Modification of potassium-containing zeolites loaded with Mo3S44+ clusters by solid-state reaction between zeolites and KCI

Article abstract of DOI:10.1021/jp982931r

By aqueous ion exchange, cationic molybdenum sulfide Mo₃S₄⁴⁺ clusters have been successfully introduced into KY and KL without destruction of the zeolite structures as verified by the measurements of X-ray diffraction and low-temperature nitrogen adsorption. Infrared and mass spectra indicate that a large quantity of acid sites is produced in the zeolites during the preparation and activation of the samples. However, through solid-state ion exchange of the zeolites with KCl, the produced acid sites are largely removed upon activation of the samples in vacuo or in helium flow at high temperatures. During sulfidation of the KCl-added samples, the solid-state reaction occurs to a greater extent without loss of zeolite crystallinity, eliminating nearly all the acidic protons and partly suppressing the production of Lewis acid sites in the zeolites. The KCl-added catalysts produce a significant amount of alcohols in CO hydrogenation. This product distribution is considered to reflect the decrease in the acid sites in the zeolites by the solid-state ion exchange. ? 1998 American Chemical Society.

Full text of DOI:10.1021/jp982931r

J. Phys. Chem. B 1998, 102, 10879-10884
10879
Modification of Potassium-Containing Zeolites Loaded with Mo3S44+ Clusters by Solid-State
Reaction between Zeolites and KCl
Ming Jiang
Department of Chemical Physics, UniVersity of Science and Technology of China,
Hefei, Anhui 230026, Peoples Republic of China
Takashi Tatsumi*,†
Department of Applied Chemistry, Graduate School of Engineering, The UniVersity of Tokyo,
Hongo, Tokyo 113-8656, Japan
ReceiVed: July 9, 1998; In Final Form: October 20, 1998
4
+
By aqueous ion exchange, cationic molybdenum sulfide Mo
3
S
4
clusters have been successfully introduced
into KY and KL without destruction of the zeolite structures as verified by the measurements of X-ray
diffraction and low-temperature nitrogen adsorption. Infrared and mass spectra indicate that a large quantity
of acid sites is produced in the zeolites during the preparation and activation of the samples. However, through
solid-state ion exchange of the zeolites with KCl, the produced acid sites are largely removed upon activation
of the samples in vacuo or in helium flow at high temperatures. During sulfidation of the KCl-added samples,
the solid-state reaction occurs to a greater extent without loss of zeolite crystallinity, eliminating nearly all
the acidic protons and partly suppressing the production of Lewis acid sites in the zeolites. The KCl-added
catalysts produce a significant amount of alcohols in CO hydrogenation. This product distribution is considered
to reflect the decrease in the acid sites in the zeolites by the solid-state ion exchange.
1
. Introduction
clusters with incomplete cubane-type structures can be intro-
duced as sulfide species into zeolites (e.g., NaY, HUSY, KL,
Molybdenum-based catalysts have been widely studied
9,10
NaMOR, NaHâ) by conventional aqueous ion exchange. The
because of their excellent properties in a variety of reactions,
e.g., hydrodesulfurization, hydrodenitrogenation, methanation
syntheses of light hydrocarbons and mixed alcohols from CO
hydrogenation, and dehydroaromatization of methane. As a
result of the well-known specific properties of zeolites, numer-
ous methods have been attempted to introduce molybdenum
species into zeolites.1-5 Impregnation of ammonia heptamo-
lybdate on zeolites has been applied to the preparation of
molybdenum-loaded zeolites but often gives rise to a poor
4
+
performance of the zeolites loaded with Mo3S4 clusters has
been tested for CO hydrogenation. The products deviate from
the typical Schulz-Flory distribution with the selectivity of C2
hydrocarbons as high as about 50% based upon the calculation
of carbon efficiency. Besides the hydrocarbons, however, no
oxygenate products, e.g., alcohols, have been detected.10
Alkali-promoted, especially potassium-promoted molybde-
num catalysts, have been extensively investigated for synthesis
1
1
1
of mixed alcohols from CO hydrogenation. It has been
recognized that properties of catalysts for yielding alcohols are
influenced by the basicity of promoters and/or catalysts them-
dispersion of molybdenum species on zeolites. Aqueous ion
exchange is an effective method for introducing transition metal
cations into zeolites. Molybdenum-loaded Y zeolites have been
prepared with Mo2(ethylenediamine)4Cl4 and MoO2Cl2 solu-
tions. So far however, only a few studies have succeeded in
incorporating molybdenum into zeolites by means of aqueous
ion exchange since cationic molybdenum species usually exist
in high oxidation states in strongly acidic solutions in which
the structures of many zeolites undergo destruction. Alterna-
tively, Dai and Lunsford succeeded in introducing molybdenum
species into zeolites by solid-state reactions of HY and ultrast-
12
selves. The acidity/basicity of zeolites can be adjusted, to some
extent, by varying the cations in zeolites. It has been shown
2
,3
+
+
+
that K , Rb and Cs cation-exchanged zeolites exhibit higher
1
3,14
basicity than NaY.
strong hydration of the cations, Rb and Cs are too large to
In aqueous solution, however, due to
+
+
penetrate into the small cages of zeolites (e.g., â cages in Y
+
+
zeolites). It is therefore difficult to obtain Rb and Cs zeolites
with high exchange degrees by aqueous ion exchange, although
4
+
15,16
able HY with MoCl5. Thermal decomposition of molybdenum
they are more basic than K -containing zeolites.
