Selective liquid phase oxidation of secondary alcohols into ketones by tert-butyl hydroperoxide on nano-fibrous Ag-OMS-2 catalyst

Article abstract of DOI:10.1016/j.molcata.2013.09.018

Selective oxidation of secondary alcohols to ketones using tert-butyl hydroperoxide was accomplished over active and reusable silver incorporated octahedral molecular sieve (Ag-OMS-2) catalyst. Different loadings of Ag (5-15% w/w) were incorporated in OMS-2 by the precipitation method among which 15% w/w Ag-OMS-2 was found to be the best. The catalyst was fully characterized. It possesses nanofibrous crystalline structure with high surface area. Oxidation of 1-phenylethanol, as a model compound, was conducted at 75 C into acetophenone by tert-butyl hydroperoxide over 15% w/w Ag-OMS-2. Effects of various parameters were investigated in detail. A mathematical model is built to interpret the experimental data and develop mechanism. The reaction is intrinsically kinetically controlled and follows second order kinetics. The modeling will help reactor design and scale-up. As an extension to the studies, oxidation of various aliphatic and aromatic alcohols was studied in the liquid phase over 15% w/w Ag-OMS-2 catalyst under optimized conditions. The catalyst is reusable up-to five runs without any loss in catalytic activity. The results obtained are novel.

Full text of DOI:10.1016/j.molcata.2013.09.018

Accepted Manuscript
Title: Selective liquid phase oxidation of secondary alcohols
into ketones by tert-butyl hydroperoxide on nano-fibrous
Ag-OMS-2 catalyst
Author: Ganapati D. Yadav Akhilesh R. Yadav
PII:
S1381-1169(13)00343-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2013.09.018
MOLCAA 8872
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
18-4-2013
11-9-2013
15-9-2013
Please cite this article as: G.D. Yadav, A.R. Yadav, Selective liquid phase
oxidation of secondary alcohols into ketones by tert-butyl hydroperoxide on nano-
fibrous Ag-OMS-2 catalyst, Journal of Molecular Catalysis A: Chemical (2013),
http://dx.doi.org/10.1016/j.molcata.2013.09.018
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
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apply to the journal pertain.

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Highlights
ꢀ Single step selective oxidation of aliphatic and aromatic alcohol.
ꢀ Nano-fibrous 15% w/w Ag-OMS-2 is an efficient and reusable catalyst.
ꢀ 100% selectivity for oxidation of secondary alcohol into ketone.
ꢀ Various parameters affecting reaction were explored.
ꢀ Kinetic modeling and energy of activation is 12.65 kcal/mol.
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Graphical abstract:
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Selective liquid phase oxidation of secondary alcohols into ketones by tert-butyl
hydroperoxide on nano-fibrous Ag-OMS-2 catalyst
Ganapati D. Yadav and Akhilesh R. Yadav
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Submitted Online to: Journal of Molecular Catalysis A: Chemical
Manuscript id: i.e.- MOLCAA-D-13-00316-Revised – Clean version
September 9, 2013
Selective liquid phase oxidation of secondary alcohols into ketones
by tert-butyl hydroperoxide on nano-fibrous Ag-OMS-2 catalyst
Ganapati D. Yadav* and Akhilesh R. Yadav
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Department of Chemical Engineering
Institute of Chemical Technology
Nathalal Parekh Marg, Matunga
MUMBAI – 400 019
INDIA
Tel: +91-22-3361-1001/1002/1111
Fax: +91-22-3361-1002/1020
E-mail: gdyadav@yahoo.com; gd.yadav@ictmumbai.edu.in
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* Author to whom correspondence should be addressed
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Abstract
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Selective oxidation of secondary alcohols to ketones using tert-butyl hydroperoxide was
accomplished over active and reusable silver incorporated octahedral molecular sieve (Ag-OMS-
2) catalyst. Different loadings of Ag (5 – 15 % w/w) were incorporated in OMS-2 by the
precipitation method among which 15% w/w Ag-OMS-2 was found to be the best. The catalyst
was fully characterized. It possesses nanofibrous crystalline structure with high surface area.
