Highly selective oxidation of benzyl alcohol over Pt-sulphated zirconia supported on SBA-15 catalyst by using a high-pressure fixed bed reactor

Article abstract of DOI:10.1016/j.poly.2018.08.053

An active platinum loaded sulphated zirconia supported SBA-15 catalyst (Pt/SO₄/ZrO₂-SBA-15) was synthesized and characterized using scanning electron microscope, transmission electron microscope, N₂adsorption-desorptionisotherms. The different percentage level (10, 20 and 30 wt.%) of ZrO₂ was loaded on SBA-15 by precipitation of zirconium oxychloride, calcined and sulfated with H₂SO₄. The sulphated zirconia supported SBA-15 catalyst were loaded with 0.5 wt.% of Pt and characterized by different characterization technique. The Pt-loaded catalysts were evaluated to the selective oxidation of benzyl alcohol to benzaldehyde by the continuous-flow reactor system. Also, the bulk sample of SO₄-ZrO₂ and Pt-SO₄-ZrO₂ was prepared for the comparison purposes. The supported catalysts, even at the lowest loading of 10% ZrO₂were more active than unsupported SO₄-ZrO₂. The catalyst containing 20% of ZrO₂ was most active for the selective oxidation of benzyl alcohol; the highest activity was obtained over this catalyst at a lower temperature (90 °C). The Pt/SZ-SBA-15 catalyst showed very high catalytic activity and selectivity to benzyl alcohol oxidation. Besides, the long-term stability of the Pt/SZ-SBA-15 catalyst was excellent and there is no loss in catalytic activity or selectivity occurred during the time of continuous operation.

Full text of DOI:10.1016/j.poly.2018.08.053

Accepted Manuscript
Highly selective oxidation of benzyl alcohol over Pt-sulphated zirconia suppor-
ted on SBA-15catalyst by using a high-pressure fixed bed reactor
P. Tamizhdurai, Subramanian Sakthinathan, P. Santhana Krishnan, A. Ramesh,
A. Abilarasu, V.L. Mangesh, S. Narayanan, K. Shanthi, Te-Wei Chiu
PII:
S0277-5387(18)30521-7
https://doi.org/10.1016/j.poly.2018.08.053
POLY 13376
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 May 2018
13 August 2018
18 August 2018
Please cite this article as: P. Tamizhdurai, S. Sakthinathan, P.S. Krishnan, A. Ramesh, A. Abilarasu, V.L. Mangesh,
S. Narayanan, K. Shanthi, T-W. Chiu, Highly selective oxidation of benzyl alcohol over Pt-sulphated zirconia
supported on SBA-15catalyst by using a high-pressure fixed bed reactor, Polyhedron (2018), doi: https://doi.org/
10.1016/j.poly.2018.08.053
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 before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Highly selective oxidation of benzyl alcohol over Pt-sulphated zirconia
supported on SBA-15catalyst by using a high-pressure fixed bed reactor
P. Tamizhdurai1,2, Subramanian Sakthinathan3, P. Santhana Krishnan2, A. Ramesh2, A.
Abilarasu4,V.L. Mangesh5, S.Narayanan6, K.Shanthi*2, and, Te-Wei Chiu3*
1National Centre for Catalysis Research, Indian Institute of Technology (IIT), Madras, Chennai 600 -
036, India
2Department of Chemistry, Anna University, Chennai 600 025, India
3Department of Materials and Mineral Resources Engineering, National Taipei University of
Technology, No. 1, Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan, ROC.
4Department of Marine Engineering, Coimbatore Marine College,, India.
5Department of Chemistry, School of Basic Science, Vels University, Chennai, India
6Department of Chemistry, Sriram college, Perumalpattu, Veppampattu,Inida .
Corresponding authors
K.Shanthi: kshanthiramesh@yahoo.com
Te-Wei Chiu: tewei@ntut.edu.tw
1

ABSTRACT
An active platinum loaded sulphated zirconia supported SBA-15 catalyst
(Pt/SO4/ZrO2-SBA-15) was synthesized and characterized using scanning electron
microscope, transmission electron microscope, N2adsorption-desorptionisotherms.The
different percentage level (10, 20 and 30wt %) of ZrO2 was loaded on SBA-15 by
precipitation of zirconium oxychloride, calcined and sulfated with H2SO4.The sulphated
zirconia supported SBA-15 catalyst were loaded with 0.5 wt.% of Pt and characterized by
different characterization technique. The Pt-loaded catalysts were evaluated to the selective
oxidation of benzyl alcohol to benzaldehyde by the continuous-flow reactor system. Also, the
bulk sample of SO4-ZrO2and Pt-SO4-ZrO2 was prepared for the comparison purposes. The
supported catalysts, even at the lowest loading of 10 % ZrO2were more active than
unsupported SO4-ZrO2. The catalyst containing 20% of ZrO2 was most active for the
selective oxidation of benzyl alcohol; the highest activity was obtained over this catalyst at a
lower temperature (90 C). The Pt/SZ-SBA-15 catalyst showed very high catalytic activity
and selectivity to benzyl alcohol oxidation. Besides, the long-term stability of the Pt/SZ-
SBA-15 catalyst was excellent and there is no loss in catalytic activity or selectivity occurred
during the time of continuous operation.
Keywords: Pt/SZ-SBA-15, Heterogeneous catalyst, Benzaldehyde, Selective oxidation and
Higher selectivity.
2

