Accepted Manuscript

Title: Preparation and characterization of Pd doped ceria-ZnOnanocomposite catalyst for methyl tert-butyl ether (MTBE)photodegradation

Author: Zaki S. Seddigi Ali Bumajdad Shahid P. Ansari SalehA. Ahmed Ekram Danish Naeema H. Yarkandi ShakeelAhmed

PII: S0304-3894(13)00821-2DOI: http://dx.doi.org/doi:10.1016/j.jhazmat.2013.10.070Reference: HAZMAT 15520

To appear in: Journal of Hazardous Materials

Received date: 24-9-2013Revised date: 27-10-2013Accepted date: 29-10-2013

Please cite this article as: Z.S. Seddigi, A. Bumajdad, S.P. Ansari, S.A.Ahmed, E. Danish, N.H. Yarkandi, S. Ahmed, Preparation and characterizationof Pd doped ceria-ZnO nanocomposite catalyst for methyl tert-butylether (MTBE) photodegradation, Journal of Hazardous Materials (2013),http://dx.doi.org/10.1016/j.jhazmat.2013.10.070

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Preparation and characterization of Pd doped ceria-ZnO nanocomposite catalyst

for methyl tert-butyl ether (MTBE) photodegradation

Zaki S. Seddigi1, Ali Bumajdad2, Shahid P. Ansari1, Saleh A. Ahmed1*, Ekram Danish3

Naeema H. Yarkandi1 and Shakeel Ahmed4

1Chemistry Department, Umm Al-Qura University, Makkah, Saudi Arabia.

2Chemistry Department, Faculty of Science, Kuwait University, Kuwait3Chemistry Department, King Abdulaziz University, Jeddah, Saudi Arabia4Center for Refining & Petrochemicals, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia

*Corresponding Author’s e-mail: saleh_63@hotmail.com

Abstract

A series of binary oxide catalysts (ceria-ZnO) were prepared and doped with different

amounts of palladium in the range of 0.5% to 1.5%. The prepared catalysts were

characterized by SEM, TEM, XRD and XPS, as well as a N2 sorptiometry study. The

XPS results confirmed the structure of the Pd CeO2-x-ZnO. The photocatalytic activity of

these catalysts was evaluated for degradation of MTBE in water. These photocatalyst

efficiently degrade a 100 ppm aqueous solution of MTBE upon UV irradiation for five

hours in the presence of 100 mg of each of these photocatalysts. The removal of 99.6% of

the MTBE was achieved with the ceria-ZnO catalyst doped with 1% Pd. In addition to the

Pd loading, the N2 sorptiometry study introduced other factors that might affect the

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catalytic efficiency is the catalyst average pore sizes. The photoreaction was determined

to be a first order reaction.

Keywords: Binary oxide catalyst; Zinc Oxide; Cerium oxide; Catalyst;

Photodegradation; MTBE.

1. Introduction

The steep increase in the concentration of pollutants in the environment has attracted

considerable interest from researchers seeking to discover efficient methods for

controlling the entry of pollutants and reducing the existing pollutant load in the

environment [1- 5]. Several decades ago, fuel oxygenates were introduced to eliminate

the use of leaded gasoline, and these molecules helped to improve the octane value of

gasoline and provide nearly complete combustion of fuel by supplying extra oxygen

during the combustion process [6]. After the passage of the clean air act in 1990, their use

increased tremendously [7]. In 1997, after the Kyoto protocol agreement to control the

emission of greenhouse gases, fuel oxygenates were in high demand worldwide [8].

There are two types of fuel oxygenates, including aliphatic alcohols and ethers. The

blending of alcohols in gasoline required careful handling to avoid water content.

However, ether is easy to mix with gasoline without any problems. Therefore, ether based

oxygenates, such as ethyl tert-butyl ether and methyl tert-butyl ether, were preferentially

blended with gasoline [9, 10]. As the application of MTBE became more common and its

consumption increased, MTBE began to appear in certain water sources, which raised

concern over human health and its increasing concentration in water bodies [11, 12].

