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Catalysis Today 227 (2014) 45–49

Contents lists available at ScienceDirect

Catalysis Today

j our na l ho me page: www.elsev ier .com/ locate /ca t tod

rønsted acidity of H-MCM-22 as probed by variable-temperaturenfrared spectroscopy of adsorbed CO and N2

ontserrat R. Delgadoa,∗, Roman Bulánekb, Pavla Chlubnác, Carlos O. Areana

Department of Chemistry, University of the Balearic Islands, 07122 Palma de Mallorca, SpainDepartment of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, 532 10 Pardubice, Czech RepublicJ. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, 182 23 Prague, Czech Republic

r t i c l e i n f o

rticle history:eceived 27 June 2013eceived in revised form0 September 2013ccepted 16 September 2013vailable online 12 October 2013

eywords:dsorptionydrogen bonding

a b s t r a c t

Brønsted acidity is a key factor controlling catalytic performance of zeolites in many technological pro-cesses, and hence the need to find a reliable means for measuring acidity strength. The enthalpy change,�H0, involved in the hydrogen bonding interaction between a weak base, such as carbon monoxideor dinitrogen, and the Brønsted acid [Si(OH)Al] hydroxyl groups should correlate with the zeolite acidstrength. However, on account of simplicity, the red shift of the O H stretching frequency, ��OH, in thehydrogen-bonded OH· · ·CO or OH· · ·N2 complexes is frequently measured (instead of �H0) and correlatedwith acid strength; and in fact it is often found that �H0 and ��OH correlate among themselves, but thismight not always be the case. We report herein on a variable-temperature IR (VTIR) spectroscopic studyof the interaction of CO and N2 with the protonic zeolite H-MCM-22 (structure type MWW). From series

R probe moleculesR spectroscopyeolite acidity

of infrared spectra taken over a temperature range, the standard enthalpy of formation of the OH· · ·COand OH· · ·N2 complexes was found to be −23.5(±2) and −14.5(±2) kJ mol−1, respectively. Corresponding��OH values are −321 and −123 cm−1, respectively. Comparison with corresponding �H0 and ��OH val-ues reported in the literature for other Brønsted-acid zeolites shows strong evidence of a limited validityof the rule correlating ��OH with �H0 for both probe molecules, which gives a clear warning about therisk of using the magnitude of ��OH as a measure of zeolite acidity.

. Introduction

Zeolites having the structural unit Si(OH)Al where a protons attached to an skeletal oxygen atom that bridges tetrahedrallyoordinated Si and Al atoms (T atoms) show distinctive Brønstedcidity, and they find vast application as solid acid catalysts in aide range of technological processes, spanning from the petro-

hemical industry to the (environmentally benign) manufacture ofne chemicals [1–11]. In many of those processes, fine control ofhe Brønsted acid strength is a key factor to optimize catalytic per-ormance (activity and selectivity). Nevertheless, fine details aboutuch a control are far from being well understood, although there is

broad agreement that main factors determining acid strength ofridging hydroxyl groups are their specific location, zeolite struc-ure and Si:Al ratio [12–15].

Another critical point in this field is the way in which Brønsted

cidity of zeolites is defined and measured [16–19]. In contrast toqueous acid solutions, where the corresponding pKa gives a quan-itative measure of acid strength, no clear cut measurement has

∗ Corresponding author. Tel.: +34 971172633; fax: +34 971173426.E-mail address: montserrat.rodriguez@uib.es (M.R. Delgado).

920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.cattod.2013.09.013

© 2013 Elsevier B.V. All rights reserved.

yet been found for solid acids, for which the notion of a homo-geneous proton accepting (and solvating) medium is no longerapplicable; and it is the interaction between the protonated base(proton accepting species) and the (local) negatively charged zeo-lite framework what largely compensates for the heterolytic O Hbond dissociation energy. Despite those limitations, and in orderto be practical, several instrumental techniques are currently usedto gather increasing information on the (relative) Brønsted acid-ity of zeolites [20]. Among them, calorimetry of an adsorbed base(such as ammonia or pyridine), temperature programmed desorp-tion and solid state NMR and IR spectroscopy; sometimes combinedwith catalytic tests of acid strength [18,21,22].