Oxidation of 1-phenylethanol, as a model compound, was conducted at 75 °C into acetophenone
by tert-butyl hydroperoxide over 15% w/w Ag-OMS-2. Effects of various parameters were
investigated in detail. A mathematical model is built to interpret the kinetic data and develop
mechanism. The reaction is intrinsically kinetically controlled and follows second order kinetics.
The modelling will help reactor design and scale-up. As an extension to the studies, oxidation of
various aliphatic and aromatic alcohols was studied in the liquid phase over 15%Ag-OMS-2
catalyst under optimized conditions. The catalyst is reusable up-to five runs without any loss in
catalytic activity. The results obtained are novel.
Keywords: Oxidation, Secondary Alcohol, Oxidation, Octahedral molecular sieve (OMS-2),
Kinetics, Redox catalyst.
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1. Introduction
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Selective conversion of alcohol into carbonyl compound is one of the most widely studied
reactions in synthetic organic chemistry [1]. Aldehydes or ketones, as well as carboxylic acids,
find wide applications in a variety of processes and products in the pharmaceutical,
agrochemical, vitamin, and perfumery industries [2]. However, oxidations are carried out by
using polluting and hazardous oxidising agents leading to high environmental factor (E-factor)
and generation of large amounts of toxic waste [3]. Conventionally oxidation is carried out using
stoichiometric amount of reagents such as chromic acid, permanganate, and ruthenium or
nitrogen oxide with nitric acid, which produces environmentally deleterious heavy metal waste
[4-8]. Many halogen-containing oxidising reagents and supported metal ions are reported for the
oxidation of various aromatic and aliphatic substrates [9-27]. These methods are beset with
several drawbacks such as use of expensive metal catalysts, severe reaction conditions and
incompatible oxidising agent [28]. Hence there is tremendous scope to design and develop new
catalytic oxidation processes which are safer, greener and economical. Recently Chen et al. [29]
have reported advantage of ionic liquid as an additive in carbon nanotube supported palladium
catalyzed aerobic oxidation of 1- phenylethanol; however, the reaction was carried out at very
high temperature. Efforts are underway in many laboratories to develop novel catalysts which are
tolerable to various functional groups and selectively able to oxidize the desired moiety.
Selectivity engineering of catalytic process is the need of modern chemical industry to reduce
waste minimisation. Yadav and Manyar [30] have reported synthesis, characterization and
application of a novel V-OMS-2 based redox catalyst UDCaT-3 in selective oxidation,
hydroxylation and hydrogenation reaction including mecapto compounds [31]. Octahedral
molecular sieves (OMS) have been reportedly used for dehydration reactions. Further, OMS-2
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having 2×2 tunnel structure doped with active metal or combination of metals is recently
reported for reduction of acetophenone to 1-phenylethanol by Yadav and Mewada [32]. OMS
and Octahedral layered (OL) materials based on porous mixed-valent manganese oxides are
potentially useful catalysts due to their unique properties such as excellent semi-conductivity,
particle size and porosity [33-35]. Catalytic properties of OMS and OL materials have been
2
+
3+
ascribed to the redox cycling of different oxidations states of manganese such as Mn , Mn ,
4
+
and Mn . The smaller pore opening is possibly is responsible higher stability of OMS-2. It is
reported that OMS-2 has better stability than OMS-1 materials [36]. The occurrence of counter
cations such as alkali and alkaline earth metals and water is shown to be the cause for the
stability and charge balance on structure of OMS-2. Inclusion of metals in the tunnel structure
leads to increase in defects inside the catalyst surface thereby creating more number of active
sites [30, 32, 37]. Our laboratory has reported hydrogenolysis of glycerol to 1, 2-propanediol
over 30% w/wAg-OMS-2 as an excellent catalyst [38]. Selective hydrogenation of nitrobenzene
to azobenzene over nano-fibrous Ag-OMS-2 is also reported [39]. Recently application of costly
gold nanoparticle and N-hydroxyphthaliminde in ionic liquid was reported, which involves
formation of undesired products and long reaction time [40].