1. Introduction
The selective oxidation of alcohols to aldehyde is one of the important reactions in
organic synthesis because the corresponding aldehyde compound could be used in
agriculture, pharmacy, and various chemical industries. Moreover, the selective oxidation
reaction contributes to 30% of the total production of chemical products in the chemical
industry [1-5]. Hence, the many key intermediates and chemicals such as ketones, alcohols,
aldehydes, epoxides, and organic acids are produced via selective oxidation [6,7]. Nowadays,
many chemical industry processes carried out by oxidation process viz., selective oxidation of
butane to maleic anhydride, ammoxidation of propylene to acrylonitrile, selective oxidation
of the propene to acrolein, selective oxidation of methanol to formaldehyde and epoxidation
of ethylene topropylene [8-11].
Selective oxidation of benzyl alcohol has been investigated by both vapor and liquid
phase [12].The oxidations in the liquid-phase generally carried out at below 100 C, while in
vaporphase, the molecular oxygen generally required the temperatures above 200 C resulting
in the formation of CO2[13,14].Moreover, large variety of oxidants such as, dioxiranes, H2O2,
TBHP, benzoyl peroxide, peroxy acidsetc. can be utilized and make liquid phase reactions
more attractive [15].The heterogeneous and homogeneous catalysts have performed in the
liquid phase selective oxidation of benzyl alcohol [16]. Besides, the heterogeneous catalysts
have major advantages such ashigh thermal stability, multiple active sites, an ease of
recovery (solid), and reusability than the homogeneous catalysts. The heterogeneous catalysts
also alternatives to the conventional stoichiometric inorganic oxidants, which are generating
large amounts of hazardous waste and expensive [17–22].Tert-Butyl hydroperoxide (TBHP)
used in the synthesis of peroxide derivatives, another catalytic oxidation reaction, epoxidation
reactions, and also polymerization reactions in the free radical initiator. Moreover, the active
3

oxygen in TBHP is a good oxygen supplier, safe to handle and reasonably thermally stable
under reaction conditions [23, 24].
In recent times, SBA-15mesoporous silicahas been recognized as a potential support
for noble metals due to their ordered structure with pore diameters(in the range from 5 to 30
nm), higher surface area (more than 1000 m2/g), high thermal stability, improved dispersion
of metal particles, and metal-support interactions [25-27]. It is known that sulfated zirconia
having both Lewis and Brønstedacid sites and are responsible for the high catalytic activity
[28]. In many reactions, sulfated zirconia supported on SBA-15 showed high activity such as
glycerol esterification with palmitic acid [29], cumene cracking [30], cellobiose hydrolysis
[31], oxybromination [32], etherification of 5-hydroxymethyl-2-furfural (HMF) with ethanol
[33].
The selective oxidation of aldehyde and alcohols are the important components of
chemical industry fractions have been extensively investigated over zirconium sulphate SO4–
ZrO2 and other catalysts [34]. Many reports available for oxidation of the benzaldehyde
reaction over ZrO2 supported on MCM-41 and ZSM-5. On the other hand, CeO2 (Ce/Si =
0.38-2.32) loading MCM-41 exhibiting an excellent activity in the selective oxidation of
benzyl alcohol [35-37].As per the literature studies, the Pt/SO4/ZrO2and Pt/SO4/ZrO2-SBA-
15 supported catalyst has not been reported for the selective oxidation of benzyl alcohol in
high-pressure fixed bed stainless steel reactor with TBHP. Hence this work presents the urea-
assisted synthesis of SO4/ZrO2-SBA-15 and Pt/SO4/ZrO2-SBA-15 catalyst have been reported
for the selective oxidation of benzyl alcohol. The preparation of the catalyst and the
evaluation utilized with TBHP as the oxidant in the selective oxidation of benzyl alcohol.
Moreover, the effects of temperature, pressure, and weight hourly space velocity (WHSV)
have been investigated in detailed.
4

2. Experimental details
2.1. Preparation of catalysts
SBA-15 was synthesized in a Teflon-lined autoclave under autogenous pressure in an
acidic medium (2 M HCl) following previously published article using Pluronic (P123)
triblock copolymer (Mol. Wt. 5800) as the template and TEOS as the silica source [38]. The
synthesized SBA-15 was dried at 373 K and calcined at 823 K after that, ZrO2 (10-30
wt.%)was deposited over calcined SBA-15 by a urea hydrolysis method. In a typical
synthesis (for 10 wt.% ZrO2), 4.0 g of calcined SBA-15 was immersed in 120 mL of distilled
water containing1.1622 g of Zirconium Oxychloride (ZrOCl.8H2O, Aldrich) and1.083 g of
urea. The mixture was heated with stirring at 363 K for 5–6h, and the resultant mixture was
filtered and washed repeatedly with distilled water to remove chloride ions. Besides, the
filtered ZrO2-SBA-15 was dried in air at 383 K for 24h followed by calcination in air at 823
K for 6h.Pure ZrO2 was prepared by adding a solution of the zirconium oxychloride salt drop
wise to well-stirred 2 M ammonium hydroxide solution at room temperature. The pH of the
mixture was adjusted to 9-10 and refluxed at 100 Cfor 4h. The precipitate was filtered and
washed with distilled water several times until the pH was close to neutral (pH 7). The
obtained product was calcined at 550oC for 5h and stored in desiccators.
Sulfation of ZrO2(SO4/ZrO2)and ZrO2-SBA samples was done by adding 4g of the
sample to60mL of 2M H2SO4 solution at room temperature and stirred for 1h. The sulphated
sample was filtered, dried at 120oC and calcined in the static at 700oC for 3h.The S-content of
the samples were similarly being 0.77 0.05 wt.%. The unsupported and supported SO4-
ZrO2 samples code-name were SZ and SZ(x)/SBA-15respectively, the x within brackets
referring to the ZrO2 content in wt.%. All the samples were then impregnated with
chloroplatinic acid by incipient wetness method. The amount and concentration of Pt-solution
were adjusted to obtain 0.5wt.% of Pt in the final catalyst. The resulting mixture was dried in
5