In this
hexacarbonyl adsorbed into zeolites has also been frequently
used for preparation of molybdenum-loaded zeolites.
work, KY and KL were used as supports for loading the cationic
Mo3S4 clusters. However, the test reaction of CO hydrogena-
5
4+
Molybdenum sulfide compound, [Mo3S4(H2O)9]Cl4, is stable
tion over the samples indicates that no oxygenate products can
be obtained (see, e.g., ref 10). The restriction of zeolite pore
structures where active phases of molybdenum sulfide clusters
stay seems not crucial for producing oxygenates with low carbon
numbers (e.g., methanol and ethanol). Thus, it is implied that
the basicity of potassium-cation-containing zeolites is not high
enough for promoting the formation of oxygenates, on one hand,
in air and soluble in aqueous solution.6 The cationic Mo3S4
-8
4+
*
To whom correspondence should be addressed.
Present address: Division of Materials Science & Chemical Engineer-
†
ing, Faculty of Engineering, Yokohama National University, Tokiwadai,
Hodogaya-ku, Yokohama 240-8501, Japan. Phone, fax: +81-45-339-
943. E-mail: tatsumi@catal.t.u-tokyo.ac.jp.
3
1
0.1021/jp982931r CCC: $15.00 © 1998 American Chemical Society
Published on Web 12/04/1998

10880 J. Phys. Chem. B, Vol. 102, No. 52, 1998
Jiang and Tatsumi
and that the acid sites may be produced in the zeolites during
activation of the incorporated Mo3S44+ species, on the other
4
+
hand. During ion exchange of the zeolites with Mo3S4 , the
solution is rather acidic with a pH value of 3-4.5, which may
also bring about the production of acid sites in the zeolites.
These findings prompt us to investigate in detail the acid
properties of the zeolites loaded with Mo3S44 clusters. To
suppress the production of the acid sites in the zeolites, KCl
was added to the samples and allowed to react with the zeolite
protons by solid-state ion exchange at high temperatures. The
production and elimination of the acid sites in the zeolites after
loading Mo3S44 species were verified by means of techniques
of infrared and mass spectroscopies, X-ray diffraction, and low-
temperature nitrogen adsorption.
+
+
2
. Experimental Section
Zeolite KY was prepared by 5-fold aqueous ion exchange of
-3
NaY (FAU, SK-40, Nikka Seiko; Si/Al ) 2.3) in 0.1 mol dm
KCl solution. The exchange degree was 98% based upon
chemical analysis of the zeolite. KL (LTL, Tosoh, TSZ-
5
00KOA; Si/Al ) 3.1) was used as supplied. The molybdenum
sulfide compound, [Mo3S4(H2O)9]Cl4, was synthesized accord-
8
ing to the procedures described by Shibahara et al. The zeolites
loaded with Mo3S44 clusters, denoted as Mo3S4-KY and
+
Figure 1. Species evolved from the temperature-programmed decom-
Mo3S4-KL, were prepared by aqueous ion exchange as
position of [Mo
spectroscopy: (a) H
m/z ) 33).
3
S
4
(H
2 9 4
O) ]Cl in helium flow as monitored by mass
9
,10
2
O (m/z ) 18); (b) HCl (m/z ) 36); (c) HS or H S
2
described before.
The molybdenum contents in the two
(
samples were 5.0 and 2.5 wt %, respectively.
The mixtures of Mo3S4-KY and Mo3S4-KL with KCl with
an atomic K/Mo ratio of 1.2 were prepared by a suspension
an automatic gas adsorption apparatus (Bel Sorp 285A, Japan).
The crystallinities of the samples were determined by means
of X-ray powder diffraction carried out on a Rigagu Denki X-ray
diffractometer using Cu KR radiation.
The test reaction of CO hydrogenation over the samples was
performed in a fixed-bed flow reactor equipped with an on-
line gas chromatograph. The reactant gas was composed of 30%
CO, 60% H2, and 10% N2. Each measurement was carried out
using 0.5 mL (ca. 0.36 g) of the sample. Under the present
experimental conditions, only trace amount of CO2 could be
detected by the thermal conductivity detector, and thus the
activity mentioned below would be referred to as that with CO2
free.
method in order to avoid possible destruction of the zeolite
structure and oxidation of Mo3S44+ clusters caused by usual
grinding in an agate mortar in the air. KCl was ground in a
mortar and mixed with Mo3S4-KY and Mo3S4-KL in hexane
solvent. The resulting suspension was stirred magnetically for
3
h and then allowed to stand for about 0.5 h. The solvent was
decanted, and the residual hexane in the mixtures was evaporated
to dryness at room temperature. The resulting samples were
denoted as Mo3S4-KY-KCl and Mo3S4-KL-KCl.
