A green synthesis of Pd nanoparticles supported on modified montmorillonite using aqueous: Ocimum sanctum leaf extract: A sustainable catalyst for hydrodechlorination of 4-chlorophenol

Article abstract of DOI:10.1039/c6ra22788k

A green synthesis process in water has been developed with the aid of Ocimun sanctum (tulsi) leaf extract for the production of Pd nanoparticles (NPs) supported on modified montmorillonite. The leaf extract serves as a mild, natural and non-toxic reducing agent for converting the K₂[PdCl₄] to Pd NPs. The synthesized Pd NPs were characterized by using PXRD, SEM, TEM, EDX, XPS, H₂-TPR and surface area analysis. TEM analysis reveals that particle sizes of the Pd NPs lie between a minimum of 10 nm and a maximum of 80 nm. The supported Pd NPs are used in the catalytic hydrodechlorination of toxic pollutant, 4-chlorophenol in water under base free conditions and showed conversion up to 98%. The catalyst is recoverable by filtration and could be recycled for several runs without any significant loss of catalytic efficiency.

Full text of DOI:10.1039/c6ra22788k

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A green synthesis of Pd nanoparticles supported on modified
montmorillonite using aqueous Ocimum sanctum leaf extract: A sustainable
catalyst for Hydrodechlorination of 4-Chlorophenol
Pallab Kumar Saikia1, Rakhi Paul Bhattacharjee1,2, Podma Pollov Sarmah1, Lakshi Saikia1*b
and Dipak Kumar Dutta1*a
1Materials Sciences and Technology Division, CSIRꢀNorth East Institute of Science and
Technology, Jorhat 785006, Assam, India.
2 Academy of Scientific & Innovative Research, Chennai 600113, India
*b Eꢀmail: lsaikia@rrljorhat.res.in, Fax: (+)91 376 2370011
*a Eꢀmail: dipakkrdutta@yahoo.com, dutta_dk@rrljorhat.res.in, Fax: (+)91 376 2370011
Abstract
A green synthesis process in water has been developed with the aid of Ocimun sanctum
(tulsi) leaf extract for production of the Pd nanoparticles (NPs) supported on modified
montmorillonite. The leaf extract serves as a mild, natural and nonꢀtoxic reducing agent for
converting the K2[PdCl4] to Pd NPs. The synthesized Pd NPs were characterized by using
PXRD, SEM, TEM, EDX, XPS, H2ꢀTPR and surface area analysis. TEM analysis reveals that
particles sizes of the Pd NPs lie between a minimum of 10 nm and up to a maximum of 80
nm. The supported Pd NPs are used in the catalytic hydrodechlorination of toxic pollutant, 4ꢀ
Chlorophenol in water under base free condition and showed conversion up to 98 %. The
catalyst is recoverable by filtration and could be recycled for several runs without any
significant loss of catalytic efficiency.
Key words: green synthesis, Pd NPs, 4ꢀChlorophenol, modified montmorillonite,
hydrodechlorination, environmental friendly.
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1. Introduction
The synthesis of nanoparticulate materials and their applications as heterogeneous
catalysts have received great attention because of their unique catalytic property and robust
catalyst stability.1ꢀ8 The high surface areaꢀtoꢀvolume ratio of metal nanoparticles provides
large number of available active sites for reaction per unit area which highly influence the
catalytic activity. However, agglomeration of metal nanoparticles without support is
inevitable, owing to their high surface energy, leading to lowering of catalytic activity. In
order to prevent agglomeration, considerable efforts have been made for development of
suitable stabilizers or supports9ꢀ11 which may play important role for controlling the particles
size, morphology, distribution as well as the activity of the synthesized nanomaterials.8ꢀ10
Controlled and precise growth of nanoparticles with the desired shape and size can be tuned
by altering the morphology of the support. Recently, porous substances, like montmorillonite
clay minerals, zeolites, charcoals containing nanosize channels, etc. have been used for the
stabilization of metal nanoparticles.12ꢀ18 From the prospective of advance catalyst design, the
strategy of using an active support which helps in the reaction process is particularly
attractive.14,19 Montmorillonite belonging to the smectite group of clay may be considered as
one such materials which is also environmentally benign. It possesses some unique
properties such as cation exchange capacity, intercalation, swelling etc. which allow tuning
its structural properties to be used as catalysts and catalysts supports.
