ORIGINAL PAPER

Facile synthesis of Pd nanoparticles on SiO2 for hydrogenationof biomass-derived furfural

Yuying Zhao

Received: 12 February 2013 / Accepted: 27 May 2013 / Published online: 7 June 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract This report shows that furfuryl alcohol can be

selectively produced from the hydrogenation of furfural

using supported Pd nanoparticles. Furfuryl alcohol is

widely used as solvent and chemical intermediate for the

synthesis of fine chemicals. Here, various Pd nanoparticles

supported on mesoporous SiO2 (Pd/SiO2) were simply

fabricated by a wet impregnation using palladium nitrate.

Physical properties of Pd/SiO2 nanoparticles were studied

by X-ray diffraction, energy-dispersive, X-ray analysis, N2

adsorption and desorption isotherms and transmission

electron microscopy. Results show a high dispersion of Pd

nanoparticles with small size. Pd nanoparticles catalyzed

very efficiently the hydrogenation of furfural to furfuryl

alcohol with 76 % selectivity under mild conditions.

Overall, the catalyst developed could find applications for

the production of chemicals from biomass.

Keywords Synthesis � Nanoparticles � Pd/SiO2 �Hydrogenation � Furfural

Introduction

With the quick economic development and the increasing

need for energy from dwindling fossil resources, a big

challenge for the researchers is to search a sustainable route

to utilize the renewable biomass or biomass-derived

chemicals (Huber et al. 2006; Lang et al. Lange et al.

2012). In the context, biomass-derived furfural has been

identified as a platform chemical for the production of

valuable chemicals, where furfural is often produced by

acid-catalyzed dehydration from hemicellulose line (Gur-

buz et al. 2012; Yan et al. 2013a, b; Weingarten et al.

2010). Several industrially value-added chemicals, e.g.,

furfuryl alcohol and tetrahydrofurfuryl alcohol (THFA),

can be obtained from the hydrogenation of furfural. Among

the various products, furfuryl alcohol is very attractive. It is

an organic compound containing a furan ring and

hydroxymethyl group, which makes it soluble in common

organic solvents and miscible with water. Besides, it is

often regarded as a useful solvent and primarily used as an

ingredient in the manufacture of various products such as

adhesives and wetting agents (Gruter and de Jong 2009).

In the last decades, the efficient production of furfuryl

alcohol from the hydrogenation of furfural has attracted

numerous research efforts. Strassberger et al. (2010)

reported ruthenium–carbine complexes were very efficient

for the hydrogenation of furfural to furfuryl alcohol. For

homogeneous catalysts, one active center often appeared

during the reaction, which often produces good activity.

However, due to the difficulty in recycling of the homo-

geneous catalysts, it would increase the cost, the waste in

the environment and limited its practical application. Het-

erogeneous catalysts appeared more attractive due to its

easy recyclability, separation and environmental benignity.

The hydrogenation of furfural has been studied using the

transitional-metal catalysts based on Ni, Co, Ru, Pd and Pt.

The second metal or promoter is sometimes added to

improve the catalytic activity (Kijenski et al. 2002; Li et al.

2003; Chen et al. 2002). In this regard, systems based on Ni

or Co, modified with Cu, Fe, Ce or heteropolyacids, have

proved to be very successful, reaching 98 % selectivity to

the unsaturated alcohol at almost perfect conversion (Li

et al. 2003; Chen et al. 2002). However, the disadvantage

of some of these systems is that they cannot be reused or

Y. Zhao (&)

Institute of Chemical and Biological Technology, Taiyuan

University of Science and Technology, Taiyuan 030021, China

e-mail: yuyingzhao03@gmail.com

123

Environ Chem Lett (2014) 12:185–190

DOI 10.1007/s10311-013-0424-4

they promote unwanted side reactions (Li et al. 2004;

Zheng et al. 2008). The metal Pd nanoparticles present

highly promising due to its low cost, relatively stable in the

air environment and easy recycle. Different advanced

methods have been employed to fabricate Pd nanoparticles

such as atomic layer methods, CO2-chemical fluid depo-

sition and wet-impregnation method. Liang et al. (2012)

have been tried to systematically deposit Pd and other

noble metal on Al2O3 using atomic layer methods.

Although the method is very attractive, no application was

reported. Kim et al. (2008) have done pioneering work

using liquid CO2-based chemical fluid deposition method

for the synthesis of supported metal Pd catalysts. Very

small Pd nanoparticle was achieved, although no applica-

tion was reported. Later, Ye et al. (2004) and Yen et al.

