70 %), acetonitrile (67
%), N,Nꢀdimethyl formaldehyde (35 %), tetrahydrofuran (20 %) and acetone (1%). Keeping the
above fact in view, it is understood that the increasing conversion by using acetic acid as a
solvent is directly proportional to the formation of peracetic acid, which is in situ generation by
30
reacted acetic acid with H2O2 in the presence of an acid catalyst . And this in turn accelerates
and acting as an oxidant source for the oxidation reaction, as shown in Scheme 2. However, the
selectivity of vanillin was significant increased when acetic acid used as a solvent compared to
other solvents 31, 32, this could be due to the possibility of formation O2 higher than radical
hydroxide. Nonetheless, acetic acid was chosen as the optimal solvent media due to formation of
peracetic acid and this led to higher conversion and increases the selectivity to vanillin. So under
these reaction conditions, in the oxidation of vanillyl alcohol to vanillin, a major role is played
by peracetic acid conversely to oxidation of vanillyl alcohol to vanillic acid a major role is
played by H2O2.
Scheme2: Role of formation peracetic acid in oxidation of vanillyl alcohol.
[Insert Figure 12 about here]

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3.2.7 Influence of basic medium
The effect of NaOH on the conversion and selectivity of aldehyde product (vanillin) in the
oxidation of vanillyl alcohol is displayed in Fig. 13A. The adding amount of the base (NaOH)
has been used equivalent to H2O2 (2.0 mmol). The role of using alkaline is probable to
deprotonate the phenolic to form the phenoxyanion, In addition, it seems that the generation of
sodium peroxide occurs immediately after adding H2O2 to alkaline oxidation reaction mixture
(Eq. 1). The latter, can be used as an oxidizing agent as well as oxygen source and that enhance
and accelerate the reaction activity and the selectivity of aldehyde. However, according to lack
solubility of NaOH in acetonitrile the acetic acid and isopropanol were choosing to examine the
effect of alkaline on the oxidation of the vanillyl alcohol reaction (referring Fig. 13B.) It has
been established that conversion and selectivity of vanillin was significantly influenced by the
change of the solvent. When the catalytic reactions were studied in acetic acid, a conversion of
99 and 68 % selectivity of vanillin product was obtained. However using isopropanol as a
solvent, slightly reduces the conversion to 91% but enhances the selectivity vanillin to 99.8%. A
comparable oxidation reaction in the present of isopropanol as solvent and without a base led to
much lower conversion (3 %) of vanillyl alcohol. As a result, this hypothesis indicates that the
alkaline an important part in the selective oxidation of the vanillyl alcohol process.
Equation 1: Reactivity of H2O2 in alkaline medium to form oxygen in oxidation reaction.
[Insert Figure 13 about here]

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3.2.8 The proposed reaction mechanism
Detection of oxidation products from the HPLC analysis suggests a free radical mechanism may
be operating for vanillyl alcohol oxidation under the studied reaction condition. Scheme 3
illustrates the suggested mechanism for oxidation of vanillyl alcohol in present of H2O2. Initially
the catalyst reacts with H2O2 to form the hydroperoxyl radial which is acting as a source of
highly reactive oxidatand, this in turn attack the catalyst forming an intermediate. The
hydroperoxyl radial is conjugate acid of superoxide anion (ꢀO2), this is a very important
intermediate in combustion chemistry and known to play major roles in the oxidation reaction
33,34. Moreover, this chemical is more stable at atmosphere than superoxide. On the other hand,
its well know the formation of hydroperoxyl radial can be through direct photolysis of H2O2 as
well as through the Fentons reaction 35. However, the vanillyl alcohol is activated on the catalyst
surface. Then the electron rich hydroperoxyl attack the partial positive carbon and the hydrogen
of the hydroxyl group abstraction by the oxygen molecular to produce activated oxygen species,
which help to remove the hydroxyl from the hydroperoxyl to produce water as a byꢀproduct.
Meanwhile, the vanilloxycation releases a proton which is attacked by electron rich oxygen of
the hydroperoxyl group and forming the final acid product. Or another possibility the electron
rich oxygen of the hydroperoxyl group attacks the proton on activated oxygen species (on
catalyst) and forms the final vanilla product. It has found that when the reaction medium more
base the formation of aldehyde product increased and that could be due to the formation of
superoxide rather that hydroperoxyl radical which is going to prefer attacking the hydrogen on
activated oxygen species (on catalyst) than the proton of vanilloxy carbon.