Therefore, MTBE was being considered a potential environmental pollutant because it

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found its way into the environment via accidents, spills, faulty gas station and leakage

from pipelines. The main reason for its accumulation in water bodies was due to its high

solubility in water water ( 50 mgl-1) [13]. MTBE has very weak partition with the

organic fraction in soil, and once released from a source, it has a tendency to spread

rapidly in groundwater where its presence in water poses a high risk to human health.

MTBE has a high affinity for blood resulting in a tendency to accumulate in the blood

stream, which can be detected during breathing. Human exposure to MTBE may result in

coughing, dizziness, fever, headaches, muscular aches, vomiting, sleepiness and skin and

eye irritation [14, 15]. In the light of available reports, there are no data on human

carcinogenicity but the evidences of exposure of MTBE on mice and rats have

demonstrated the carcinogenicity and therefore, human carcinogenic nature of MTBE

cannot be ruled out. MTBE concentration for carcinogenicity varies depending on subject

and condition and it can be broadly grouped as concentration higher than 300 ppm but

below this concentration and above the advised concentration by EPA (20-40 ppb) it is

toxic to human on long term exposure. Therefore, The United States Environment

Protection Agency (USEPA) has also suggested that at higher concentrations, MTBE

may be carcinogenic [16, 17]. In addition, MTBE affects the taste and odor of water.

Based on taste and odor, the USEPA has issued limits for MTBE in drinking water in the

range of 20-40 ppb [18, 19]. The special characteristics of MTBE and its effects on the

environment and human health have attracted much interested from scientists seeking to

control its entry into the environment and to degrade the MTBE currently in the

environment. Previously, different conventional techniques have been used with limited

success including activated carbon treatments, aerobic/anaerobic biodegradation, air-

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stripping to remove MTBE from water [20, 21]. MTBE was determined to be highly

resistant to biodegradation due to its ether linkage and tertiary carbon. In addition, MTBE

has a high solubility in water, a very low Henry’s law constant (5.5 x 10-4 atm m3mol-1 at

25 °C), which hinders its partition from the liquid phase to the vapor phase, and a

moderate affinity toward carbon, which resulting in the high cost of activated carbon

adsorption [22, 24].

Recently, heterogeneous photocatalysis, which is an advanced oxidation processes

(AOP), has become widely applied to the treatment of toxic and non-biodegradable

compounds from the environment. Photocatalysis is a simple and very promising

technique for solving various environmental and energy issues. Environmental pollution

as well as the problems associated with the presence and ever increasing mass/volume of

organic, toxic and nonbiodegradable pollutants provide the impetus for fundamental and

applied research to solve these issues [25]. Typically, photocatalysis is initiated by the

irradiation of a photocatalyst, which are primarily composed of semiconducting metal

oxides, with a light source with sufficient energy to excite an electron from the valence

band of the photocatalyst to the conduction band, which creates a hole in the valence

band. Therefore, the electron-hole pair is generated due to photoexcitation and reacts with

hydroxyl ions/oxygen/water to produce hydroxyl (•OH) radicals. These hydroxyl (•OH)

radicals react with the organic molecules adsorbed on the photocatalyst and degrade them

to CO2 and H2O through a series of chemical reactions. Many metal oxides have been

reported to be active photocatalysts for the degradation of organic pollutants. However,

each of these photocatalysts has its own drawbacks that limit its usage under particular

conditions [26, 27]. In addition, a rare earth cerium oxide (CeO2) has also been studied

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and applied in heterogeneous catalysis due to its ability to release and absorb oxygen

through a fast Ce4+/ Ce3+ cycle [28- 30]. Recently, ceria-ZnO composites have been

reported to exhibit enhanced photoactivity in the photocatalytic degradation of

Rhodamine B by Li et al. [31] compared to their individual components, which might be

due to improved separation of the photogenerated electron/hole pairs, larger surface area

and enhanced adsorption ability of the surfaces and interfaces in nanosize ceria-ZnO.