Regarding IR spectroscopy, Brønsted acidity of zeolites is fre-quently correlated with the magnitude of the red shift of O Hstretching frequency, ��OH, of the involved OH acidic group wheninteracting (at a low temperature) with an adsorbed weak baseby hydrogen bonding [19,23,24]. Since ��OH is directly measur-able from the corresponding IR spectra, this method has the meritof simplicity; however its use is not free from some controversy,

as recently pointed out by Hadjiivanov et al. [25,26]. We reportherein on a variable-temperature IR (VTIR) spectroscopic study ofthe interaction of CO and N2 with the protonic zeolite H-MCM-22 (structure type MWW, Si:Al ratio 24.5:1). The VTIR method

4 lysis Today 227 (2014) 45–49

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nables one to perform simultaneous measurement of ��OH andH0, the enthalpy change involved in the hydrogen bonding inter-

ction [27,28], which should correlate with Brønsted acidity of thenvolved Si(OH)Al groups. Note also that carbon monoxide andinitrogen are probe molecules frequently used for IR spectro-copic characterization of both, basic [29–33] and Brønsted acideolites [34–37]. The results are discussed in the broader con-ext of relevant data available in the literature for other protoniceolites.

. Materials and methods

.1. Sample preparation

The NH4-MCM-22 sample used was synthesized following therocedure described in detail elsewhere [38]. Briefly, the parentaterial, Na-MCM-22P, was prepared from a synthesis gel consist-

ng of 1.16 g of NaOH dissolved in 251.2 g of water, to which 1.68 gf sodium aluminate and 62 g of colloidal silica (LUDOX AS 30) weredded; to the gel thus obtained, 17.2 g of hexamethylenimine wasdded as a template. The final mixture was stirred for 2 h at roomemperature, and then charged into a Teflon-lined steel autoclavehere crystallization proceeded at 423 K under agitation and auto-

eneous pressure for 5 days. The solid product was collected byltration, washed with distilled water and dried at 333 K overnight.he solid was then calcined at 813 K for 6 h with a temperatureamp of 2 K min−1. The thus obtained Na-MCM-22 zeolite was ion-xchanged into the NH4

+ form by treating it four times with a 1.0 MH4NO3 solution for 4 h at room temperature, 100 mL of solutioner 1 gram of zeolite. The Si:Al ratio of the zeolite was 24.5:1. Theoncentration of Brønsted acid sites was determined by quanti-ative analysis of ammonia evolved from the NH4

+ form of theeolite during ammonia temperature programmed desorption, andesulted to be 0.395 mmol g−1. Crystallinity of the 3D structure washecked by powder X-ray diffraction on a Bruker D8 X-ray powderiffractometer equipped with a graphite crystal monochromatornd a position sensitive detector (Våntec-1), using CuK� radiationat 40 kV and 30 mA) in a Bragg–Brentano geometry.

.2. Variable-temperature IR spectroscopy (VTIR)

For VTIR spectroscopy, a thin self-supported wafer of the NH4-CM-22 sample was prepared and subjected to thermal treatment

n a dynamic vacuum (residual pressure smaller than 10−4 mbar)or 4 h at 663 K inside an IR cell, described elsewhere [39], whichllowed in situ sample treatment, gas dosage and variable temper-ture IR spectroscopy to be carried out. After sample outgassinghe cell was dosed with 0.2 Torr of helium (to improve thermalontact between the cell body and the sample wafer) and cooledith liquid nitrogen. After recording the background spectrum at

7 K the cell was dosed with either carbon monoxide or nitrogennd closed, and series of IR spectra were recorded upon gradualarming up of the IR cell. Simultaneously, temperature and gas

quilibrium pressure inside the cell were registered by using a plat-num resistance thermometer (Tinsley) and a capacitance pressureauge (MKS, Baratron). Pressure correction (for helium) was deter-ined from a calibration plot as described elsewhere [40]. Precision

f these measurements was better than ±10−2 mbar and ±2 K forressure and temperature, respectively. Transmission FTIR spectraere recorded, at 2 cm−1 resolution, on a Bruker IFS66 spectrome-

er, accumulating 64 scans for each spectrum.Assuming Langmuir-type gas adsorption, series of IR spec-

ra obtained over a relatively large temperature range can besed [27,28] to determine the corresponding standard adsorption

