Use of but-1-yne as a probe for the characterization of the basicity of alkali-exchanged zeolites

Article abstract of DOI:10.1039/a705221i

But-1-yne has been adsorbed at room temperature on a series of LiNa, Na and CsNaX and Y zeolites and also on CsNaX,9Cs and CsNaY,9Cs samples containing nine Cs atoms occluded by a unit cell. An IR study of the 3000-2800 cm^-1 frequency range clearly showed that but-1-yne isomerized into but-2-yne on CsNaX,9Cs whereas the observation of a band near 1950 cm^-1 in the case of CsNaY,9Cs characterized the formation of buta-1,2-diene. Such partial transformation of but-1-yne to isomers did not occur on LiNa and Na samples, allowing one to study the basicity of such zeolites from the v(≡CH) shift which decreases in the following order: NaX > LiNaX > NaY > LiNaY. The main feature is the observation of at least two perturbed v(≡CH) bands for the NaX and NaY samples, revealing the heterogeneity of the basic sites. This result is discussed taking into account the presence of cations in different positions.

Full text of DOI:10.1039/a705221i

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Use of but-1-yne as a probe for the characterization of the basicity of
alkali-exchanged zeolites
Jean-Claude Lavalley,a* Jean Lamotte,a Arnaud Travert,a Jolanta Czyzniewskab and Maria
Ziolekb
a L aboratoire Catalyse et Spectrochimie, UMR CNRS 6506; ISMRA-Universite de Caen 6,
Boulevard du Marechal JuinÈ14050 Caen Cedex, France
b Faculty of Chemistry, A. Mickiewicz UniversityÈ60-780 Poznan, Poland
But-1-yne has been adsorbed at room temperature on a series of LiNa, Na and CsNaX and Y zeolites and also on CsNaX,9Cs
and CsNaY,9Cs samples containing nine Cs atoms occluded by a unit cell. An IR study of the 3000È2800 cm~1 frequency range
clearly showed that but-1-yne isomerized into but-2-yne on CsNaX,9Cs whereas the observation of a band near 1950 cm~1 in the
case of CsNaY,9Cs characterized the formation of buta-1,2-diene. Such partial transformation of but-1-yne to isomers did not
occur on LiNa and Na samples, allowing one to study the basicity of such zeolites from the l(y CH) shift which decreases in the
following order: NaX [ LiNaX [ NaY [ LiNaY. The main feature is the observation of at least two perturbed l(y CH) bands
for the NaX and NaY samples, revealing the heterogeneity of the basic sites. This result is discussed taking into account the
presence of cations in di†erent positions.
The growing interest in the study of the basic properties of
alkali exchanged zeolites is due to their potential application
in catalysis, particularly in Ðne organic chemistry.1 In order to
understand these catalytic properties, it is of great importance
Experimental
Catalyst preparation
Zeolites NaX Linde (Si/Al \ 1.21) and NaY Katalistiks (Si/
to characterize their basicity, i.e. the assessment of the
Al \ 2.55) were used as starting materials. Prior to modiÐ-
strength, the concentration and the nature of basic sites. If IR
spectroscopy of adsorbed probe molecules, like pyridine or
carbon monoxide, is very often used to characterize the
surface acidity of oxides and zeolites,2 the method is not so
convenient to apply to basic materials since no probe can be
universally used.3 However, recently, some papers reported
interesting results obtained using pyrrole,4,5 chloroform6 and
acetylene derivatives.7 If it was previously shown that pyrrole
adsorption is complex, since non-dissociatively and disso-
ciatively adsorbed species can be formed,8 the Ðrst results
published by Uvarova et al.7 look very promising, in particu-
lar, those relative to the use of acetylene whose l(y CH) fre-
quency appears sensitive to the strength of basic sites of a
series of sodium zeolites.
cation, the samples were treated with 0.25 M NaCl to remove
cations other than Na` and to bring the Al/Na ratio to equi-
librium. The obtained samples were used in studies as parent
NaX and NaY zeolites.
