Microporous and Mesoporous Materials 49 (2001) 45±56
www.elsevier.com/locate/micromeso
Solid-state modi®cation of Y zeolites (NaY or LaNaY)
by MnCl2 xH2O: comparison with V2O5, MoO3 and Sb2O3
J. Thoret, P.P. Man, P. Ngokoli-Kekele, J. Fraissard *
Laboratoire de Chimie des Surfaces, CNRS ESA 7069, Universit
e Pierre et Marie Curie, case 196, Tour 54-55, 4 place Jussieu,
75252 Paris Cedex 5, France
Received 9 November 2000; received in revised form 29 May 2001; accepted 5 June 2001
Abstract
Solid-state modi®cation of Y zeolites (NaY or LaNaY) with MnCl2 xH2 O leads to three successive phenomena
depending on the thermal treatment temperature, Tt : maximum halide insertion into the supercages at low temperature
(433 K), exchange with Na‡ and NH‡
4 in the zeolites at 613±793 K and solid±solid reactions with the appearance above
1073 K of new crystalline phases, most of which are identi®ed. The results are compared with those for V2 O5 , MoO3
and Sb2 O3 . Ó 2001 Elsevier Science B.V. All rights reserved.
Keywords: NaY and LaNaY zeolites; MnCl2 xH2 O;
129
Xe NMR; X-ray di€raction
1. Introduction
Zeolites are microporous materials with a high
internal surface area; their acidic properties and
composition as well as the geometry of the porous
system can be modi®ed by dispersing oxides, halides or salts on the internal surface. The ®rst
modi®cations were made during synthesis, consisting in the replacement of one element of the
framework by another [1±7]. Next the compensating cations were exchanged either in solution or
in the solid state; most of these exchanged zeolites
are excellent catalysts [8±15]. More recently, modi®cations were made after synthesis, almost always
*
Corresponding author. Tel.: +33-1-442-76013; fax: +33-1442-75536.
E-mail address: jfr@ccr.jussieu.fr (J. Fraissard).
in the solid state, leading to interesting physicochemical and catalytic properties [16±23].
We have continued these studies in the solid
state by interacting and reacting NaY or LaNaNH4 Y zeolites with oxides: V2 O5 , MoO3 and
Sb2 O3 [24±27]. The maximum degree of insertion of
these oxides is related to their physical and chemical properties as well as to di€erences in the structural composition of the zeolites; this corresponds
to the maximum increase in the cell parameters of
NaY or LaNaNH4 Y for a residual crystallinity of
at least 90%. In this article we extend this study to
(NaY or LaNaY)±MnCl2 4H2 O systems and compare them with the oxides listed above. The physical properties of MnCl2 xH2 O predispose it to
be inserted into the cavities of Y zeolite: relatively
low melting point and high solubility in hot water
(652 g/l) [28]. It is tetrahydrated up to 333 K, dihydrated up to 443 K and monohydrated up to 583
K. Between 583 and 873 K it is anhydrous. Beyond
1387-1811/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved.
PII: S 1 3 8 7 - 1 8 1 1 ( 0 1 ) 0 0 4 0 1 - 2
46
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
873 K it is transformed into oxides, Mn2 O3 and
Mn3 O4 .
In some previous work, the solid state interactions of manganese salts with di€erent zeolites
have already been described [29,30]. The catalytic
applications of Y zeolites containing manganese
are particularly interesting [31±33], for example,
the production of adipic acid and the oxidation of
cyclohexene by H2 O2 on a catalyst consisting of
cis-manganese bis-2,20 -bipyridyl inserted in the
supercages of NaX or NaY.
2. Experimental
The starting materials are: MnCl2 4H2 O (Fluka);
NaY (LZY-52 from UOP with an Si/Al ratio of
2.44), La(NO3 )3 6H2 O (Fluka) and NH4 Y (LZY64 from UOP). LaNaNH4 Y (13La, 10Na, 7NH4 )
is obtained from LZY-64 by cation exchange with
La(NO3 )3 6H2 O [26,27]. This sample is calcined
for 12 h at 593 K so that the La3‡ ions lose their
hydration sphere and migrate into the sodalite
cages [34]. We shall denote La13 Na10 -(NH4 )7 Y by
LaNaY in what follows, in order to remain consistent with previous publications.