In recent years, due to stringent and growing environmental regulations, the chemical
industries need the development of eco friendly and sustainable synthetic methods for the
synthesis of metal nanoparticles. The synthetic routes that use nontoxic solvents like water,
reducing agents like biological extracts and microwave assisted synthesis etc. are becoming
attractive.20–24 Biosynthesis of NPs has several advantages over chemical synthesis from its
2

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simplicity, cost effectiveness, compatibility for biomedical and pharmaceutical application
point of view.25ꢀ28
Ocimum sanctum, commonly known as Tulsi, is a plant native to the Indian
subcontinent and widespread as a cultivated plant throughout the Southeast Asian tropics.
[Fig. 1]. The leaves of this plant are rich in phenolic acids, flavonoids, propenyl phenols,
terpenoids etc.29,30 The bioꢀchemicals act as an excellent reducing agent that are easy
accessible, nontoxic, cheap and environment friendly natural source of reductant for the
synthesis of metal nanoparticles.
Chlorophenols (CPs) are present in waste water from paper, dyes, pesticides, textiles,
and petrochemicals industries.31ꢀ34 Among the CPs and other most harmful organic
contaminants, 4ꢀCP is considered as a hazardous pollutant because of its acute toxicity and
strong bioaccumulation potential.35 The presence of the stable chlorineꢀcarbon bond in CPs
made it difficult to biodegrade. Hence, to develop mild methods for dechlorination of CPs is
of great importance. Among the different dechlorination techniques, catalytic
hydrodechlorination (HDC) is considered as a suitable process for the treatment of
wastewater containing organochlorinated pollutants.36,37 Compared to other techniques, HDC
has the advantages like, mild operating condition, converts the CPs to value added products
which can be recovered and reused. In catalytic HDC, mainly supported or unsupported noble
metals are used as the active phase but nowꢀaꢀdays supported bimetallic metal NPs are also
extensively studied. Moreover, HDC is a structureꢀsensitive reaction,38ꢀ42 hence designing
catalysts with wellꢀdefined nanoparticles sizes and with uniform distribution is of great
interest. In this regard the nanoporous supports also play an important role in designing the
NPs of desired size.
The present work reports a green synthesis process of Pd NPs with particle size
ranging from 10ꢀ80 nm using aqueous Ocimum sanctum leaf extract as a reducing agent
3

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supported on modified montmorillonite. The modification of montmorillonite is done in order
to increase the surface area and also for generation of pores which can act as good support
and stabilizer in the synthesis of metal nanoparticles. The synthesized NPs are used in the
catalytic HDC of the hazardous pollutant 4ꢀCP in water under base free and mild reaction
conditions. This synthesized catalyst is of heterogeneous in nature and can be easily
recovered and reused several times without any significant loss in its catalytic efficiency.
2 Experimental
2.1 Materials and Methods
Bentonite (procured from Gujarat, India) containing quartz, iron oxide etc. as
impurities was purified by sedimentation technique to collect the < 2 µm fraction. The basal
spacing (d001) of the air dried sample was about 12.5 Å. The specific surface area determined
by N2 adsorption was 101 m2gꢀ1. The analytical oxide composition of the bentonite
determined was SiO2: 49.42%; Al2O3: 20.02%; Fe2O3: 7.49%; MgO: 2.82%; CaO: 0.69%;
loss on ignition (LOI): 17.51%; and others (Na2O, K2O and TiO2): 2.05%. The purified clay
(i.e. montmorillonite) is then treated with 4 M hydrochloric acid in order to increase the
surface area by generating pores. Potassium tetrachloropalladate and 4ꢀchlorophenol were
purchased from Alfa Aesar, U.K. and were used as supplied.