Exchange. Lithium forms of X and Y zeolites were prepared
by conventional cation-exchange procedures with a 0.1 M
solution of LiNO at room temperature (r.t.). For the caesium
3
exchange, sodium cations in NaX and NaY were exchanged at
r.t. with 0.1 M solution of caesium acetate. Three exchanges
were performed, the Ðrst two for 24 h time periods, the third
for 48 h. Then the catalysts were Ðltered and rinsed with
deionized water and dried at 373 K for 5 h. The degree of
Na` to Li` or Cs` exchange, obtained from atomic absorp-
tion spectroscopy, allows one to determine the formula of the
The aim of the present paper is to determine to what extent
an acetylene compound can be used as a probe of basicity for
a series of di†erent alkali exchanged zeolites. In addition to
the overall characterization of basicity, we focus on the
heterogeneity of the basic sites of the di†erent compounds
used and the results are compared to those obtained with
chloroform.6
compounds so prepared: Li Na (AlO ) (SiO )
30 55 2 86 2 106
(LiNaY), H Cs Na (AlO )
32 41 2 86
(CsNaX) and H Cs Na (AlO ) (SiO )
(LiNaX),
Li Na (AlO ) (SiO )
22 32 2 54 2 138
(SiO )
x
2 106
x
30 19
2 54
2 138
(CsNaY). A partial decationisation could occur during prep-
aration of caesium samples.
Impregnation. The so-obtained CsNaX and CsNaY
samples, calcined at 673 K for 2 h, were wetted in a dry box
by a precalculated volume of 0.2 M caesium acetate in order to
obtain nine caesium acetate molecules per unit cell, following
the procedure described in ref. 14. After evacuation at r.t. in
an evaporator, the temperature was raised to 313 K (3 h) and
353 K (2 h) to remove bulk water and leave caesium acetate
occluded in the zeolites. The samples were then calcined at
In order to overcome the difficulty due to the presence of
two coupled l(y CH) vibrations in acetylene, we use but-1-
yne, CH CH Cy CH, as a probe. Its IR spectrum in solution
3
2
was carefully studied by two of us some time ago,9 as was also
its adsorption on ZnO10 and Al O .11 It should be noted
2
3
that but-1-yne partly dissociates on both oxides, the lack of
the l(y CH) vibration preventing the use of but-1-yne as a
probe to determine the basicity of these two oxides.
673
K for 2 h. The so-obtained samples are denoted
The materials used in the present study are faujasite type
zeolites (X and Y) exchanged with di†erent alkali cations. It is
known from literature that their basicity increases in the fol-
lowing order:12 Li-FAU \ Na-FAU \ K-FAU \ Cs-FAU.
Moreover X zeolites are more basic than the corresponding Y
ones. To improve the basicity of the most basic Cs-FAU
CsNaX,9Cs and CsNaY,9Cs (nine Cs atoms occluded per unit
cell).
X-Ray analyses indicated that the crystallinity of all pre-
pared samples was largely retained.
IR experiments
zeolite, the encapsulation of Cs O in its framework cavities
2
has been carried out.13,14 Therefore but-1-yne has been
Zeolite samples were pressed into self-supported wafers (ca. 15
mg with diameter of 16 mm). They were activated in situ at
chemisorbed on a wide range of basic zeolite materials.
J. Chem. Soc., Faraday T rans., 1998, 94(2), 331È335
331

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673 K under vacuum for 5 h. Portions of CH CH Cy CH
LiNa and Na faujasites
3
2
were then introduced at room temperature. All the spectra
were recorded on a Nicolet 60-SX spectrometer. The spectrum
of the activated catalyst was automatically subtracted in order
to obtain that of the adsorbed species formed.
Fig. 2 shows in the 3400È2700 cm~1 range the spectra of
species formed when a small (30 lmol g~1) or a large amount
(1 mmol g~1) of but-1-yne was introduced on LiNaY, NaY,
LiNaX and NaX.
