IntroductionIn the recent years, many efforts have been made in the field of transformation the renewable resources into value added

chemicals. New starting materials, so called „platform molecules” are expected to supply fossil resources and contribute to a sustainable chemistry [1]. Glycerol obtained from biomass represents one of the twelve platform molecules proposed by U.S. Department of Energy [2]. Palladium, platinum and gold particles in liquid phase oxidation of glycerol have been the subject of intensive studies. The most common supports for the metal particles are activated carbon and graphite [1,3].

In several cases metal oxides (TiO2, CeO2 and Al2O3) were employed [4]. Recently, Prati et al. [5] have demonstrated liquid

phase oxidation of glycerol in the presence of Au species supported into macroporous resin Dowex M-43. Au nanoparticles stabilized by tetrakishydroxypropyl-phosphonium chloride on support showed better activity than Au particles adsorbed on Dowex M-43.

In the present work macroporous and microporous poly(styrene-co-divinylbenzene) ion exchange resins as supports for Pd-Bi particles in liquid phase oxidation of glycerol in batch and fixed bed reactor were compared.

ExperimentalCatalyst preparationCatalyst preparation The Dowex 1x4 anion exchanger was metallated by ion exchange method using solution of PdCl2 and BiCl3 in aqueous HCl. The macroporous resins (Dowex66, DowexSD2) were impregnated with solution of [PdCl4]2- and [BiCl4]- in aqueous HCl for 24 h. The metallated resins were reduced with sodium borohydride dissolved in a mixture of water and isopropanol for 1 h at laboratory temperature with occasional stirring.Catalytic reactionsCatalytic reactions The glycerol oxidation was carried out under atmospheric pressure in a thermostated semi-batch glass reactor equipped with a magnetic stirrer, inlet for nitrogen or oxygen and pH-meter. A jacketed tubular glass reactor heated by water and equipped with feed lines for aqueous solution of glycerol (NaOH/glycerol=2 mol/mol) and molecular oxygen or nitrogen, an output line cooled by water was used.Samples were analyzed by high performance liquid chromatography on an Alltech OA-1000 column with 0.1 N aqueous H2SO4 as eluent using a SPD 10AVp (210 nm) and RID-10A detectors.FTIR measurementsFTIR measurementsTransmission IR spectra were recorded on Shimadzu IRAffinity FTIR Spectrometer equipped with Specac Golden Gate TM in the range 4000-570 cm-1 at room temperature.

ResultsCommercial poly(styrene-co-divinylbenzene) anion-exchange resins with different

surface areas 7 and 800 m2/g (Dowex 1x4 and Dowex Optipore SD-2) and with varied

total swelling from 5 to 20% (Dowex Optipore SD-2 and Dowex 66) were used as

support for palladium and bismuth nanoparticles (NPs). The macroporous ion-

exchange resins with tertiary ammonium groups were compared with the microporous

gel-type resin containing quaternary ammonium groups.

Oxidation of glycerol with molecular oxygen in the liquid phase over the supported Pd-

Bi catalysts in batch and fixed bed reactors were studied. The reactions at

temperature of 50C were carried out in alkaline region adjusted by caustic soda. The

type of the support used strongly influenced the activity and selectivity of the

catalysts in both batch and fixed bed reactors. As it is shown in Figure 1, the glycerol

(GLY) conversion over the Pd-Bi NPs loaded on macroporous resins in batch reactor is

more than twofold higher than that in the fixed bed system. On the other hand, higher

selectivity to glyceric acid (GLYA) and tartronic acid (TARA) formation in fixed bed

reactor was observed.

Figure 1 Influence of reactor configuration (batch (B) and fixed bed (FB)) on the activity and selectivity of the Pd-Bi nanoparticles loaded into different supports

AcknowledgementsThis work was supported by the Slovak Research and Development Agency under the contract No.

APVV-0133-11 and ERDF under the contract No. HUSK/1101/1.2.1/0318

References[1] P. Gallezot, Catal. Today, 2007, 121, 76- 86;[2] F. Ma, M. A. Hanna, Bioresource Technology, 1999, 70, 1-15;[3] L.Bianchi, N. Dimitratos, F. Porta, L. Prati, Catal. Today, 2005, 102, 212;[4] I. Sobczak, K. Jagodzinska, M. Ziolek, Catal. Today, 2010, 158, 121-129;[5] A. Villa, C. E. Chan-Thaw, L. Prati, Applied Catal. B: Environ., 2010, 96, 547.

The reactor configuration had almost no influence on the activity and

selectivity of the Pd-Bi NPs loaded on microporous gel type resin. In this

case, 32 % selectivity to GLYA at the conversion of glycerol more than

93% was obtained at the temperature of 50°C. Decreasing the

temperature to 40°C in fixed bed reactor led to increasing the selectivity

of GLYA to 55% at unchanged 16.5% selectivity to TARA. Under these

conditions the conversion of glycerol about 85 % was reached. It implies

that at lower temperature the consecutive oxidation of GLYA to TARA is

lower, the overoxidation of TARA is not so significant, moreover loss of

the catalyst activity expressed by glycerol conversion is not too

substantial.

Changes in the chemical structure of used supports after the precursors

preparation and their reduction with sodium borohydride under the

chosen conditions were studied by infrared spectrometry.

Figure 2 Catalytic performance of Pd-Bi NPs supported onto Dowex 1x4 at 40°C in fixed bed reactor

As it is shown in Figures 3 A,B and C, the spectra do not exhibit noteworthy

variations of the vibration bands for the individual supports, precursors and the

prepared catalysts.

Figure 3 FTIR spectra of supports, precursors and prepared catalysts for Dowex SD-2 (A), Dowex 1x4 (B) and Dowex 66 (C)

ConclusionsThe Pd-Bi particles supported onto commercial poly(styrene-co-divinylbenzene) gel type

strong anion-exchange resin containing quaternary ammonium groups prepared by ion-

exchange method showed better catalytic performance than those particles obtained by

adsorption on macroporous resins with tertiary amine groups.

Activity and selectivity of Pd-Bi NPs supported onto Dowex 1x4 remained almost the same

during the 8 h of time on stream.

No significant changes of supports were observed after the precursors and reduced

catalysts preparation in IR spectra.