Powder XRD spectra were recorded on a Rigaku, Ultima IV Xꢀray
diffractometer of 2θ range 2ꢀ80o using CuꢀKα source (λ = 1.54 Å). Specific surface area, pore
volume, average pore diameter were measured with the AutosorbꢀiQ (Quantachrome USA).
Specific surface areas of the samples were measured by adsorption of nitrogen gas at 77 K
and applying the BranauerꢀEmmettꢀTeller (BET) calculation. Prior to adsorption, the samples
o
were degassed at 200 C for 3 h. Pore size distributions were derived from desorption
isotherms using BarrettꢀJoynerꢀHalenda (BJH) method. TPD/TPR experiments were
performed in Quantachrome “ChemBET Pulsar TPR/TPD instrument in a quartz Uꢀtube
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using a TCD detector. The presence of surface acidity of the samples was qualitatively
studied by temperature programmed desorption of ammonia (NH3ꢀTPD). Prior to ammonia
sorption, the sample was outgased in a flow of pure N2 at 200 ◦C for 2 h. Subsequently, the
sample was saturated in a flow of NH3 for about 30 min. Physically adsorbed ammonia was
removed in a flow of helium at 800 ◦C for 1 h. Finally NH3 desorption was carried out with a
linear heating rate of 20 ◦C/min, in the temperature range of 50–700 ◦C under flow of pure
helium. Temperature programmed reduction (TPR) of the sample was performed by taking
80 mg of the sample. The reducing gas was a mixture of 5 vol.% H2 in N2, at a flow rate of 80
1
o
1
o
ml min− . The temperature was increased at a rate of 20 C min− from 40 C to 750 ◦C.
Scanning electron microscopy (SEM) images were obtained using ZEISS, SIGMA
instrument. The energy dispersive Xꢀray spectroscopy (EDX) and elemental dot mapping
were obtained with OXFORD XꢀMaxN instrument. Prior to examination, the samples were
coated with gold. Transmission electron microscopy (TEM) and high resolution transmission
electron microscopy (HRTEM) images were recorded on a JEOL JEMꢀ2011 electron
microscope and the specimens were prepared by dispersing powdered samples in isopropyl
alcohol, and placing them on a carbon coated copper grid and allowing them to dry. The Pd
contents were determined by Inductively Coupled Plasma Atomic Emission Spectroscopy
(ICPꢀAES) using Perkin Elmer, OPTIMA 2000 instrument. Samples taken during the
reaction were analyzed with a Trace GC 700 series GC System (Thermo Scientific) coupled
with a FID detector and capillary column.
2.2 Preparation of support
2 % dispersion of 4 g purified powdered montmorillonite in 4 M hydrochloric acid
was made in a round bottom flask. The resulting dispersion was then refluxed for 1.5 h. After
cooling, the supernatant liquid was discarded and the activated montmorillonite was dialised
with deionised water till the conductance of the water becomes nearly equal to that of
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o
deionised water. The resulting mass was dried in an air oven at 50 ± 5 C and designated as
ATꢀmont.
2.3 Preparation of TL extract
20 g of fresh Tulsi leaves was washed with double distilled water and chopped well to
small pieces. The chopped leaves were taken in a conical flask with 100 ml of double
distilled water and heated at 60 oC for 1 h. The resulting mixture was allowed to cool to room
o
temperature and filtered. The filtrate was collected in a glass bottle and stored at 4 C. The
filtrate was designated as TLE.
2.4 Preparation of Palladium nanoparticles suppoted on AT-mont.
1.2 g powdered ATꢀmont. was taken in a 100 ml round bottom flask and 32 ml (1.2
mmol) aqueous solution of K2[PdCl4] was added slowly under vigorous stirring condition.
