Electronic Supplementary Information

Fabrication of a Highly Dispersed/Active Pd Nanoparticles

Supported catalyst: a Cation-assisted Reduction Method in

Ethylene Glycol-water Solution at Mild Temperature

Chunpeng Xiang,a Yanhua Xiao,a Hang Bai,a Xia Yin,a Meng Peng,a Xiaojun Yang,a,b Yigang

Ding,a Zhiping Dua*

a. Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Chemical Reactor

and Green Chemical Technology, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan

430205, P. R. China.

b. Bioproduct Sciences and Engineering Laboratory, Department of Biological Systems Engineering, Washington State

University, Richland, WA 99354, USA

Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2020

Materials:

Palladium chloride (PdCl2, 59.8%), aluminum nitrate nonahydrate (Al(NO3)3·9H2O), urea,

ethylene glycol (EG), manganese sulfate monohydrate (MnSO4·H2O), zinc sulfate heptahydrate

(ZnSO4·7H2O), copper sulfate pentahydrate (CuSO4·5H2O), hydrochloric Acid (HCl, ~35%),

benzyl alcohol, benzaldehyde, 2,4-dinitrophenylhydrazine, silver nitrate (AgNO3), potassium

chromate (K2CrO4), sodium chloride (NaCl) and sodium hydroxide (NaOH) were purchased from

Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Aluminum oxide (Al2O3, gamma

phase) and titanium dioxide (TiO2) were purchased from Aladdin Chemical Reagent Co. Ltd.

(Shanghai, China). H2 (99.999%), Ar (99.999%) and CO2 (99.999%) were purchased from Wuhan

Iron & Steel Group Gas Co. Ltd. The water used in experiments was ultrapure (18.2 MΩ). All

chemicals were used as received without further purification.

Preparation of Al2O3 (gamma phase):

0.72 mol (43.243 g) of urea and 0.12 mol (45.015 g) of Al(NO3)3·9H2O were dissolved in

deionized water and the total volume was kept at 200 ml. The mixed solution was stirred for 10

min, transferred to a 250 mL hydrothermal kettle, and hydrothermally reacted at 110 °C for 24 h.

The hydrothermal kettle was cooled to room temperature, and suction filtration was carried out to

obtain a white precipitate. The mixture was washed with deionized water to neutrality, washed

with ethanol, placed in an oven at 60 °C, and dried for 12 h. The dried product was calcined in a

muffle furnace at 700 °C for 2 h to obtain a carrier Al2O3, and the heating rate was controlled at

1°C/min. The carrier of Al2O3 was characterized by XRD, and the result shows in Fig. S1.

Preparation of Pd/Al2O3-CARM (M = Mn, Zn or Cu) and Pd/Al2O3-CARMn-X (X = 1, 2

and 3):

Typically, 0.5 g of Al2O3 (gamma phase, Fig. S1†) and freshly prepared H2PdCl4

solution (5 mL, PdCl2 was dissolved in HCl solution with a pH value of 1) were added into a

three-necked flask. The mixture was sonicated for 10 min and then immersed at room

temperature for 12 h. 5 mL of EG was added into a stirred MSO4 solution (6.0 mmol in 15

mL of water) at 323 K. After stirred for 10 min, the mixture was added into the above

H2PdCl4-immersed system and kept at 323 K for 20 min. Finally, the precipitate was

filtered, and thoroughly washed successively with water and ethanol. The washed solid

was dried in vacuum at 323 K overnight, and the obtained catalyst was denoted as the

Pd/Al2O3-CARM catalyst.

Furthermore, the filtrate liquid from the preparation of Pd/Al2O3-CARMn was recycled to

prepare Pd/Al2O3-CARMn-X (X = 1, 2 and 3) catalysts.

Preparation of PdCl2/Al2O3:

0.5 g of Al2O3 (gamma phase) was added into the H2PdCl4 solution (5 mL). The

mixture was sonicated for 10 min and then immersed for 12 h at room temperature. The

precipitate was filtered, and thoroughly washed successively with water. The washed solid

was dried in vacuum at 323 K overnight to obtain PdCl2/Al2O3.

