Catalysis Today 172 (2011) 132 135

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Catalysis Today

j ourna l ho me p ag e: www.elsev ier .com

IR stud es bio-fue

Andrey P nceFrancoiseLaboratoire Ca , 1405

a r t i c l

Article history:Received 30 NReceived in reAccepted 4 FebAvailable onlin

Keywords:HydrodeoxygeIR spectroscopSulded CoMoPhenolCarbon monox

ed su interadingn alumcessired byditioningde sl

shoul

1. Introduction

In order to develop sustainable transportation fuels, the contri-bution of biomass derived feedstocks is set to grow above todayslevels. For eing with throute. One waste and biomass). Soxygenatedtion (HDO) catalysts likin the hydrcandidates tions [38].in pyrolyticobserved duin pioneerindeactivationdene the d

We repoadsorption properties l

CorresponE-mail add

proposed for hydroprocessing catalysts, (ii) alumina supported sul-ded CoMo catalysts. In addition, the accessibility of the catalystssites after phenol adsorption is monitored by IR spectroscopy ofadsorbed CO.

0920-5861/$ doi:10.1016/j.thical reasons, the use of raw materials not compet-e food production chain should be the most preferredoption is to produce biofuels by pyrolysis of organiclignocellulosic plant material (i.e. second generationince these pyrolytic oils contain very large quantities of

compounds (up to 40 wt% O), their hydrodeoxygena-is a way to produce stable fuels [1,2]. Hydroprocessinge the supported sulded ((Co,Ni)Mo) catalysts usedodesulfurization (HDS) of oil fractions could be goodif their deactivation can be limited under HDO condi-

The high concentration of phenolic compounds found oils (220 wt%) was related to the fast deactivationring their HDO on the supported sulded catalysts usedg studies [3]. Our goal is to identify the cause of catalyst

during HDO of phenolic compounds in order to betteresign rules of effective HDO catalysts.rt the use of infrared (IR) spectroscopy to determine themodes of phenol on (i) oxides with different acidbaseike alumina and silica, they are the supports commonly

ding author. Tel.: +33 231 452 824; fax: +33 231 452 822.ress: francoise.mauge@ensicaen.fr (F. Maug).

2. Experimental

2.1. Materials

The silica sample is an Ultrasil 7000 (from Evonik) with a surfacearea of 173 m2 g1. The alumina is a CatapalC (from Grace Davison)with a surface area of 292 m2 g1. The CoMo/Al2O3 catalyst (9.2%Moto 4.2% Co) is prepared by a classical impregnation using hepta-molybdate ammonium and cobalt nitrate deposition on alumina(from Sasol) with a surface area of 255 m2 g1. Phenol is suppliedby Prolabo (purity 99.5%).

2.2. Infrared spectroscopy

Each sample is pressed into a self-supported disc (10 mg,2 cm2). The disc is introduced in the infrared cell for in situ sul-dation. The sample is rst dried under an Ar ow (30 ml/min) for0.5 h at 423 K and, then cooled down to 298 K. The catalyst is thensulded under an H2S (10%)/H2 (30 ml/min) ow up to 623 K (rampof 3 K/min). After 1 h of suldation at 623 K, the sample is evacuatedat the same temperature.

see front matter 2011 Elsevier B.V. All rights reserved.cattod.2011.02.010y of the interaction of phenol with oxidl hydrodeoxygenation

opov, Elena Kondratieva, Jean-Pierre Gilson, Laure Maug

talyse et Spectrochimie, ENSICAEN Universit de Caen CNRS, 6, Bd du Marchal Juin

e i n f o

ovember 2010vised form 1 February 2011ruary 2011e 22 March 2011

nationy/Al2O3

ide

a b s t r a c t

The adsorption of phenol on supportspectroscopy. On silica, phenol mainlyon the acidbase pairs of this oxide lea sulded CoMo catalyst supported ostrongly with the sulde phase. The acinvestigated by CO adsorption monitothe accessibility of support sites. In adThis is indicative of an indirect poisothe support and in the vicinity of sulacidbase paired sites of the support / lo cate /ca t tod

and sulded CoMo catalysts for

Mariey, Arnaud Travert,

0 Caen, France

lde CoMo catalysts and on oxides is investigated using IRacts via hydrogen-bonding, whereas on alumina it dissociates

to the formation of strongly adsorbed phenolates species. Onina, phenol dissociates on the support but does not interact

bility of the various sites of the catalyst after phenol contact is IR spectroscopy. As expected, phenolate formation decreasesn, a decrease of the sulde site accessibility is also observed.

of the sulde edge sites by phenolate species anchored onabs. Consequently, decreasing the amount or strength of thed be a way to limit deactivation.