Before mixing each of the Y zeolites (NaY or
LaNaY) with MnCl2 4H2 O it is necessary to
pretreat both compounds separately. NaY and
LaNaY must be kept for 96 h in a dessicator
containing a supersaturated solution of NH4 NO3
in order to saturate them with water. The samples
are weighed regularly in order to follow water
uptake with time; when the weight is constant
within experimental error (0.5%), the zeolite is
ready to be mixed with the chloride. All the mixtures are de®ned by RMn which corresponds to the
number of Mn equivalents per TO4 tetrahedron
(T ˆ Al, Si). To obtain exact and reproducible
compositions certain precautions regarding hydrated manganese chloride are required. Since it is
hygroscopic its weight increases by about 1.5%
every hour in air at 298 K, but at 328 K no hydration occurs. Therefore, before mixing with the
zeolites it is necessary to heat the chloride to 328 K
for 12 h, to weigh out a sample immediately and to
run an X-ray di€ractogram (which is absolutely
identical with that given by the JCPDS no. 22-721
card). For the weight m of manganese chloride it
is easy to take the weight m0 of the hydrated zeolite(which hardly varies in the time required for
the measurement) to obtain a mixture with the
exact composition. About 2 g of each zeolite±
chloride mixture with di€erent RMn values (0±0.200)
were prepared. After homogenization by magnetic
grinding the mixtures are deposited in rectangular
refractory boats, about 20 cm2 in area, are raised
to the treatment temperature Tt (to 10 K) between 313 and 1173 K at 24 K h 1 and are held at
this temperature for 16 h. Because MnCl2 4H2 O
is slightly hygroscopic at room temperature, the
weight di€erence of the mixtures before and after
thermal treatment is random. This, however, does
not prevent one from following the evolution (Da0 )
of the cell parameter a0 and the crystallinity of the
zeolite by X-ray di€raction of the mixtures, since
the cell parameter (a0 ) depends very little on the
degree of hydration. In the composition range
where RMn is 0±0.100, the ratio is varied in 0.005
steps, except in the range close to the highest level
of inclusion where the step is 0.001; in the 0.100±
0.200 range the step is only 0.050.
The treated samples (one-phase or multiphase
system) are thoroughly washed with warm water
(about 323 K) (in which MnCl2 2H2 O is highly
soluble) at slight pressure of warm water in order
to remove the added material (reversible insertion). Finally, the elements contained in the zeolite
are determined by elemental analysis before and
after thermal treatment, and after washing the
one-phase and multiphase systems. The amount of
Mn (RMn ) incorporated in the zeolite during insertion (occlusion) cannot be followed from the
concentration variation of the other elements of
3‡
the zeolite (La3‡ , Na‡ , NH‡
4 or Al ) since the
process is not of chemical origin (elimination of
the insertion in warm water). This is con®rmed by
elemental analysis, which indicates the same content of structural elements before and after the
thermal treatment at Tt , as well as after washing. It
is quite di€erent for the exchange process, where
Mn replaces part of the initial compensating cations
(Na‡ , NH‡
4 ); after washing, elemental analysis
shows a decrease in the content of compensating
cations, corresponding exactly to the manganese
content.
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
The variation of a0 , the crystallinity, the pore
volume and the Si/Al ratio of each treated zeolite is obtained from the X-ray diagrams, adsorption isotherms, 129 Xe and 29 Si NMR; the various
methods have been described in previous work
[25±27]. The percentage increase in a0 of the zeolite
is given by D0 ˆ 100…Da0 †=a0 . The maximum extent
of insertion RMn (max) is that which corresponds
to the greatest increase in the cell parameter; the
zeolite must remain a one-phase system (corresponding to an X-ray di€raction diagram where
only the NaY or LaNaY zeolite can be detected)
with a crystallinity of at least 90%.
3. Results
3.1. X-ray di€raction at ambient temperature
We shall study in turn the temperature ranges
corresponding to insertion (403±603 K), the coexistence of cation exchange and insertion (613±
793 K), cation exchange alone (793±913 K) and
solid±solid reactions above 913 K.
3.1.1. Insertion
The maximum degree of insertion RMn (max)
depends only on Tt and the halide concentration in
the initial mixture for a thermal treatment time of
16 h. Further heating does not modify the degree
of insertion at a given Tt . Fig. 1 gives the variations
Fig. 1. Unit cell parameter (a0 ) of NaY or LaNaY at di€erent
RMn values and treatment temperatures Tt : NaY:
433 K;
503 K;
558 K. LaNaY:
433 K;
503 K; 558 K.
47
of the cell parameter of the zeolite versus RMn at
various Tt .