-
3
The activation of the samples was performed in vacuo (<10
-
1
Pa) at 300 °C or in helium flow (50 mL min ) at 400 °C for
2
5
h. The sulfidation of the samples was carried out in a flow of
% H2S/H2 mixed gas (50 mL min ) at 400 °C for 2 h. Prior
-
1
3
. Results and Discussion
Acid Sites of the Zeolites Loaded with Mo3S44 Clusters
to sulfidation, the samples were activated in helium flow at 200
+
°
C for 2 h to remove weakly adsorbed water.
Infrared spectra were recorded on a Perkin-Elmer model 1600
and Their Elimination. The evolved species resulting from
FTIR spectrometer. The samples were pressed into self-
supporting wafers and loaded into an infrared cell connected to
a vacuum line. Prior to measurements, the samples were
dehydrated in vacuo at 200 °C for 2 h. Pyridine was then
introduced onto the samples for adsorption for 0.5 h. After
outgassing of pyridine at 200 °C for 0.5 h, the spectra were
subsequently recorded by accumulating 64 scans at a resolution
the decomposition of [Mo S (H O) ]Cl as monitored by mass
3
4
2
9
4
spectroscopy are shown in Figure 1. A strong desorption peak
(m/z ) 18) arising from weakly adsorbed water in the compound
is observed at about 85 °C (Figure 1, spectrum a). With a further
increase in temperature, the intensity of the mass signal of water
decreases remarkably and levels off at about 500 °C. The water
desorption over 160 °C may correspond to the release of the
coordinated water in the compound. The decomposition of the
compound starts to occur at about 200 °C as indicated by the
evolution of HCl (m/z ) 36) (Figure 1, spectrum b).
-
1
of 4 cm .
Temperature-programmed decomposition of [Mo3S4(H2O)9]-
Cl4 and Mo3S44 clusters loaded into the zeolites, the solid-
state reaction between the zeolite protons and KCl, and the
desorption of ammonia adsorbed on the samples were performed
+
No mass signals corresponding to HS and H S are observed
2
(e.g., Figure 1, spectrum c), suggesting that the sulfur-containing
-
1
in helium flow of 50 mL min , and the products were
monitored by a M-QA100TS mass spectrometer (Anelva,
molybdenum species do not form hydrogen sulfide species with
the trapped water in the compound but directly decompose into
molybdenum sulfide species. For Mo S -KY and Mo S -KL,
-
1
Japan). The temperature increase was 5 °C min . Powder
samples, 20 mg of [Mo3S4(H2O)9]Cl4 and 50 mg of the zeolites
loaded with Mo3S44 clusters, were used.
3
4
3 4
in contrast, their mass spectra measured under the same
conditions exhibit no evolution of HCl with increasing temper-
ature (Figure 2, spectra a and b). This observation proves the
previous conclusions obtained from the chemical analyses and
+
The surface areas and pore volumes of the samples were
measured at -196 °C using nitrogen as the adsorption gas on

Modification of Potassium-Containing Zeolites
J. Phys. Chem. B, Vol. 102, No. 52, 1998 10881
Figure 2. HCl (m/z ) 36) evolved from the temperature-programmed
decomposition of the molybdenum sulfide clusters loaded into the
zeolites in helium flow, as monitored by mass spectroscopy: (a)
Mo
KCl.
3
S
4
-KY; (b) Mo
3
S
4
-KL; (c) Mo
3
4 3 4
S -KY-KCl; (d) Mo S -KL-
Figure 4. Infrared spectra of pyridine adsorbed on (a) Mo
activated in vacuo, (b) Mo -KL-KCl in vacuo, (c) sulfided Mo
KL, and (d) sulfided Mo -KL-KCl.
3 4
S -KL
3
S
S
3 4
4
3 4
S -
detected, as revealed by the weak band appearing at about 1452
-
1
-1
+
cm . The band at 1438 cm arises from the interaction of K
cations in the zeolite with the adsorbed pyridine, in comparison
with the spectrum of pyridine adsorbed on the parent KY (not
shown in the figure). Similar spectra are also observed with
Mo3S4-KL. As an example, the spectrum of pyridine adsorbed
on Mo3S4-KL activated in vacuo is presented in Figure 4
-
1
(
spectrum a). The strong band at 1542 cm and the weak one
-
1
at 1452 cm correspond to Brønsted and Lewis acid sites,
respectively. The infrared spectra of the parent KY and KL
zeolites activated in vacuo at 400 °C and after subsequent
pyridine adsorption have also been measured, no 1542 and 1452
cm bands corresponding to Brønsted and Lewis acid sites
being found (not shown in the figures). Therefore, the acid sites
do not originate from the parent zeolites themselves.