Fig. 1. X-ray diffraction pattern (CuK� radiation) of the H-MCM-22 sample; onlythe main diffraction peaks are indexed.

enthalpy, �H0, and entropy, �S0, of the gas adsorption process byusing Eq. (1):

ln

[�

[(1 − �)p]

]= −�H0

RT+ �S0

R(1)

Note that in the present case, for any given temperature (T) andcorresponding gas equilibrium pressure (p) inside the closed IR cell,the corresponding value of coverage (�) can be directly determinedfrom the integrated intensity of the characteristic IR absorptionband (O H stretching mode) of the Brønsted acid Si(OH)Al group,which results (partially) eroded upon formation of hydrogen-bonded OH· · ·CO (or OH· · ·N2) adsorption complexes [27].

3. Results and discussion

Fig. 1 shows the XRD pattern (CuK� radiation) of H-MCM-22. ForCuK� radiation, the main fingerprint region of the MCM-22 groupof zeolites comes in the range 5–10◦, 2�. The main reflections inthis region are centred at 7.2◦, 8.1◦ and 10.2◦ (2�) and correspondto planes (1 0 0), (1 0 1) and (1 0 2), respectively. Clear separation of(1 0 1) and (1 0 2) diffraction peaks, together with absence of (0 0 1)and (0 0 2) peaks, suggest a well-ordered 3D-structure [41–43], andgood crystallinity was also confirmed by the sharpness of the maindiffraction peaks.

As shown in Fig. 2 (bottom inset) the blank spectrum of H-MCM-22 displays characteristic IR absorption bands at 3750 and3626 cm−1 arising, respectively, from silanols and from bridgedSi(OH)Al hydroxyl groups which constitute the zeolite Brønstedacid sites [44,45]; no bands from ammonium ions were seen, thusproving complete transformation of NH4-MCM-22 into H-MCM-22 during thermal treatment of the NH4-MCM-22 zeolite wafer.Several authors [46–49] have pointed out that the (clearly dis-symmetric) band at 3626 cm−1 can be resolved into two or threecomponents. In fact, Garrone et al. [46] used computer resolu-tion to simulate the band envelope as the addition of three bands,at 3628, 3618 and 3585 cm−1, which they tentatively assigned tobridged hydroxyl groups located inside the supercages, in the 10-membered ring channels and in the double six-membered ringsconnecting supercages, respectively. Recent calculations (using

DFT, with the B3LYP functional, applied to cluster models) by Zhouet al. [50] gave the �OH values, 3628, 3618 and 3592 cm−1 (cor-rected with a scaling factor) for the hydroxyl groups of the threemost preferable Brønsted acid sites of H-MCM-22; the first two

M.R. Delgado et al. / Catalysis Today 227 (2014) 45–49 47

3000320034003600-0,2

-0,1

0,0

0,1

0,2

320034003600

210021502200

98765432

1

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87

654

1

3

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orba

nce

Wavenumber (c m-1)

3626

3305

2

0,1a.u.

36263750

0,05a.u.

2174

2139

Fig. 2. Representative variable-temperature IR spectra (O H stretching region) ofCO adsorbed on H-MCM-22. The spectra are shown in the difference mode (zeoliteblank subtracted). From 1 to 9, temperature goes from 168 to 221 K; and equilibriumpressure from 5.40 to 6.02 mbar. Bottom inset shows IR spectra in the O H stretch-ing region of the blank zeolite wafer (bold line), and after dosing with CO at 77 K(sc

lo

(aisHr(btbsfiat

ieSimo�

6.05.55.04.5-4

-3

-2

-1

0

1

2

ln{ θ

/[(1-

θ)p]

}

1000/T (K-1)

R2 = 0,997SD = 0,072

Fig. 3. Plot of the left-hand side of Eq. (1) against the reciprocal of the temperature

dotted line). Top inset shows the C–O stretching region of spectrum 1; the bandeen at 2174 cm−1 corresponds to hydrogen bonded CO, while that at 2139 cm−1

omes from free CO gas.

ocated on the 12-membered rings in the supercages, and the thirdne in 10-membered rings of the sinusoidal channels.