Noble metal (Pt, Rh, Pd) doping on ceria, which can be used as a support or promoter, is

very important due to the unique acid-base and redox properties of ceria that further

influences the redox reactions of supported noble metals, the catalytic property of metal

crystallites, the thermal resistance of supporting material and dispersion of supported

metals [32]. In addition, Pd loading onto ceria has been reported to alter the surface

properties of the support material due to the electron-transfers between Ce and Pd [33].

Therefore, encouraged by the properties described above, we synthesized a novel catalyst

by combining CeO2 and ZnO and doped it with different amount of Pd to study the

photocatalytic degradation and kinetics of MTBE in the presence of UV radiation.

2. Experimental:

2.1. Materials

Cerium nitrate hexahydrate, zinc nitrate hexahydrate and methyl tert-butyl ether (MTBE)

were obtained from Sigma-Aldrich, USA in 99.9% purity. Palladium (II) nitrate dihydrate

was obtained from Merck and double distilled water were used in this work.

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2.2. Preparation of the Catalyst

Palladium doped composite ceria-ZnO photocatalyst nanoparticles were prepared via a

co-precipitation method. In a typical co-precipitation method, an aqueous solution of the

required molar ratios of zinc nitrate hexahydrate and cerium nitrate hexahydrate are

mixed with continuous stirring at room temperature for 2 hours. In addition, a small

amount of ethylene glycol was added as a structure modifying agent to the above

solution. Then, an appropriate amount of sodium carbonate was added to the solution to

obtain a pH of 10.0. A precipitate was formed and separated by centrifugation. The

prepared precipitates, which are the precursors of the ceria-ZnO composite, were

thoroughly washed with de-ionized water and then with ethanol. The prepared

precipitates were dried in air at 100 °C overnight. The dried ceria-ZnO composite

precursors were calcined at 450 °C for 6 hours to obtain the ceria-ZnO particles.

Palladium was impregnated onto the composite oxide using the incipient wetness

impregnation method. The Pd loadings ranged from 0.5% to 1.5% based on the weight of

the composite ceria-ZnO support.

2.3. Photocatalytic Reaction Procedure

Methyl tert-butyl ether used in the photodegradation experiments was used as received

from Aldrich. A 100 ppm MTBE stock solution was prepared in distilled water. The

photodegradation experiments were performed in a photoreactor made of quartz and

equipped with a specific tubular space for the UV lamp as well as a cooling jacket. A

high pressure mercury UV lamp (125 W) was placed at its specified position using a

special rod in the reactor. A continuous cold water (16±1°C) supply was maintained

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during the experiment to control the temperature of the reaction mixture. 350 ml of the

100 ppm MTBE stock solution previously prepared and the required amount of the

selected photocatalyst were stirred for 30 min to prepare a uniform dispersion of the ZnO

particles at room temperature followed by passage of oxygen current through an inlet

tube for 30 min at a moderate rate. After the specified time, the oxygen current was

ceased, and the UV lamp was turned on. The experimental setup was completely covered

with aluminum foil, and samples were collected every hour for a period of five hours for

analysis.

2.4. Characterization Techniques

The synthesized photocatalyst samples were characterized using advanced

instrumentation techniques. Scanning electron microscopy and transmission electron

microscopy of the samples were performed to determine the morphology and size of the

particles, and x-ray diffraction patterns were obtained using an X-ray diffractometer

equipped with a monochromatic high-intensity Cu K radiation (= 1.5418 Å, 40 kV, 100

mA).

The X-ray photoelectron spectroscopy (XPS) surface elemental analysis was conducted

using a Thermo ESCALAB 250 Xi with Al K Alpha radiation (1486.6 eV). The spectra

acquisition and processing were performed using the Thermo Avantage Software, version

4.58. The binding energy was referenced to the C1 s line at 284.6 eV for calibration. The

sample was introduced into the preparation chamber with the sample holder and degassed

until a good vacuum achieved. Then, the sample was transferred to the analysis chamber

where the vacuum was set to 10-9 – 10-10 mBar. The analyses were performed using the

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following parameters: Pass energy of 20 eV, Dwell time 50 ms and step size 0.1 eV. A

flood gun with a standard charge compensation mode was employed to neutralize the

charge build up on the surface of the insulating samples.