(2007) employed supercritical CO2 chemical fluid deposi-

tion method to synthesize monometallic Pd and Pt as well

as bimetallic Pt–Cu, Pt–Ru, Pt–Au, Pt–Pd and Pt–Ni

nanoparticles on carbon nanotubes. The resultant nano-

particles were employed for fuel cell. To our limited

knowledge, few works have been done on the hydrogena-

tion of furfural using the relatively cheap Pd/SiO2 catalysts,

which were prepared using a cheap palladium nitrate pre-

cursor. Herein, we report the metal Pd nanoparticles were

efficiently confined inside the mesoporous channel of SiO2

by a modified impregnation method using the cheap pal-

ladium nitrate as metal precursor. The successfully result-

ing Pd nanoparticle catalysts were highly uniform with

small sizes, and the resultant Pd nanoparticles (Pd/SiO2)

display efficient performance in the hydrogenation of fur-

fural to furfuryl alcohol. The resulting Pd/SiO2 nanoparti-

cles did not produce any waste during the reaction and

were easy to be recycled after reaction, which can be

considered as simple and ecofriendly.

Experimental section

Mesoporous SiO2 synthesis

The typical process for mesoporous SiO2 synthesis was

used a modified procedure (Zhao et al. 1998) as follows:

6.0 g triblock copolymer P123 [poly(ethylene glycol)-

poly(propylene glycol)-poly(ethylene glycol)] was dis-

solved in 100 mL of water in a polypropylene bottle at

35 �C for 24 h under stirring conditions of 750 rpm. Sub-

sequently, 4 g of concentrated HCl (37 wt%) was added

into the solution at 35 �C for 24 h, followed by the addition

of *12 g tetraethylorthosilicate (TEOS) at 35 �C. The

suspension was further stirred at 35 �C for 24 h. The

resulted solution was placed into an air oven at 90 �C for

48 h hydrothermal treatment. The obtained solution was

separated through centrifugation of 3,500 rpm and washed

with pure water for three times. After this step, the sample

was dried at 100 �C for 24 h and then calcinated at 550 �C

for 10 h with a heating rate of 120 �C/h.

Preparation of different loadings of Pd supported

on mesoporous SiO2

The typical procedure for catalyst synthesis was performed

as follows: Firstly, a constant amount of mesoporous SiO2

support (*200 mg) and 5 mL ethanol were added into a

25-mL round flask, and the calculated palladium(II) nitrate

was then added into the flask under stirring condition for

24 h. After this process, the catalysts were dried overnight

at 110 �C and then calcined in air at 500 �C for 3 h in air

atmosphere. The obtained solid samples were further

reduced with H2 (10 %) -Ar (90 %) with a speed of

20 mL min-1 at 200 �C for 3 h.

Characterizations of mesoporous SiO2

and the supported Pd catalysts

The powder X-ray diffraction patterns for qualitative phase

analysis were collected on a Rigaku D/max-2500 trans-

mission diffract meter with Cu Ka radiation

(k = 1.5406 A) in transmission geometry with a primary

monochromatic curved germanium (111) and a linear

position sensitive detector with a data set in a continuous

scan mode in the range of 30–75� with a step width of

0.05�/2h.

Transmission electron microscopy (TEM) and energy-

dispersive X-ray analysis (EDX) were used to investigate

structural features and the existence of the resultant Pd

nanoparticles catalysts with a JEOL-2010 instrument.

Nitrogen adsorption data have been measured on an

ASAP 2000 sorption analyzer (Micromeritics) at 77 K. The

samples have been activated under a vacuum of 0.01 mbar

at 200 �C for 10 h prior to measurements. Data evaluation

was performed with the Autosorb 1.52 software package.

The surface area was calculated from the adsorption iso-

therm. Pore size distributions were calculated using the

Barrett–Joyner–Halenda (BJH) method employing models

for nitrogen adsorption on silica with cylindrical pores at

77 K, both for the adsorption and desorption branch of the

isotherms. The total volume (Vp) was estimated from the

adsorbed amount at a relative pressure P/P0 of 0.995.

Catalytic tests in the hydrogenation of furfural

The typical hydrogenation of furfural was performed in a

50-mL autoclave, and the general procedure was as fol-

lows: furfural (0.012 mol) was added into organic solvent

octane (0.03 mol), followed by addition of 105 mg catalyst

into the solution under continuous stirring (1,000 rpm). To

186 Environ Chem Lett (2014) 12:185–190

123

remove most of the air, the autoclave was flushed with

nitrogen for three times before it was pressurized with

hydrogen. After reaction, the autoclave was cooled down to

room temperature in a controlled manner using a water

bath. The product mixture was firstly centrifuged for

30 min and then filtrated over neutral aluminum oxide,

followed by a second filtration and dilution by dichloro-

methane. The subsequent samples were analyzed by GC

(Agilent 6890A, column: 25 m SE-54 G/17, FID). The

column temperature was raised from 40 to 300 �C with a

heating rate 5 �C/min. The injector temperature was set to

360 �C, which was loaded with a sampling volume of

1 lL.