an air oven at 100oC for 12h, and calcined at 400oC for 4 h in static air. To obtain the reduced
form of Pt catalysts were treated in a hydrogen flow at 200°C for 1 h. The reduction was done
in situ in the reactor prior to the start of the reaction.
2.2. Characterization of support and catalysts
The specific surface area was measured by BET specific surface area N2 adsorption-
desorption isotherms method (Micromeritics ASAP 2020). The samples were degassed at
350 C for 3h prior to adsorption of N2. Further, the pore volumes and average pore size of
the prepared sample were calculated by the BJH method. The crystalline structures of the
calcined materials were identified by X-ray diffraction (XRD) patterns recorded using Cu K
radiation (RigakuMiniflex II). FT-IR spectra of the samples were recorded at room
temperature by the KBr disc method (Perkin-Elmer, Spectrum One) and TEM studies of the
samples were obtained using a JEOL (JEM 2010) instrument. Moreover, the product
compositions were monitored and analyzed witha gas chromatograph (Mayura, India) with a
FID detector and 60m capillary column. Besides, an octane number of the feed (LN) and
products were calculated from GC composition and blending octane numbers for the
individual compounds. At the experimental condition, the cracked products were not detected
and the products were entirely in the gaseous state in the pure compounds. Some condensed
liquid was also obtained when light naphtha was the feed in some runs. In these cases, both
the liquid and gaseous products were analyzed separately and integrated.
2.3 Data treatment
The conversion and selectivity of benzyl alcohol were calculated from theinitial and
final amounts of benzyl alcohol obtained from GC results after every hour of reaction
Conversion % = Xin−Xout X 100 (1)
( )
푋푖푛
6

Product
( )
Selectivity % = Consumed reactant X 100 (2)
The specific reaction rate (r, mol g−1 s−1) was calculated using theequation
푟 = F0 A(3)
푤
Where, F0 = molar flow rate of n-C5 & n-C6 (mol s−1) and w = catalyst weight (g). Turnover
frequency was calculated employing the following equation
I specific reaction rate [ r,mol−1 g s−1]
푇푂퐹 (푠 − 1) =
(4)
Quantity of sites [ mol/g]
The quantity of sites (μmol/g) was derived from the amount of Zr present (ICP) and their
actual sites exposed to reaction (dispersion %).
2.4 Catalytic studies
The reactions were carried out in a high-pressure fixed bed stainless steel reactor (i.d
= 8 mm) operated in the down-flow mode. The catalyst (1–2 mm in size) was loaded and
dried in situat 250 C in CO2free air for 6 h. The reactor was then cooled to reduce in CO2 free
air at atmospheric pressure in the temperature range of 60–110 C for 1 h. The CO2 free
airflow, pressure and temperature were then adjusted to the desired values and the feed
injected. The general conditions of the reactions were: pressure: 10 bar, catalyst loading: 3.2
g, WHSV (h−1: 1, and temperature: 60-100 C. The CO2 free air/feed (mole ratio) was 2 inthe
caseof benzyl alcohol (20 mmolbenzyl alcohol (BzOH), 25 mmol aqueous tertbutyl hydro
peroxide (TBHP) as the oxidant and 10 ml of acetonitrile as the solvent). The products were
analyzed in a gas chromatograph with a flame ionization detector, using a SGE BPX70
capillary column (70% Cyanopropyl Polysilphenylene-siloxane, 30 m × 0.53 mm × 0.50 ml)
and N2 as the carrier gas.
3. Results and discussion
3.1. Physicochemical and spectroscopic characterization
3.1.1 X-Ray diffraction studies
7

The low angle XRD patterns of SBA-15 and different ratio of the Pt-SZ/SBA-15
samples are presented in Fig. 1 A. The SBA-15 sample exhibits the typical patterns expected
for the sample, the intensity peaks are continuous decrease after loading of each of the
catalyst components, viz. ZrO2, SO4, and Pt. This suggests that continuous loss in the
orderliness of the mesoporous structure due to the sequential impregnation and calcination. A
slight shift in the position of the lines towards larger angles is also noticed in Fig 1. Earlier
workers have suggested that the deposition of oxides inside the pores of SBA-15 could cause
such a shift [39]. The shift in the peaks is noticed even on loading small amounts of SO4 and
Pt4+ (Fig. 1A), it is likely that at least a part of the shift in our case is due to changes in the
structure of the pores. The high angle XRD patterns of Pt-SZ and Pt-SZ/SBA-15 catalysts are
presented in Fig. 2. The pattern for Pt-SZ reveals a highly crystalline ZrO2with both
monoclinic and tetrahedral structures, with a predominance of the monoclinic form [40].The
supported catalysts do not exhibit any pattern through a broad peak at about 2ϴ=23° for the
amorphous silica structures is noticed. The absence of lines due to ZrO2 in Pt-SZ(30)/SBA-15
reveals that the Zr is well dispersed even at the high loading of 30 %.
3.1.2 N2 adsorption/desorption isotherms (BET)
The N2-adsorption desorption isotherms of SBA-15 and the catalysts are presented in
Fig. 3. The adsorption-desorption isotherm is typical of that expected for a material with
uniform pores, though some distortion in the hysteresis loop is noticed after loading of ZrO2
and the other components. This is probably due to differences in the thickness of the
deposited ZrO2 inside the pores. The BET surface area and pore volumes of the samples are
presented in Table 1. The surface area (SA) of the SZ catalyst is 166 m2/g,and that of SBA-15
is 672 m2/g. Similarly, the pore volume (PV) of SBA-15 is larger than that of SZ, being
0.90cm3/g for SBA-15 and 0.151 cm3/g for SZ. Deposition of the components decreases both
the SA and PV of SBA-15, the decrease being substantial even at 10 wt.% ZrO2 loading. The
8

