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Supplementary information to

Ligand-controlled fabrication of core-shell PdNi bimetallic nanoparticles

as a highly efficient hydrogenation catalyst

Zuojun Wei,a,* Dilantha Thushara,a Xinghua Li,a Zuyi Zhang,a Yingxin

Liu,b, Xiuyang Lu,a

a Key Laboratory of Biomass Chemical Engineering of the Ministry of

Education, College of Chemical and Biological Engineering, Zhejiang

University, 38 Zheda Road, Xihu District, Hangzhou 310027, P.R. China

b Research and Development Base of Catalytic Hydrogenation, College of

Pharmaceutical Science, Zhejiang University of Technology, 18

Chaowang Road, Xiacheng District, Hangzhou 310014, P.R. China

(* Corresponding Author’s E-mail: [email protected])

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mailto:[email protected]

Experimental

Palladium chloride (PdCl2) and polyvinylpyrrolidone were purchased

from Shanghai RC Chemicals Co. Ltd and 2,6-pyridine dicarbonitrile

(>98% purity) was purchased from Shanghai Jiuling Chemicals Co. Ltd.

Other chemicals and organic solvents were analytically pure and

purchased from Sinopharm Chemical Reagent Co. Ltd. Deionized water

was used throughout the study.

Synthesis of monometallic and bimetallic catalysts

The synthesis of 2,6-bis(5,6-dimethyl-1,2,4-triazine-3-yl) pyridine (BTP)

was carried out as described in our own study [1]. We started with

commercially available 2,6-pyridine dicarbonitrile where 5.48 g of it was

initially dissolved in 90 ml of deionized water and followed by addition

of 30 ml of hydrazine hydrate (85%, w/w). Then the reaction was carried

out in a 250 ml of three-neck flask at 30 °C for 30 h under N2 atmosphere.

After completion of the reaction 5.98 g of a yellow colored 2,6-

pyridinecarboxamidehydrazone was filter out and dried in vacuum dryer

at 100 °C. After that 4.30 g of 2,3-butanedione and 55 ml of

dichloromethane were added in a 100 ml of three-neck flask followed by

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addition of 3.86 g of 2,6-pyridinecarboxamidehydrazone and 1.70 g of

anhydrous magnesium sulfate to react at 40 °C for 3 h under N2

atmosphere. Afterwards, magnesium sulfate was filter out, and the

filtrate was rotary evaporated, crystallized with ethanol and dried under

vacuum overnight to obtain 4.24 g of khaki color BTP as solid powder.

PVP was taken directly from the vender without further purification. We

dissolved calculated amount of metals in 3.5 g of distilled water alone or

with calculated amount of ligands (BTP or PVP). Then the sol-gel method

was initiated by dissolving 4.6 g of ethanol and 5.2 g of TEOS and

agitating for 10 min for proper mixing. 1g of water with an excess

amount of dissolved NaBH4 (5:1 molar ratio with respect to total metals)

was slowly added to the system with 15 min of followed continuous

agitation. Then keep the system idle for 2 days for gelation and 12 h at

110 °C in vacuum dryer to obtain solid materials in pebble form, which

was easily ground to powders. In order to ensure the consistency of

experiment we controlled the SiO2 particle size fractions to be 63-74 μm

using two sieves (-200/+230 mesh). This facile synthesis method was

repeated to obtain series of monometallic and bimetallic compounds,

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while the total metal loading of each catalyst was fixed around 2.5 wt%

(see Table S1).

Table S1 List of the bimetallic catalysts used for experiment

Catalyst Total Metal loading

(% w/w)

Pd loading (% w/w)

Pd/SiO2 2.6 2.6

Ni/SiO2 2.7 -

Pd-BTP/SiO2 2.3 2.3

Pd5Ni5/SiO2 2.4 1.5

Pd5Ni5-BTP/SiO2* 2.3 1.4

Pd5Ni5-PVP/SiO2* 2.5 1.6



*. Ligand to Pd molar ratio was always 1:1. The metal loading was calculated as weight percentage of the Pd and Ni to the total weight of the catalyst.