Preparation of Pd/Al2O3-EG:

The mixture of 0.5 g of Al2O3 (gamma phase) and 5 mL of the H2PdCl4 solution was

treated with ultrasound for 10 min, and immersed for 12 h at room temperature. Then 30 mL

of ethylene glycol was added into the mixture and maintained under reflux for 3 h. Finally,

Pd/Al2O3 was filtered, thoroughly washed successively with water and ethanol, and dried

in vacuum at 323 K overnight.

Activity evaluation:

The solvent-free selective oxidation of benzyl alcohol over Pd/Al2O3 was performed under

atmosphere pressure. 10 mg of Pd/Al2O3 was dispersed in 48.5 mmol of benzyl alcohol in a three-

necked batch reactor with a reflux condenser under stirring. The suspension was kept at 413 K for

1 h with oxygen bubbled at a flow-rate 50 mL/min. After the reaction, the catalyst was separated

by centrifugation, and the liquid products were quantitatively analyzed by Shimadzu GC-2014

after the addition of an internal standard (n-hexane). The conversion of benzyl alcohol and the

selectivity toward benzaldehyde and turnover frequency (TOF) are defined as follows:

𝐶𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 (%) = 100% ×𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑡ℎ𝑒 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑟𝑒𝑠𝑖𝑑𝑢𝑎𝑙 𝑏𝑒𝑛𝑧𝑦𝑙 𝑎𝑙𝑐𝑜ℎ𝑜𝑙 + 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑡ℎ𝑒 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

𝑆𝑒𝑙𝑒𝑐𝑡𝑖𝑣𝑖𝑡𝑦(%) = 100% ×

𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑏𝑒𝑛𝑧𝑎𝑙𝑑𝑒ℎ𝑦𝑑𝑒 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑎𝑙𝑙 𝑡ℎ𝑒 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

𝑇𝑂𝐹 (ℎ ‒ 1) = 100% ×

𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑏𝑒𝑛𝑧𝑎𝑙𝑑𝑒ℎ𝑦𝑑𝑒 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑃𝑑 × 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 𝑡𝑖𝑚𝑒

X-ray diffraction (XRD) characterizations:

The samples were characterized on Bruker D/max-r C using Cu Kα radiation. The operation

voltage and current was 40 kV and 40 mA, respectively. The scanning speed was set as 10

degree/min in the scanning range of 5 ~ 90°.

Transmission electron microscope (TEM) characterizations:

Morphology and structure of the catalysts were investigated on JEM-2010 transmission electron

microscope with energy-dispersive spectrometer (EDS) accessory. The high-angle annular dark-

field (HAADF) image was acquired on JEM-2100F (JEOL). The samples were prepared by

dropping ethanol dispersion of samples onto 300-mesh carbon-coated copper grids and

immediately evaporating the solvent.

X-ray photoelectron spectroscopy (XPS) characterizations:

The surface chemical composition and electronic structure of the catalysts were analyzed on

Thermo ESCALAB 250XI. XPS signals were corrected by means of the C 1s peak energy of

284.8 eV.

Fourier transform infrared spectroscopy (FT-IR) characterizations:

The analysis of the sample was carried out on an infrared spectrometer (Nicolet iS50, Thermo

Scientific). The sample was mixed with KBr at a ratio of 1:50 and then pressed into tablets. The

scanning range was 400-4000 cm-1.

Electrochemical characterizations:

Linea sweep voltammetry (LSV) and cyclic voltammetry (CV) measurements were performed

on an electrochemical workstation (PGSTAT 302 N, Metrohm) in a three-electrode system.

The platinum wire and platinum plate electrodes were used as the working and counter

electrodes during the LSV, respectively, while two graphite sticks were used as the working and

counter electrodes in the process of CV, respectively. An Ag/AgCl (sat. KCl) electrode was used

as the reference electrode. All the LSV and CV measurements were carried out in 0-1 V at a

sweeping rate of 10 mV s-1 in a mixed solution of 30 mL of H2O and 5 mL of H2PdCl4 solution

under the nitrogen atmosphere. According to the need of measurement, 5 mL of EG and/or 1.014

g of MnSO4·H2O were added during the LSV measurements. The MnSO4 solution included

1.014 g MnSO4·H2O, 30 mL of H2O and 5 mL of HCl solution (pH = 1) in the CV measurements.

Ultraviolet–visible spectroscopy determination:

In the preparation of Pd/Al2O3-CARMn, the total manganese content in the supernatant was

measured by formaldehyde oxime spectrophotometry [1] in a Shimadzu UV-2600 spectrometer.