Tt < 403 K: The two initial phases (NaY or
LaNaY and MnCl2 4H2 O) coexist whatever the
composition up to 353 K. Above 353 K, apart
from NaY or LaNaY indicated above, there is also
dihydrated manganese chloride (MnCl2 2H2 O)
corresponding to the tetrahydrate which has lost
two molecules of water.
403±483 K: (Fig. 1, Tt ˆ 433 K) ± The maximum degree of insertion is for RMn …max† ˆ 0:052
for NaY and RMn …max† ˆ 0:066 for LaNaY at
Tt ˆ 433 K. This corresponds to the maximum
percentage of occupation, in volume and in area of
the additive with respect to the total volume and
the total area of the supercages of a single unit cell
of NaY or LaNaY (Appendix and Tables 1 and 2).
Fig. 2a shows the XRD pattern of NaY with
RMn ˆ 0:052 and Tt ˆ 433 K. This maximum degree of insertion decreases slightly up to the end
of the temperature range. In this range of Tt ,
MnCl2 2H2 O by a wetting phenomenon partially
lines the zeolite cavities (4.94% and 6.28% of the
surface of the supercages of NaY or LaNaY for
RMn ˆ 0:052 and 0.066, respectively, at 433 K).
This maximal insertion leads to an increase in the
cell parameter D0 of 0.08% and 0.09% for NaY and
LaNaY, respectively.
Elemental analysis on the RMn …max† ˆ 0:052
(NaY) or 0.066 (LaNaY) sample before and after
treatment for 16 h at 433 K gives the same values
for Cl, Mn, Na, Si and Al, showing that the
MnCl2 2H2 O is inside the pores. After prolonged
washing with water at slight pressure, elementary
analysis shows that the Na, Si, Al contents are the
same but Cl and Mn have completely disappeared.
The crystallinity of these two treated and washed
zeolites remains 99%, with Si=Al ˆ 2:44, which
con®rms their high stability in this temperature
range. This insertion is reversible and there is no
cation exchange at 433 K. After washing, NaY
and LaNaY are dried in an oven for 1 h, then
rehydrated for 96 h over a supersaturated solution
of NH4 NO3 , giving cell parameters a0 of 24.662
(NaY) and 24.670 A
(LaNaY), practically the
A
(NaY)
same as those of the reference: 24.659 A
(LaNaY) with exactly the same
and 24.672 A
crystallinity (99%). When the rehydrated zeolite is
0.050, 9.6
at. V
0.075, 14.4
at. Mo
0.070,
13.44 at. Sb
0.052, 9.98
at. Mn
V2 O5
X ˆ V, Mo, Sb, Mn.
9.98
MnCl2 2H2 O
6.72 Sb2 O3
14.4 MoO3
4.8 V2 O5
Total number
of motifs
25-1043,
2MnCl2 2H2 O
11-0689, Sb2 O3
05-0508, 4 MoO3
41-426, 2V2 O5
JCPDS no./number of motifs
unit cell of
additive
4.99
1.68
3.60
2.40
Number of
unit cells of
additive
237.98
332.13
202.98
179.05
Volume of
a unit cell
of additive
3 )
(A
1187.52
557.98
730.73
429.72
Total volume of the
unit cells of
3 )
additive (A
14.18
6.66
8.73
5.13
Volume
occupied
(%)
27.03
61.26
54.91
40.96
Area of
unit cell of
additive
2 )
(A
136.32
102.91
197.64
98.3
Total area
of unit cells
of additive
2 )
(A
0.075, 14.4
at. V
0.105, 20.16
at. Mo
0.085, 16.32
at. Sb
0.066, 12.67
at. Mn
V2 O5
a
X ˆ V, Mo, Sb, Mn.
MnCl2 2H2 O
Sb2 O3
MoO3
RX (max)/
number at.