If the results obtained on LiNaY are simple since mainly a
sharp l(y CH) band with a weak shoulder at 3252 cm~1 is
observed, those relating to the other zeolites are more
complex. When a large amount of but-1-yne is introduced,
two l(y CwH) bands (LiNaX, NaX) or even three (NaY) are
clearly apparent (Fig. 2). That at low wavenumber (LW), Ðrst
appears when a small amount of but-1-yne is added, suggest-
ing it corresponds to but-1-yne adsorption on the most basic
sites. Its wavenumber decreases in the following order: LiNaY
(3252) [ NaY (3248) [ LiNaX (3230) [ NaX (3142 cm~1).
The same order is observed for the high wavenumber (HW)
Results
The spectrum of species formed upon adsorption of large
amounts of but-1-yne on LiNaY is shown in Fig. 1. It mainly
presents bands at 3290 [l(y CH)], 2986 [l , l@(CH )], 2946
a
s
3
[l (CH )], 2927 [sh, l(CH )], 2887 [2 d(CH )], 2153, [vw,
s
3
2
3
u(CH ) ] l (CCC)], 2105 [l(Cy C)], 1462 [d , d@(CH )], 1438
2
s
a
s
3
[d(CH )], 1384 [d [CH )] and 1319 cm~1 [u(CH )]. All these
2
s
3
2
values are very close to those reported for but-1-yne in solu-
tion.9 However, when very small doses of but-1-yne are intro-
duced (30 lmol g~1), a shoulder near 3250 [l(y CH)] and
another near 2097 cm~1 [l(Cy C)] are noted (Fig. 2). We do
not observe any band higher than 3300 cm~1, assignable to
an OH group, resulting from a dissociative but-1-yne adsorp-
tion. We conclude that no dissociation occurs, in contrast to
that observed before on metal oxides.10,11
band:
LiNaY
(3290) [ NaY
(3289,
3276) [ LiNaX
(3272) [ NaX (3222 cm~1).
The wavenumber of the bands in the range below 1600
cm~1 is quite similar to that reported above in the case of
LiNaY. As for the l(Cy C) band, its wavenumber is situated
near 2095È2097 cm~1. A shoulder is noted at 2105 cm~1
when a large amount of but-1-yne is introduced on NaY.
Cs compounds
But-1-yne adsorption on CsNaY leads to the appearance of
two l(y CH) bands, one at 3278 (sharp) the other at 3258
cm~1 with probably a broad shoulder near 3225 cm~1 (Fig.
3). In contrast to the results reported above, their intensity
increases almost in unison. When the Ðrst amounts of but-1-
yne are introduced, the l(Cy C) band is Ðrst observed at 2096
cm~1 and its wavenumber shifts to 2103 cm~1 by adding
more but-1-yne. The bands below 1600 cm~1 are similar to
those reported above.
An important point is the relative intensity of the main
l(CH) bands observed at ca. 2975, 2938 and 2882 cm~1: that
at 2938 cm~1 is the most intense whereas that at ca. 2980
cm~1 predominated in the case of LiNa and Na faujasites
(Fig. 1 and 2).
The spectrum for the l(CH) range when adsorbing but-1-
yne on CsNaX is similar to that reported for CsNaY but is
even more complex since for instance the 2975 cm~1 band
presents two shoulders at ca. 2989 and 2966 cm~1. As for the
l(y CH) vibration, it gives rise to a very broad band near
3230 cm~1. Below 2300 cm~1, the spectrum is similar to that
observed for CsNaY.
Fig. 1 IR spectra of species formed from but-1-yne introduction (1
mmol g~1) on LiNaY
The results obtained on CsNaY, 9Cs are quite di†erent (Fig.