The UV-Vis spectra of MnSO4, 2,4-Dinitrophenylhydrazine (DNPH), DNPH+MnSO4,

DNPH+EG and DNPH+MnSO4+EG were scanned on the UV-2600 spectrometer in the range of

200-600 nm.

Effect of MnSO4 on the oxidation of EG:

To remove 1 mL of EG was added to a test tube containing 5.5 mL of the DNPH solution

(1.838×10-3 mol L-1), shaken well, and placed in dark for 24 h. The red precipitation of 2,4-

dinitrophenylhydrazone was filtered to obtain a yellow solution.

1 mL of the above solution and 0.5 mL of DNPH were added in each of two test tubes. Then 1

mL of MnSO4 solution (1.014 g of MnSO4·H2O in 15 mL of water) was added to one tube, and 1

mL of water was added to the other. Two test tubes were heated to 50 oC for 20 min in a water

bath, and then placed in dark for 1 h. Finally, 0.2 mL of the supernatant was diluted in a 10-mL

volumetric flask with water, and analyzed.

Preparation of Pd/Al2O3-CARMn-Ar:

Typically, 0.5 g of Al2O3 (gamma phase) and 5 mL of H2PdCl4 solution were added into

a three-necked flask. The suspension was sonicated for 10 min and then impregnated at

room temperature for 12 h. 5 mL of EG was added into a stirred MnSO4 solution (6.0

mmol in 15 mL of water). The mixture and the suspension mentioned above were stirred

for 2 h in the Ar flow to displace the air, and then heated to 323 K. The mixture was added

into the suspension under the atmosphere of Ar and kept at 323 K for 20 min. Finally, the

precipitate was filtered, thoroughly washed successively with water and ethanol, and dried

in vacuum at 323 K overnight. The obtained catalyst was denoted as Pd/Al2O3-CARMn-Ar.

Temperature programmed desorption of CO2 (CO2-TPD) for Al2O3

The distribution of basic centers was detected on 2920 Chemisorption Analyzer (Micromeritics

Instrument Corp.). Before the measurement, the sample was pretreated under flowing helium at

300 °C for 60 min, and then cooled to room temperature. After the sample was exposed to CO2 for

30 min, the gas flow was switched to pure He, and the residuary CO2 was taken away until the

stable baseline was established. Finally, the catalyst was heated linearly to 900 °C at a heating rate

of 10 °C /min. CO2 in effluent gas was recorded continuously as the function of temperature.

Zeta-potential characterizations of Al2O3:

10 mg of Al2O3 was dispersed in 15 mL water to determine the zeta-potential of Al2O3 on a

Nano-ZS zetasizer (Malvern Instruments, UK), and the measurements were conducted for 3 times

to obtain an average value and standard deviations.

Specific surface area characterizations:

Specific surface area was determined on ASAP-2460 Surface Area and Porosity Analyzer

(Micromeritics Instrument Corp.). The sample was first degassed at 200 oC for 4 h, and then

cooled to room temperature, and finally, detected under the condition of liquid nitrogen.

Determination of the molar ratio of Cl-/Pd in PdCl2/Al2O3:

The content of Cl- ions on the surface of PdCl2/Al2O3 was determined by the Mohr titration

method using K2CrO4 as an indicator.[2] PdCl2/Al2O3 was dissolved in HNO3 by the reflux,

and then the Pd amount was determined by inductively coupled plasma mass spectrometry

(ICP-MS). The molar ratio values of Cl- to Pd were the average values of 5 parallel tests.

Fig. S1 XRD pattern of Al2O3. Compared with the standard JCPDS card (46-1045), the main

phase structure was ascribed to a gamma phase, but the crystallinity was poor.

Fig. S2 N2 adsorption/desorption isotherm of the Al2O3 at 77K. The sample was degassed at 200

C for 4 h before the determination. The BET specific surface area was 240.0 m2 g-1.

Table S1 Average numbers of NPs/square area (N) of different catalysts

Catalysts Sizes Pd content (%) N (m-2)

Pd/Al2O3-CARMn 3.6 0.60 8.42×1013

Pd/Al2O3-CARZn 5.5 0.62 2.44×1013

Pd/Al2O3-CARCu 27.4 0.59 1.88×1011

Assuming that the present Pd nanoparticles are cuboctahedra in shape with a cubic close-packed

structure in this size range, the model of full-shell nanoparticles is adopted.[3] The total number of

the Pd atoms of nanocluster (NT) [3] can be calculated from

(1)𝑑𝑠𝑝ℎ = 1.105𝑑𝑎𝑡𝑁1/3

𝑇

where dsph is the mean diameter of the Pd crystallites obtained from TEM analysis and dat is the

atom diameter of Pd, 0.274 nm.