decrease in SA and PV is due to deposition of the oxide inside the pores and blocking of
some of the pores at high loadings. The average pore diameter calculated from the SA and
PV data reveals a substantial narrowing of the pores at high loadings of ZrO2.
3.1.3 FT-IR Spectroscopy
The FTIR (Fourier Transform infra-red) spectra of SZ and the supported catalysts in
the framework region of 4,000-450 cm−1 are presented in Fig. 4. The SZ exhibits multiple
peaks between 900-1200 cm-1 attributed by earlier workers to (ZrO)3S=O species and at least
two absorption peaks between 1375-1450 due to S=O bending mode besides a strong
absorption at about 1620 cm-1 attributed to OH associated with sulfate groups [41]. In the
case of SBA-15, broad and strong absorptions are noticed due to external and internal SiO2-
tetrahedral vibrations along with a lower intensity peak at about 1625 cm-1 attributable to –
OH groups. The different characteristic absorptions observed at around 1625 cm-1 is present
in the supported catalysts. This absorption is probably mainly from the support and to a
smaller extent from SZ. The absence of absorption bands in the 1375–1450 range in the
supported catalysts could suggest structural dissimilarities between bulk and supported SZ.
The bending, symmetric stretching and asymmetric stretching of Si-O-Si vibration
bands which are usually present in SBA-15observed in all samples at 470, 795 and 1,080
cm−1 respectively. This indicates that the support maintained the framework of silica, even
after the sulfated zirconia loading of 30%. In addition, a shoulder at about 1240 cm−1 for the
band at 1,080 cm−1 becomes broad after the zirconia addition. It indicates that the existences
of sulfur ions coordinated to zirconia cation are responsible for changes in the intensities of
the band. An intense and broad band which is seen in all samples at 3,450 cm−1, possibly, be
assigned to the stretching vibrations of OH and Si-OH bonds. The intensity of the IR band at
960 cm−1decreases after the introduction of zirconia, which could probably be because of the
stretching mode of[SiO4] unit bonded to heteroatoms [42-47].
9

3.1.4 Transmission electron microscopy(HR-TEM) studies
The transmission electron microscope (TEM) pictures of (a) SBA-15, (b) SZ
(20)/SBA-15, (c) Pt-SZ (20)/SBA-15 (reduced) and (d) Pt-SZ (reduced) samples are
presented in Fig.5.The structure of SBA-15 is found to possess a very ordered arrangement of
mesopores (Fig. 5a). When 20% of ZrO2 is deposited, the orderliness of the pores is
decreased and deposited ZrO2 are seen (Fig. 5 b). The picture of a reduced sample of Pt-
SZ(20)/SBA-15 exhibit the dispersed Pt particles of size less than 10 nm, revealing a
reasonably good dispersion of the metal in the catalyst (Fig. 5c). Fig 5d is the micrograph of
reduced Pt-SZ, as seen from the figure the SZ particles are found to be small (about 10 -15
nm) comparable with the size of Pt particles.
3.1.5 Temperature programmed desorption (NH3TPD)
The acidity of the Pt/SZ and Pt/SO4/ZrO2-SBA-15(Zr: Molar ratio= 10, 20, and 30%)
catalysts was investigated using the NH3 temperature programmed desorption (NH3TPD).
Table 1shows the acidity levels of the catalysts measured by the temperature programmed
desorption method. The high amounts of acid sites were measured on thePt/SO4/ZrO2(20)-
SBA-15 and Pt/SO4/ZrO2(10)-SBA-15 catalysts, respectively, whereas SZ had only 1.61
(mmol/g) of catalyst; these results indicate that the synthesized catalysts generally had much
higher densities of acid sites. The NH3 TPD profiles of Pt/SZ and Pt/SO4/ZrO2-SBA-15(Zr:
Molar ratio= 10,20, and 30%) are shown in Figure 6. The prepared catalysts except SZ
showed broad distributions of acid strengths. Whereas the SZ catalyst displayed a single peak
at 420 C, and the supported catalysts (Pt/SO4/ZrO2-SBA-15(Zr: Molar ratio= 10, 20 and
30%) displayed two peaks 420 C and 530 C. The additional NH3TPD peak at higher
temperature suggests that the Pt/SO4/ZrO2(20%)-SBA-15 catalysts have higher acid strength
10