-
1
Figure 3. Infrared spectra of pyridine adsorbed on (a) Mo
activated in vacuo, (b) Mo -KY in helium flow, (c) Mo
KCl in vacuo, (d) Mo -KY-KCl in helium flow, (e) sulfided
Mo -KY, and (f) sulfided Mo -KY-KCl.
3
S
4
-KY
As described above, during the aqueous ion exchange step
in the preparation of the samples, the acidic [Mo3S4(H2O)9]Cl4
solution may bring about the production of the acid sites in the
zeolites. Considering activation of an aqueous ion-exchanged
Cu(II)Y (exchange degree ∼ 85%) in vacuo at 400 °C, where
a part of the Cu(II) cations underwent autoreduction, the acidic
O-H groups were also observed by infrared spectroscopy. It
is worthy to mention that in the parent NaY zeolite used for
the preparation of Cu(II)Y there were no Brønsted and Lewis
acid sites being detected by infrared spectroscopy. Therefore,
the acid sites produced in Cu(II)Y should result from the
3
S
4
S -KY-
3 4
3 4
S
S
3 4
3 4
S
UV-visible spectra of the samples that the tetravalent Mo3S44+
cations are indeed ion-exchanged onto the cationic positions of
the zeolites instead of [Mo3S4(H2O)9]Cl4 molecules being
occluded in the zeolites.10 Similar to the mass spectra of [Mo3S4-
(H2O)9]Cl4, no signals corresponding to HS and H2S species
are detected. The profiles of H2O desorption from both Mo3S4-
KY and Mo3S4-KL were also monitored by mass spectroscopy.
They are similar to those from their parent KY and KL zeolites;
that is, substantial amount of physisorbed water desorbs at about
1
7
autoreduction of Cu(II) cations. It implies that Brønsted acid
sites produced in the activated Mo3S4-KY and Mo3S4-KL
samples may also result from the decomposition of the loaded
1
20 °C (not shown in the figures).
4
+
The infrared spectra of pyridine adsorbed on Mo3S4-KY
Mo3S4 species, which make the protons from the zeolite-
trapped water migrate to the cationic positions of the zeolites.
Brønsted acid sites in zeolties can be eliminated by heat
activated in vacuo and in helium flow are shown in Figure 3.
The spectra of the samples prior to pyridine adsorption display
the stretching bands of the typical acidic O-H groups at about
treatment of the zeolites mixed with metal chlorides or oxides
-
1
15,18-26
3
650 and 3560 cm (not shown in the figures). As shown in
via a solid-state ion exchange.
The process of the solid-
+
+
+
+
+
Figure 3 (spectra a and b), after pyridine adsorption and
state reaction of alkali cations (Li , Na , K , Rb and Cs ) in
chlorides with zeolite protons has been systematically investi-
gated by Karge et al. using infrared and mass spectros-
subsequent outgassing at 200 °C for 0.5 h, a strong band is
-
1
observed at 1542 cm for the sample activated in vacuo or in
helium flow, indicating the production of Brønsted acid sites
in the zeolite. A small quantity of Lewis acid sites are also
1
5,21-24
copies.
It was found that, upon heat treatment of the
mixture, the exchanging species, i.e., the molecules of alkali

10882 J. Phys. Chem. B, Vol. 102, No. 52, 1998
Jiang and Tatsumi
chloride, would migrate and diffuse from the outer surface into
the pores or channels of the zeolites; thus, the chloride would
become well dispersed, although it may not be homogeneously
mixed with the zeolites at the very beginning.25,26 This method
is proved efficient for reducing the number of Brønsted acid
sites in the zeolites due to the substitution of the cations in alkali
chlorides for the zeolite protons.1
5,21-24
From this point of view,
a certain amount of KCl was mixed with the molybdenum-
sulfide-loaded samples in order to suppress the production of
the acid sites, especially Brønsted acid sites. Upon thermal
activation, the solid-state ion exchange between the zeolite
+
protons and K cations in KCl occurred. The infrared spectra
of pyridine adsorbed on Mo3S4-KY-KCl and Mo3S4-KL-KCl
activated in vacuo and in helium flow are presented in Figure
3
(spectra c and d) and Figure 4 (spectrum b). It can be seen
that with the addition of KCl to the samples the intensity of the
-
1
Figure 5. Profiles of the temperature-programmed desorption of
band at about 1542 cm is significantly decreased, indicating
the removal of Brønsted acid sites in the zeolites by the solid-
state ion exchange. The solid-state ion exchange has also been
monitored by mass spectroscopy. It starts to occur at about 300
ammonia (m/z ) 16) adsorbed on (a) Mo
flow, (b) sulfided Mo -KY, (c) Mo -KY-KCl activated in helium
flow, and (d) sulfided Mo -KY-KCl.
3 4
S -KY activated in helium
S
3 4
3 4
S
3 4
S
°
C, as indicated by HCl evolution (Figure 2, spectra c and d).