Nitrogen (N2) adsorption-desorption isotherms were determined at the liquid nitrogen

temperature (−195 ◦C) using an automatic ASAP 2010 Micromeritics sorptiometer

equipped with an outgassing platform and an on-line data acquisition and handling

system operating standard BET [34] and BJH [35] analytical software for the adsorption

data following the experimental recommendations previously reported [36]. The N2 gas

was 99.999% pure KOAC (Kuwait), and the test samples cerias (300 ± 2 mg) were pre-

outgassed at 110 ◦C and 10−5 Torr for 3 h. The reproducibility of the adsorption-

desorption isotherms was better than 95%.

3. Results and Discussion:

3.1. Electron Microscopy and X-ray Diffraction Studies

The morphology of the particles of the photocatalyst plays an important role in its

photoactivity. Therefore, the prepared photocatalysts were characterized by SEM and

TEM to study the shape and size of the 1% Pd doped ceria-ZnO. The morphology of

these particles observed by SEM is shown in Fig. 1, and these particles are round with a

uniform size distribution. The particles size of the 1% Pd doped ceria-ZnO are in the

range of 6-33 nm. The presence of Pd in the composites was not observed in the SEM

image of the sample, which might be due to the low amount of Pd doping. This result was

confirmed by TEM images, which are shown in Fig. 2. Two types of particles are clearly

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shown in the ceria-ZnO catalyst. Clear identification of the 1% Pd was not achieved due

to the small amount and high dispersion of the Pd over the composite oxide support.

Moreover Table 1 is showing atomic % of Pd in the samples investigated. In addition, the

EDX analysis that was conducted to semi-quantify the surface and near surface amount

of each element present. The Pd loading was confirmed by various methods including XPS,

EDX and the effect of Pd was clearly visible by the photocatalytic activity of the Pd supported

ceria-ZnO composite catalysts. However, EDX analysis of 1.0% Pd doped ceria-ZnO

indicated the presence of all of the components including Pd (Table 1, Fig. 3). The 1% Pd

doped ceria-ZnO sample was also analyzed with an XRD diffractometer. The crystalline

structure of the 1% Pd doped ceria-ZnO was characterized using a rotating-target X-ray

diffractometer (Japan Rigaku D/Max-2400) equipped with monochromatic high-intensity

Cu K radiation (= 1.5418 Å, 40 kV, 100 mA). The average crystalline size of the catalyst

nanoparticles was estimated from the full width half maximum (FWHM) and the peak

position of an XRD line broadened according the Scherrer formula [37]:

d = [0.9 λ /B cos θ] (1)

Where d is the average crystallite size, λ is the wavelength of the X-ray (0.15418 nm),

B is the full width at half maximum (FWHM, radian) and θ is the Bragg angle (degree).

The value of the FWHM was obtained by performing profile fitting using XRD pattern

processing software. The characteristic strong diffraction peaks obtained for the 1% Pd

doped ceria-ZnO composite catalysts are shown in Fig. 4. The characteristic peaks for Pd

were not observed in the diffractogram of the photocatalyst, which is most likely due to

the small amount of highly dispersed Pd present in the photocatalyst. The results of

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catalyst composition determined by EDX (Table 1) clearly show the amount of Pd loaded

is close to the nominal amount impregnated on ceria-ZnO photocatalysts. The XRD

spectrum peaks are summarized in Table 2 were a few of the peaks from the individual

components overlap with each other. All of the characteristic peaks are in good

agreement with those reported in the literature. Therefore, these results confirm the

existence presence of a ceria-ZnO composite system [31, 33]. The average crystallite size

of the 1% Pd doped ceria-ZnO was 20 nm. However, the characteristic peaks of the

individual oxide phase indicate that the ceria particles are much smaller in size

(approximately 6 nm) compared to the ZnO particles (20+ nm).