Results and discussion

Catalyst analysis

Fig. 1a shows the X-ray diffraction patterns of the resultant

Pd/SiO2 catalysts with different loadings ranged from 1 to

5 wt%. Because of 1 wt% loading of Pd, it is beyond the

detected limit of the XRD fixture, which was not included

in the Fig. 1. The XRD analysis show very weak peaks of

the fresh 3 wt% Pd/SiO2 (Fig. 1a), indexed as 2h = 40.1�(111) identified as single fcc phase of palladium (JCPDS

card, File No. 46–1,043). By comparison, we found that the

diffraction peak of Pd nanoparticle became more pro-

nounced with Pd loading increasing to 5 wt%. Meanwhile,

the diffraction peaks of Pd indexed at 2h = 47.3� (200) and

70� (220) presented clearly in the case of 5 wt% loading.

Energy-dispersive X-ray (EDX) was further employed

to confirm the existence of Pd nanoparticle and obtain the

information about the brief amount of Pd in the sample.

One representative example of the EDX spectrum of

5 wt% Pd/SiO2 was given in Fig. 1b. The EDX spectrum

detected the peaks positions of Pd, Si, and O, which con-

firmed that the Pd existed in the resulting 5 wt% Pd/SiO2

sample. Besides, no distinct difference of Pd amount was

revealed by the EDX analysis in several different areas,

indicating the uniform dispersion of Pd nanoparticles in the

resulting samples.

N2-BET tests were employed to understand the infor-

mation about the resulting surface area, pore volume and

pore size. The BET surface area was calculated using BJH

(Barrett, Joyner and Halenda) method. The type IV

adsorption isotherm curves were observed in the resulting

mesoporous SiO2 support and the supported 5 wt% Pd,

which indicated that the typical mesoporous materials were

achieved in each case. Fig. 3b shows one representative N2

adsorption–desorption curve of the resultant 5 wt% Pd/

SiO2. It was observed type IV adsorption curve with a H3-

type hysteresis loop (P/P0 [ 0.4), implying the presence of

the ordered mesopores. All samples showed a very large

BET surface area and high pore volume. With Pd loading

increasing, the decent decreases in the surface area and

pore volume were most probably due to the Pd molecule

bonding in the mesochannel of mesoporous SiO2. A high

surface area of 686 m2/g with a pore volume of 0.508 cm3/

g and a pore size of 5.5 nm was obtained in the case of

mesoporous SiO2 (Fig. 2a). With the introduction of Pd

into the skeleton of silicon, it was rational to find that the

surface areas were smaller than the value of mesoporous

SiO2. Increasing Pd loading, the surface area, pore diam-

eters and the total volume decreased clearly (Fig. 2b),

which confirmed that more Pd was confined inside the

mesoporous channel of SiO2.

Transmission electron microscopy analysis was applied

to observe the textural information. TEM images of mes-

oporous SiO2 show the parallel and hexagonal pores in a

clear manner (Fig. 3a). The cross-unit contained several

crystalline domains of diverse size which stacked together.

35 40 45 50 55 60 65 70 75

5 wt%

2θ(Degree)

3 wt%

(220)

(200)

(111) a b

Fig. 1 a X-ray diffraction patterns of the resulting 3 and 5 wt% Pd/SiO2 nanoparticles; b Energy-dispersive X-ray analysis of 5 wt% Pd/SiO2

nanoparticles. X-ray diffraction patterns indicated that all the resulting Pd nanoparticles were successfully synthesized

Environ Chem Lett (2014) 12:185–190 187

123

Representative TEM image of 3 wt% Pd/SiO2 (Fig. 3b)

presented very nice, and small nanoparticles were distrib-

uted inside the mesochannel of mesoporous SiO2. Besides,

hexagonally ordered mesoporous channels were kept stable

after Pd was introduced into the skeleton of mesoporous

SiO2. Moreover, no detectable aggregation of Pd nano-

particles was found, and the mean size of Pd nanoparticles

was less than 5 nm. Increasing the Pd loading to 5 wt%,

representative TEM image of 5 wt% Pd/SiO2 (Fig. 3c)

indicated that the detectable aggregation of Pd nano-

particles, and bigger particles were distributed across the

mesochannel of SiO2. Besides, hexagonally ordered meso-

porous channels were kept stable after Pd was introduced

into the skeleton of mesoporous SiO2.