Infrared spectra shown in the main body of Fig. 2 clearly suggestas expected) that the characteristic band of the zeolite Brønstedcid sites (centred at 3626 cm−1) is not a single band; note, not onlyts asymmetrical shape, but also the presence of shoulders on bothides of the main peak (at 3305 cm−1) after interaction with CO.owever, attempts at band resolution did not give quantitatively

eliable results regarding calculation of CO adsorption enthalpybecause of the inherent uncertainty about how the band shoulde decomposed). Hence, we decided to use integrated intensity ofhe 3626 cm−1 band envelope as it appears in the spectra. Note thatoth, the regular shape of the 3626 cm−1 band across the wholeeries of spectra (Fig. 2) and the fact that the derived van’t Hoff plotts well to a single straight line strongly suggest that the molarbsorption coefficients involved in the main sub-bands giving riseo the overall envelope do not differ much from each other.

Interaction of the zeolite with adsorbed CO resulted in anntensity decrease of the IR absorption band at 3626 cm−1, to anxtent which (for a fixed CO dose) is a function of temperature.imultaneously, a new (and much broader) band correspond-

ng to hydrogen-bonded OH· · ·CO species appeared, showing the

aximum at 3305 cm−1, which implies a bathochromic �OH shiftf −321 cm−1, which practically coincides with the value of�OH = −318 cm−1 reported by Garrone et al. [46]. This is shown in

for CO adsorbed on H-MCM-22; data obtained from the O H stretching band at3626 cm−1. R, linear regression coefficient; SD, standard deviation.

the main body of Fig. 2, which depicts representative variable tem-perature IR spectra in the difference mode, i.e., after subtracting theblank zeolite spectrum. At the lowest temperature the silanol bandat 3750 cm−1 was also slightly affected, but that is of no concernherein. From the whole series of VTIR spectra covering the tem-perature range 168–221 K, the van’t Hoff plot shown in Fig. 3 wasobtained. Note that the integrated intensity of the 3626 cm−1 banddivided by its maximum (i.e., the intensity value corresponding tothe zeolite blank spectrum) gives directly the fraction (1 − �) of freeOH sites, from which the corresponding value of � needed for plot-ting Eq. (1) was obtained. From the linear plot in Fig. 3, the valueof �H0 = −23.5 kJ mol−1 was obtained for the standard enthalpyof H-bond formation (OH· · ·CO complexes) between CO and theBrønsted acid sites of H-MCM-22, the corresponding value of �S0

was −130 J mol−1 K−1. The estimated error limits are ±2 kJ mol−1

for enthalpy and ±10 J mol−1 K−1 for entropy. Formation of thesehydrogen-bonded complexes resulted also in the appearance of thecorresponding IR absorption band in the C–O stretching region, asshown in the upper inset of Fig. 2, where the C–O stretching modeof OH· · ·CO species is seen at 2174 cm−1.

Fig. 4 shows that, upon interaction of the H-MCM-22 zeo-lite with adsorbed dinitrogen, the Brønsted acid Si(OH)Al bandat 3626 cm−1 is increasingly eroded when the temperature isdecreased, in a similar fashion as that already described for CO.Simultaneously, a new (broader) band having its maximum at3503 cm−1, and which comes from hydrogen-bonded OH· · ·N2species, builds up. The corresponding ��OH value is therefore,−123 cm−1. The characteristic IR absorption band of the (IR acti-vated) N–N stretching mode appeared at 2332 cm−1, as shown inthe inset of Fig. 4. From the integrated intensity of the whole setof IR absorption bands at 3626 cm−1 measured over the tempera-ture range 147–196 K, the linear plot shown in Fig. 5 was obtained.This linear plot gave the values of �H0 = −14.5(±2) kJ mol−1

and �S0 = −105(±10) J mol−1 K−1 for the standard enthalpy andentropy (respectively) of adsorption of N2; that is, for hydrogenbonding between N2 and the H-MCM-22 Brønsted acid sites.