3.2. X-ray photoelectron spectroscopy and N2 Sorptiometry studies

Fig. 5 shows the Zn (2p), Ce (3d), Pd (3d), and O (1 s), XPS peaks of PCZ1.0. The peaks

were deconvoluted using standard software. Using the integrated peak areas and element

sensitivity factors, the total atomic percentage of the elements on the surface was

determined and reported in Table 3. The symmetry and binding energy of the Zn (2p)

peak confirm a +2 oxidation state. This oxidation state was further confirmed by

calculating the difference between the binding energies of the 2p3/2 and ep1/2 peaks,

which was determined to be 23.1 eV in good agreement with the literature values [28,

34]. The multi-peaks spectra (fundamental and satellite) of Ce (3d) are also shown in

Fig. 5. The relatively small peaks at 884.5 and 902.8 eV indicated a small amount of

Ce+3, and the pronounced peak at 916 eV confirmed that Ce+4 was the major species [39,

40]. The peaks at 337.1 and 342.3 eV in Fig. 5 correspond to Pd+2 [41]. Therefore the

XPS results confirm a structure consisting of Pd CeO2-x-ZnO with an atomic surface

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composition as reported in Table 3. Similar results (not presented) were found for

PCZ0.5 and PCZ1.5.

The N2 sorptiometry results are shown in Fig. 6 and Table 3. The isotherms of the

samples are type II and exhibited type H3 hysteresis (indicative of parallel plate or open

slits shape) [42]. The closure of the hysteresis at a low relative pressure for all of the

samples confirmed the wide pores, which are reported in Table 4 (18-27 nm). In

addition, the late and steep adsorption of N2 on the samples indicates a large pore size

and narrow pore size distribution [42]. Sample PCZ1.0 exhibits a lower specific surface

area (37 m2/g) and a larger pore size (27.1 nm). The hysteresis of sample PCZ1.0 was

determined to be the narrowest among the studied samples, which is due to its wider

pores. SBET SCfor PCZ1.0, and SBET < SC for PCZ0.5 and PCZ1.5. These results imply

that PCZ1.0 possesses cylindrical mesopores while the PCZ0.5 and PCZ1.5 samples

possess non-cylindrical mesopores [42]. The higher activity of sample PCZ1.0 may be

related to the pore size and shape.

3.3. Kinetic and Photodegradation Studies of MTBE in Water

The photocatalytic degradation of MTBE in water was studied by employing the ceria-

ZnO nanoparticles doped with 0.5% Pd, 1% Pd and 1.5% Pd as photocatalysts. The data

obtained from photocatalytic degradation of MTBE was plotted as degradation as a

function of time (Fig. 7). The 1% Pd doped ceria-ZnO nanoparticles exhibited the highest

photocatalytic activity compared to the other samples (i.e., 0.5% Pd doped and 1.5% Pd

doped ceria-ZnO). Nearly complete degradation of MTBE (99.6%) was observed with

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1% Pd doped ceria-ZnO after 5 hours compared to the other two catalysts 0.5% Pd doped

ceria-ZnO (90%) and 1.5% Pd doped ceria-ZnO (88.9). Therefore, the 1% Pd doped

ceria-ZnO nanoparticles with an optimum Pd loading are considered to be an effective

photocatalyst for the degradation of MTBE in water. Initially, the rate of the

photodegradation of MTBE was determined to be very fast, as shown in Fig. 7. After the

first hour of UV irradiation, the concentration of MTBE in the reaction medium was

determined to be 28.2 ppm for the ceria-ZnO nanoparticles doped with 1% Pd. The fast

photodegradation of MTBE in the first hour can be attributed to the presence of hydroxyl

radicals (•OH) whose concentration increases with UV irradiation and catalyst surface

area for adsorption of MTBE. However, as the reaction proceeds, photocatalytic

degradation of MTBE decreases due to the competition offered by the presence of other

species in the reaction medium for the hydroxyl radical and the adsorption surface. The

increased efficiency of the ceria-ZnO nanoparticles doped with 1% Pd is due to the fast

transfer of the photoexcited electrons from the surface of the semiconducting

photocatalyst to the noble metal, which acts as an electron reservoir [43-45]. Therefore,

the recombination of the photogenerated electrons and holes will be efficiently controlled

resulting in an increase in the photocatalytic activity of the catalyst [46, 47].