Characterization method

X-ray diffraction (XRD) patterns were recorded with an XRD-6000

diffractometer (Shimadzu Co., Japan) using a Cu-Kα radiation

(λ=0.15406 nm) in a Bragg-Brentano para-focusing optics configuration

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(40 kV, 40 mA). Samples were scanned from 5 to 80 ° with a scanning

rate of 4 °min-1 and a step size of 0.02 °. The crystalline phases were

identified by reference to the JCPDS database. TEM images were

obtained using a Tecnai G2 F30 S-Twin instrument (FEI Co., USA)

operated at an accelerating voltage of 300 kV. Samples were prepared by

dispersing the catalyst powder in ethanol under ultrasound for 120 min

and then dropping the suspension onto a copper grid coated with carbon

film. BET specific surface area and pore structures were measured by

pulsed nitrogen adsorption-desorption method at -196 C using an ASAP

2010 instrument (Micromeritics Instrument Co.). Prior to N2

physisorption, the samples were degassed under vacuum at 250 °C

overnight. XPS spectrum was obtained using an Escalab Mark II X-ray

spectrometer (VG Co., United Kingdom) equipped with a magnesium

anode (Mg Kα=1253.6 eV), 50 eV pass energy, a 0.2 eV kinetic energy

step, and 0.1 s dwelling time. Energy corrections were performed using a

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1s peak of the pollutant carbon at 284.6 eV. The sample was prepared by

pressing the catalyst powder onto the surface with silver sol gel.

Palladium content in the catalyst was determined using a Varian AA 240

FS atomic adsorption spectrophotometer (AAS; Varian, Inc., USA). TOC

analysis was conducted in 5000 Model TOC-VCPN analyzer (Shimadzu

Co., Japan).

Catalytic test

All the catalysts were tested using hydrogenation of nitrobenzene. All

reactions involved 5 mL of 0.02 g·ml-1 solution of nitrobenzene in ethanol

and 20 mg of catalysts. It was conducted in liquid phase using a 25 mL of

batch reactor. The reactor was sealed, deflated with N2 three times, and

heated to desired temperature at a magnetic stirring speed of 1000 rpm.

Based on our experience, the external diffusion resistance can be greatly

decreased at high stirring speed [2]. The reaction was then initiated by

introducing H2 with required pressures. After the reaction was over, the

reaction mixture was cooled down and used catalyst was separated using

centrifugation. The solid catalyst was washed with double-distilled water

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for the next cycle; the supernatant was sampled and analyzed with gas

chromatography using Agilent 6820 series GC system with a flame

ionization detector (FID) and column HP-5 30 m × 0.25 mm × 0.25 μm

provided by Agilent Technologies Inc., USA. The representative method

was started with the oven temperature at 40 °C and the coil was kept at 40

°C for 5 min, and then temperature was gradually increase up to 200 °C at

a ramp of 10 °Cmin-1 within another 16 min. The determination of

nitrobenzene and aniline was conducted with reference substances.

Furthermore, the corresponding calibration was conducted using toluene

as the internal standard. The particle sizes of the SiO2 supports we have

used are 63-74 μm and internal diffusion can be neglected for such small

particle size which is essential to ensure that mass transport (G-L and L-

S) does not hinder the surface chemical reaction. Furthermore, we used

Weisz-Prater criterion to verify the negligence of internal diffusion in the

reaction.

Weisz-Prater criterion

φW−P=Rate∗R p

2

CsDeff ≤ 3β (Eq. 1)

(Where Rate = reaction rate per volume of catalyst, Rp = catalyst particle

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radius, Cs = reactant concentration, Deff =effective diffusivity)

For pores radius less than 100 nm size, the diffusion is in Knudsen regime

and for typical cylindrical pores in SiO2 we can calculate it as follows

Deff=Dkn=9700 r ( TM

)1 /2

(Eq. 2)

(Where r = pore radius, T = temperature, M = molar mass)

And β for it smaller values can be found from

ƞ=1−n β4

(Eq. 3)

(Where ƞ = effectiveness factor and n = reaction order)

According to the Weisz-Prater criterion, when effectiveness factor is η ≥

0.95 and reaction order n=1, the dimensionless Weisz-Prater parameter

(φW-P) value is less than 3β, which can be consider as sufficient condition

neglect the pore diffusion limitations.

Evaluation of PdNi-BTP/SiO2 on Weisz-Prater criterion

We evaluated the catalyst, PdNi-BTP/SiO2 for three temperature

8

conditions 25, 50 and 80 °C using Weisz-Prater criterion. Initially we

calculated reaction rates and reaction order. We conducted hydrogenation

of nitrobenzene with PdNi-BTP/SiO2 under 1.5 MPa and 25, 50 and 80

°C in time range of 1 hour with 10 min intervals. Then calculated reaction

rate and reaction order as follows. Reaction order is 1 and Reaction rates

are as follows.