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The current work describes the use of nano-fibrous Ag-OMS-2 as the catalyst for the oxidation
of various secondary aliphatic and aromatic alcohols to ketones. We have carried out both batch
and continuous mode of operations to determine stability of the catalyst. Different loadings of
Ag on OMS-2 were incorporated by the precipitation method. This paper reports a
comprehensive account of this catalytic process.
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2. Experimental Section
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2.1. Chemicals. All chemicals were procured from reputed firms and used without further
purification. 1-Phenylethanol, benzhydrol, 2-hydroxy-1-phenylethanol, 4-hydroxy-1-
phenylethanol, 4-methoxy1-phenylethanol, 4-chloro-1-phenylethanol, 3-methyl-1-phenylethanol,
potassium permanganate, silver nitrate, 2-propanol and nitric acid (70% w/v) were purchased
from M/s s. d. Fine Chem Ltd., Mumbai, India.
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2.2. Catalyst Synthesis.
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Ag doped manganese oxide octahedral molecular sieves (OMS-2) was synthesized by
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precipitation method as follows [13]. Manganese acetate (21.0 g) was dissolved in 67.5 cm
deionised water and then concentrated nitric acid was added. Silver nitrate (9.97 g) was dissolved
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o
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in 50 cm distilled water and added to acidic manganese acetate at 30 C. KMnO (13.3 g) was
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taken in 275 cm distilled water and added to the above solution dropwise at 70 °C and the black
precipitate so obtained was agitated and refluxed at 100 °C for 24 h. The precipitate was washed
several times with deionised water to pH of 7. The resulting material was filtered and dried at
120 °C for 12 h to obtain 15% w/w Ag-OMS-2 [32, 37, 38]. These catalysts have typical
cryptomelane structure with a one-dimensional 2 × 2 channel structure.
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2.3. Experimental Setup
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All experiments were conducted in 50 cm glass reactor. A four bladed –pitched turbine impeller
was used for reaction. The temperature was maintained at the selected value. Weighed quantities
of reactants and catalyst were charged to the reactor and then the temperature raised to the
desired value. Thereafter the agitation was commenced. An initial sample was taken and further
sampling was done periodically up to 4 h. A standard experiment was performed with 0.01 mol
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1-phenylethanol, 0.03 mol TBHP and catalyst quantity of 0.012 g/ cm . The temperature was
normally maintained at 75 °C at 900 rpm as speed of agitation. The total volume of liquid phase
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was 15.0 cm in which 0.2 cm n-decane was used as internal standard. At the end of experiment,
the catalyst was filtered and the organic layer was concentrated and purified by column
chromatography.
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2.5. Method of Analysis.
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Clear liquid samples of reaction mass were analysed by GC (Chemito, model 1000) using FID
and a capillary wax column BP-20 (0.25 mm diameter and 30 m length). The product was
confirmed by GC–MS (Perkin Elmer instrument, Clarus 500) with BP-1 capillary column (0.25
mm i.d., 30 m length) and EI mode of MS. The injector and detector temperatures were
maintained at 220 °C. The oven temperature was programmed from 90 °C to 220 °C, with a
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ramp rate of 15 °C/min. Nitrogen was employed as the carrier gas at a flow rate of 0.5 cm /s. The
quantification of data was based on the disappearance of the limiting reactant. The products were
also confirmed by GC-MS.
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2.6. Reaction scheme: Oxidation of 1-phenylethanol using 15%Ag-OMS-2 is given by Scheme
1
1. In this reaction 1-butanol is the co-product along with water. The alcohol can be recycled.
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Scheme 1. Oxidation of 1-phenylethanol with TBHP over Ag-OMS-2
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3. Results and Discussion
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3.1. Catalysts characterization
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Ag-OMS-2 was characterized by various techniques such as SEM, TEM, ammonia-TPD, XRD,
BET surface area, FTIR and elemental analysis and more details have been published recently by
our group [32, 37, 38]. Only a few prominent features are presented here to put the current
studies in perspective.