4). (i) A broad l(y CH) band at 3254 cm~1 is accompanied by
a rather sharp shoulder at 3276 cm~1. (ii) The spectrum in the
l(CH) range changes with the amount of but-1-yne intro-
duced. Four main bands are observed at 2971, 2937, 2924 and
Fig. 2 IR spectra of species formed from but-1-yne introduction (30
lmol g~1) (a) then 1 mmol g~1 (b) on LiNaY, NaY, LiNaX and NaX
Fig. 3 IR spectra of species formed from but-1-yne introduction [15
(a), 90 (b), 190 (c), 380 (d) and 900 (e) lmol g~1] on CsNaY
332
J. Chem. Soc., Faraday T rans., 1998, V ol. 94

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band is noted at ca. 1430 cm~1 whatever the amount of but-1-
yne introduced.
Discussion
Spectra assignment: but-1-yne reactivity
The spectra obtained adsorbing but-1-yne on LiNa and Na
faujasites in the l(CH) (3000È2700 cm~1) and d(CH) (l \ 1500
cm~1) ranges are close to those of but-1-yne in solution.
However, we note that for LiNaX and NaX (Fig. 2) that the
l(CH) bands are broader than those observed for LiNaY and
NaY. As we will see later, this could be due to a strong inter-
action of but-1-yne with the X zeolites and also to the forma-
tion of at least two species.
Fig. 4 IR spectra of species formed from but-1-yne introduction
[160 (a), 300 (b), 630 (c), 1000 (d) lmol g~1 followed by evacuation at
r.t. (e)] on CsNaY,9Cs
Results obtained on Cs compounds are more surprising. Let
us consider Ðrst the case of CsNaX,9Cs. l(CH) bands are
found for the Ðrst doses of but-1-yne introduced whereas no
l(y CH) and l(Cy C) bands are observed. This result can be
explained considering the formation of but-2-yne from isomer-
ization of but-1-yne, since the spectrum of but-2-yne in the
considered frequency ranges agrees very well with that report-
ed in Fig. 5. In CCl solution, l(CH ) bands are noted at 2964
2879 cm~1, but the relative intensity of those at 2937 and
2924 cm~1 changes with the amount of probe added, that at
2924 cm~1 being Ðrst predominant and later becoming a
shoulder of that at 2937 cm~1. Moreover, after evacuation of
but-1-yne at room temperature, l(CH) bands as that at 2924
cm~1 persist whereas no l(y CH) is visible. (iii) In the region
below 2300 cm~1, in addition to the bands observed from
but-1-yne adsorption on the other zeolites, a weak band near
1950 cm~1 is noted. Moreover, in addition to the 1460 and
1435 cm~1 bands, a broad band appears at ca. 1447 cm~1
which persists after evacuation at r.t., with two other broad
bands at ca. 1370 and 1378 cm~1 (Fig. 4).
Interestingly, introduction of but-1-yne to CsNaX,9Cs does
not lead, for the Ðrst doses introduced, to any l(y CH) band,
nor to a l(Cy C) band, whereas three well resolved l(CH)
bands at 2960 (medium), 2922 (strong) and 2866 cm~1 are
clearly observed (Fig. 5). It is only when a large amount of
but-1-yne is introduced (400 lmol g~1) that a l(y CH) band
clearly appears at 3210 cm~1 along with a l(Cy C) bond at
2100 cm~1. In the region below 1500 cm~1, the spectrum is
also very di†erent from the previous ones since only one sharp
4
3
(l ), 2919s (l ), 2848 (2l ) and 2735 cm~1, [vw, 2d ], whereas in
a
s
a
s
the d(CH ) range, the main band occurs at 1435 cm~1 (d ),
3
a
that at 1375 cm~1 (d ) being very weak. Note, owing to the
s
presence of a center of symmetry, that no l(Cy C) is clearly
observed by IR spectroscopy.