2011 Elsevier B.V. All rights reserved.

A. Popov et al. / Catalysis Today 172 (2011) 132 135 133

After activation in the IR cell, calibrated doses (from 0.015 molto 0.775 mol) of phenol are introduced stepwise on the oxides andthe sulde catalyst. The nal equilibrium pressure in the infraredcell is set to 20 Pa. Afterwards, the cell is evacuated at 298 K for15 min. In another set of experiments, a phenol pressure of 20 Pa isintroduced directly on the samples at 623 K, followed by evacuationat the same temperature for 15 min.

In order to evaluate the interaction of phenol with the suldephase, CO is adsorbed before and after phenol introduction. Again,calibrated doses of CO are introduced on the sample, at 100 K,followed by a desorption stage from 100 K up to 298 K.

The infrared spectra are recorded with a FT-IR spectrometerNicolet Magna AEM equipped with a MCT detector (64 scans, reso-lution 4 cm1, zero lling 1 level). All the spectra are normalizedto a mass of 5 mg cm2.

3. Results and discussion

3.1. Phenol adsorption on silica

Fig. 1 shows the adsorption of phenol on silica at 298 K (spec-trum a). Table 1 reports assignments based on work reportedelsewhere [9,10]. The adsorption of phenol on silica leads to bandsat 1599 cm1 (with a shoulder at 1606 cm1) and 1500 cm1assigned to (CC) ring vibrations. Bands at 1474 and 1360 cm1

contain a signicant contribution of (OH) vibration (20%). Notethat the band at 1474 cm1 is generally attributed to (CC) ring

1597

1498

1470

1606

1360

1344

1474

14961599

1500

0.5

a

b

c

PhOHin CC l4

Fig. 1. Infrareat room tempwith phenol in

Table 1Assignments o

Assignment

(OH) (CHring) (CH3) (CCring) (CCring) (CCring) (CCring) + (CH3)(CCring) + (CCring) + X-sensitive (

a Assignmen

vibrations [9,10]. However, this mode includes a (OH) contribution(15%), also observed (not shown) on the spectra recorded withdeuterated phenol (OD position). These characteristic (OH) vibra-tions highlight the presence of molecular phenol. After evacuationat 373 K (spectrum b), an important part of the perturbed SiOHbands disappears along with those at 1474 and 1360 cm1. How-ever, the bands characteristic of (CC) ring vibrations at 1599 cm1

and 1496 cm1 remain. They are still present even after evacuationat 673723 K (spectrum c). The OH region of silica shows that theband at 3745 cm1 (silanol groups) shifts to lower wavenumbers,giving rise to two broad components at 3620 and 3490 cm1. Evac-uation at 373 K almost completely removes, these perturbed SiOHgroups.

The IR spectrum of phenol absorbed on silica indicates a hydro-gen bonded interaction (Fig. 1). This is substantiated by: (i) thepresence of phenol (OH) bands and the shift of the 1344 cm1

band to 1360 cm1 with a broadening and splitting into severalcomponents, (ii) a decrease of the SiOH band intensity with theappearance of several new bands corresponding to perturbed SiOHbands, (iii) the restoration of a signicant fraction of the silanolband after evacuation at 373 K. In conclusion, at room temperature,the predominant adsorption mode of phenol on silica is hydrogenbonding.

3.2. Phenol adsorption on alumina

The infrpresents bamatic ring presented hnot observeappears at tion at 373(1300 to 12similar for t

Fig. 2 shto the forming to aromvibrations ((OH) groupcoverage aence of two

95/1and

0

b

PhOin C

c

a

frare tempenol in1300 1400 1500 1600 Wavenu mbers (cm-1)

d spectra of phenol adsorbed on silica. Equilibrium pressure of 20 Paerature (a); after evacuation at 373 K (b), and 673 K (c). Comparison

CCl4.

f the IR bands of liquid phenol.