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The catalyst was nano-fibrous and nano-crystalline as revealed by SEM (Fig. 1) and TEM (Fig.
2). The TEM also showed a fibrous nano-rod shaped structure.
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Fig. 1. SEM of catalyst 15%Ag-OMS-2
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Fig. 2. TEM of catalyst 15%Ag-OMS-2
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Replacement of K ions with metal ions Ag inside the tunnel framework is confirmed by EDX
[32, 37]. The difference in physical and chemical properties of metal cation dopants was
responsible for their content in OMS structure during synthesis. As a consequence, all metal
cations have variations in their theoretical and actual compositions. For 15 % w/w Ag-OMS-2
+
synthesis, almost 15% Ag ions were retained in the catalyst. The size of Ag , which is smaller
+
than K , is favorable to fit into the 4.6 A° tunnel of OMS-2 and also more surface area than
parent OMS-2. TPD analysis of 15% w/w Ag-OMS-2 with ammonia and carbon dioxide as
probe molecule confirmed the existence of mild acidic and basic sites [32, 37, 38]. Incorporation
of silver into OMS-2 resulted in strong interaction of silver with OMS surface leading to a
drastic decrease in reduction temperature from 280 °C of K-OMS-2 to 162 °C for 15% w/w Ag-
OMS-2, which was revealed by TPR. The XRD of K-OMS-2 and Ag-OMS-2 had revealed well
crystalline structure characteristic of octahedral molecular sieve material and the reflections and
2θ values obtained were characteristic of 2 × 2 tunnel structured manganese oxide phase
(KMn
8
O16, JCPDS 34-168) [32, 37]. The crystal domain size of cryptomelane phase derived
from the XRD peaks broadening was 20 nm [32, 37]. FT-IR studies showed OMS-2 structure
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was intact after inclusion of metal in the tunnel framework [32]. The BET surface area, pore
volume and pore diameter for 15% w/w Ag-OMS-2 is much better than OMS-2. A surface area
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118.8 m /g was obtained for 15% w/w Ag-OMS-2 as compared to 89.1 m /g of OMS-2 [32, 37,
38]. The adsorption-desorption isotherm was type III isotherm, suggesting a porous structure.
Such type of adsorption occurs in cases where heats of adsorption are lower than the adsorbate
heat of liquefaction.
3.2. Effect of oxidant
The rate of activation of reactant is governed by the nature of catalyst, oxidizing agent, and
temperature. The effect of various oxidants on liquid phase oxidation of 1-phenylethanol, the
model compound, was conducted at 75 °C. In this case, neither hydrogen peroxide nor air was
found to be suitable as oxidising agent, with no conversion, whereas tert-butyl hydroperoxide
(TBHP) was effective. A control experiment was also performed in the absence of catalyst to
ascertain that the reaction did not proceed without catalyst.
3.3. Activity of Various Catalysts
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The efficacies of UDCaT-3 and different Ag-OMS-2 are shown in Fig. 3. It is evident that
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Catalyst
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Fig. 3. Efficacy of various catalysts.
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Reaction conditions: 1-Phenylethanol-0.01 mol, TBHP-0.03 mol, Catalyst loading: 0.012 g/cm ,
Speed of agitation-900 rpm, Temperature -75 °C, solvent-Acetonitrile.
incorporation of silver inside the framework of the catalyst enhances the activity of catalyst
considerably. Mesoporous redox catalyst UDCaT-3 [30,31] lead to good conversion. A
conversion of 45% was achieved in case of K-OMS, which is OMS-2, whereas with increasing
Ag content in the OMS-2, there was increase in conversion and yield. There is a synergistic
effect of silver in presence of manganese and potassium ions in the catalyst. The further increase
in loading of silver ion does not so any significant difference in the conversion of oxidation
reaction. Hence further reactions were performed with 15%Ag-OMS-2.