The stirring was continued for 6 h followed by evaporation to dryness of the whole dispersion
in a rotary evaporator. 300 mg of the dried mass was then dispersed in 5ml deionised water
and to it was added 30 ml TLE as reducing agent under continuous stirring condition. The
o
dispersion was then heated to 90 C under stirring condition for 10 h and the colour changed
from brown to black which indicates the reduction of Pd2+ to Pd0. The black solid mass was
then filtered using whatman 42 filter paper and washed repeatedly with distilled water and
finally dried in a vacuum desiccator. The material thus prepared was designated as
PdNP@ATꢀmont.
2.5 Catalytic hydrodechlorination of 4-Chlorophenol
4ꢀCP (1 mmol), H2O [3 ml = 18 mmol (approx)] and 30 mg PdNP@ATꢀmont. were
added and the reaction mixture was stirred at different temperatures for different time. In
order to check the recyclability, the used catalyst was separated from the reaction mixture by
filtration. The recovered catalyst was washed with acetone and dried in desiccator which
thereby becomes ready for the second run. The same process was applied for reuse of the
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catalyst up to 5th run. On completion of the reaction, DCM is added to the mixture where the
substrate and all the probable products are easily soluble. The water and DCM mixture is then
separated using a separating funnel and sodium sulphate. The DCM part is then taken for GC
analysis to identify and determine the conversion of reactants into products.
3. Results and discussion
3.1. Characterization of Support
The PXRD analysis of the parent montmorillonite exhibited an intense basal
reflection at 2θ value of 7.06o corresponding to a basal spacing of 12.5 Å [ESI:Fig. 1]. After
1.5 h of acid activation, the intensity of basal reflection decreases which implies that the
layered structure of the clay is disrupted. A low intense broad reflection of 2θ in the range 0–
30o confirmed the formation of amorphorous silica12. The ATꢀmont. shows microꢀ (<2 nm)
and mesopores (2–50 nm) with average pore diameters ~ 3.4 nm, a high specific surface area
up to 346 m2 gꢀ1 as compared to that of parent mont. (101 m2gꢀ1), and specific pore volume of
~ 0.3 cm3gꢀ1 [Table 1]. The N2 sorption isotherm [ESI: Fig. 2] was of typeꢀIV with a H3
hysteresis loop at P/Po ~ 0.4–0.9, indicating a mesoporous solid. The increase of surface area
as well as pore volume is due to the leaching of Al from the clay matrix during acid
activation, which also introduced permanent porosity on the clay surface. The differential
volumes versus pore diameter plot [ESI: Fig. 2 (inset)] indicated relatively narrow pore size
distributions and these nano range pores can be advantageously utilized for the in situ
synthesis of various metal nanoparticles8,19
.
The presence of the acid sites of the ATꢀmont. was qualitatively evaluated by thermal
desorption of ammonia.43 Ammonia, being a strong base, reacts even with extremely weak
acid sites, which therefore makes NH3ꢀTPD a useful technique for evaluating the presence of
acid sites on a surface. The acid strength of ATꢀmont. corresponded to a higher desorption
temperature of NH3 adsorbed on acid sites. The NH3ꢀTPD spectra of ATꢀmont. exhibits
weak, medium and strong acid sites which are included in the region at 160ꢀ300 and 330ꢀ500
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oC [Fig. 2]. The SEM image of ATꢀmont. [ESI: Fig. 3(a)] showed the presence of layered
structure and formation of pores on the clay surface. The EDX pattern of the surface [ESI:
Fig. 3(b)] revealed the presence of predominant amounts of Si compared to Al on the surface
along with other elements of clay.