The enhancement of the photoactivity for different catalysts with the same pollutants is

not purely a function of BET surface area, and the presence of Nobel metals has a large

effect on the efficiency [48]. In our work, because the cumulative pore volume (Vp) was

determined to be similar for the three samples studied, the increase in photoactivity may

be related to the pore sizes and not the pore volumes (Table 4).

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It is known that the presence of a noble metal, (e.g., gold or palladium) on the surface of

a semiconducting metal oxide photocatalyst lowers the work function at the interface

with the adsorbed oxygen. Therefore, the electron transfer between the photocatalyst and

the adsorbed oxygen increases resulting in an increase in the number of peroxy/superoxy

species, which are highly oxidizing in nature, and an increase in the rate of the

photocatalytic reaction [49-53]. However, the concentration of the doped metallic

particles was also reported to affect the activity of the photo catalyst. For the ceria-ZnO

nanoparticles doped with 1.5% Pd, the activity of the catalyst decreased due to an

increase in the number of particles of the doped metal on the surface of the ceria-ZnO

nanoparticles resulting in a reduction in the adsorbed MTBE and less surface are

available for irradiation to initiate photoexcitation. The smaller pores in this sample (see

Table 4) may contribute to this lower adsorption tendency [53]. Therefore, the

photocatalytic activity of the catalyst decreased.

The heterogeneous photocatalysis is initiated by with the adsorption of organic

contaminant molecules onto the surface of the photocatalyst. These adsorbed contaminant

molecules react with hydroxyl radicals produced from the reaction between water and the

photogenerated electrons/holes generated in the photoexcitation process. The

heterogeneous photocatalytic degradation of the various pollutants in water follows the

Langmuir-Hinshelwood kinetic model [37, 38]. Therefore, the rate of the photocatalytic

degradation of the organic pollutants is proportional to the surface area coverage of the

photocatalyst by the organic pollutant molecules:

Rate (R) = - (dC/dT) α θ (2)

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= krθ = (krKC/1+KC), (3)

If KC<<1 and negligible

-ln(C/C0) = Kappt (4)

where θ, kr, K and C define the surface area covered, rate constant of the photocatalytic

degradation reaction, the adsorption coefficient of the reactant and the reactant

concentration, respectively. If the concentration (C) becomes very low, KC would be

negligible compared to 1. A plot of ln (C0/C) as a function of the irradiation time results

in a straight line representing a first order reaction. The rate constant of this reaction can

be obtained from the slope of the line in Fig. 8 [37]. The rate constant for the

photodegradation reaction increased as the percentage of Pd increased, and then, the rate

constant decreased after an optimum doping level was achieved. Fig. 8 shows that the 1%

Pd doped ceria-ZnO nanoparticles exhibit the highest rate constant (0.87 h-1), and the rate

constant obtained for 0.5% Pd and 1.5% Pd doped ceria-ZnO nanoparticles are 0.37 h-1

and 0.4 h-1, respectively.

4. Conclusions

Photocatalytic degradation of MTBE in water was evaluated using ceria-ZnO doped with

Pd as a photocatalyst. Nearly complete removal of MTBE was achieved within five hours

of UV irradiation using ceria-Z

nO nanoparticles doped with 1% Pd. The efficient

removal of MTBE is due to the higher concentration of hydroxyl radicals and the

presence of Pd, which controls the recombination of photogenerated electron hole pair. In

addition to the Pd loading, the N2 sorptiometry study introduced other factors that can

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affect the catalytic efficiency, such as the average catalyst pore sizes. The kinetics of the

photocatalytic degradation reaction of MTBE was observed to follow first order kinetics.

Acknowledgments: The authors wish to acknowledge the support by King Abdul Aziz

City for Science and Technology (KACST) through the Science & Technology Unit at

Umm Al-Qura University for funding from project No. 10-wat1240-10 as part of the

National Science, Technology and Innovation Plan. A. B. is acknowledges the support

provided through the general facilities projects GS01/01 and GS01/05 under the SAF

program of the Faculty of Science, Kuwait University.