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3.4. Effect of various solvents
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The effect of solvents in the liquid phase oxidation of secondary alcohol using TBHP as oxidant
is given in Fig. 4. Solvents such as acetonitrile, toluene, dioxane, DMF and DMSO were
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Solvent
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Fig. 4. Effect of solvent
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Reaction conditions: 1-Phenylethanol-0.01 mol, TBHP-0.03 mol, Catalyst loading-
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g/cm , Speed of agitation-900 rpm, Temperature -75 °C.
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screened for the reaction. In case of non-polar solvent like toluene, 75% conversion was
achieved, on the other hand, in polar aprotic solvents such as DMF and DMSO conversion of
50% and 27% was obtained, respectively. Acetonitrile was the best solvent under optimized
reaction conditions; the results obtained were in accordance with the literature reports on use of
acetonitrile.
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3.5. Effect of Speed of Agitation
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Fig. 5 depicts the effect of speed of agitation on conversion from 700 rpm to 1100 rpm at 75 °C
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at the catalyst loading of 0.012 g/cm (Fig. 5).
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Time, mins
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Fig. 5. Effect of speed of agitation
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Reaction conditions: 1-Phenylethanol-0.01 mol, TBHP-0.03 mol, Catalyst loading - 0.012 g/cm ,
Temperature -75 °C, solvent-Acetonitrile. ( 700rpm, 900rpm, 1100rpm)
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In the range of 900 to 1100 rpm, the conversion was practically the same. Thus, the external
resistance to mass transfer was absent beyond 900 rpm. However, to avoid catalyst abrasion and
to ensure complete absence of mass transfer resistance, 900 rpm was used as minimum speed in
further runs.
3.6. Effect of Catalyst loading
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Time,mins
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Fig. 6. Effect of catalyst loading
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Reaction conditions: 1-Phenylethanol-0.01 mol, TBHP-0.03 mol, Speed of agitation-900 rpm,
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Temperature -75 °C, solvent-Acetonitrile. ( 0.006g/ cm , 0.008g/ cm , 0.012g/ cm ,
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0.015g/ cm )
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a mole ratio of 1-phenylethanol to TBHP of 1:3 (Fig. 6). Both conversion and rate of reaction
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increased up to 0.012 g/cm with increase in catalyst loading due to the corresponding increase in
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active sites. The conversion and rate of reaction were nearly identical at 0.012 g/cm and
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0.015g/cm . It would suggest that the number of catalyst sites at catalyst loading of 0.015
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g/cm was greater than that required by the reacting species. Theoretical calculations using
Wiesz-Prater criterion were also done to show absence of intra-particle resistance [41].
3.7. Effect of mole ratio
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The mole ratio of 1-phenylethanol to TBHP was changed from 1:1 to 1:3 with a catalyst loading
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of 0.012 g/cm at 75 °C (Fig. 7). The initial rate of the reaction increased with increase in mole
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Fig. 7. Effect of mole ratio
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Reaction conditions: 1-Phenylethanol: TBHP, Catalyst loading-0.012 g/cm , Speed of agitation-
900 rpm, Temperature -75 °C, solvent-Acetonitrile. ( 1:01, 1:02, 1:03)
ratio. It can be concluded that there was not much difference in the conversions between mole
ratios of 1:2 to 1:3. Therefore next set of reactions were conducted at a mole ratio of 1:3 of 1-
phenylethanol to TBHP.
3.8. Effect of Temperature
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The temperature effect on conversion and rate was studied from 65 °C to 80 °C (Fig. 8). With an
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Fig. 8. Effect of temperature
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Reaction conditions: 1-Phenylethanol-0.01 mol, TBHP-0.03 mol, Catalyst loading 0.012 g/cm ,
Speed of agitation-900 rpm, solvent-Acetonitrile. ( 65°C, 70°C, 75°C, 80°C)
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increase in temperature the rate of reaction and conversion increased significantly, which
indicated that reaction was intrinsically kinetically controlled. This would be discussed later.
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3.9. Substrate study
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To explore the scope and generality of the developed protocol for the oxidation of secondary
alcohols using nano-fibrous 15% w/w Ag-OMS-2, oxidation of various alcohols was studied at
the same conditions (Table 1). Cyclic alcohols like cyclohexanol and cyclopentanol are
efficiently oxidized with conversions of 90 % and 85 %, respectively. Good results were
obtained for the
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Table 1. Effect of various substrates
Entry
Alcohol
Ketone
Conversion % Yield %
2
OH
CH3
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1.