additivea
System LaNaY/additive
12.67
MnCl2 H2 O
8.16 Sb2 O3
20.16 MoO3
7.20 V2 O5
Total number of motifs
41-1426,
2V2 O5
05-0508, 4
MoO3
11-0689, 4
Sb2 O3
25-1043, 2
MnCl2 2H2 O
JCPDS no./
number of
motifs unit cell
of additive
6.34
2.04
5.04
3.60
Number of
unit cells of
additive
237.98
332.13
202.98
179.05
Volume of
unit cell of
additive
3 )
(A
1508.79
677.54
1023
644.58
Total volume
of unit cells
of additive
3 )
(A
18.01
8.09
12.24
7.70
Volume occupied (%)
27.03
61.26
54.91
40.96
Area of
unit cell of
additive
2 )
(A
171.37
124.97
276.74
147.45
Total area
of unit cells
of additive
2 )
(A
Table 2
Percentage of volume and area occupied by the additive (V2 O5 , MoO3 , Sb2 O3 or MnCl2 2H2 O) in the supercages of one unit cell of LaNaY unit cell
a
MnCl2 2H2 O
Sb2 O3
MoO3
RX (max)/
number at
additivea
System NaY/
Additive
Table 1
Percentage of volume and area occupied by the additive (V2 O5 , MoO3 , Sb2 O3 or MnCl2 2H2 O) in the supercages of one unit cell of NaY
6.28
4.58
10.13
5.40
Area occupied (%)
4.94
3.77
7.24
3.60
Area occupied (%)
48
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
49
Fig. 2. XRD patterns of NaY ‡ MnCl2 2H2 O samples: (a) RMn ˆ 0:052, Tt ˆ 433 K; (b) RMn ˆ 0:100, Tt ˆ 683 K and (c)
RMn ˆ 0:200, Tt ˆ 913 K.
Degree of
exchange (%)
24.672
24.666
24.667
24.664
24.665
0
22.2
24.6
24.6
24.2
17
4.5
3
3
3.2
12.48
13.82
13.82
13.64
0, 0
0.065,
0.072,
0.072,
0.071,
24.659
24.653
24.647
24.650
24.648
0, 0
0.074,
0.088,
0.086,
0.088,
14.20
16.90
16.50
16.90
56
41.6
38.8
39.3
38.8
0 (one-phase)
16.70 (one-phase)
19.20 (multiphase)
28.8 (multiphase)
38.40 (multiphase)
0
0.087
0.100
0.150
0.200
Number of
Na‡ , NH‡
4/
u.c.
RMn /number
of Mn2‡ /u.c.
Inital number of
Mn2‡ /unit cell (u.c.)
Initial RMn
0
25.4
30.5
29.7
30.5
Degree of
exchange (%)
Number of
Na‡ , NH‡
4/
u.c.
RMn /number
of Mn2‡ /u.c.
Washed LaNaY (one-phase)
a0 (A)
Washed NaY (one-phase)
3.1.2. Cation exchange
613±793 K: (Table 3, Tt ˆ 683 K) ± For initial
RMn ˆ 0:087 at 683 K all the (NaY or LaNaY)±
MnCl2 4H2 O mixtures treated for 16 h give a onephase system corresponding to NaY or LaNaY.
When washed with warm water at slight pressure,
Cl is completely eliminated; the other ions: Mn2‡ ,
Na‡ and NH‡
4 are partially eliminated (elemental
analysis) in contrast to the one-phase systems from
the previous temperature ranges, where the manganese chloride was completely eliminated. In this
composition range there are, therefore, both insertion and cation exchange. At Tt ˆ 683 K for
initial RMn ˆ 0:087 corresponding to 16.7 Mn2‡ /
cell, we obtain after warm water wash: 14.20
Mn2‡ /NaY unit cell and 12.50 Mn2‡ /LaNaY unit
cell corresponding to RMn ˆ 0:074 for NaY and
RMn ˆ 0:065 for LaNaY. The di€erences, 2.50
Mn2‡ /NaY unit cell and 4.20 Mn2‡ /LaNaY unit
cell, correspond to reversible insertion, with RMn ˆ
0:013 for NaY and 0.022 for LaNaY. The partial
elimination of Mn2‡ can be used to calculate the
di€erent degrees of cation exchange. Table 3 gives
the degree of cation exchange for each initial
RMn at 683 K; the maxima (30.3%, NaY) and
Unwashed zeolite
again mixed with manganese chloride under the
same conditions of composition (RMn ) and temperature as before, the manganese chloride is inserted again.
483±543 K: (Fig. 1, Tt ˆ 503 K) ± RMn …max† ˆ
0:049 (NaY) or 0.061 (LaNaY) at 483 K, decreases
slightly down to 0.047 (NaY) and 0.055 (LaNaY)
at 503 K, and remains close to this value up to 543
K.
543±613 K: (Fig. 1, Tt ˆ 558 K) ± RMn (max) is
now only 0.039 for NaY or 0.043 for LaNaY at
Tt ˆ 558 K and remains at this value to the end of
the Tt range.
In these last two temperature ranges the decrease in the maximum degree of insertion is not
accompanied by a decrease in the crystallinity
(close to 99%).