This means that when in contact with CsNaX,9Cs, but-1-
yne isomerization is fast at room temperature. We note that a
similar isomerization has been reported on basic oxides, such
as ZnO, on which intermediate species of the propargylic type
have been detected.10
The formation of but-2-yne, which is less evident on the
other Cs compounds, can explain the complexity of the
spectra observed in the l(CH) range. It is worth noting that an
intermediate compound from but-1-yne to but-2-yne isomer-
ization is buta-1,2-diene, the IR spectrum of which presents a
band near 1950 cm~1, as observed from but-1-yne adsorption
on CsNaY,9Cs (Fig. 4). In such a case the isomerization would
not be so complete. This compound readily gives rise to poly-
mers, which explains the fact that after evacuation at r.t. some
l(CH) remains whereas no l(y CH) band is observable (Fig.
4).
We therefore conclude that the partial transformation of
but-1-yne to isomers on Cs zeolites prevents any useful infor-
mation from the study of the l(y CH) range. Taking into
account that X zeolites are more basic than Y ones, as also
shown below, and that zeolites with encapsulated Cs O are
2
more basic than zeolites without Cs O, the analysis of the
2
spectra tends to show that the degree of isomerization of
but-1-yne increases with the zeolite basicity.
Basicity of LiNa and Na faujasites
The two main l(y CH) bands observed in the series of spectra
reported in Fig. 2 indicate the presence of basic sites with dif-
ferent strengths in the compounds studied. Our results relative
to NaY and NaX seem clearer than those reported in ref. 7
using acetylene as a probe. This is certainly due to the pres-
ence of two l(y CH) vibrations in acetylene, which are strong-
ly coupled, the perturbation of one modifying the frequency of
the other. Note that pyrrole adsorption on LiY, NaY, LiX and
NaX led to one broad l(NH) band located at 3435, 3390, 3295
and 3280 cm~1, respectively, indicating the same order of
basicity as reported here.15 We also note that for pyrrole
adsorption on an NaX sample, an asymmetric hydrogen
double-well potential has been suggested.8 The complexity of
the spectrum observed suggested the formation of
a
Fig. 5 Comparison of IR spectrum (2800È3000 cm~1) of species
C H NH É É É O hydrogen bonded species of pyrrole adsorbed
formed from but-1-yne adsorption on CsNaX,9Cs (a) with that of the
4
4
l(CH ) bands of but-2-yne in the liquid state (b)
on weak basic sites and the formation of a C H N~ É É É `HO
3
4
4
J. Chem. Soc., Faraday T rans., 1998, V ol. 94
333

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species adsorbed on relatively strong basic sites. The present
results conÐrm the coexistence of both type of sites and so the
heterogeneity of zeolite basic sites.
samples, the negative partial charge on zeolite framework
oxygens being higher for the former materials, in agreement
with the higher frequency shift, *l(y CH), observed for X
samples.
Note that Huang and Kaliaguine15 by computer deconvol-
ution of the perturbed l(NH) band of pyrrole suggested the
existence of three individual l(NH) components. Fig. 2 indi-
cates that such a number of components is apparent when
but-1-yne is used in the case of NaY and possibly also NaX, if
a weak shoulder near 3280 cm~1 is taken into account. Spec-
tral deconvolution is quite easy when but-1-yne is used (Fig.
2), in contrast to pyrrole,4,5 allowing us to conclude that the
former probe is more informative than the latter.
Chloroform adsorption on a similar series of zeolites6 led to
the same order of basicity from the l(CH) frequency which
decreased when the basicity increased: LiNaY (3028
cm~1) \ NaY (3017 cm~1) \ LiX (3016 cm~1) \ NaX (2995
cm~1). However, for these compounds, only one band was
observed, showing again that the use of but-1-yne is more
informative concerning site heterogeneity. By contrast, chloro-
form adsorption on K, Rb, Cs faujasites led to determination
of the basicity of these materials without taking into account
any decomposition or rearrangement.