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Figure Captions:

Fig. 1. SEM micrograph of 1% Pd doped ceria-ZnO.

Fig. 2. TEM image of the 1% Pd/ceria-ZnO photocatalyst.

Fig. 3. EDX spectra of the 1% Pd doped ceria-ZnO photocatalyst.

Fig. 4. XRD diffractogram of 1% Pd doped ceria-ZnO.

Fig. 5. Deconvoluted XPS peaks for Zn (2p), Ce (3d), Pd (3d) and O (1s) for the PCZ1.0

sample.

Fig. 6. N2 adsorption-desorption isotherms determined at -195 °C for the indicated

samples.

Fig. 7. Photocatalytic degradation of MTBE in water in the presence of the Pd doped

ceria-ZnO catalyst.

Fig. 8. Reaction kinetics of the photocatalytic degradation of MTBE in water in the

presence of the Pd doped ceria-ZnO catalyst.

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Table 1. Results of EDX analysis of Pd doped ceria-ZnO photocatalyst.

Elements (Weight %)

Sample O.K Zn K Pd K Ce K

PCZ0.5 14.25 71.54 0.40 13.81

PCZ1.0 14.15 71.01 1.06 13.78

PCZ1.5 15.04 69.93 1.43 13.60

Ceria-ZnO 25.48 60.58 NA 13.95

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Table 2. Details of XRD spectrum of 1% Pd doped ceria-ZnO photocatalyst.

S. No. Position 2θ (deg) Phase Name Size (nm)

1 28.70 Ceria, syn(1,1,1) 5.8

2 31.89 Zinc Oxide(1,0,0) 23.3

3 34.47 Zinc Oxide(0,0,2) 32.9

4 36.33 Zinc Oxide(1,0,1) 22.1

5 47.68 Zinc Oxide(1,0,2),Ceria,

syn(2,2,0)

10.4

6 56.67 Zinc Oxide(1,1,0),Ceria,

syn(3,1,1)

20.3

7 62.98 Zinc Oxide(1,0,3) 19.3

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Table 3. XPS-determined photoelectron binding energies (BE/±0.5 eV) and surface

atomic % of the studied samples.

Sample Zn 2p Ce 3d Pd 3d O 1s

PCZ0.5 37.6 6.7 0.4 48.8

PCZ1.0 39.6 8.5 0.7 50.3

PCZ1.5 37.6 5.9 0.6 50.3

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Table 4. Surface characteristics of the catalysts. BET-specific surface area (SBET ±2

m2/g), BJH-cumulative surface area (SC ±3 m2/g), BJH-average cumulative pore volume

(VpC ± 0.002 cm3/g) and pore diameter (dp ± 0.2 nm).

Catalyst SBET SC VpC dp

PCZ0.5 47 57 0.260 18.4

PCZ1.0 37 41 0.279 27.1

PCZ1.5 49 58 0.293 20.3

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Graphical Abstract

To create your abstract, type over the instructions in the template box below.Fonts or abstract dimensions should not be changed or altered.

Preparation and characterization of Pd doped

ceria-ZnO nanocomposite catalyst for

methyl tert-butyl ether (MTBE) photodegradation

Zaki S. Seddigi, Ali Bumajdad, Shahid P. Ansari, Saleh A. Ahmed,

Ekram Danish, Naeema H. Yarkandi and Shakeel Ahmed

Leave this area blank for abstract info.

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Highlights

Novel Pd supported ceria-ZnO photocatalysts were prepared with different

amounts of palladium.

The photocatalytic activity of these catalysts was evaluated for degradation of

MTBE in water.

Near complete removal of MTBE was achieved using 1% Pd doped ceria-ZnO

catalyst and UV irradiation.

Highest rate constant was obtained in case of 1% Pd doped ceria-ZnO

catalyst.

Shape and size of pores are important factors for high photoactivity of

catalyst.

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List of figures

Figure 1

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Figure 2

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Figure 3

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Figure 4

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Figure 5

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Figure 6

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Figure 7

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Figure 8