In the three previous ranges, above the curve
of RMn …max† ˆ f …Tt †, the system is multiphase:
the zeolite (NaY or LaNaY) coexists either with
dihydrated, monohydrated or anhydrous manganese chloride.
a0 (A)
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
Table 3
2‡
Dependence on RMn of the degree of exchange of Na‡ and NH‡
in washed NaY and LaNaY zeolites calcined at Tt ˆ 683 K
4 by Mn
50
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
(24.6%, LaNaY) are reached as of initial
RMn ˆ 0:100 and are almost constant up to initial
RMn ˆ 0:200. Fig. 2b shows the XRD pattern of
NaY with RMn ˆ 0:100 and Tt ˆ 683 K. These
maximally exchanged zeolites at 683 K show some
di€erences in the intensities of the di€raction peaks
‡
(partial replacement of NH‡
by Mn2‡
4 and Na
leads to di€erent structure factors, the scattering
factor of Mn2‡ being higher than that of Na‡ or
NH‡
4 ).
For initial RMn ˆ 0:087 the system is one-phase
at Tt ˆ 683 K, which makes it possible, after hot
water wash, to evaluate exactly the degree of exchange and of insertion. At 683 K, for RMn > 0:87
the system becomes multiphase (Y zeolite + anhydrous MnCl2 ); only the degree of exchange can
be evaluated after washing.
Below 683 K, the degree of exchange is less than
mentioned above; for example, at 628 K the
maximum is only 20.7% for NaY and 15.4% for
LaNaY. Above 683 K, but only for RMn (initial) ˆ
0.067, the system stays one-phase: insertion (RMn ˆ
0:009) and exchange (RMn ˆ 0:058) coexist for
NaY at 753 K, and higher insertion for LaNaY
(RMn ˆ 0:017) and a smaller degree of exchange
(RMn ˆ 0:049) at the same Tt . These di€erences
between NaY and LaNaY can be explained by the
lesser population of Na‡ and NH‡
4 in the supercages of LaNaY and the absence of substitution of
La3‡ by Mn2‡ .
Up to 793 K, the system stays one-phase for
more limited values of RMn ; thus, at 790 K the
system is one-phase for RMn (initial) ˆ 0.049.
After washing with hot water under slight pressure, elemental analysis indicates the same concentration of Mn as that of initial RMn ˆ 0:049;
insertion and exchange no longer coexist at this
temperature but only cation exchange. For NaY,
the degree of exchange decreases from 25.4% for
RMn ˆ 0:074 (683 K) to 20% for RMn ˆ 0:049 (790
K). It is the same for LaNaY whose degree of
exchange, albeit smaller, decreases in the same
proportions.
In the 613±793 K temperature range, we conclude
that exchange and insertion phenomena coexist, and
that the latter fall to zero at 793 K.
Between 793 and 913 K the system is much
more complex than in the previous temperature
51
ranges. Thus, for NaY, for example, the system is
one-phase in a more limited composition range:
RMn (initial) < 0:014, at 867 K. For RMn (initial) ˆ
0.014, washed with hot water, elementary analysis
gives the same manganese content as for the initial
mixture, which shows that only cation exchange
occurs, but it is no more than 4.75% for RMn ˆ
0:014 at 867 K. Therefore, the extent of exchange
increases progressively from 613 to 683 K and then
decreases, becoming zero at about 913 K. Above
RMn > 0:014, at the same Tt (867 K), the system
is multiphase: apart from the partially exchanged
Y zeolite, there are traces of anhydrous MnCl2
and the oxide Mn2 O3 (bixbyite). Finally, at about
913 K, whatever RMn , the system is multiphase:
amorphized Y zeolite (crystallinity 77%) is accompanied by the same phases as previously. At this
temperature, after removal of the oxides by magnetic sorting and washing with hot water under
slight pressure, elemental analysis shows that there
is no Mn, indicating that the zeolite is no longer
exchanged. 29 Si NMR shows that there is extraframework Al, in agreement with a decrease in the
number of compensating cations, NH‡
4 only.
3.1.3. Solid±solid reactions
For RMn ˆ 0:150, between 913 and 1073 K, apart
from slightly amorphized MnO2 and Mn2 O3 , there
appear new, poorly developed lines which cannot
be identi®ed but correspond to the beginning of a
solid±solid reaction. Fig. 2c shows the XRD pattern of NaY with RMn ˆ 0:200 and Tt ˆ 913 K.
For both NaY and LaNaY, for RMn > 0:150 at
1053 K there is a solid±solid reaction with the
appearance of new crystalline phases: Na0:2 MnO2 ,
Na4 MnO4 and Na2 Mn5 O10 . All these phases are
known: their structural properties are summarized
in the JCPDS cards: 27-747, 32-1127 and 27-749,
respectively; apart from these new phases there is
degraded Y zeolite, although it was never possible
to detect manganese aluminate or silicate.