However, the concept of SandersonÏs electronegativity does
not explain the heterogeneity of the basic sites observed for
NaX and NaY samples (Fig. 2). Murphy et al.4 considered
that the Lewis basicity in zeolites is a local property depen-
dent on the nature of the adjacent cations. Since the exchange
of Na` by Li` is incomplete, unexchanged sodium cations in
LiNaX and LiNaY samples can induce a basicity close to that
observed in the parent samples, which could explain the
occurrence of the band at 3230 cm~1 for LiNaX, close to that
found at 3222 cm~1 for NaX, and that at 3252 cm~1 for
LiNaY, close to that observed at 3250 cm~1 for NaY.
The presence of at least two l(y CH) perturbed bands for
NaX and NaY is proof of the heterogeneity of Lewis basic
sites in these zeolites.
The strongest basic sites in NaX involved in the formation
of the l(y CH) band at 3143 cm~1 probably correspond to
framework oxygens coordinated with Na` in S positions. It
III
is known that faujasite type zeolites, in which cations occupy
Complexation of 1-alkynes with bases has been studied by
IR spectroscopy in solution.16 It is interesting to compare the
results obtained with those reported in the present study. We
note that the l(y CH) wavenumber of 1-alkynes in the liquid
phase (3292È3000 cm~1) is close to that observed for but-1-
yne adsorbed on LiNaY showing that the basicity of this
zeolite is quite low. The l(y CH) wavenumber of the HF band
for LiNaX (3272 cm~1) and NaY (3289, 3276 cm~1) indicates
an interaction similar to that reported for 1-alkynes with
S
positions, are able to dissociate compounds such as H S 18
III
2
and CH SH 19 owing to their strong basicity. Sodium cations
in S position are located between O and O zeolite frame-
3
III
1
4
work oxygens.1,20. Their occupation in this position decreases
when the Si/Al ratio increases18 and is not clear in NaY zeo-
lites.21h23 We could expect a small level of sodium localized in
the S position in NaY, explaining the occurrence of the
III
shoulder near 3250 cm~1 (Fig. 2). The higher wavenumber of
this band compared to that observed at 3142 cm~1 for NaX is
due to the general feature reported above, namely that the
negative partial charge of the zeolite framework oxygens is
lower for Y type zeolites than for X zeolites.
ketones (pk \ 21) whereas those of the LF band of LiNaX
b
(3230 cm~1) and HF band of NaX (3222 cm~1) are not very
di†erent from that resulting from the interaction of 1-alkynes
with pyridine (pk \ 8.8). Finally the value of 3143 cm~1 char-
The two other clearly evident IR bands in Fig. 2 for NaX
and NaY zeolites could be due to but-1-yne adsorption on
b
acterizing the LF band for NaX is very low, much lower than
that reported for 1-alkynes interacting with trimethylamine
framework oxygens adjacent to sodium cations in S position
II
(3206 cm~1, pk \ 4) indicating that the corresponding basic-
(i.e. coordinated with oxygens in O position and in S posi-
b
2
I{
ity is quite high. In agreement with results obtained in solu-
tion [linked to O (ref. 20)].
3
tion,16 the present results show that the l(Cy C) band is
Exchange of Na` by Li` changes the cations positions. It is
almost insensitive to CH CH Cy CwH É É É OZ interaction.
well known from the literature24 that Li` cations prefer S
3
2
I{
As for the relative number of basic sites for each zeolite
studied, we do not think it is possible to deduce this directly
from the intensity of the l(y CH) components. Indeed, it is
well known that, when hydrogen bonding occurs, the intensity
of the perturbed band increases with the strength of the per-
turbation. For instance, it has been reported that the inte-
grated intensity of the l(y CH) band is 2.7 times greater when
1-heptyne is complexed to a ketone compared with when it is
positions, localized in the centre of the framework six rings.
The maximum occupancy of I@ positions is 32 per unit cell,
which is just the limit of the exchange of the studied samples.