than the other catalyst. Therefore, the higher acidity of Pt/SO4/ZrO2(20%)-SBA-15 catalysts
is due to the dispersion of active sites on the support and the interaction between the
sulphated zirconia and the SBA-15 support.
3.2 Selective oxidation activity of the catalysts
The selective oxidation of benzyl alcohol (BzOH) was carried out over the bulk
Pt/SO4/ZrO2 and different Pt/SZ-SBA-15 (Zrmolar ratio = 10, 20, and 30 %) samples with
constant reaction conditions. The optimization of the process parameters for maximizing
BzOH conversion and benzaldehyde (BzH) selectivity was done by investigating the
influence of the variation in reaction parameters, such as reaction temperature (60–100 C),
reaction pressure. Besides, the WHSV was studying using the most active sample of
Pt/SZ(20%)-SBA-15 and the sample was also investigated for reusability.
3.2.1 Influence of the reaction temperature
The effect of temperature of benzyl alcohol conversion of (a) Pt-SZ, (b) Pt-SZ (10)/SBA-15,
(c) Pt-SZ(20)/SBA-15 and (d) Pt-SZ(30)/SBA-15 is mentioned in Figure. 7A &B.The vapor
phase aerobic oxidation of benzyl alcohol was carried out over SZ supported on SBA-15
catalysts (Zr = 10, 20, and 30) in the temperature range of 60-100 C. The benzyl alcohol
oxidation oxygen flow rate was maintained at 0.1 mol h−1and weight hourly space velocity
(WHSV) was mentioned at 1.0 h−1. In benzyl alcohol oxidation, benzaldehyde was the major
product and the selectivity was increased for increasing the temperature. The selective
oxidation of benzyl alcohol conversions over the different catalysts at the temperatures
between 60–100 C are presented in Figure 7A.The SZ is found to be the least active among
the others catalysts. However, 20 % of SZ supported catalysts are the most selective
oxidation and selectivity of benzyl alcohol than that of the other catalysts at the temperature
between 60–100 Cis presented in Figure 7B.Moreover, at the lower temperature the
11

selectivity of the catalyst is high and the higher temperature the selectivity is decreasing in
conversions of benzyl alcohol reaction. It is clear that the catalytic activity of Pt-SZ
(20)/SBA-15is comparatively higher than unsupported and other catalysts. The higher (%)
loading of the ZrO2 content can lead to accumulation whereas low loading of ZrO2 content is
not sufficient for the adsorption of reactant molecule on the ZrO2 surface. Moreover, the
optimum (%) loading of ZrO2 which result in enhanced surface acidity (2.48 mmol/g) and
ordered porosity with well dispersed Pt particles on the ZrO2/SBA-15 surface (Figure 5 (b &
c). Thus, optimum (%) loading of ZrO2 (20 %) tunes the pore size and pore volume
effectively which can control the diffusion limitation of the reactant molecule on the surface
of the catalyst compared to unsupported SZ and ZrO2 loaded catalysts (10 and 30 %).
Therefore, appears that 90 C is the optimum reaction temperature for the maximum yield of
oxidation of benzyl alcohol conversion.
3.2.2 Specific reaction rate (SRR) and turnover frequency (TOF)
The calculated specific reaction rate (mole g-1s-1) and turnover frequency (TOF)of
selective oxidation of benzyl alcohol reaction is given in Table 2. Among the bulk Pt/SZ and
different Pt/SZ-SBA-15 (Zr- 10, 20 and 30) catalyst was tested for selective oxidation of
benzyl alcohol were observed higher catalytic activity for Pt/SZ(20%)-SBA-15 catalysts
which corresponds to higher specific reaction rate (SRR) and turnover frequency (TOF) of
benzyl alcohol are 8.40× 10−4 (mol g−1 s−1) & 6.80× 10−4 (molg−1 s−1) and 3.69 & 3.01 s-
1respectively, as compared with others Si/Al ratio catalyst. Its reasonable for which may be
the reason for the high activity of the catalyst and highest conversion. Finally, Pt/SZ catalysts
were found to be very low activity of the SRR value and TOF value are 7.29 & 6.09× 10−4
(mol g−1 s−1) and 3.23 & 2.7s−1this might be due to the unavailability of activity sites over the
catalyst. A direct trend in the catalytic activity of Pt/SZ(20%)-SBA-15 catalysts was obtained
12

with maximum conversion compared to the other catalysts. The order of as catalytic activity
can be put asPt/SZ (20%)-SBA-15 > Pt/SZ (30%)-SBA-15> Pt/SZ (10%)-SBA-15.
Comparison of TOF results obtained from previous literature with the Pt/SZ (20%)-SBA-
15catalysts are presented in Table S1
3.2.3 Influence of the reaction pressure
The selective oxidation conversions of benzyl alcohol over the different catalysts at a
pressure between 0–20 bar is presented in Figure 8A. The reaction was monitored, the
constant WHSV and temperature 90 ºC as the change in the pressure was investigated in the 0
to 20 range. The SZ is found to be the least active among the other catalysts. In the case of
the supported catalysts, the 20% of SZ catalyst is the most active one. With the increase in
the pressure, the selectivity is decreased and the conversion is increasing at an optimum level.
When the H2 pressure raised from 10 bar to 20 bar, the feed conversion increased. As
expected, further increasing CO2free air pressure from 10 bar there is an appreciable
conversion observed. However, further increasing CO2free air pressure to 15 and 20 bar, only
a small change in conversion observed. The selectivity of benzyl alcohol oxidation over the
different catalysts at the temperature between 60-100 C are mentioned in Figure 8B. The
selectivity of SZ is found to be the least active among the other catalysts. In the case of the
supported catalysts, the selectivity of 20% of SZ catalyst is the most active than that of the
other ratio catalyst. Considering the conversion and selectivity of feed, 10 bar CO2free air
pressure would be enough to carry out the selective oxidation of benzyl alcohol.
3.2.4 Influence of the reaction WHSV
Figure.9Ashows the effect of WHSV was tested the conversion in the over the bulk
Pt/SO4/ZrO2 and different catalyst Pt/SZ-SBA-15 (Zrmolar ratio = 10, 20, and 30 %) for
selective oxidation of benzyl alcohol monitor the constant pressure 10 bar and temperature
13