Above 1073 K and RMn > 0:100, with NaY a new
crystalline phase appears: Na2 Mn6 Si7 O21 (JCPDS
no. 30-1220), accompanied by other, unidenti®ed
crystalline phases. With LaNaY, upon treatment
at high temperature (Tt ˆ 1173 K) for 72 h, a
new identi®ed phase appears: LaMNO3 (JCPDS
no. 33-713).
52
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
3.2. Xenon adsorption and
129
Xe NMR
Xenon adsorption and 129 Xe NMR spectroscopy can be used to determine the variations of
the free volume in the supercages after insertion
and cation exchange.
The xenon adsorption isotherms for Y zeolites
and the mixtures treated at 433 K for 16 h (maximal insertion) and at 683 K for 16 h (maximal
cationic exchange) are determined at 299.5 K. All
these isotherms are reversible, and there is no adsorption of Xe by MnCl2 2H2 O (433 K) and anhydrous MnCl2 (683 K). The plots of log (N ) vs.
log (P ) are almost parallel, for all the samples (Fig.
3) except for those corresponding to exchange,
where the isotherms are curved at low Xe pressure; N is the number of xenon atoms adsorbed
per gram of dehydrated zeolite and P is the equilibrium xenon pressure. For P < 1000 Torr the
isotherm of LaNaY is above that for NaY (supercages less crowded and stronger interaction with
the La3‡ cations). It is the same for the isotherm
of the LaNaY±MnCl2 2H2 O (RMn …max† ˆ 0:066)
sample treated at 433 K, which is above that of
Fig. 3. Log±log plots of the number N of adsorbed xenon
atoms per gram of anhydrous zeolite at 299.5 K vs. xenon
pressure P for samples treated at 433 K for 16 h (maximal insertion): ( , full line) NaY; ( , full line) NaY±MnCl2 4H2 O
(RMn ˆ 0:052); ( , full line) LaNaY; ( , full line) LaNaY±
MnCl2 4H2 O (RMn ˆ 0:066). Samples treated at 683 K for 16 h
then washed with warm water (maximal exchange): (H, dashes)
NaY±MnCl2 4H2 O (RMn ˆ 0:088); (I, dashes) LaNaY±
MnCl2 4H2 O (RMn ˆ 0:072).
the NaY±MnCl2 2H2 O (RMn …max† ˆ 0:052) sample treated at the same temperature. However,
both these isotherms are below that for pure zeolites. These results show that the pore system has
been a€ected by the introduction of the halide.
On the other hand, the isotherms for the samples
treated at 683 K, which show the greatest cation
exchange (30.5% for NaY, corresponding after
washing to RMn ˆ 0:088, and 24.6% for LaNaY,
corresponding to RMn ˆ 0:072), di€er slightly from
those where insertion occurs (Fig. 3). The isotherms are curved at low Xe pressures and then run
almost parallel to the isotherms for pure NaY and
LaNaY zeolites; both are close to the corresponding zeolite. For a given Xe pressure the quantity
adsorbed is much greater for the exchanged zeolites
than when there is insertion, exchange modifying
the supercage volume less than insertion.
Whatever the sample, the 129 Xe NMR spectrum
consists of only one line. For the pure zeolites the
chemical shift dXe increases linearly with N (Fig.
4). For the mixtures treated at 433 K, where insertion is greatest, the dXe ˆ f …N † plots go through
a shallow minimum at low xenon concentrations
and are then straight lines slightly above the previous ones, with a somewhat greater slope. This
variation of the slope expresses the decrease in the
free pore volume in which the xenon is adsorbed.
The increase in dXe (N ! 0) and the presence of
a minimum indicate that there are stronger xenon
adsorption centers in the supercages than in the
pure zeolites and that these can only be inserted
species. In this case, when the xenon concentration
is low it is mainly adsorbed on these sites; then,
when the concentration increases, adsorption on
the weaker sites occurs. As a result of fast exchange between sites the chemical shift of the single
coalescence signal falls when N increases, goes
through a minimum and then increases when Xe±
Xe interactions become important.