O
CH3
2
2
77
78
78.9
71.5
O
OH
CH3
CH3
HO
HO
2
79
2.
3.
82
69
70
O
OH
OH
CH3
CH3
OH
OH
280
81
78
2
O
CH3
CH3
H CO
H CO
3
3
2
2
82
83
4.
5.
85
74
OH
CH3
Cl
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O
CH3
Cl
2
2
85
86
75
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OH
CH3
H C
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6.
3
O
CH3
H C
2
2
88
89
3
80
73
OH
O
2
2
90
91
7.
8.
80
67
OH
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O
2
2
93
94
90
82
OH
O
2
2
95
96
9.
89.2
80
3
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298
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Reaction Conditions: Alcohol-0.01 mol, TBHP-0.03 mol, Catalyst loading 0.012 g/cm , Speed
of agitation-900 rpm, Temperature -75 °C, solvent-Acetonitrile. All products were confirmed by
GC-MS
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oxidation of substituted 1-phenylethanol. It should be recognized that temperature plays a very
important role and higher conversions could be obtained at higher temperatures for less reacting
molecules. The purpose here was to use the same reaction conditions to understand their
reactivity. Selectivity is 100% for the oxidation of secondary alcohols because even though
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conversion is low, no other product except ketone was observed. Other groups present in the
moiety such as phenolic –OH (entry 2 and 4), methyl (entry 6) and methylene (entry 8 and 9) are
unaffected under the mild set of conditions used here.
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3.10. Development of mechanistic model and kinetics of the reaction
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The reaction of 1-phenylethanol with TBHP in presence of 15% Ag-OMS-2 gives acetophenone
at 75 °C. It is assumed that reaction follows Langmuir-Hinshelwood-Hougen-Watson (LHHW)
type mechanism with participation of two sites. Both reacting molecules are adsorbed on active
sites and undergo surface reaction to produce acetophenone, tert-butanol and water. The
concentration-time profiles of reactants and products confirmed that reactant and products are
weakly adsorbed on the surface and get desorbed very fast. Thus, surface reaction of adsorbed
species could control the overall rate of reaction.
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18
Adsorption of 1-phenylethanol (A) on a vacant site S is given by
K
A
'
3
A+ S ←⎯ ⎯→ AS
(1)
K
A
3
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Adsorption of TBHP (B) on vacant site S
K
B
'
3
B + S ←⎯ ⎯→ BS
(2)
K
B
3
21
22
Surface reaction between AS and BS, in the vicinity of the active site, leading to formation of
product “acetophenone (C), tert-Butanol (D), and water (W)” as follows
3
k
2
3
23
24
AS + BS + S ⎯⎯→CS + DS +WS
(3)
3
Desorption of products from the surface of catalyst:
2
0
Page 20 of 30

1
/
k
C
3
25
26
CS ←⎯ ⎯→ C + S
(4)
(5)
1
k
D
DS ←⎯ ⎯→ D + S
3
1
k
W
3
3
3
27
28
29
WS ←⎯ ⎯→ W +S
(6)
The total concentration of sites, C
t
given by
C = C +C +C +C +C +C
(7)
(8)
t
S
AS
BS
CS
DS
WS
3
30
31
C = C + K C C + K C C + K C C + K C C + K C C
t
S
A
A
S
B
B
S
C
C
S
D
D
S
W
W
S
3
Therefore concentration of vacant site is given by
Ct
332
C =
(9)
S
(
1 + K C + K C + K C + K C + K C )
A
A
B
B
C
C
D
D
W
W
3
33
34
If equation (3) controls the rate of reaction, then the rate of reaction of A is given by
dCA
3
rA = −
rA = −
= k C C C
(10)
(11)
2
AS BS
S
dt
dCA
3
S
3
35
36
= k K K C C C
2
A
B
A
B
dt
3
After substituting the value of C
S
from equation (9) we get
3
t
dCA
k K K C C C
2
A
B
A
B
−
=
3
37
38
(12)
3
dt (1+K C +K C +K C +K C +K C )
A
A
B
B
C
C
D
D
W
W
3
When the reaction is far away from the equilibrium
2
1
Page 21 of 30

3
t
dCA k K K C C C
2
A
B
A
B
3
39
−
−
=
(13)
(14)
3
dt
(1+∑
K C )
i i
k wC C
B
dCA
dt
R
A
2
3
40
41
=
3
(1+∑
K C )
i i
3
t
3
Where k w = k K K C and w is catalyst loading.