90 C as the change in the WHSV was investigated in the 0.5 to 2.0h-1 range. With the
increase in the space velocity, the conversion is decreased at an optimum level. The SZ is
found to be the least active among the other catalysts. In the case of the supported catalysts,
the 20% SZ catalyst has the most active conversion. Figure 9B shows the selective oxidation
of benzyl alcohol was carried out over the different catalysts at WHSV between 0.5 to 2,0h-
1range. With the increase in the space velocity, the selectivity is increasing at an optimum
level. The WHSV can be strongly influenced by the contact area of feed and catalyst affect
the conversion and selectivity. In order to evaluate the effect of WHSV, the catalyst loading
amount was kept constant (~3.2 g) and by varying the feed flow rate. It can be seen that the
conversion of benzyl alcohol feed decreased gradually with an increase of WHSV. The
benzyl alcohol showed higher conversion compared to the other two at WHSV at 0.5h-1.Only
a small difference in conversion is observed between WHSV at 0.5 h-1and 2.0 h-1. Hence, the
WHSV=1.0 h-1 is advisable for effective for benzyl alcohol conversion reaction.
3.2.5 Effect of time on stream
The effect of time on stream on benzyl alcohol conversion and product selectivity of
benzaldehyde is studied over the bulk Pt/SO4/ZrO2 and different catalyst Pt/SZ-SBA-15
(Zrmolar ratio = 10, 20, and 30 %) catalyst at 90 C with O2flow rate of 1.0 mol h−1(Fig. 7D).
The percentage of conversion and selectivity of the product was considerably slowly change
throughout the reaction for 10 h, which shows that the catalyst was not get deactivate by coke
formation till that reaction period. Further, increasing the stability of the catalyst may be the
formation of carbon during reaction, which may give structural strength to prevent the
sintering nature of catalyst. The stability of the catalyst was repeated and tested by using are
generated spent catalyst. The spent catalyst was regenerated before each cycle by activation
at 100 C after washing with ether. The activity and selectivity were found to remain the same.
14

The reaction is carried out for five cycles after regeneration under similar conditions and it
was found that the catalyst showed similar activity up to five cycles. Hence, the Pt/SZ (20
%)-SBA-15 catalyst has the most stability towards the selective oxidation of benzyl alcohol
to benzaldehyde in a fixed bed reactor.
4. Conclusion
The Pt-SO4-ZrO2 supported on the high surface area SBA-15 possesses a higher
catalytic activity in the of selective oxidation of benzyl alcohol to benzaldehyde than the bulk
material. This is attributed to the good dispersion of ZrO2 over the support. Even at 30%
loading, ZrO2 could not be detected by X-ray diffraction in the catalyst. Among the supported
catalysts, the 20% catalyst is more active in the selective oxidation of benzyl alcohol to
benzaldehyde, the maximum conversion and selectivity being observed over this catalyst at
90 C and 10 Bar. We conclude that the Pt/SZ(20%)-SBA-15 catalysts were long-term
stability, excellent selectivity and higher conversion towards the benzyl alcohol conversion.
Acknowledgments
The authors are thankful to Prof. S.Sivasanker for his guidelines and constant support
for carrying out the reaction and thanking Prof. B. Viswanathan NCCR, IIT-Madras for
providing laboratory and characterization facilities. The authors are also thankful to DRDO,
UGC-DRS, and DST-FIST for providing an instrumentation facility in the Department of
Chemistry, Anna University, Chennai.
References
[1] M.G. Clerici, O.A. Kholdeeva, Liquid Phase Oxidation via Heterogeneous Catalysis:
Organic Synthesis and Industrial Applications, John Wiley and Sons, 2013.
[2] R.V. Sharma, K.K. Soni, A.K. Dalai, Catal. Commun. 29 (2012) 87.
15

[3] Y. Pérez, R. Ballesteros, M. Fajardo, I. Sierra, I. del Hierro, J. Mol. Catal. A: Chem.352
(2012) 45.
[4] S.Ajaikumar, A. Pandurangan, J. Mol. Catal. A: Chem. 290 (2008) 35.
[5] Y. Yu, B. Lu, X. Wang, J. Zhao, X. Wang, Q. Cai, Chem. Eng. J. 162 (2010) 738.
[6] D. Han, T. Xu, J. Su, X. Xu, Y. Ding, ChemCatChem 2 (2010) 383.
[7] J. Fan, Y. Dai, Y. Li, N. Zheng, J. Guo, X. Yan, G.D. Stucky, J. Am. Chem. Soc. 131
(2009) 15568.
[8] P.A. Jacobs, E.M. Flanigen, J.C. Jansen, H. V. Bekkum, Introduction to ZeoliteScience
and Practice, Elsevier Science, 2001.
[9] M.D. González, Y. Cesteros, P. Salagre, Microporous Mesoporous Mater. 144 (2011)162.
[10] N. Viswanadham, M. Kumar, Microporous Mesoporous Mater. 92 (2006) 31.
[11] M. Boveri, C. M. Álvarez, M.Á. Laborde, E. Sastre, Catal. Today 114 (2006) 217.
[12] K.-H. Chung, Microporous Mesoporous Mater. 111 (2008) 544.
[13] M. Lenarda, M. D. Ros, M. Casagrande, L. Storaro, R. Ganzerla, Inorg. Chim. Acta, 349
(2003) 195.
[14] C. Hammond, S. Conrad, I. Hermans, ChemSusChem, 2012, 5, 1668–1686.
[15] R. Palkovits, C. V. Malotki, M. Baumgarten, K. Mullen, C. Baltes, M. Antonietti, P.
Kuhn, J. Weber, A. Thomas, F. Schuth, ChemSusChem, 2010, 3, 277–282.
[16] Q. Yuan, W. Deng, Q. Zhang and Y. Wang, Adv. Synth. Catal., 2007, 349, 1199 1209.
[17] A.N.C. V. laak, R.W. Gosselink, S.L. Sagala, J.D. Meeldijk, P.E. de Jongh, K.P. deJong,
Appl. Catal. A 382 (2010) 65.
[18] Y. Guo, H. Wang, Y. Guo, L. Guo, L. Chu, C. Guo, Chem. Eng. J. 166 (2011) 391.
[19] C. Ragupathi, J.J. Vijaya, L.J. Kennedy, Mater. Sci. Eng. B 184 (2014) 18.
[20] A.W. Chester, E.G. Derouane, Zeolite Characterization and Catalysis: A
Tutorial,Springer, 2009.
16