3.2. Characterization of PdNP@AT-mont.
Powder XRD analysis of Pd NP@ATꢀmont. [Fig. 3] shows three peaks at 2θ values
40.1, 46.6 and 68.1 due to the (111), (200) and (220) indices of face centered cubic (fcc)
lattice of metallic Pd.44 Among the peaks observed, the intensity of (111) peak is the
strongest, indicating that this plane was predominant crystal facet in PdNP@ATꢀMont. The
incorporation of the Pd NPs into the nanopores of the ATꢀmont. has made a change in the
textural parameters of the materials. The N2ꢀsorption analysis of the ATꢀmont. before loading
and after loading [ESI: Fig. 4] of the Pd NPs, shows the same type IV isotherm with a H3
hysteresis loop at P/Po ~ 0.4ꢀ0.9. This reveals that the ordered porous structure of clay exists
even after the incorporation of Pd NPs. The BET surface area and total pore volume of ATꢀ
mont. decreased after the incorporation of Pd NPs [Table 1] which might be due to clogging
of some pores by the Pd NPs. The absence of an abrupt change in the surface area and pore
volume of the support after incorporation of Pd NPs also confirms that pores of the support
are not blocked by Pd particles larger than the pore size of the support. This suggests that the
wellꢀtuned nanopores on the support materials do not allow the agglomeration of the NPs but
instead stabilize or anchor them on the pore wall structure. In addition, the presence of Pdoꢀ
nanoparticles may cause complexities in porosity measurement with N2 sorption, because the
electrostatic forces between an adsorbate (i.e. N2) and metallic surface may affect the
measured values to some extent.
The SEM and EDX analysis also substantiated the possible formation and the
presence of Pd NPs on the wellꢀtuned surface of the ATꢀmont. along with other elements of
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clay [Fig. 4(a)]. Furthermore, the elemental mapping [Fig. 4(b)] clearly indicates the presence
and distribution of Pd along with other elements in the support. The TEM image of
PdNP@ATꢀmont. [Fig. 5(a)] indicates that most Pd NPs are well distributed on the surface of
ATꢀmont. and the particle size distribution histogram [Fig. 5(b)] reveals that there is a wide
distribution of particles sizes from 10 to 80 nm. The XPS spectra [Fig. 6(a)] of Pd gives two
peaks at 335.3 eV and 340.5 eV, which are the characteristic of Pd 3d5/2 and 3d3/2 respectively
and corresponds to fully reduced Pd(0) NPs. The satellite peaks at 337.6 eV (3d5/2) and 342.8
45
eV (3d3/2) suggest the presence of some PdO particles.44,
The H2ꢀTPR profile for
PdNP@ATꢀmont. [Fig. 6(b)] is characterized by the presence of a negative peak at 70ꢀ110
oC, which is related to the desorption of weakly adsorbed hydrogen from the Pd surface, and
decomposition of the βꢀPdHx phase formed at room temperature by diffusion of hydrogen
into the Pd crystallites.46 The reduction process observed in the temperature range 200–460
oC is attributed to the reduction of PdO particles, interacting strongly with the surface of the
support.47 This result shows that not all of the Pd(II) was reduced to Pd(0), which is probably
due to the acidic environment of the TLE.44,48 The residual palladium(II) should be easily
reduced to palladium(0) in the catalytic hydrogenation reaction under hydrogen atmosphere.
The Pd content in 100 mg of Pd NP@ATꢀmont. is found to be 8.14 mg.
3.3 Catalytic activity
The bioꢀsynthesized PdNP@ATꢀmont. was investigated for the HDC of 4ꢀCP at
different temperatures in water under hydrogen balloon pressure and good to excellent
conversions were obtained [Table 2]. The efficiency of the catalyst for HDC of 4ꢀCP with
respect to time and temperature were also studied. In all the cases, only phenol was found as
the HDC product. HDC is a size sensitive reaction in which NPs of sizes around 3.5ꢀ6 nm
were reported to show best results.39,40,49 However, in the present study with particle sizes of
catalyst greater than 10 nm also showed comparative results with extended reaction time and
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higher temperature. This is because, with increase in particle sizes, the solubility of hydrogen
increases thereby leading to forward reaction. However, at lower temperature the conversion
was slow because the reaction equilibrium reaches fast for the formation of HCl as byꢀ
product. Also the generated HCl may poisoned the Pd NPs and thereby reducing its
efficiency.49,50 With the increase of temperature, enhancement of rate was observed i.e.
shifting the reaction equilibrium occurs to forward direction. In the present study, the
reactions were performed in six different temperatures with different time period [Fig. 7(a)].