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Scheme 3: The suggested mechanism for the formation of main oxidation product (vanillin and
vanillic acid) from vanillyl alcohol in presence of CoTiO3.
4. Conclusion
The CoTiO3 catalyst was prepared by mixing equivimolar Co(OAc)2 and Ti(iPro)4 in methnol
and followed by calcination at 500 °C. However the applicability of this process demand a
heterogeneous catalyst which can offer potential advantages of easy handling, separation,
reusability and cost effectiveness. The as synthesized CoTiO3 material was characterizaed by
XRD, SEM, EDX and XPS analyses and employed for the catalytic oxidation of vanillyl model
compound with the help of H2O2 in acid and base medium. Presence of titanium species were
responsible for their enhanced catalytic activity. In the oxidation of vanillyl alcohol, the vanillin
product was obtained as the major component in a basic condition (99.8 %) while the highest
conversion obtained in the acid medium (99 %). No products were obtained without the presence

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of the catalyst. However, in the present study, we identified that CoTiO3 possesses these catalytic
properties and can be used for practical applications. Through a simple regeneration technique,
the prepared catalyst was found to be stable and could be reused several times with minor loss
was observed initially.
Acknowledgement
The authors are grateful for the financial support from High Impact Research HIR Fꢀ000032 to
complete this work.

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List of Figures Captions
Fig. 1. Xꢀray diffractogram offreshly prepared CoTiO3(blue line) catalyst prepared at 500 ˚C.
Green line represents the Xꢀray diffractogramof reused catalyst after performing the
oxidation reaction.
Fig. 2. Raman spectrum of CoTiO3 catalyst.
Fig. 3. Surface topographic images of CoTiO3 catalyst (a and b) before vanilline oxidation
reaction; (c and d) after vanilline oxidation reaction.
Fig. 4. EDX spectra revealing the stoichiometric composition of CoTiO3catalyst (a-c) before
and (d-f) after oxidation reactions.
Fig. 5. EDX mapping revealing the distribution of Co, Ti and O atoms on the surface of catalyst
beforeand after oxidation reactions.
Fig 6. XPS spectra of CoTiO3 powder prepared at 500 °C (a) Survey scan plot. (b) Co 2p (c) Ti
2p (d) O1s.
Fig. 7. Effect of time on conversion and selectivity. Reaction condition: amount of CoTiO3 (100
mg); molar ratio of vanillyl alcohol:H2O2 (1:2); reaction temperature (358 K); acetonitrile
as solvent (25 ml).
Fig. 8. Effect of catalyst loading on conversion and selectivity. Reaction condition: reaction time
(5 h); molar ratio of vanillylalcohol :H2O2 (1:2); reaction temperature (358 K); acetonitrile
as solvent (25 ml).

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Fig. 9. Effect of reaction temperature on conversion and selectivity. Reaction condition:
reaction time (5 h); molar ratio of vanillyl alcohol:H2O2 (1:2); amount of CoTiO3(100
mg); acetonitrile as solvent (25 ml).
Fig. 10. Effect of molar ratio on conversion and selectivity. Reaction condition: reaction time (5
h); amount of CoTiO3 (100 mg); reaction temperature (358 K); acetonitrile as solvent
(25 ml).
Fig. 11. Effect of reꢀused catalyst (reusability) on conversion and selectivity. Reaction condition:
reaction time (5 h); amount of CoTiO3(100 mg); molar ratio of vanillyl alcohol:H2O2
(1:2); reaction temperature (358 K); acetonitrile as solvent (25 ml).
Fig. 12. Effect of solvent on conversion and selectivity. Reaction condition: reaction time (5 h);
amount of CoTiO3(100 mg); molar ratio of vanillyl alcohol:H2O2 (1:2).
Fig. 13. Effect of basic medium on conversion and selectivity. Reaction condition: amount of
CoTiO3 (100 mg); amount of NaOH (2.0 mmol); molar ratio of vanillyl alcohol:H2O2
(1:2); reaction temperature (358 K); solvent A): acetic acid (25 ml), B): isopropanol (25
ml).

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6
Survey
Co2p
Ti2p
O1s

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Figure 7
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Guaiacol
Vanillin
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Figure 8
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Amount of catalyst (mg)