The dXe ˆ f …N † plots for the systems which
exchange the most at Tt ˆ 683 K (Fig. 4) exhibit
the same shape, but they show a higher shift and
a more pronounced minimum, displaced towards
high concentrations. This di€erence can be attributed to an even stronger interaction than before
between the xenon and the strong sites. It can
easily be explained by the fact that in cation ex-
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
Fig. 4. 129 Xe chemical shift dXe , vs. the number N of adsorbed
xenon atoms per gram of anhydrous zeolite for samples treated
at 433 K for 16 h (maximal insertion): ( , full line) NaY; ( ,
full line) NaY±MnCl2 4H2 O (RMn ˆ 0:052); ( , full line) LaNaY; ( , full line) LaNaY±MnCl2 4H2 O (RMn ˆ 0:066).
Samples treated at 683 K for 16 h, then washed with warm
water (maximal exchange): (H, dashes) NaY±MnCl2 4H2 O
(RMn ˆ 0:088); (I, dashes) LaNaY±MnCl2 4H2 O (RMn ˆ
0:072).
change the Mn2‡ cations are free to interact directly with the xenon. In the case of insertion the
Mn2‡ interaction is more or less masked and hindered by the presence of Cl . Finally, the smaller
slope observed for the samples which were exchanged and washed with hot water clearly corresponds to the elimination of the inserted phase.
4. Discussion and conclusion
Compared to the insertion of oxides in Y zeolites (those which insert: V2 O5 , MoO3 , Sb2 O3 )
[24±27], that of manganese chloride has certain
particularities.
The maximal insertion of manganese chloride
dihydrate (MnCl2 2H2 O) in the Y zeolites (NaY
and LaNaY) occurs at a thermal treatment temperature Tt much lower than that for the insertion
53
of the oxides previously studied (at about 430 K
instead of 680 K for the oxides). On the other
hand, whatever the nature of the additive, the
maximum degree of insertion is always associated
with the greatest increase in the cell parameter a0
whose order of magnitude changes little on going
from one additive to another.
Despite the high solubility of MnCl2 2H2 O in
water, compared to that of the oxides, the maximum degree of insertion is of the same order of
magnitude as for the oxides, although the volume
occupied by the additive in the supercages of NaY
or LaNaY is markedly greater for MnCl2 2H2 O.
Depending on the nature of the additive, for a
maximum degree of insertion, it appears that a
small volume of the supercages is occupied by the
additive (thus, with MnCl2 2H2 O, 14.2% of the
supercages is occupied for NaY and 18.0% for
LaNaY), which is in favor of a lining of the supercages. The percentage area or volume occupied
by the additive is small (cf. Appendix: area and
volume calculations). The occupation of the supercages of NaY and LaNaY by a small amount
of additive is con®rmed by the isotherms of the
zeolites treated at 433 K (maximum insertion) and
by the 129 Xe NMR spectra of these zeolites treated
at the same temperature. The isotherms of the
treated zeolites lie slightly below those of the untreated zeolites, showing that the pore system
(supercages) has been a€ected by this occlusion;
moreover, the dXe ˆ f …N † curves have a slightly
higher slope for the treated samples, which corresponds to a decrease in the free pore volume in
which the xenon is adsorbed.
Regardless of the nature of the additive (halide
or oxide) the insertion is greater for LaNaY than
for NaY (lesser crowding of the supercages and
stronger interaction with the cations remaining
in the cages); this is con®rmed by the isotherm
of LaNaY which lies above that for NaY. At the
present stage of this work it is impossible to know
in what form (molecular or ionic) the manganese
chloride or the oxides enters the zeolite during
insertion.
In contrast to the metal oxides, there is a phenomenon of partial cation exchange with the
halide in a 613±793 K range, demonstrated by elemental analysis on the treated and washed zeolites.
54
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
The exchange capacity is less for LaNaY than for
NaY (24.6% instead of 30.6% for NaY at 683 K),
which can be explained by a lower population of
‡
NH‡
4 and Na cations in LaNaY and the lack of
substitution, even partial, of La3‡ by Mn2‡ . This
cation exchange phenomenon can be explained by
the fact that the Mn±Cl bonds (ionic) are weaker
than the V±O or Mo±O bonds (covalent). In this
range of temperature, apart from the exchange
phenomenon, there is also insertion, the extent of
which decreases as Tt increases, disappearing at
about 750±790 K.
Above 790 K, the extent of cation exchange by
Mn2‡ is only 4.75% at 867 K, for initial RMn <
0:014 (one-phase system after thermal treatment).
For RMn > 0:014 at the same Tt , the system is multiphase: the partially exchanged zeolite is accompanied by Mn oxides and by anhydrous MnCl2 .