The best result was found at reaction temperature of 80 oC with 3 h reaction time and showed
a conversion up to 97 %. The rate constant for the pseudo first order rate of HDC of 4ꢀCP (80
oC) is determined by the method of linear regression [Figs. 7(b)]. The pseudo first order rate
constants was found to be 0.019 minꢀ1 calculated from the slope of the plot of ln(A0/At)
versus time, where A0 is the initial concentration and At is the concentration at time with the
r2 value 0.983 which indicates first order kinetics.
The catalyst recyclability was investigated for the HDC of 4ꢀCP at 80 oC. The catalyst
was separated from the reaction mixture after every reaction by simple filtration and then
washed with acetone, followed by drying in a desiccator and reused in fresh reaction and the
process of recycling was repeated up to fifth run. It was observed that the recycled catalyst
remained active without any significant loss in efficiency [Fig. 8].
The possible change of morphology of the recovered catalyst was further investigated
through N2ꢀsorption analysis. A decrease in the BET surface area of the recovered catalyst
was found to a certain extent from that of the fresh catalyst [Table 1]. The BJH pore size and
pore volume of the recovered catalysts after 5th run remained same [ESI Fig. 5]. The
decrease in the BET surface area after the reactions may be due to clogging of some pores.
To check the heterogeneity of the catalyst, hot filtration test was also performed for HDC of
o
4ꢀCP at 80 C, in which the reaction was allowed to run for two hour and then the catalyst
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was separated from the reaction mixture and it was allowed to run without the catalyst for
next three hours. The conversion before separation of the catalyst remained unchanged after
its removal, which indicates that no leaching of any active species of the catalyst took place.
A possible reaction pathway for the HDC of 4ꢀCP in presence of Pd NPs supported on
ATꢀmont. and molecular hydrogen is shown in scheme 1. The acid sites present in the
support may be responsible for the attachment of the Cl atom of 4ꢀCP leading to the initiation
of the reaction.42,49 A comparison of different reported catalysts for HDC with the present
catalyst is shown in Table 3. It is observed that the present catalyst is found good to better in
comparison to the other catalysts excluding the temperature factor which is almost
comparable.
4. Conclusion
PdNP@ATꢀmont. catalyst has been synthesized by a green biosynthesis process
where Pd NPs generated in-situ into the nanopores of modified montmorillonite. It was
characterized using PXRD, TEM, SEMꢀEDX, XPS, TPR and Surface Area analysis. The
catalyst showed efficient activity for hydrodechlorination of hazardous 4ꢀchloro phenol in
water under base free condition with 100 % selectivity and maximum conversion up to 98 %.
The catalyst was recovered by simple filtration and recycled for five runs without any
significant loss of efficiency. The simple green process, easy recovery and operational
simplicity with green reaction condition are the advantages of the synthesized catalyst.
Acknowledgments
The authors are grateful to Dr. D. Ramaiah, Director, CSIRꢀNorth East Institute of
Science and Technology, Jorhatꢀ785006, Assam, India for his kind permission to publish the
work. The authors thank Dr P. Sengupta, Head, Materials Sciences and Technology Division,
CSIRꢀNEIST, Jorhat, for his constant encouragement. Thanks to CSIR, New Delhi [Project
No. CSCꢀ0125, CSCꢀ0135 and BSCꢀ0112] for the financial support. The authors P. K. Saikia
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and R.P. Bhattacharjee thankful to CSIR, New Delhi for providing the fellowship under
Project No. CSCꢀ0135 and BSCꢀ0112 respectively.
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Figures:
Fig. 1: Image of Ocimum sanctum (Tulsi) plant.
10
5
0
100 200 300 400 500 600 700 800
o
Temperature ( C)
Fig. 2: NH3ꢀTPD profile of ATꢀmont. indicating the presence of different types of acid sites
on the surface.