Phenol

361030743021160816001502

(OH)a 1473a

(OH), polymer 1362(OH), monomer 1344(CCring) + (CO)) 1259

t based on experiments with deuterated molecules.

and 12mono-

Fig. 2. Inat roomwith phared spectrum of phenol adsorbed on alumina (Fig. 2a)nds at 1597, 1498/1492 cm1, characteristic of aro-vibrations. For small amounts of phenol adsorbed (notere), the (OH) bands at 1470 and 1340 cm1 ared. With increasing phenol coverage, only a shoulder

1470 cm1 (spectrum a) and disappears after evacua- K (spectrum b). A multi-component (CO) broad band30 cm1) develops also [2,3]. These observations arehe two alumina sources (Grace Davison and Sasol).ows that the interaction of phenol with alumina leadsation of phenolate species. Indeed, bands correspond-atic rings (1597 and 1498/1492 cm1), and to (CO)1295/1250 cm1) appear, while those characteristic ofs (at 1470 and 1340 cm1) are absent, except at high

nd with a very low intensity (spectrum a). The pres- different components in the (CO) band (1498/1492250 cm1) suggests the formation of two phenolates,bi-dentate, as illustrated in Fig. 3.

1200 1300 1400 1500 1600

Wavenu mbers (cm-1)

.5 ua

HCl4

1597

1498

1492

1295 1250

14701344 1259

d spectra of phenol adsorbed on alumina. Equilibrium pressure of 20 Paerature (a); after evacuation at 373 K (b), and 673 K (c). Comparison

CCl4.

134 A. Popov et al. / Catalysis Today 172 (2011) 132 135

Al Al

O

Al Al

O

1295 cm-1

I II

1250 cm-1

Fig. 3. Structure of phenolates species on alumina.

3.3. Phenol adsorption on a sulded catalyst

Phenol was adsorbed on sulded CoMo/Al2O3 at 623 K (Fig. 4).The spectra display the same main bands positioned at 1597 cm1,1498/1492 cm1 ((CC) ring vibrations) and 1296/1245 cm1

((CO) vibrations) as observed on alumina alone. The absence ofbands at 1470 and 1340 cm1, characteristic of a (OH) vibra-tion, indicates the formation of phenolate species on alumina alone.Moreover, the normalization of the spectra to the most intenseband (see Fig. 4 insert) conrms the similarity in the (CO) regionbetween the two samples. This indicates that there is no struc-tural difference between the phenolate species formed on suldedCoMo/Al2Oof phenol aCoMo/Al2Ophenolate stion of alumon the sulders at 1564on the suld

Al2O3

OMoS2 MoS2 OMoS2O

Fig. 5. Phenol interaction on sulded CoMo/Al2O3.

adsorption at RT on the sulded catalyst and indicate that phenolreacts with the sulde phase at high temperature.

3.4. Phenol and CO co-adsorption on the sulded catalyst

On sulded CoMo/Al2O3, CO adsorption is characterized bybands at 2188, 2156, 2110, 2070 and 2055 cm1 (Fig. 6). The bandat 2188 cm1 corresponds to the interaction of CO with Lewis acidsites of alumina (LAS Al3+) and the one at 2156 cm1 to its interac-tion with hydroxyl groups. The other bands characterize the suldephase. The one at 2110 cm1 is due to the adsorption of CO on non-promoted Mo sites, while those at 2070 and 2055 cm1 belong toCO on Co promoted sites [11].

CO adsorption on sulded catalysts in interaction with phe-nol shows a signicant decrease in the accessibility of the supportsites. The intensity decrease of the band of CO adsorbed on LAS isexpected, since the formation of phenolates on alumina involvesAl3+ sites. In addition, phenolate formation on the alumina sup-port should indirectly perturb OH groups and therefore limit theinteraction CO/OH (decrease of the band at 2110 cm1).

