Catalytic activity of NaZSM-5 supported Cu catalysts with or without added alkali metal in benzyl alcohol oxidation

Article abstract of DOI:10.1039/a606974f

The vapour-phase catalytic oxidation of benzyl alcohol has been carried out over NaZSM-5 supported copper and alkali-metal-added NaZSM-5 supported Cu catalysts. The NaZSM-5 zeolite supported copper catalyst has been prepared by three different methods, im

Full text of DOI:10.1039/a606974f

View Article Online / Journal Homepage / Table of Contents for this issue
Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Catalytic activity of NaZSM-5 supported Cu catalysts with or
without added alkali metal in benzyl alcohol oxidation
Souichi Sueto, Satoru Nishiyama, Shigeru Tsuruya* and Mitsuo Masai¤
Department of Chemical Science and Engineering, Faculty of Engineering, Kobe University,
Nada, Kobe 657 Japan
The vapour-phase catalytic oxidation of benzyl alcohol has been carried out over NaZSM-5 supported copper and alkali-metal-
added NaZSM-5 supported Cu catalysts. The NaZSM-5 zeolite supported copper catalyst has been prepared by three di†erent
methods, impregnation (Cu
/NaZSM-5), modiÐed impregnation (Cu
/NaZSM-5) and also ion-exchange (Cu ÈNaZSM-5)
imp1 imp2
ex
methods. The preparation method of the NaZSM-5 supported Cu catalyst inÑuenced the oxidation activity of the catalysts,
regardless of the alkali-metal addition. The NaZSM-5 supported copper catalyst (Cu
/NaZSm-5) prepared by the impregna-
imp1
tion method was found to show the highest oxidation activity among the prepared catalysts. Addition of alkaliÈmetal to the
NaZSM-5 supported Cu catalysts prepared by the di†erent methods enhanced the oxidation activity, particularly the partial
oxidation activity of the Cu-NaZSM-5 catalysts. The Na ions originally present in the NaZSM-5 support which maintain the
charge neutrality were found not to a†ect substantially the catalytic activity. The redox behaviour and the structure of the Cu
species anchored in the NaZSM-5 support were investigated using O uptake, CO adsorption and XRD measurements. The
2
interaction of the Cu species impregnated in the NaZSM-5 zeolite with O was promoted by adding alkali metals. The alkali
2
metals added to the Cu /NaZSM-5 zeolites were suggested to enhance the formation of the oxidic Cu species, which are
imp
considered to be responsible for the oxidation activity.
Because Cu ions are well known to show redox properties, a
variety of homogeneous Cu complexes have been reported1 to
show catalytic behaviour for liquid-phase oxidation. Cu
species anchored on supports such as oxides have also been
studied as catalysts for gas-phase catalytic reactions incorpor-
ating a redox cycle.2,3 Among supported Cu catalysts, interest
has been focused on Cu ion-exchanged ZSM-5 zeolite as an
supported NaZSM-5 zeolites prepared by di†erent methods
on the catalytic activity of benzyl alcohol oxidation were
examined in connection with the di†erence in the structure
and the redox properties of the supported Cu species.
Experimental
e†ective catalyst for catalytic NO decomposition.4h7 The oxi-
x
Catalyst preparation
dative coupling polymerization of 2,6-dimethylphenol to the
corresponding polyphenylene oxide, an important engineering
plastic, using a CuÈpyridine complex as the catalyst dis-
covered by Hay et al.8,9 has been one of the most successful
industrial utilizations of a homogeneous Cu complex. We
have previously reported10 that alkali-metal addition to the
CuÈpyridine complex caused an increase in the catalytic activ-
ity for the oxidative coupling reaction of 2,6-dimethylphenol.
A CuÈalkali (basic copper) system in the absence of an organic
base such as pyridine has been reported11h13 to show e†ective
catalytic activity for the oxidative coupling reaction of 2,6-
dimethylphenol. We have also reported14h16 the e†ect of
alkali-metal addition to Cu ion-exchanged NaZSM-5 zeolite
catalyst in the gas-phase catalytic oxidation of benzyl alcohol.
The added alkali metals were found14h16 to be e†ective pro-
moters for the oxidation of benzyl alcohol, particularly partial
oxidation to form benzaldehyde. Cu-supported silica catalysts
prepared by an impregnation method have been found17 to
show higher catalytic activity for benzyl alcohol oxidation
than the corresponding Cu catalyst prepared by ion-exchange.
In this study, we have investigated the catalytic activity for
benzyl alcohol oxidation of the Cu-supported NaZSM-5 cata-
lyst prepared by the two di†erent impregnation methods to
compare the catalytic activity of the Cu ion-exchanged
NaZSM-5 zeolite reported previously. The inÑuence of the
method of supporting Cu on the NaZSM-5 zeolite, the sup-
ported amount of Cu, and the alkali metal added to the Cu
NaZSM-5 zeolite (Si/Al atomic ratio, 40) was synthesized by a
method similar to that previously reported.18h20 The Cu-
supported NaZSM-5 catalysts were prepared by the following
three methods: (A) Cu-supported NaZSM-5 catalyst
(Cu
imp1
the NaZSM-5 zeolite was immersed in ca. 5 cm3 of an
/NaZSM-5) prepared by impregnation method: after
aqueous solution of prescribed amount of
a
Cu(CH COO) É H O, the Cu salt was quickly impregnated in
3
2
2
the NaZSM-5 zeolite by evaporating the solvent within about
5 min. The Cu /NaZSM-5 was dried at 393 K overnight
imp1
and calcined at 773 K for 3 h in Ñowing air. (B) Cu-supported
NaZSM-5 catalyst (Cu /NaZSM-5) prepared by an impreg-
imp2
nation method: the synthesized NaZSM-5 zeolite was
immersed in 100 cm3 of an aqueous solution of a prescribed
amount of Cu(CH COO) É H O for ca. 2 h. After standing for
3
2
2
2 h, the solvent was gradually evaporated within about 40
min. The Cu /NaZSM-5 zeolite was dried at 393 K over-
imp2
night and calcined at 773 K for 3 h in Ñowing air. (C) Cu
supported NaZSM-5 catalyst (Cu ÈNaZSM-5) prepared by
ex
an ion-exchange method: NaZSM-5 zeolite was ion-
exchanged using 100 cm3 of an aqueous solution containing a
dissolved prescribed amount of Cu(CH COO) É H O. After
3
2
2
Ðltration of the resulting Cu ion-exchanged NaZSM-5 zeolite,
the Cu ÈNaZSM-5 was dried at 393 K overnight and cal-
ex
cined at 773 K for 3 h in Ñowing air.
Alkali-metal Cu-supported NaZSM-5 zeolites were pre-
pared by impregnating a prescribed amount of alkali-metal
acetate into each NaZSM-5 supported Cu catalyst followed
by drying at 393 K overnight and calcination at 773 K for 3 h
in Ñowing air.
¤ Present address: Department of Applied Physics and Chemistry,
The Fukui University of Technology, Gakuen 3-6-1, Fukui, 910
Japan.
J. Chem. Soc., Faraday T rans., 1997, 93(4), 659È664
659