At about 920 K, there is practically no exchange
and the system consists of manganese oxides, accompanied by anhydrous MnCl2 . No solid±solid
reaction is detected, in contrast to what occurs
with the oxides. The solid±solid reactions occur at
820 K with the oxides and 1070 K for the halide,
producing many more new phases with the halide
than with the oxides.
volume and the area of the spherical caps (four per
supercage, corresponding to 4 circular windows).
· Total volume of the supercages/NaY or LaNaY
unit cell:
(a) volume of the eight spheres corresponding to
eight supercages
3
8…4=3†pR3 ˆ 9200 A
(b) total volume of the spherical caps
3
8 4p‰h2 =3Š‰3R hŠ ˆ 827 A
(high of the spherical cap), with
with h ˆ 1:16 A
four spherical caps per supercage
(c) total volume of the supercages
9200
3 ˆ 8373 A
3
827 A
· Total area of the supercages/NaY or LaNaY
unit cell:
(a) area of the eight spheres corresponding to
eight supercages
2
8 4pR2 ˆ 4244 A
(b) total area of the spherical caps
2
8 4…2pRh† ˆ 1515 A
(c) total area of the supercages
Appendix A
Percentage of volume and area occupied by the
additive (MnCl2 2H2 O) in the supercages of one
unit cell of NaY or LaNaY at 433 K:
Assuming that the additive enters in the same
form as it was introduced into the initial mixture
(at 433 K and atmospheric pressure) and that it is
deposited as a monolayer inside the supercages, if
the total volume and the total area of both the
supercages of a unit cell of the zeolite and of the
additive are known, it is possible to calculate
the degree of occupation (by volume and area) of
the additive/((NaY, LaNaY) unit cell) when RMn is
maximal for the halide studied.
A host cell contains eight supercages. Each
has
spherical supercage with radius R ˆ 6:5 A
and is
four circular windows with radius r ˆ 3:7 A
adjacent to four other supercages. The total volume and total area are calculated by deducting the
4244
2 ˆ 2729 A
2
1515 A
We propose to describe the method for calculating the volume and the area occupied by
MnCl2 xH2 O in the supercages of a unit cell of
NaY or LaNaY. The results for this system and
other systems (oxides-NaY or LaNaY) are presented in Tables 1 and 2.
A.1. MnCl2 2H2 O±NaY
% volume occupied by MnCl2 2H2 O: volume
of the MnCl2 2H2 O unit cells/volume of all the
supercages of a unit cell of NaY.
Given that RMn …max† ˆ 0:052; that is: 0:052 192 (number of tetrahedra per unit cell) = 9.98
Mn/NaY unit cell, that is, 9.98 MnCl2 2H2 O
motifs/NaY unit cell. Volume of the MnCl2 2H2 O
3 corresponding to
unit cell/NaY unit cell: 240.5 A
2 MnCl2 2H2 O motifs. Number of MnCl2 2H2 O
J. Thoret et al. / Microporous and Mesoporous Materials 49 (2001) 45±56
unit cells/NaY unit cell ˆ 9:98=2 ˆ 4:99. Occupation volume of MnCl2 2H2 O unit cells ˆ 240:45
3 4:99 ˆ 1200 A
3 . % volume occupied ˆ 1200=
A
8373 ˆ 14:33.
% area occupied by MnCl2 2H2 O: area of the
MnCl2 2H2 O unit cells/area of all the supercages
of a unit cell of NaY.
Assuming that MnCl2 2H2 O is deposited in the
form of a monolayer along the a- and c-axes of
the monoclinic unit cell, the area of the latter be2 ˆ 27:32 A
2 , (given that the
comes 3:68 7:41 A
angle b is close to 90° and that there are 4.99
MnCl2 2H2 O unit cells/NaY unit cell), we deduce
that the2total area of the MnCl2 2H2 O unit cells:
4:99 ˆ 136:32 A
2 . % area occupied ˆ
27:32 A
136:32=2729 ˆ 5:01
A.2. MnCl2 2H2 O±LaNaY
% volume and area occupied by MnCl2 2H2 O:
volume of the MnCl2 2H2 O unit cells/volume of
all the supercages of a unit cell of LaNaY.
Given that RMn …max† ˆ 0:066 (LaNaY); that is:
0:066 192 ˆ 12:67 Mn/LaNaY unit cell, that is
12.67 MnCl2 2H2 O motifs/LaNaY unit cell. By
an analogous calculation, we deduce:
% volume occupied ˆ 1524:45=8373 ˆ 18:21
% occupation area ˆ 173:20=2729 ˆ 6:34
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