Considering the possible oxidation of the Mo3S44 clusters
+
loaded into the zeolites in the air, an alternative treatment was
performed by sulfiding the samples in a flow of H2S/H2 at 400
°
C. The infrared spectra of pyridine adsorbed on the sulfided
samples are presented in Figures 3 and 4. Compared with those
of pyridine adsorbed on Mo3S4-KY and Mo3S4-KL activated
in vacuo or in helium flow, the infrared spectra of the respective
sulfided samples exhibit an even stronger band at about 1542
-
1
-1
cm . Moreover, the intensity of the band at 1452 cm is
somehow also increased (Figure 3, spectrum e, and Figure 4,
spectrum c). These results imply that, due to the reducing
atmosphere of H2S/H2, more acid sites are produced in the
zeolites during sulfidation. However, with the addition of KCl
to the samples, the intensities of the two bands become lower
than those for the activated samples (compare spectrum f with
a or b in Figure 3, and spectrum d with b in Figure 4). They
indicate that the solid-state ion exchange between the zeolite
Figure 6. Profiles of the temperature-programmed desorption of
ammonia (m/z ) 16) adsorbed on (a) Mo -KL activated in helium
flow, (b) sulfided Mo S -KL, (c) Mo S -KL-KCl activated in helium
3 4
S
3
4
3 4
+
protons and K cations in KCl occurs to a greater extent during
3 4
flow, and (d) sulfided Mo S -KL-KCl.
sulfidation than by usual thermal activation and that the
production of Lewis acid sites in the zeolites is also suppressed
somehow.
The acid properties of KY and KL loaded with Mo3S44
TABLE 1: Concentrations of the Acid Sites in the
Molybdenum-Sulfide-Loaded Zeolites Determined by
Temperature-Programmed Desorption of Ammonia
Monitored by Mass Spectroscopy
+
clusters and elimination of the acid sites by the solid-state
reaction of the zeolites with KCl have been investigated in detail
by temperature-programmed desorption of ammonia adsorbed
on the samples monitored by mass spectroscopy. The spectra
corrected to those of ammonia adsorbed on the parent KY and
KL zeolites are presented in Figures 5 and 6. On the basis of
the desorption spectrum of ammonia adsorbed on a standard
H-ZSM-5 sample, the concentrations of the acid sites in the
samples were calculated as listed in Table 1.
sample
acid sites (mmol/g)
Mo
Mo
3
S
S
4
-KY (activated in He)
1.29
0.81
1.85
0.59
0.62
0.44
0.42
0.11
3
4
-KY-KCl (activated in He)
Mo S -KY (sulfided)
3
3
3
3
3
3
4
4
4
4
4
4
Mo
Mo
Mo
Mo
Mo
S
S
S
S
S
-KY-KCl (sulfided)
-KL (activated in He)
-KL-KCl (activated in He)
-KL (sulfided)
-KL-KCl (sulfided)
As described above, no acid sites were detected by the
infrared spectra of pyridine adsorbed on KY and KL. However,
in the case of ammonia adsorption on KY, one desorption peak
was observed at about 185 °C on its mass spectrum (not shown
in the figure). Niwa et al. ascribed it to the weakly held ammonia
der can be assigned to the desorption of ammonia adsorbed on
27-31
Brønsted acid sites in the zeolites.
The quantity of the acid
sites in the sulfided Mo S -KY is much larger than that in the
3
4
same sample activated in helium flow (see also Table 1). This
result is consistent with the infrared spectra of pyridine adsorbed
on the respective samples as mentioned above. With the addition
of KCl to the samples, the intensity of the low-temperature peak
decreases and the shoulder corresponding to the strong acid sites
in the zeolites is completely removed for both sulfided and
activated samples (Figure 5, spectra c and d), proving the
conclusion drawn from the infrared measurements that the solid-
state ion exchange between the zeolites and KCl suppresses not
2
7-29
in zeolites.
sulfided at the same temperature, one desorption peak at about
80 °C together with a shoulder at about 230 °C are observed
Figure 5, spectra a and b). The low-temperature peak would
For Mo3S4-KY activated in helium flow or
1
(
be tentatively assigned to the weak acid sites (most probably,
Lewis acid sites as described below) in the zeolites, although
its assignment remains disputable. The high-temperature shoul-

Modification of Potassium-Containing Zeolites
J. Phys. Chem. B, Vol. 102, No. 52, 1998 10883
the sulfidation by about 30% in comparison with that given by
activation in helium flow, but with 95% of the remaining acid
sites being strong ones (Table 1 and Figure 6, spectrum b). In
a manner similar to the case of Mo3S4-KY, with the addition
of KCl to the sample, the intensities of the low- and high-
temperature desorption peaks for Mo3S4-KL-KCl decrease upon
activation in helium flow due to the removal of the acid sites
by the above-mentioned solid-state ion exchange (Figure 6,
spectrum c). After sulfidation, both peaks become very weak
(
Figure 6, spectrum d). Compared with Mo3S4-KL activated
in helium flow, about 83% of the acid sites are removed (Table
). This verifies the conclusion obtained from infrared measure-
1
ments that the sulfidation of Mo3S4-KL-KCl not only facilitates
the solid-state ion exchange between the zeolites and KCl but
also suppresses the production of Lewis acid sites in the zeolites.