Temperature

(°C)

Rate1

(mol cm-3 s-1)

Rp2

(cm)

Cs3

(mol/cm3)

Deff4

(cm2/s)

φW−P5 β6

80 3.89×10−5 6.85 × 10-3 7.12×10− 4 1.476×10−3 3.541×10−3 0.2

50 3.71×10−5 6.85 × 10-3 7.16×10−4 1.412×10−3 3.514×10−3 0.2

25 3.18×10−5 6.85 × 10-3 7.28×10−4 1.356×10−3 3.084×10−3 0.2

Note: 1. Rates of reaction per volume of catalysts was derived by taking average rate of production of aniline during first 10 min. 2. Catalyst particle size is same for all cases. 3. Considering the reactant concentration decline during the reaction cycle C s

was calculated by taking average values for initial 10 min 4.Deff was calculated using Eq. 2 for different temperatures where r (pore size, radius) = 2.2 x10−7 cm (2.2 nm) and M of reactant nitrobenzene is 123.06). 5. Weisz-Prater value was calculated using Eq. 1. 6. β was calculated using Eq. 3 where the order of reaction is 1 and Takingƞ, effectiveness factor as 0.95.

As it is shown from calculation,

φW−P ≪ 3β

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Therefore, we can conclude that under all considered temperatures φW−P ≤

3β and according to the Weisz-Prater criterion the internal diffusion can

be neglected for the sol-gel silica catalysts series we have evaluated in the

work. We included this detailed explanation in the catalysts test section of

the modified supporting document to justify our establishment on kinetic

regime of the reaction model.

10

0

20

40

60

80

100

Pd C

onte

nt w

t. %

DCB

Catalysts

Yield

%

A 0

1

2

5th5th

5th5th

1st

1st

1st1st

Fig. S1 Recyclability and Pd content of A. Pd3Ni7-BTP/SiO2, B.

Pd3Ni7-BTP/SiO2 with BTP removed, C. Pd5Ni5-PVP/SiO2 and D.

Pd5Ni5-PVP/SiO2 with PVP removed. Reaction conditions: 0.1 g of

nitrobenzene; 5 ml of ethanol, ambient pressure, room temperature,

time of 1.0 h and 20 mg of catalyst. The Pd contents were

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determined by the AAS method after digesting the samples with 7

mol·l-1 of nitric acid at 65 ºC.

12

13

Fig. S2 TEM micrographs of (a) Pd5Ni5-BTP/SiO2; (b) Pd5Ni5/SiO2, (c) Pd7Ni3-BTP/SiO2; (d) Pd5Ni5-PVP/SiO2; (e) Pd/SiO2 and (f) Pd-BTP/SiO2

14

350 345 340 335 330

Orbits B.E. / eV AR %Pd (0) 3d 5/2 338 72Pd (+2) 3d 5/2 339 13Pd (0) 3d 3/2 343 11Pd (+2) 3d 3/2 344 4

890 880 870 860 850

Orbits B.E. / eV AR %Ni (0) 2p 3/2 856 35Ni (+2) 2p 3/2 862 26Ni (0) 2p 1/2 874 21Ni (+2) 2p 1/2 880 18

15

350 345 340 335 330


890 880 870 860 850


16

348 344 340 336 332


868 864 860 856 852


17

350 345 340 335 330


890 880 870 860 850


Fig. S3 - high-energy bands (Pd3d3/2), (Ni 2p3/2) and a low-energy

band (Pd3d5/2), (Ni 2p1/2) for palladium and nickel, (a-b) Pd5Ni5-

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BTP/SiO2, (c-d) Pd5Ni5-PVP/SiO2, (e-f) Pd5Ni5/SiO2 and (g-h)

Pd7Ni3-BTP/SiO2

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Table S2 Molar ratio of Pd/Ni on the bimetallic shell surface by XPS

analysis

Catalyst Pd/Ni ratio(at synthesis mixture)

Pd/Ni ratio(at surface of shell by XPS)

Pd enrichment

on surfacePd% Ni % Pd% Ni %

Pd5Ni5/SiO2 50 50 29 71 -21

Pd5Ni5-PVP/SiO2 50 50 57 43 +7

Pd5Ni5-BTP/SiO2 50 50 62 38 +12

Pd3Ni7-BTP/ SiO2 30 70 42 58 +12

Pd7Ni3-BTP/ SiO2 70 30 85 15 +15

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Reference

[1] Z.J. Wei, D. Thushara, Y.X. Liu, A.Y. Zhang, S.G. Deng, Novel Pd-

BTP/SiO2 as an Effective Heterogeneous Catalyst for Heck Reactions,

Chem. Eng. Commun., 203 (2016) 488-495.

[2] Y.X. Hou, L.B. Xu, Z.J. Wei, Y.X. Liu, X.H. Li, S.G. Deng,

Reaction process and kinetics of the selective hydrogenation of

resorcinol into 1,3-cyclohexanedione, J. Taiwan Ins. Chem. Eng. 45

(2014) 1428-1434.

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