In this position, cations are coordinated with O oxygens.1,20
3
In LiNaX, the S position is not occupied by either Li or Na
III
cations24 and is the reason for the lack of any band near 3143
cm~1 after but-1-yne adsorption. The presence of a new band
at 3272 cm~1 (which appears as a shoulder on NaX) when
adsorbing but-1-yne on LiNaX (Fig. 2) can be explained due
to the following features: (i) the fact that Li wO distance is
in CCl solution.17 Fig. 2 demonstrates such an e†ect: intro-
4
duction of the Ðrst dose, which is sufficiently small to be con-
I{
3
sidered as completely chemisorbed on all the samples, gives
rise to a perturbed l(y CH) band much more intense on NaX
(Fig. 2). Its intensity decreases in the following order:
NaX [ LiNaX [ NaY, LiNaY mirroring the basicity of the
samples. Note that Murphy et al.4 when adsorbing pyrrole on
alkali cation exchanged EMT zeolites, directly deduced the
relative population of sites from the l(NH) band intensity
characteristic of the interaction, assuming that the molar
absorption coefficient e(NH) is independent of the interaction
strength which has yet to be established.
shorter than that for NawO, (ii) the TwO wT angle
3
decreases from Na to Li decreasing the oxygen basicity24 and
(iii) as recently shown4 the strength of the basic sites decreases
for the framework oxygens associated with Na` cations in the
following order: II [ I [ I@. In LiNaX, S positions are fully
I{
occupied by lithium cations and the oxygen associated with
this position shows the lowest basicity.
Conclusion
The present results show that but-1-yne is a very sensitive
probe to study, from the *l(y CH) shift, the basicity of zeo-
lites when this basicity is rather weak (LiNaY, NaY, LiNaX,
NaX). In particular, it clearly reveals the heterogeneity of
basic sites, which is not the case when chloroform is used.6
This heterogeneity was already reported for EMT zeolites
using pyrrole as a probe,4 but this result was obtained after
computer deconvolution of the l(NH) band which is always
difficult to achieve when the band is broad. On more basic
Heterogeneity of sites
Finally, the origin of the heterogeneity of basic sites has to be
considered. Previous work showed that IR data relative to
pyrrole or chloroform adsorption can be correlated with the
oxygen charge calculated from SandersonÏs electronega-
tivity.6,15 It explains the di†erence observed between X and Y
334
J. Chem. Soc., Faraday T rans., 1998, V ol. 94

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9
J. Saussey, J. Lamotte and J. C. Lavalley, Spectrochim. Acta, Part
A, 1976, 32, 763.
zeolites, isomerization occurs which prevents the use of but-1-
yne from the spectroscopic point of view at least at r.t. Other
probes, like acetylene, in spite of the coupling between the two
l(y CH) modes, or 3,3-dimethylbut-1-yne which cannot isom-
erize, would be more convenient. However, but-1-yne isomer-
ization itself could be an interesting reaction to compare the
basicity of zeolites, since it has been well known for a long
time25 that this reaction occurs under basic conditions. The
present results indeed suggest that the more basic the material
(CsNaX,9Cs), the greater the rate of isomerization.
10 J. Saussey, J. C. Lavalley and N. Sheppard, J. Chim. Phys., 1977,
74, 329.
11 J. Saussey, J. Lamotte, J. C. Lavalley and N. Sheppard, J. Chim.
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12 M. Huang, A. Adnot and S. Kaliaguine, J. Catal., 1992, 137, 322.
13 I. Rodriguez, H. Cambon, D. Brunel, M. Lasperas and P.
Geneste, Stud. Surf. Sci. Catal., 1993, 78, 623.
14 P. E. Hathaway and M. E. Davis, J. Catal., 1989, 116, 263.
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16 P. V. Huong, J. Lascombe and M. L. Josien, J. Chim. Phys., 1961,
58, 694.
17 P. V. Huong, Rev. Inst. Fr. Petrole Ann. Combust. L iq., 1963, 18,
1.
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Financial support from the Ministere Francais des A†aires
Etrangeres and the Polish Committee for Research (KBN) is
highly acknowledged.
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