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(111)
2000
1500
1000
500
(200)
(220)
35 40 45 50 55 60 65 70 75
2 theta (degree)
Fig. 3: PXRD spectra of PdNP@ATꢀmont. showing the different planes of Pd NPs.
(1)
(2)
Fig. 4(a): (1) SEM image and (2) EDX spectra of PdNP@ATꢀmont.
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Fig. 4(b): Elemental dot mapping of Al, Si, Mg, O, Fe and Pd on PdNP@ATꢀmont.
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60
50
40
30
20
10
0
80
27
20
40
60
67
Particle Si3z3e (nm)
10 13
17
(a)
(b)
Fig. 5: (a) TEM image and (b) particle size distribution of PdNP@ATꢀmont
750
700
650
600
550
500
100
50
0
Pd(0) 3d5/2
Pd(0) 3d3/2
PdO 3d5/2
PdO 3d3/2
-50
100 200 300 400 500 600 700
330
335
340
345
o
Binding Energy (eV)
Temperature ( C)
(a)
(b)
Fig. 6: (a) XPS spectra of PdNP@ATꢀmont. showing the presence of Pd(0) with formation of
PdO and (b) H2ꢀTPR of PdNP@ATꢀmont.
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4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
100
80
60
40
20
0
i
RT
o
40
50
60
C
C
C
o
o
o
i
70 C
o
80
C
0
20 40
80 100 120 140 160 180 200
60 time (min)
0
1
2
3
4
5
6
7
time (h)
(a)
(b)
Fig. 7: (a) Pattern of progress HDC of 4ꢀCP with time at different temperature and (b) the
dynamics of HDC of 4ꢀCP at 80 oC.
100
80
60
40
20
0
3rd
Runs
4th
1st
2nd
5th
Fig. 8: Bar diagram showing the conversion of 4ꢀCP up to 5th run of the recovered catalyst.
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HO
HO
HO
HCl
H
Cl
H
H
H
Cl
Pd
Pd
Pd
Pd
Pd
Pd
AT-mont.
acid sites on AT-mont.
Scheme 1: A possible reaction pathway for the catalytic HDC of 4ꢀCP on PdNP@ATꢀmont.
Tables :
Table 1: Surface properties of ATꢀmont. and PdNP@ATꢀmont.
Surface properties of support/catalysts
BET Surface
area (m2gꢀ1)
423
Average pore
diameter (nm)
3.81
Pore volume
(cm3gꢀ1)
0.346
Samples
ATꢀmont.
Catalyst
Fresh
After 5th run
PdNP@ATꢀmont.
284
195
3.76
3.79
0.194
0.194
Table 2: Catalytic HDC of 4ꢀCP using PdNP@ATꢀmont. in water and H2 balloon pressure at
different temperature and time.
Temperature
Conversiona
Selectivity
(%)
Sl. No
Time (h)
(oC)
(%)
50
96
86
92
98
97
1
2
3
4
5
6
Room Temp.
7
6
5
5
4
3
100
100
100
100
40
50
60
70
80
100
100
Substrates: 4ꢀCP ꢀ 0.5 mmol, H2O – 2 ml, PdNP@ATꢀmont. – 20 mg, aGC analysis
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Table 3: Comparison of the present catalyst with some of the reported catalyst for HDC of 4ꢀCP
Sl.
No.
Temperature
(oC)
Conversion/
Yield (%)
Catalyst
Solvent Base
Time (h)
AgPd4 supported on
carbon49
1
2
3
THF
NaOH
25
RT
75
4
3
99
Pd/C51
H2O HCOONa
H2O Not used
100
>95
Pd/AC with modified
active carbon support52
Not clearly
mentioned
Not Clearly
mentioned
4
5
Pd/Clay53
H2O Not used
H2O Not used
5
3
~25
97
PdNP@ATꢀmont.
(present work)
80
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Graphical Abstract
A green synthesis of Pd nanoparticles on montmorillonite clay using Ocimum sanctum leaf
extract and its application in hydrodechlorination of 4-Chlorophenol in water.