By means of DFT calculations on relatively small (22 T atoms)cluster models, Zhou et al. [50] found values in the range of−10 to −15 kJ mol−1 (depending on the location of the Brønsted

acid hydroxyl group) for the energy of formation of hydrogen-bonded OH· · ·N2 complexes in H-MCM-22. More recently, Li et al.[51], using a more computationally demanding ONIOM method,arrived at values spanning the range −9.8 to −17.3 kJ mol−1. The

48 M.R. Delgado et al. / Catalysis Today 227 (2014) 45–49

3400350 03600

-0,2

-0,1

0,0

0,1

0,2

0,3

340 0350036003700

232023302340

7654

32

1

7

6

5

4

1

3

Abs

orba

nce

Wavenumber (cm-1)

3626

3503

2

0,1a.u.

36263750

0,01a.u.

2332

Fig. 4. Representative variable-temperature IR spectra (O H stretching region) ofN2 adsorbed on H-MCM-22. The spectra are shown in the difference mode (zeoliteblank subtracted). From 1 to 7, temperature goes from 147 to 196 K; and equilib-rium pressure from 7.62 to 8.95 mbar. Bottom inset shows IR spectra in the O Hs7a

ef�O−w

sm[Hh

7,06,56,05,55,0

-4

-3

-2

-1

0

ln{θ

/[(1-

θ )p]

}

1000/T (K-1)

R2 = 0,997SD = 0,051

Fig. 5. Plot of the left-hand side of Eq. (1) against the reciprocal of the temperature

TR

tretching region of the blank zeolite wafer (bold line) and after dosing with N2 at7 K (dotted line). Top inset shows the IR spectrum (N–N stretching region) of N2

dsorbed on H-MCM-22 at 77 K.

xperimental value of �H0 = −14.5(±2) kJ mol−1 reported hereinalls within that range. Similarly, the VTIR experimental value of

H0 = −23.5(±2) kJ mol−1 found herein for the hydrogen-bondedH· · ·CO complexes in H-MCM-22 is within the range of −15.6 to24.9 kJ mol−1 reported by Li et al. [51], no corresponding valueas reported by Zhou et al. [50].

In order to discuss the above results in a broader context, Table 1ummarizes relevant data reported in the literature for carbon

onoxide and dinitrogen adsorption on other protonic zeolites

24,40,52], together with corresponding data reported herein for-MCM-22. �H0 values involved in the formation of CO and N2ydrogen-bonded species were determined, in all cases, by means

able 1elevant data for CO and N2 hydrogen bonding in protonic zeolites.

Zeolite Structuretype

Si/Alratio

�OH

(cm−1)−��OH(CO)a

(cm−1)−��OH(N2)b

(cm−1)

H-Y FAU 5.6 3645 275 98

H-FER FER 27.5 3605 297 110

H-ZSM-5 MFI 30 3618 303 116

H-MCM-22 MWW 24.5 3626 321 123

a Red-shift of the Brønsted-acid OH group upon hydrogen bonding with CO.b Red-shift of the Brønsted-acid OH group upon hydrogen bonding with N2.c Standard enthalpy and entropy change in the formation of the OH· · ·CO complex.d Standard enthalpy and entropy change in the formation of the OH· · ·N2 complex.

for N2 adsorbed on H-MCM-22; data obtained from the O H stretching band at3626 cm−1. R, linear regression coefficient; SD, standard deviation.

of VTIR spectroscopy. Note that for different H-ZSM-5 zeolites arange of ��OH(CO) values going from −310 to −320 cm−1 werereported by Kubelková et al. [53], while Knözinger et al. [54] givethe value of −317 cm−1. However, no corresponding values of �H0

(to compare with) were reported by these authors.Inspection of Table 1 shows that the zeolites H-Y, H-FER and