Catalytic hydrogenation of furfural

The successfully fabricated Pd/SiO2 nanoparticles catalysts

were used for the hydrogenation of furfural; the catalytic

results were summarized in Table 1. It was found the Pd

loading has clear influence on the catalytic activities,

whereby furfuryl alcohol was mainly produced. It con-

firmed that the hydrogenation of furfural using Pd nano-

particles catalysts was more preferred to occur on the

carbonyl (C=O) group to form furfuryl alcohol and further

on the conjugated (C=C–C=C) system to produce THFA

(Yan et al. 2013a, b), where the small and uniform size of

Pd would play an important role. In terms of conversion, it

was found the conversion of furfural (from 37.1 to 75 %)

increased clearly with the loading of Pd increasing from 1

to 5 wt% (No. 2–4). In the comparative reaction using the

SiO2 support as catalyst (No. 1), only 7 % conversion was

achieved and no detectable products were found, which

strongly argued for the introduction of Pd nanoparticle had

crucial effect on the catalytic activities. However, with the

loading increasing to 5 wt% (Table 1, No. 4), 70.9 %

selectivity of furfuryl alcohol with 18.1 % selectivity of

THFA was achieved. Much higher selectivity of THFA

was achieved, which confirmed that the higher loading of

Pd nanoparticles was good for deep hydrogenation, possi-

bly due to better H2 transportation in this case. In com-

parison with previous works from literatures (Yan et al.

0.0 0.2 0.4 0.6 0.8 1.050

100

150

200

250

300

Vol

ume(

cc/g

)

P/P0

Surface area: 686 m²/gPore diameter: 5.5 nmPore volume: 0.508 cm3/g

0.0 0.2 0.4 0.6 0.8 1.080

120

160

200

240

280

Vou

me(

cc/g

)

P/P0

Surface area: 415 m²/gPore diameter: 4.1 nmPore volume: 0.405 cm3/g

a bFig. 2 N2 adsorption–

desorption curves of the

mesoporous SiO2 (a) and 5 wt%

Pd/SiO2 (b). N2 adsorption–

desorption tests display type IV

adsorption curve with a H3-type

hysteresis loop, implying the

presence of the ordered

mesopores. With the

introduction of Pd into the

skeleton of silicon, the surface

area, pore diameters and the

total volume decreased clearly

100 nm

a

100 nm

b c

100 nm

Fig. 3 Transmission electron microscopy (TEM) images of the

support and the Pd nanoparticle catalysts: mesoporous SiO2 (a),

3 wt% Pd/SiO2 (b), 5 wt% Pd/SiO2 (c). TEM images indicated that

hexagonally ordered mesoporous channels were kept stable after the

introduction of Pd in the skeleton of mesoporous SiO2

188 Environ Chem Lett (2014) 12:185–190

123

2013a, b; Kijenski et al. 2002; Li et al. 2003; Lange et al.

2012), to our limited knowledge, our results are among the

top list. Besides, our catalyst was easy to be fabricated,

which is potential for wide application.

Conclusion

Different loadings of Pd nanoparticles was successfully

confined inside the mesoporous channel of SiO2 by a mod-

ified wet-impregnation method using a cheap palladium

nitrate. XRD characterization confirmed the successful

introduction of Pd nanoparticles inside the mesochannel of

SiO2, and the supported Pd nanoparticles would not change

or influence the skeleton of mesoporous SiO2. Besides, it was

found very nice, and homogeneous distribution of Pd nano-

particles was achieved when the Pd loading was less than

5 wt% as confirmed by TEM. With the Pd loading increasing

to 5 wt%, clear aggregation and bigger size of Pd nanopar-

ticles were observed. The resultant Pd/SiO2 catalysts pre-

sented efficient performance in the hydrogenation of

biomass-derived furfural, furfuryl alcohol was selectively

produced under mild conditions, whereby 71 % furfuryl

alcohol was achieved at 75 % conversion of furfural.

Acknowledgments This work was supported by the Fundamental

Research Funds from the University and development projects in

Shanxi Province (200811027).

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Table 1 Catalytic evaluation of the resulting Pd/SiO2 with different loadings

Furfural

O

O

Furfuryl alcohol

OOH

OOH

+ H2

THFA

+H2

No. Catalyst Conv./% S1/% S2/% Sothers/%

1 Mesoporous SiO2 6.9 0 0 0

2 1 wt% Pd/SiO2 37.1 80.8 4.5 14.7

3 3 wt% Pd/SiO2 65.2 76.9 9.6 13.5

4 5 wt% Pd/SiO2 75.0 70.9 18.1 11.0

All the resulting Pd/SiO2 catalysts display high selectivity toward the formation of furfuryl alcohol

Reaction note, S1: the selectivity of furfuryl alcohol, S2: the selectivity of tetrahydrofurfuryl alcohol (THFA), Sothers: the selectivity of all the

other compounds

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