The IR spectra also show a decrease in the accessibility of the phase: both bands characteristic of CO adsorption on Co-ted aspec

phas in tde

the p not

Fig. 4.3 and on pure alumina. However, the adsorption bandsre clearly less intense (about 3040%) on the sulded3 catalyst than on pure alumina. This implies that thepecies on the sulded catalyst are located on the frac-ina support not covered by the sulded phase and notde phase, as described in Fig. 5. Two additional shoul-

and 1450 cm1, not present on alumina alone, appeared CoMo/Al2O3 catalysts. They are absent after phenol

suldepromoof the suldespeciethe sultion toshould

1597

1498

0.1

A1200 1400 1600

Wavenumbers (cm-1)

12961245

Infrared spectra of phenol adsorbed on alumina (a) and sulded CoMo/Al2O3 (b) after adnd unpromoted sulde sites decrease. Since the analysistra does not indicate any interaction of phenol withse (Fig. 4), we propose that the presence of phenolatehe vicinity of the support prevents the access of CO tophase sites. The carbonaceous species, formed in addi-henolates species, in the static conditions reported herebe considered as poisons because they are not detected

a

1200 1400 1600 Wavenu mbers (cm-1)

CoMo/Al2O3

Al2O3

spectra normali zed to the height of the most intense bandb

sorption of 20 Pa of phenol followed by evacuation at 673 K.

A. Popov et al. / Catalysis Today 172 (2011) 132 135 135

1950 2000 2050 2100 2150 2200Wavenumbers (cm-1)

b

a2188

21562110

2070

2055Mo

CoMo

Al3+

OH

Fig. 6. Infrared spectra of CO adsorbed on sulded CoMo/Al2O3, before adsorptionof phenol (a), and after adsorption and desorption of phenol at 623 K (b).

on used catalysts tested under ow conditions of HDO of modelmolecules [12].

4. Conclusion

The adsorption mode of phenol on oxides such as silica or alu-mina is related to their acidbase properties. On silica, phenolinteracts mainly via hydrogen-bonding, whereas on alumina it dis-sociates on acidbase pairs leading to the formation of stronglyadsorbed phenolates species. On a sulded CoMo catalyst sup-ported on alumina, phenol dissociates on the support but does notstrongly interact with the sulde phase. As expected, the accessibil-ity of suppo

a decrease of the accessibility of the sulde sites is also observed;it is accounted by an indirect poisoning of the sulde edge sites byphenolate species anchored on the support and in the close vicin-ity of sulde slabs. As a practical consequence, a modulation (i.e.decrease) of the amount or strength of the acidbase pairs of thealumina support could be a way to limit deactivation by phenol.Recent results obtained using more complex phenolic compoundssuch as guaiacol, lead to similar conclusions [12]. This study is oneof the rst steps in the rational design of more efcient and stableHDO catalysts of pyrolytic oils. However, each step from a funda-mental understanding of materials to a working catalyst with realfeedstocks should be monitored by catalytic testing with modeland synthetic feedstocks in order to validate the pertinence of allspectroscopic characterizations.

Acknowledgement

This work is funded by the French ANR Programme National deRecherche sur les Bionergies ECOHDOC, a joint project betweenthe Centre National de la Recherche Scientique (CNRS), the uni-versities of Caen, Lille and Poitiers and TOTAL.

References

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(2000) 247.[10] J.C. Evans, Spectrochim. Acta 16 (1960) 1382.[11] F. Maug, J.C. Lavalley, J. Catal. 137 (1992) 69.[12] A. Popov, E. Kondratieva, J.M. Goupil, L. Mariey, J.P. Gilson, A. Travert, F. Maug,

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rt sites is decreased after phenol adsorption. Moreover,

IR study of the interaction of phenol with oxides and sulfided CoMo catalysts for bio-fuel hydrodeoxygenation1 Introduction2 Experimental2.1 Materials2.2 Infrared spectroscopy

3 Results and discussion3.1 Phenol adsorption on silica3.2 Phenol adsorption on alumina3.3 Phenol adsorption on a sulfided catalyst3.4 Phenol and CO co-adsorption on the sulfided catalyst

4 ConclusionAcknowledgementReferences