H-ZSM-5 display the expected trend, in the sense that increasing(absolute) values of ��OH(CO) correlate with increasing (absolute)values of �H0(CO), and the same trend applies to dinitrogen; it isalso worth of note that regardless of zeolite structure type and Si:Alratio, the enthalpy of formation of the hydrogen-bonded OH· · ·COspecies is about 10 kJ mol−1 greater (in absolute value) than theenthalpy of formation of the corresponding OH· · ·N2 species. Nev-ertheless, the most remarkable fact to consider is that the zeoliteH-MCM-22 breaks the rule correlating ��OH with �H0 for both,carbon monoxide and dinitrogen probe molecules. In fact, thiszeolite shows larger −��OH values than the other protonic zeolites,and yet the corresponding −�H0 values are smaller. This observa-tion should alert to the risk of using ��OH values (after interactionof a protonic zeolite with CO or N2) as a measure of relative Brønstedacid strength; as shown herein, this practice can be misleading(at least in some cases). Determination of the correspondinginteraction energy between the probe molecule and the Brønstedacid sites seems to be a more reliable test. For that purpose, VTIRspectroscopy can profitably be used, but other means are alsoavailable, both experimental and computational. Indeed, Li et al.

[21] and Tsai et al. [55] found by using TPD of adsorbed ammoniathat (for the same Si:Al ratio) H-MCM-22 has a distinctively weakerBrønsted acidity than H-ZSM-5; which is in agreement with thecorresponding smaller values of �H0(CO) and �H0(N2) shown

−�H0(CO)c

(kJ mol−1)−�S0(CO)c

(J mol−1 K−1)−�H0(N2)d

(kJ mol−1)−�S0(N2)d

(J mol−1 K−1)Ref.

25.6 – 15.7 121 [24,40]28.4 145 19.1 128 [52]29.4 150 19.7 – [24]23.5 130 14.5 105 This work

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M.R. Delgado et al. / Cata

n Table 1, but not so with the larger values of ��OH shown by-MCM-22.

The reason why H-MCM-22 shows a larger bathochromic shiftf the O H stretching frequency than H-FER and H-ZSM-5 uponnteraction with a weak base, and yet a smaller interaction energy,ould well be found in the role of long range dispersion forces, theontribution of which to �H0 would depend on pore size and localurvature of the zeolite framework (close to the Brønsted acid OHite). However, validation of this hypothesis would require veryetailed theoretical calculations.

Regarding adsorption entropy, data summarized in Table 1 showhat, in general terms, there is a positive correlation between �H0

nd �S0 (for both, CO and N2) in the sense that the (absolute) valuef �S0 increases with increasing (absolute) value of �H0. In thisegard H-MCM-22 follows the general trend shown by the otherrotonic zeolites. Note that a positive correlation between adsorp-ion enthalpy and entropy has also been observed for CO on several

etal oxides [40], as well as for hydrogen adsorption on zeolitesnd metal-organic frameworks [56–58].

. Conclusions

The standard enthalpy change, �H0, involved in hydrogen bond-ng of Brønsted-acid hydroxyl groups of an H-MCM-22 zeoliteSi:Al = 24.5:1) with adsorbed CO and N2 was determined by VTIRpectroscopy. The obtained values of �H0 resulted to be −23.5(±2)nd −14.5(±2) kJ mol−1, respectively. Taking these values as a mea-ure of acid strength, comparison with corresponding �H0 valuesor H-ZSM-5 (−29.4 and −19.7 kJ mol−1, for CO and N2, respectively)how that H-MCM-22 shows a distinctively weaker acidity than H-SM-5; which is in agreement with reported measurements basedn TPD of ammonia adsorbed on H-MCM-22 and H-ZSM-5 zeo-ites having a similar Si:Al ratio. Nevertheless, the bathochromichift, ��OH, of the characteristic O H stretching frequency afterormation of the hydrogen-bonded adsorption complexes wasound to be considerably larger for H-MCM-22 (��OH(CO) = −321nd ��OH(N2) = −123 cm−1) than for H-ZSM-5 (��OH(CO) = −303nd ��OH(N2) = −116 cm−1). This, rather surprising, finding shouldlert to the limited validity of using ��OH values as a measure ofelative Brønsted-acid strength among protonic zeolites.

cknowledgement

The financial support of the Czech Science Foundation underhe project of Centre of Excellence No. P106/12/G015 (RB and PC)InDeNAC, www.zeolites.cz) is highly acknowledged.

eferences

[1] W.F. Hölderich, J. Röseler, G. Heitman, Catal. Today 37 (1997) 353.[2] U. Freese, F. Heinrich, F. Roessner, Catal. Today 49 (1999) 237.[3] K. Tanabe, W.F. Hölderich, Appl. Catal. A 181 (1999) 399.[4] I. Rodriguez, M.J. Climent, S. Iborra, V. Fornes, A. Corma, J. Catal. 192 (2000) 441.