Crystallinity and Pore Volume of the Zeolites Loaded with
4
+
Mo3S4 Clusters. The crystallinity of the zeolites loaded with
3 4
Figure 7. X-ray diffraction patterns of (a) KY, (b) Mo S -KY-KCl
4
+
activated in vacuo, (c) sulfided Mo
3
S
4
-KY-KCl, (d) KL, and (e)
Mo3S4 clusters was evaluated by X-ray diffraction measure-
ments. Some representative patterns of the samples treated under
different conditions are presented in Figure 7. The introduction
of molybdenum species into zeolites often gives rise to a loss
of the zeolite crystallinity because of their acidity. As mentioned
above, the [Mo3S4(H2O)9]Cl4 solutions used for ion-exchanging
sulfided Mo -KL-KCl.
3 4
S
TABLE 2: Measurements of N
2
Adsorption on the
Molybdenum-Sulfide-Loaded Zeolites
treatment in
A
Lang.
2
pore volume
(mm /g)
3
sample
vacuo
(m /g)
4
+
the cationic Mo3S4 clusters into the zeolites are rather acidic
KY
300 °C, 2 h
200 °C, 2 h
300 °C, 2 h
400 °C, 2 h
400 °C, 2 h
820.4
758.1
773.8
790.2
672.5
800.3
291.4
263.0
270.9
278.5
236.8
277.6
with a pH value of 3-4.5. Nevertheless, the incorporation of
Mo
Mo
Mo
Mo
3
S
4
S
4
S
4
S
4
-KY
4
+
Mo3S4
cations into KY and KL does not result in the
3
3
3
-KY
destruction of the zeolite structures (see, e.g., ref 10). After
activation of the samples in vacuo or in helium flow at different
temperatures up to 500 °C, no detectable loss of the zeolite
crystallinity in Mo3S4-KY and Mo3S4-KL is observed by their
X-ray diffraction patterns (not shown in the figure), in com-
parison with those of the parent zeolite KY and KL. However,
with the addition of KCl to the samples, the activation of the
samples at high temperatures results in, to some extent, the loss
of the zeolite crystallinity. As an example, the X-ray diffraction
patterns of KY and Mo3S4-KY-KCl activated in helium flow
are presented in Figure 7 (patterns a and b). Compared with
the pattern of KY, the relative ratio of the two strongest peaks
appearing at 2θ of 6.2° and 23.5° for Mo3S4-KY-KCl
activated in helium flow is rather small. It indicates the loss of
zeolite crystallinity because of the solid-state ion exchange
between the zeolite and KCl at high temperature. However, no
detectable loss of the zeolite crystallinity is observed for the
sulfided Mo3S4-KY-KCl and Mo3S4-KL-KCl samples (Fig-
ure 7, compare pattern c with a and e with d), although, as
described above, the solid-state ion exchange during sulfidation
occurs to a greater extent.
-KY
-KY-KCl
3 4
sulfided Mo S -KY-KCl 200 °C, 2 h
only the production of Brønsted acid sites but also, to some
extent, that of Lewis acid sites in the zeolite. It is important to
mention that for the sulfided Mo3S4-KY-KCl sample the
intensity of the low-temperature peak is reduced more remark-
ably than that for the activated sample; namely, the acid sites
of the zeolites are more efficiently eliminated by sulfidation.
Compared with that of Mo3S4-KY activated in helium flow,
the overall concentrations of the acid sites decrease by about
3
7% and 55% for the activated and sulfided Mo3S4-KY-KCl
samples, respectively (Table 1), with only the weak acid sites
remaining (Figure 5, spectra c and d).