Average numbers of NPs/square area can be calculated from

(2)𝑁 =

𝑚𝑤𝑃𝑑𝑁𝐴

𝑀𝑃𝑑𝑁𝑇(𝑚𝑆𝐵𝐸𝑇)=

𝑤𝑃𝑑𝑁𝐴

𝑀𝑃𝑑𝑁𝑇𝑆𝐵𝐸𝑇(𝑚 ‒ 2)

Where wPd is the weight percent of Pd from the measurement of ICP-MS (seeing Table 1); NA is

the Avogadro's contant, 6.022 1023 mol-1; MPd is the atomic weight of Pd, 106.42 g mol-1, and ×

SBET is the specific surface area of Al2O3, 240.0 m2 g-1 (seeing Fig. S10 in the supplementary

information). The detailed calculation process is as follows：

Pd/Al2O3-CARCu: 𝑁𝑇 = (𝑑𝑠𝑝ℎ/ 1.105𝑑𝑎𝑡)

3 = (27.4

1.105 × 0.274)3 = 741162

𝑁 =𝑤𝑃𝑑𝑁𝐴

𝑀𝑃𝑑𝑁𝑇𝑆𝐵𝐸𝑇=

0.0059 × 6.022 × 1023

106.42 × 741162 × 240= 1.88 × 1011(𝑚 ‒ 2)

Pd/Al2O3-CARZn: 𝑁𝑇 = (𝑑𝑠𝑝ℎ/ 1.105𝑑𝑎𝑡)

3 = (5.5

1.105 × 0.274)3 = 5994

𝑁 =𝑤𝑃𝑑𝑁𝐴

𝑀𝑃𝑑𝑁𝑇𝑆𝐵𝐸𝑇=

0.0062 × 6.022 × 1023

106.42 × 5994 × 240= 2.44 × 1013(𝑚 ‒ 2)

Pd/Al2O3-CARMn: 𝑁𝑇 = (𝑑𝑠𝑝ℎ/ 1.105𝑑𝑎𝑡)

3 = (3.6

1.105 × 0.274)3 = 1681

𝑁 =𝑤𝑃𝑑𝑁𝐴

𝑀𝑃𝑑𝑁𝑇𝑆𝐵𝐸𝑇=

0.006 × 6.022 × 1023

106.42 × 1681 × 240= 8.42 × 1013(𝑚 ‒ 2)

Fig. S3 TEM images and the corresponding particle size distributions for Pd/γ-Al2O3-Mn (a),

Pd/TiO2-Mn (b). Pd/γ-Al2O3-Mn and Pd/TiO2-Mn were prepared by the CAR with γ-Al2O3 and

TiO2 as the carriers, respectively.

Fig. S4 CV curves of H2PdCl4 and MnSO4 at the same pH value. In order to avoid the hydrogen

evolution on platinum electrodes, the graphite electrodes were used to replace platinum electrodes.

The CV curve of H2PdCl4 exhibited obvious redox peaks, while no peak was observed on the

CV curve of the MnSO4 solution. The result showed that Mn2+ ions did not undergo redox

reaction with PdCl42- in the mixed solution of H2PdCl4 and MnSO4. In addition, it could be

seen from their standard electrode potentials, (EΘ(PdCl42-/Pd) = 0.62 V,[4] EΘ(Pd2+/Pd) =

0.987 V,[4] EΘ(Mn3+/Mn2+) = 1.5415 V,[5] EΘ(MnO2(beta)/Mn2+) = 1.23 V,[6] EΘ(Mn2+/Mn) =

-1.18V[6]), that the reduction of PdCl42- by Mn2+ was thermodynamically unfavorable. As a

result, both of them could confirm each other.

Fig. S5 Reaction of 2,4-Dinitrophenylhydrazine (DNPH) with various substances. After EG or

MnSO4 was added to DNPH solution, respectively, no precipitation was observed by heat

treatment, while the red precipitation, 2,4-dinitrophenylhydrazone, was produced with the

simultaneous addition of EG and MnSO4, suggesting that Mn2+ ions could accelerated the

oxidation of EG to aldehyde.