[5] M.G. Clerici, Top. Catal. 13 (2000) 373.[6] W.F. Hölderich, Catal. Today 62 (2000) 115.[7] A. Corma, J. Catal. 216 (2003) 298.[8] B. Xu, C. Sievers, S.B. Hong, R. Prins, J.A. van Bokhoven, J. Catal. 244 (2006)

163.

[

[[

oday 227 (2014) 45–49 49

[9] D. Prochazkova, L. Kurfirtova, J. Pavlatova, Catal. Today 179 (2012) 78.10] J. Cejka, G. Centi, J. Perez-Pariente, W.J. Roth, Catal. Today 179 (2012) 2.11] N. Zilkova, M. Shamzhy, O. Shevets, J. Cejka, Catal. Today 204 (2013) 22.12] D. Barthomeuf, Stud. Surf. Sci. Catal. 65 (1991) 157.13] R.A. van Santen, Stud. Surf. Sci. Catal. 85 (1994) 273.14] R.A. van Santen, G.J. Kramer, Chem. Rev. 95 (1995) 637.15] L. Grajciar, C.O. Arean, A. Pulido, P. Nachtigall, Phys. Chem. Chem. Phys. 12

(2010) 1497.16] M. Brändle, J. Sauer, J. Am. Chem. Soc. 120 (1998) 1556.17] P. Nortier, A.P. Borosy, M. Allavena, J. Phys. Chem. B 101 (1997) 1347.18] S. Kotrel, J.H.L. Lunsford, H. Knözinger, J. Phys. Chem. B 105 (2001) 3917.19] A. Zecchina, G. Spoto, S. Bordiga, Phys. Chem. Chem. Phys. 7 (2005) 1627.20] W.E. Farneth, R.J. Gorte, Chem. Rev. 95 (1995) 615.21] Z. Zhu, Q. Chen, Z. Xie, W. Yang, C. Li, Micropor. Mesopor. Mater. 88 (2006) 16.22] L.R. Aramburo, S. Wirick, P.S. Miedema, I.L.C. Buurmans, F.M.F. de Groot, B.M.

Weckhuysen, Phys. Chem. Chem. Phys. 14 (2012) 6967.23] E.A. Paukshtis, E.N. Yurchenko, Russ. Chem. Rev. 53 (1983) 242.24] C.O. Arean, J. Mol. Struct. 880 (2008) 31.25] K. Chakarova, K. Hadjiivanov, Chem. Commun. 47 (2011) 1878.26] K. Chakarova, K. Hadjiivanov, J. Phys. Chem. C 115 (2011) 4806.27] C.O. Arean, O.V. Manoilova, G.T. Palomino, M.R. Delgado, A.A. Tsyganenko, B.

Bonelli, E. Garrone, Phys. Chem. Chem. Phys. 4 (2002) 5713.28] E. Garrone, C.O. Arean, Chem. Soc. Rev. 34 (2005) 846.29] E. Garrone, B. Fubini, B. Bonelli, B. Onida, C.O. Arean, Phys. Chem. Chem. Phys.

1 (1999) 513.30] D. Nachtigallova, O. Bludsky, C.O. Arean, R. Bulanek, P. Nachtigall, Phys. Chem.

Chem. Phys. 8 (2006) 4849.31] R. Bulanek, I. Voleska, E. Ivanova, K. Hadjiivanov, P. Nachtigall, J. Phys. Chem. C

113 (2009) 11066.32] P. Nachtigall, M.R. Delgado, D. Nachtigallova, C.O. Arean, Phys. Chem. Chem.