R
2
A
B
2
3
42
43
If adsorption and desorption of the species are very weak and values of equilibrium constants are
very small then above equation can be given as
3
dCA
3
3
3
44
45
46
= k wC C
(15)
R
A
B
2
dt
LetC C = M , the molar ratio of 1-phenylethanol at t=0. Then the above equation
B
A
o
o
dXA
dt
= k wC
(
1− XA )(M − XA
)
(16)
(17)
R
Ao
2
dXA
dt
3
47
48
= k C
( )
1− XA )(M − XB
1
Ao
3
Integrating above equation
⎧
⎛
⎞⎫
⎪
⎪
M − XA
349
ln
= k C
(
M −1
)
t
(18)
⎨
⎜
⎟⎬
⎟
1
Ao
⎜
M
(
1− XA
)
⎪
⎩
⎝
⎠⎪
⎭
⎧
⎪
M
− X A
⎫
⎪
(
)
)
3
50
51
The plot of ln
against t was made at different temperature to get an excellent fit,
⎨
⎬
M
(
1− X A
⎪
⎩
⎪
⎭
3
thereby supporting the model (Fig. 9).
2
2
Page 22 of 30

0
.4
y = 0.00040x
R² = 0.99635
0
0
0
0
.35
0
.3
y = 0.00034x
R² = 0.98783
.25
y = 0.00026x
R² = 0.98791
0
.2
.15
y = 0.00018x
R² = 0.98574
0
.1
.05
0
0
200
400
Time,sec
600
800
1000
3
52
53
3
a a
Fig. 9. Kinetic plot of ln{(3-X )/3(1-X )} Vs time
3
3
54
55
Reaction conditions: 1-Phenylethanol-0.01 mol, TBHP-0.03 mol, Catalyst loading 0.012 g/cm ,
Speed of agitation-900 rpm, solvent-Acetonitrile. ( 65 °C, 70 °C, 75 °C, 80 °C)
3
8
8
8
8
7
7
.7
.5
.3
.1
.9
.7
y = 6369.x - 10.27
R² = 0.975
0
.00282
0.00285
0.00288
0.00291
/T
0.00294
0.00297
1
3
56
57
3
Fig. 10. Arrhenius plot (–lnk Vs. 1/T)
358
2
3
Page 23 of 30

3
59
60
This is an overall second order reaction. Energy of activation was calculated by plotting
Arrhenius plot as 12.65 kcal/mol for oxidation of 1-phenylethanol (Fig. 10).
3
361
3.11. Reusability of Catalyst
362
363
364
365
366
367
368
369
370
The reusability of 15% w/w Ag-OMS-2 was tested by conducting 6 runs. After each run the
3
catalyst was filtered and refluxed with 50 cm of acetonitrile in order to remove any adsorbed
material from the catalyst surface, then it was dried in an oven at 120 ºC for 2 h. In a typical
batch reaction, there was an inevitable loss of particles during filtration due to attrition. The
catalyst was reused without any make up quantity and the experiments were done under
otherwise similar conditions. The volume of reaction mixture was adjusted to make the catalyst
3
loading of 0.012 g/cm . It was observed that there is only no decrease in the conversion (Fig. 11).
Thus, the catalyst was active and reusable even after six runs for the liquid phase oxidation of
secondary alcohols.