Fig. S6 C 1s and O 1s XPS spectra of Pd/Al2O3-CARMn before and after washing. Fig. 5a-b

exhibited three types of carbon with different chemical states, which appeared at 284.8 eV for

graphite-like C, 286.2 eV for C-O and 288.8 eV for O-C=O,[7-9] respectively. The O 1s spectra

were also divided into three types including lattice oxygen (O, 530.9 eV), surface hydroxyl (OH,

531.7 eV) and lattice water (H2O, 532.8 eV). Since the O 1s signal of hydroxyl oxygen in

carboxylic acid appeared at ~531.5 eV [10], it was considered to be obscured by the peaks of the

surface hydroxyl groups. According to C 1s and O 1s XPS spectra, the peak at 288.8 eV (Fig. S3c)

representing carboxylic acid was considered to be the product of aldehyde group oxidized by Pd2+.

Comparison of Fig. S5a and S5b showed that peak areas at 286.2 eV for C-O drastically

decreased after Pd/Al2O3-CARMn was washed, and those at 288.8 eV for O-C=O were changed

slightly. The result suggested that the carboxylic acid should be more easily adsorbed on the

catalyst than EG.

Fig. S7 UV-vis spectra of the supernatant from the preparation of Pd/Al2O3-CARM by the CAR.

Since hydroxyl groups of parts of HOCH2CH2OH···[M(H2O)(n-1)]2+···SO42- could bind to

the defect sites on the surface of Al2O3,[11’12] and the [M(H2O)n]2+ ion could return to the

solution after the ligand EG was oxidized to HOCH2CHO, the Mn content in the

supernatant first decreased and then increased.

Fig. S8 XPS survey spectra for Pd/Al2O3-CARMn and Mn 2p XPS core-level spectra. No Mn

elements were detected.

Fig. S9 SEM-EDS analysis of Pd/Al2O3-CARMn. No Mn elements were detected.

Table S2 Zeta-potential of Al2O3 and molar ratio of Cl to Pd in PdCl2/Al2O3

Samples Zeta potential Molar ratio of Cl to Pd

PdCl2/Al2O3 - 2.2 ± 0.1

Al2O3 36.2 ± 0.7 mV -

The Cl- and Pd contents were determined by Mohr titration method and ICP-MS, respectively.

The molar ratio of Cl- to Pd of 2.2 showed that there existed a ligand exchange between Cl- and

surface OH in the adsorption of PdCl42-. The process could be described as follows:

Scheme S1 The adsorption process of PdCl42- on the surface of Al2O3

The zeta potential of Al2O3 was 36.2 ± 0.7 mV, showing a positive surface potential in a neutral

environment. Thus, PdCl42- could be adsorbed on the surface of Al2O3 by the electrostatic

interaction.

Fig. S10 Pd 3d XPS spectra of Pd/Al2O3-CARMn-Ar (a), Pd/Al2O3-CARMn (b) and Pd/Al2O3-No

(c). A similar process under argon (Ar) atmosphere was carried out to prepare the catalyst, which

was marked as Pd/Al2O3-CARMn-Ar, for better understanding the effect of metal ions addition.

During the experiment, it was also found that the color of the catalyst varied from yellow to light

gray. The obtained Pd/Al2O3-CARMn-Ar was characterized by XPS. It could be seen from Fig.

S10 and Table S3 that the content of the surface Pd0 on Pd/Al2O3-CARMn-Ar was higher than that

on Pd/Al2O3-No, indicating that a part of Pd2+ were reduced. The literature has been reported that,

when the ligand LH (L– = CH3COO–, HCOO– and Cl–) was more acidic than ethylene glycol (AH),

dehydrated ternary complexes of the type AH···M2+···L– (M = Mn, Cu and Zn) were found by

MALDI (matrix assisted laser desorption ionization) and ESI (Electron Spray Ionization) in the

study on the coordination of M2+ with AH, and zinc-induced oxidation of ethylene glycol to

glycolaldehyde by consecutive hydrogen shifts was detected by MS/MS[13]. Thus, we thought that

glycolaldehyde was generated by the hydrogen transfer of the ternary complex

(HOCH2CH2OH···[Mn(H2O)5]2+···SO42-) under the Ar atmosphere, and further Pd2+ was

reduced by the glycolaldehyde.