Phys. 14 (2012) 1552.33] B. Bonelli, E. Garrone, B. Fubini, B. Onida, M.R. Delgado, C.O. Arean, Phys. Chem.

Chem. Phys. 5 (2003) 2900.34] M.E. Malyshev, E.A. Paukshtis, L.V. Malysheva, A.V. Toktarev, L.A. Vostrikova,

Kinet. Catal. 46 (2005) 100.35] T. Montanari, E. Finocchio, G. Busca, J. Phys. Chem. C 115 (2011) 937.36] F. Geobaldo, C. Lamberti, G. Ricchiardi, S. Bordiga, A. Zecchina, G.T. Palomino,

C.O. Arean, J. Phys. Chem. 99 (1995) 11167.37] E.N. Gribov, D. Cocina, G. Spoto, S. Bordiga, G. Ricchiardi, A. Zecchina, Phys.

Chem. Chem. Phys. 8 (2006) 1186.38] R. Bulanek, M. Kolarova, P. Chlubna, J. Cejka, Adsorption 19 (2013) 455.39] A.A. Tsyganenko, P.Yu. Storozhev, C.O. Arean, Kinet. Catal. 45 (2004) 530.40] C.O. Arean, O.V. Manoilova, A.A. Tsyganenko, G.T. Palomino, M.P. Mentruit, F.

Geobaldo, E. Garrone, Eur. J. Inorg. Chem. (2001) 1739.41] W.J. Roth, J. Cejka, Catal. Sci. Technol. 1 (2011) 43.42] W.J. Roth, P. Chlubna, M. Kubu, D. Vitvarova, Catal. Today 204 (2013) 8.43] S.L. Lawton, A.S. Fung, G.J. Kennedy, L.B. Alemany, C.D. Chang, G.H. Hatzikos,

D.N. Lissy, M.K. Kubin, H.-K.C. Timken, S. Steuernagel, D.E. Woessner, J. Phys.Chem. 100 (1996) 3788.

44] J.C. Lavalley, Catal. Today 27 (1996) 377.45] A. Zecchina, C. Otero Arean, Chem. Soc. Rev. 25 (1996) 187.46] B. Onida, F. Geobaldo, F. Testa, F. Crea, E. Garrone, Micropor. Mesopor. Mater.

30 (1999) 119.47] D. Meloni, S. Laforge, D. Martin, M. Guisnet, E. Rombi, V. Solinas, Appl. Catal. A

215 (2001) 55.48] Z. Sobalik, Z. Tvaruzkova, B. Wichterlova, V. Fila, S. Spatenka, Appl. Catal. A 253

(2003) 271.49] P. Ayrault, J. Datka, S. Laforge, D. Martin, M. Guisnet, J. Phys. Chem. B 108 (2004)

13755.50] D. Zhou, Y. Bao, M. Yang, N. He, G. Yang, J. Mol. Catal. A 244 (2006) 11.51] Y. Li, W. Guo, W. Fan, S. Yuan, J. Li, J. Wang, H. Jiao, T. Tatsumi, J. Mol. Catal. A

338 (2011) 24.52] P. Nachtigall, O. Bludsky, L. Grajciar, D. Nachtigallova, M.R. Delgado, C.O. Arean,

Phys. Chem. Chem. Phys. 11 (2009) 791.53] L.M. Kustov, V.B. Kazansky, S. Beran, L. Kubelková, P. Jirú, J. Phys. Chem. 91

(1987) 5247.54] S. Kotrel, J.H. Lunsford, H. Knözinger, J. Phys. Chem. B 105 (2001) 3917.55] C.C. Tsai, C.Y. Zhong, I. Wang, S.B. Liu, W.H. Chen, T.C. Tsai, Appl. Catal. A 267

(2004) 87.56] C.O. Arean, D. Nacthigallova, P. Nachtigall, E. Garrone, M.R. Delgado, Phys. Chem.

Chem. Phys. 9 (2007) 1421.57] E. Garrone, B. Bonelli, C.O. Arean, Chem. Phys. Lett. 9 (2008) 1747.58] G.T. Palomino, C.P. Cabello, C.O. Arean, Eur. J. Inorg. Chem. (2011) 1703.