90
80
70
60
50
40
30
20
10
0
Fresh
1st reuse
2nd reuse
3rd reuse
4th reuse
Reuse number
3
71
72
3
Fig. 11. Reusability of Catalyst
2
4
Page 24 of 30

3
373
374
375
Reaction conditions: 1-Phenylethanol-0.01 mol, TBHP-0.03 mol, Catalyst loading 0.012 g/cm ,
Speed of agitation-900 rpm, Temperature -75 °C, solvent-Acetonitrile, Internal standard-n-
Decane-200 µL.
376
4. Conclusion
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
The liquid phase oxidation of various secondary alcohols was carried out using Ag-OMS-2 at 75
3
°C with catalyst loading of 0.012 g/cm . TBHP was the most effective oxidising agent. Addition
of silver ion from 5 to 15wt% in the pores of K-OMS significantly improves the redox property
of catalyst and 15% w/w Ag-OMS-2 was the most active and selective catalyst. The synergistic
effect among Ag, Mn and K ions was responsible for the enhancement in the activity of catalyst.
Various parameters affecting the rate of reaction and conversion were discussed in detail. It was
found that a mole ratio of 1:3 of alcohol to TBHP, speed of agitation 900 rpm, catalyst loading of
3
0.012 g/cm , and temperature of 75 °C in acetonitrile were the best conditions to get good
activity of catalyst. Increase in temperature can be beneficial for oxidation of the least reactive
alcohol since it can provide sufficient energy for higher conversion and rate. A detailed kinetic
study was carried out, which indicates that reaction follows Langmuir-Hinshelwood-Hougen-
Watson type of model with weak adsorption of all species. The energy of activation was found to
be 12.65 kcal/mol for 1-phenylethanol. The optimized conditions were very effective for
oxidation of various alcohols. So the catalyst is tolerable to various functional groups present in
the molecule and has given well to excellent conversion for the oxidation reaction.
392
Acknowledgement
393
394
395
G.D.Y. received support from R.T. Mody Distinguished Professor Endowment and as J.C. Bose
National Fellow from Department of Science and Technology, Government of India. A.R.Y.
thanks UGC for providing JRF under its BSR in Green Technology.
2
5
Page 25 of 30

396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
Conflict of interest
The authors declare no conflict of interest.
Nomenclature
A
reactant species A, 1-phenylethanol
B
reactant species B, TBHP
acetophenone
C
D
t-butanol
AS
BS
CS
DS
WS
W
S
chemisorbed 1-phenylethanol
chemisorbed TBHP
chemisorbed acetophenone
chemisorbed t-butanol
product species D, product
product species W, water
vacant site
3
C
C
C
A
concentration of A in (mol/cm )
3
Ao
AS
initial concentration of A in bulk liquid phase, (mol/cm )
3
concentration of A at catalyst surface, (mol/cm )
2
6
Page 26 of 30

3
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
C
C
C
C
C
C
C
B
concentration of B, (mol/cm )
3
Bo
BS
D
initial concentration of B in bulk liquid phase, (mol/cm )
3
concentration of B at solid surface, (mol/cm )
3
concentration of D, (mol/cm )
3
CS
DS
WS
concentration of C at solid surface, (mol/cm )
3
concentration of D at solid surface, (mol/cm )
3
concentration of W at solid surface, (mol/cm )
3
Cs
concentration of vacant sites, (mol/cm )
3
C
T
total concentration of sites, (mol/cm )
6
-1 -1
k
R2
reaction rate constant, cm gmol s
3
K
w
X
i
adsorption equilibrium constant for species i, cm /mol
3
catalyst loading g/cm of the liquid volume
A
fractional conversion of A
-
3 -1
-r
A
rate of surface reaction, g mol cm s
k
R1
second order surface reaction constants
-
1
-1
K
K
A
, K
B
Equilibrium constant for adsorption of A and B on catalyst surface (mol min )
-1
-1
C
, K
D
, K
W
Equilibrium constant for adsorption of C, D, W on catalyst surface (mol min )
2
7
Page 27 of 30

430
431
432
433
434
S
Vacant site
X
A
Fractional conversion of A
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