When the Ar atmosphere was replaced with the air, the hydrogen removed from

HOCH2CH2OH···[Mn(H2O)5]2+···SO42- was highly active and easily oxidized by O2 in the

air. The generation rate of glycolaldehyde increased. As shown in Table S3, the Pd0 content

of 90.0% on Pd/Al2O3-CARMn was higher than that of 80.4% on Pd/Al2O3-CARMn-Ar.

Thereby, the hydrogen from HOCH2CH2OH···[Mn(H2O)5]2+···SO42- transferred into water

in the proposed reaction mechanism for Pd/Al2O3 catalysts prepared by the CAR.

Table S3 Percent of surface Pd0 on the catalysts

Peak areas of Pd 3d5/2Catalysts

S(Pd0) (~335.1 eV) S(Pd2+) (~336.7 eV)

S(Pd0) / S(Pd0 + Pd2+)

(%)

Pd/Al2O3-CARMn-Ar 1144.7 278.7 80.4

Pd/Al2O3-CARMn 9587.3 1062.0 90.0

Pd/Al2O3-No 576.5 4435.4 11.5

Fig. S11 CO2-TPD profiles of Al2O3. CO2 desorption peaks were observed at 478 and 673 K,

indicating there were basic centers on the surface of Al2O3.

Fig. S12 TEM image and the corresponding particle size distribution for Pd/Al2O3-CARCo.

Recently, Fe2+ and Co2+ were selected for the experiment. Since Fe2+ was easily hydrolyzed and

oxidized under reaction conditions, no corresponding catalyst was obtained. The average size of

Pd particles on Pd/Al2O3-CARCo was 4.4 nm.

Fig. S13 Comparative diagram of TOF values. The turnover frequency of benzaldehyde

reached 29977 h-1 on Pd/Al2O3-CARMn, which was far higher than the literature values.

Fig. S14 Recycling of Pd/Al2O3-CARMn for the oxidation of benzyl alcohol at 413K. The

conversion of benzyl alcohol and the selectivity of benzaldehyde did not undergo significant

changes during the reuse for 5 times.

Fig. S15 TEM image and corresponding particle size distribution for the fresh catalyst (a) and the

catalyst (b) reused 5 times. The average size of Pd NPs on the used catalyst was about 3.7 nm,

which was similar to that of the fresh catalyst (3.6 nm).

Fig. S16 Pd 3d XPS core-level spectra of the fresh catalyst (a) and the catalyst (b) reused for 5

times. It was found that the chemical states of Pd were unchanged basically. It was further

illustrated that Pd NPs were stable after 5 cycles.

Fig. S17 TEM image and theparticle size distributions for Pd/Al2O3-EG. Since 0.090% of Mn2+

ions by the detection of ICP-MS could be adsorbed during the preparation of the catalyst,

Pd/Al2O3-EG was prepared by the ethylene glycol reduction to investigate the influence of Mn2+

ions on the solvent-free oxidation of benzyl alcohol to benzaldehyde. It was found form Fig. S17

and Table 1 that the size of Pd NPs and the TOF of BzH on Pd/Al2O3-EG were close to those on

Pd/Al2O3-CARMn, indicating that there was no synergistic effect between Mn2+ ions and Pd.

Fig. S18 Effect of reaction time on the conversion of benzyl alcohol (BzOH) on Pd/Al2O3-No and

Pd/Al2O3-CARMn. The reaction time dependences of catalytic performances in selective oxidation

of benzyl alcohol were tested, and the results are listed in Fig. S18. Because it took 20 minutes for

the reaction temperature to rise to 413K, a part of Pd2+ was in stiu reduced by benzyl alcohol to

metal Pd, which led to a 0.21% conversion of benzyl alcohol over Pd/Al2O3-No. Since then,

Pd/Al2O3-No had an induction period of about 10 min, in which a concomitant color change of the

catalyst from yellow to light gray was observed. However, the conversion of benzyl alcohol over

Pd/Al2O3-CARMn increased almost linearly within 1 h. All of these showed that Pd nanoparticles

were the true active phases, and the ionic Pd species underwent reduction by alcohols during the

reaction. This result is in agreement with the conclusion drawn by Kaneda et al.[14] and Wang et

al.[15].

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