[21] J.J. Vijaya, L.J. Kennedy, G. Sekaran, K.S. Nagaraja, Mater. Res. Bull. 43 (2008) 473.
[22] S. Yang, G. Sheng, X. Tan, J. Hu, J. Du, G. Montavon, X. Wang, GeochimCosmochim.
Acta 75 (2011) 6520.
[23] Y. Ni, A. Sun, X. Wu, G. Hai, J. Hu, T. Li, G. Li, Microporous Mesoporous Mater.143
(2011) 435.
[24] S.R. Ali, V.K. Bansal, A.A. Khan, S.K. Jain, M.A. Ansari, J. Mol. Catal. A: Chem.
303(2009) 60.
[25] T.Li.Yuan, Tse C. Chen Yi K. Lan, Bo S. Chen, Jiann H. You, Chia M. Yang, Nien C.
Lai, Jia H. Wu, and Ching S. Chen., ACS Catal. 2014, 4, 3824−3836
[26] J.Zhu; T.Wang; P.Xu, X.; Xiao; Li, J. Appl. Catal., B 2013,130, 197.
[27] R. H. Acuna, R. Nava et. al. Materials 2013, 6, 4139-4167
[28] T. Geng, Q. Li, Y. Jiang and W. Wang, J. Surfactants Deterg., 14, 15(2011).
[29]M. H. M. Yusoff and A. Z. Abdullah, J. Taiwan Inst. Chem. Eng.,60, 199 (2016).
[30] S. Garg, K. Soni, G. M. Kumaran, R. Bal, K. Gora-Marek, J. K.Gupta, L. D. Sharma and
G. M. Dhar, Catal. Today, 141, 125 (2009).
[31] V. Degirmenci, D. Uner, B. Cinlar, B. Shanks, A. Yilmaz, R. Santenand E. M. Hensen,
Catal. Lett., 141, 33 (2011).
[32]A. L. Paul, B. B. Banerjee, A. Bhaumik, N. M. Ali,Journal of Solid State Chemistry 237
(2016) 105–112.
[33] M. Ilyas, M. Sadiq, Chem. Eng. Technol. (2007), 10, 1391–1397.
[34] A. Jia, L. Lou, C. Zhang, Y. Zhang, S. Liu, J. Mol. Catal. A: Chem. 306 (2009) 123.
[35] C. Ragupathi, J.J. Vijaya, S. Narayanan, L.J. Kennedy, S. Ramakrishna, Chin. J.Catal.
34 (2013) 1951.
[36] P. Paraskevopoulou, N. Psaroudakis, S. Koinis, P. Stavropoulos, K. Mertis, J. Mol.Catal.
A: Chem. 240 (2005) 27.
[37] X. Huang, X. Wang, M. Tan, X. Zou, W. Ding, X. Lu, Appl. Catal. A 467 (2013) 407.
[38] S. Endud, K.-L. Wong, Microporous Mesoporous Mater. 101 (2007) 256.
[39] J. K. Edwards and G. J. Hutchings, Angew. Chem., Int. Ed., 2008, 47, 9192–9198.
17

[40] S. Chempath and A. T. Bell, J. Catal., 2007, 247, 119–126.
[41] K. Otsuka and Y. Wang, Appl. Catal., A, 2001, 222, 145–161.
[42] K. Tabata, Y. Teng, T. Takemoto, E. Suzuki, A. A. Banares, M. A. Pena and J. L. G.
Fierro, Catal. Rev. Sci. Eng., 2002, 44,1–58.
[43] A. Arena, A. Parmaliana, Acc. Chem. Res., 2003, 36, 867–875.
[44] Y. Luo, Z. Mei, N. Liu, H. Wang, C. Han and S. He, Catal. Today,(2017),
DOI:10.1016/j.cattod.2017.05.047.
[45] K. Saravanan, B. Tyagi and H. C. Bajaj, J. Porous. Mater., 23, 937(2016).
[46] F. Azimov, I. Markova, V. Stefanova and K. Sharipov, J. Univ.Chem. Technol. Metall.,
47, 333 (2012).
[47] Y. Shao, L. Wang, J. Zhang, M. Anpo, J. Phys. Chem. B, 109,20835 (2005).
18

Figure 1
Figure. 1. Low anglepowder X-ray diffraction patters of (a) SBA-15,(b) ZrO2 (20)/SBA-15,
(c) SZ (20)/SBA-15 and (d) Pt-SZ (20)/SBA-15.
19