In the spectrum of temperature-programmed desorption of
ammonia adsorbed on Mo3S4-KL activated in helium flow, two
well-resolved desorption peaks are observed (Figure 6, spectra
a). The assignment of the low-temperature peak at about 170
°
C is the same as that for Mo3S4-KY. The other desorption
peak appears at a much higher temperature (∼320 °C) compared
with that observed for Mo3S4-KY (∼230 °C), indicating that
stronger acid sites are produced in KL zeolite. Unlike the case
with Mo3S4-KY, the low-temperature peak can be mostly
removed upon sulfidation of the sample. Instead, an intense peak
appears at an even higher temperature (∼370 °C) (Figure 6,
spectrum b). It reveals that stronger acid sites are formed during
sulfidation of the sample in the reducing atmosphere. The
concentration of the acid sites in Mo3S4-KL is declined due to
This conclusion can be further confirmed by the measure-
ments of nitrogen adsorption on the samples at a low temper-
ature (ca. -196 °C). The Langmiur instead of BET adsorption
model was used for the calculation of zeolite surface area. The
collected data are listed in Table 2. Compared with those of
KY, the pore volume and surface area of Mo3S4-KY can be
gradually recovered upon activation of the sample at elevated
temperatures up to 400 °C. With the addition of KCl to Mo3S4-
TABLE 3: Performance of CO Hydrogenation over the Molybdenum-Sulfide-Loaded Zeolitesa
hydrocarbons (%CO)
activity
alcohols (%CO)
OH C3+OH
sulfided sample
time (h)
(C-mmol/g-Mo min)
C
1
C
2
(C2)b)
C
3
C
4+
C
1
OH
C
2
Mo
Mo
3
S
S
4
-KY
-KL
12
6
0.95
3.73
2.63
0.85
3.90
3.29
53.3
40.7
53.1
33.6
33.6
28.3
24.5
33.3
28.7
16.4
28.9
30.7
(14.5)
(19.8)
(19.6)
(9.9)
(17.0)
(18.2)
16.0
7.2
5.5
10.8
7.3
7.3
6.2
18.8
12.7
0.4
14.4
13.2
3
4
12
Mo
Mo
3
3
S
S
4
-KY-KCl
-KL-KCl
24
6
22.5
11.7
14.5
5.7
3.8
5.4
10.6
0.3
0.6
4
24

10884 J. Phys. Chem. B, Vol. 102, No. 52, 1998
Jiang and Tatsumi
KY, the activation of the sample in vacuo at 400 °C brings
about a loss of about 20% of the zeolite pore volume because
of the solid-state ion exchange. For the sulfided Mo3S4-KY-
KCl sample, however, the zeolite pore volume is very much
similar to that of the parent zeolite KY. This result is in
accordance with that obtained from the corresponding X-ray
diffraction measurements.
The activation in vacuo (or in helium flow) or sulfidation of
the samples results in the production of acid sites in the zeolites.
With the addition of KCl to the samples, however, the
production of the acid sites can be suppressed upon activation
or sulfidation of the samples because of the solid-state ion
exchange between the zeolites and KCl. It has been found that
the solid-state reaction occurs to a greater extent during
sulfidation of the samples, which removes almost all the acid
sites in Mo3S4-KL-KCl and almost all the strong ones in
Mo3S4-KY-KCl. The test reaction of CO hydrogenation over
the two samples also indicates the removal of the acid sites in
the zeolites.
CO Hydrogenation over the Zeolites Loaded with Mo3S44
Clusters. It has been reported that over Mo3S4-NaY and
Mo3S4-KL pretreated in helium flow at 300 °C only hydro-
carbon products, mainly methane and ethane (about 45% and
+
5
0%, respectively) were obtained.10 As mentioned above, the
sulfidation of the samples produces a large quantity of acid sites
in the zeolites, while, with the addition of KCl to the samples,
the produced acid sites can be efficiently eliminated. Therefore,
Mo3S4-KY, Mo3S4-KL, and the respective samples added with
KCl were sulfided and tested for CO hydrogenation to inves-
tigate the effect of the acid sites in the zeolites upon the product
distribution. The collected data are listed in Table 3.
References and Notes
(
1) For example, see: Laniecki, M.; Zmierczak, W. Zeolites 1991, 11,
2) Ward, M. B.; Mizuno, K.; Lunsford, J. H. J. Mol. Catal. 1984, 27,
18.
(
1.
(3) Huang, M.; Howe, R. F. J. Catal. 1987, 108, 283.
(4) Dai, P. E.; Lunsford, J. H. J. Catal. 1980, 64, 173.
Over the sulfided Mo3S4-KY and Mo3S4-KL samples, only
hydrocarbon products are obtained. The selectivities on the two
samples are similar, the main products being methane and
ethane/ethylene (about 50% and 30%, respectively). The activi-
ties decrease with increasing time of stream on the samples (e.g.,
compare the data in Table 3 obtained from the reaction over
the sulfided Mo3S4-KL for 6 and 12 h). These results indicate
that the acidity of the zeolites may play an important role in
CO hydrogenation, which gives rise to mere hydrocarbon
products and results in deactivation of the samples, probably
due to the coke formation on the acid sites. Similar to the results
reported before, the activities obtained with L-type zeolite are
(5) For example, see: Gallezot, P.; Condurier, G.; Primet, M.; Imelik,
B. Am. Chem. Soc. Symp. Ser. 1977, 40, 144.
(6) Cotton, F. A.; Dori, Z.; Llusar, R.; Schwotzer, W. J. Am. Chem.
Soc. 1985, 107, 6734.
(7) Martinez, M.; Ooi, B. L.; Sykes, A. G. J. Am. Chem. Soc. 1987,
1
09, 4615.
8) Shibahara, T.; Yamasaki, M.; Sakane, G.; Minami, K.; Yabuki, T.;
Ichimura, A. Inorg. Chem. 1992, 31, 640.
9) Taniguchi, M.; Ishii, Y.; Murata, T.; Tatsumi, T.; Hidai, M. J. Chem.