Figure 2
Figure. 2. High angle PowderX-ray diffraction patterns: (a) Pt-SZ, (b) Pt-SZ(10)/SBA-15, (c)
Pt-SZ(20)/SBA-15 and (d) Pt-SZ(30)SBA-15.
Figure 3
Figure 3. N2 adsorption–desorption isotherms of(a) SBA-15, (b) Pt-SZ, (c) Pt-SZ(10)/SBA-
15, (d) Pt-SZ(20)/SBA-15 and (e) Pt-SZ(30)/SBA-15.
20

Figure4
Figure. 4. FTIR spectra of samples: (a) SBA-15, (b) Pt-SZ, (c) Pt-SZ(10)/SBA-15 and (d) Pt-
SZ(20)/SBA-15, (e) Pt-SZ(30)/SBA-15.
Figure 5
21

b
a
c
d
Figure. 5. Transmission electron microscopic pictures of (a) SBA-15, (b) SZ(20)/SBA-15,
(c) Pt-SZ(20)/SBA-15 (reduced) and (d) Pt-SZ (reduced).
22

Figure 6
Figure. 6.Temperature programmed desorption of selective oxidation in various (a) Pt/SZ,
(b) SZ (20)/SBA-15, (c) Pt-SZ (20)/SBA-15 (reduced) and (d) Pt-SZ (reduced).
Table. 1. Textural properties of different bulk Pt/SZ and supported Pt/SZ-SBA-15 (Zr-
Molar ratio: 10,20, & 30).
SBET
Pore
Averag Acidity (mmol/g)2
Catalysts entry
(m2/g)
volume e pore
(cm3/g) diamete
r (nm)
Therotical Zr (%)
content (%) by ICP-
Totald *LT *HT
peak peakd
d
ZrO2 (Zr)
OES
Pt-SZ
98.7 (73.03)
72.2
166
672
339
0.151
0.950
0.484
3.5
5.7
5.4
1.61
-
1.07
-
0.54
-
SBA-15
-
Pt-SZ(10)/SBA-15
10 (7.4)
6.2
1.42
1.70
0.90
0.78
2.32
2.48
Pt-SZ(20)/SBA-15
Pt-SZ(30)-/BA-15
20 (14.8)
30 (22.2)
13.8
317
282
0.309
0.237
4.2
3.1
21.4
1.79
1.11
0.68
23

Table 2. TOF and Specific Reaction Rate for selective oxidation of benzyl alcohol over
bulk Pt/SZ and different Pt/SZ-SBA-15 (Zr- 10,20,30) Catalysts at 90 °C and 10 bar H2
pressure.
SRR (r) × 10−4
S.N
o
Catalysts
Conversion (%)a
Selectivity(%)b
(mol g−1 s−1)
TOF s-1
T(oC)
P(bar)
T(oC)
P(ba T(oC) P(bar) T(oC) P(bar)
r)
1
2
Pt/SZ
67
62.1
78.8
97
97.1
7.29
6.09
3.23
2.7
Pt/SZ(10)-
SBA-15
87.2
97.6
97.2
7.7
8.40
8.3
6.49
3.43
3.694
3.68
2.88
3
4
Pt/SZ(20)-
SBA-15
98
97.6
91.7
98
98.1
96.8
6.80
6.48
3.01
2.78
Pt/SZ(30)-
SBA-15
97.5
89.8
a&bConversion& selectivity of the different catalysts carried out at 90 C and 10 bar H2
o
pressure.
Figure 7
Figure. 7A& B. The effect of temperature conversion and selectivity of benzyl alcohol (a)
Pt-SZ, (b) Pt-SZ(10)/SBA-15, (c) Pt-SZ(20)/SBA-15, (d) Pt-SZ(30)/SBA-15.
24

Figure 8
Figure. 8A & B, The effect of pressure Conversion and Selectivity of benzyl alcohol (a) Pt-
SZ, (b) Pt-SZ(10)/SBA-15, (c) Pt-SZ(20)/SBA-15, (d) Pt-SZ(30)/SBA-15.
Figure9
Figure. 9 A, & B. The effect of WHSV Conversion and Selectivity of benzyl alcohol (a) Pt-
SZ, (b) Pt-SZ(10)/SBA-15, (c) Pt-SZ(20)/SBA-15, (d) Pt-SZ(30)/SBA-15.
25

Figure 10
Figure. 10A, &B.Effect of time on stream on catalytic activity.(a) Pt-SZ, (b) Pt-SZ
(10)/SBA-15, (c) Pt-SZ(20)/SBA-15, (d) Pt-SZ(30)/SBA-15. Reaction condition: catalyst
weight = 3.2 g; temperature = 90°C, WHSV = 1.0 h–1and O2flow rate = 1.0 mol h–1.
26

Graphical abstract
TOC Graphic, Pt/SO4/ZrO2-SBA-15 catalyst for highly selective oxidation of benzyl alcohol
to benzaldehyde.
27

Highlights of this work
1. Pt/Sulphate/Zirconium substituted mesoporous SBA-15 molecular silica with
different Si/Zr ratios of 10, 20,& 30% have been successfully synthesised by simple
hydrothermal method.
2. The presence of multiple components (
bifunctional catalytic activity
exhibited the
3. The catalytic activity of the Pt/SO4/ZrO2(20%)-SBA-15samples were using oxidation
of benzyl alcohol converted in to benzaldehyde at 90 °C with higher conversion and
selectivity.
4. The used bulk Pt/SO4/ZrO2 and Pt/Sulphate/Zirconium substituted mesoporous SBA-
15 catalyst was reused and regain several times without significant loss in activity.
28

Graphical abstract
TOC Graphic, SBA-15 supported zirconia/sulphate catalysts for highly selective oxidation
of benzyl alcohol to benzaldehyde and heavy metal ions detection.
29