(
(
Soc., Chem. Commun. 1995, 2533.
(10) Taniguchi, M.; Ishii, Y.; Murata, T.; Hidai, M.; Tatsumi, T. Stud.
Surf. Sci. Catal. 1997, 105, 893.
(11) For example, see: Santieseban, J. G.; Bogdan, G. E.; Herman, R.
G.; Klier, K. Proceedings of the 9th International Congress on Catalysis;
Phillips, M. J., Ternan, M., Eds.; Chemical Institute of Canada: Ottawa,
1988; Vol. 2, p 561.
10
much higher than those with Y zeolite. With the addition of
KCl to the samples, a substantial amount of alcohol products
can be obtained without obvious loss of the activities. It is clear
that the formation of the alcohol products is due to the
elimination of the acid sites in the zeolites by the above-
mentioned solid-state ion exchange during sulfidation of the
samples. From Table 3, the activity for alcohol formation
obtained at the reaction time of 24 h over the sulfided Mo3S4-
KL-KCl is twice as much as that over the sulfided Mo3S4-
(12) Bian, G.; Fan, L.; Fu, Y.; Fujimoto, K. Ind. Eng. Chem. Res. 1998,
7, 1736.
3
(
(
(
13) Barthomeuf, D. J. Phys. Chem. 1984, 88, 42.
14) Barthomeuf, D. Stud. Surf. Sci. Catal. 1991, 65, 157.
15) Karge, H. G.; Mavrodinova, V.; Zheng, Z.; Beyer, H. K. Guidelines
for Mastering the Properties of Molecular SieVes; Barthomeuf, D.,
Derouane, E. G., Hoelderich, W., Eds.; NATO ASI Series B221; Plenum
Press: New York, 1990; p 387.
-1
-1
(16) Jiang, M.; Karge, H. G. Unpublished results.
KY-KCl (0.67 and 0.33 C-mmol (g Mo) min , respectively).
As shown in Figure 6 (spectrum b), the solid-state reaction
between the zeolite and KCl that occurred during sulfidation
of Mo3S4-KL-KCl removes nearly all the weak and strong
acid sites in the zeolite. In the case of Mo3S4-KY-KCl (Figure
(17) Borovkov, V.; Jiang, M. Unpublished results.
(18) Clearfield, A.; Saldarriaga, C. H.; Buckley, R. C. Proceedings of
the 3rd International Conference on Molecular SieVes; Uytterhoeven, J.
B., Ed.; University of Leuven Press: 1973; p 241.
(19) Kucherov, A. V.; Slinkin, A. A. J. Mol. Catal. 1994, 90, 32.
(20) Hartmann, M.; Boddenberg, B. Microporous Mater. 1994, 2, 127.
(21) Beyer, H. K.; Karge, H. G.; Borbely, G. Zeolites 1988, 8, 79.
(22) Beran, S.; Wichterova, B.; Karge, H. G. J. Chem. Soc., Faraday
5
, spectrum b), however, large numbers of the weak acid sites
remain in KY, although the strong ones are totally removed
after sulfidation. The different acid properties of the sulfided
Mo3S4-KL-KCl and Mo3S4-KY-KCl may be responsible for
the large difference in the activities of alcohol formation between
the two samples. Over the sulfided Mo3S4-KY-KCl, about
Trans. 1990, 86, 3033.
(
(
23) Karge, H. G.; Beyer, H. K.; Borbely, G. Catal. Today 1988, 3, 41.
24) Karge, H. G.; Wichterova, B.; Beyer, H. K. J. Chem. Soc., Faraday
Trans. 1992, 88, 1345.
(25) Karge, H. G. Stud. Surf. Sci. Catal. 1994, 83, 135.
3
0% of the alcohol products are C3+OH, while in the case of
(26) Jiang, M.; Karge, H. G. Synthesis of Porous Materials: Zeolites,
the sulfided Mo3S4-KL-KCl, nearly only methanol and ethanol
are obtained. Moreover, the selectivities for alcohols over the
latter is also lower. The different product distributions may be
due to the different zeolite pore structures.
Clays, and Nanostructures; Occelli, M. L., Kessler, H., Eds.; Marcel
Dekker: New York, 1997; p 335.
(27) Katada, N.; Igi, H.; Kim, J. H.; Niwa, M. J. Phys. Chem. B 1997,
101, 5969.
(28) Sawa, M.; Niwa, M.; Murakami, Y. Zeolites 1990, 10, 532.
4
. Conclusions
The cationic molybdenum sulfide Mo3S44 clusters can be
introduced into KY and KL zeolites by aqueous ion exchange.
(29) Sawa, M.; Niwa, M.; Murakami, Y. Zeolites 1991, 11, 94.
(30) Karge, H. G.; Dondur, V. J. Phys. Chem. 1990, 94, 765.
+
(31) Karge, H. G.; Dondur, V.; Weitkamp, J. J. Phys. Chem. 1991, 95,
283.