View Article Online
Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Gas-phase catalytic oxidation of benzyl alcohol
Cu(1)
/NaZSM-5 catalysts. The oxidation activity
imp1
increased on adding alkali metal to the Cu
zeolite, regardless of the alkali metal. The Na [the amount of
the added Na was the same as that added to the
Cu(1)
imp1
did not promote the catalytic activity (Table 1). Addition of
alkali metals to the Cu(1) /NaZSM-5 catalysts was found
to inhibit the deactivation of the initial oxidation activity
based on a comparison with the relationship between the con-
version and time on-stream over the Cu
lysts with or without added alkali metal.
Increase in the reaction temperature led to an increase in
the yields of benzaldehyde and carbon dioxide in both
Cu(1)
imp2
Cu \ 4) (Fig. 1). The yield of benzaldehyde catalysed by
K(4)ÈCu(1) /NaZSM-5 zeolite increased signiÐcantly with
increased reaction temperature, in contrast to the yield of
carbon dioxide which showed only a gradual increase.
The yield of benzaldehyde catalysed by the Cu
5 zeolite increased with an increase in the amount of Cu
added up to ca. 1 wt.% Cu but then decreased at higher load-
ings [Fig. 2(a)]. Yet a further increase in the amount of the
impregnated Cu did not lead to a large increase in the yield of
benzaldehyde [Fig. 2(a)]. The yield of carbon dioxide cataly-
/NaZSM-5
imp1
The gas-phase catalytic oxidation was performed in a conven-
tional Ðxed-bed type vertical microreactor under a continuous
gas Ñow at atmospheric pressure. Further details for the reac-
tion procedure and the analyses of the reaction products are
given elsewhere.16 The main oxidation products were benz-
aldehyde and carbon dioxide. The conversion of benzyl
alcohol and the yields of both benzaldehyde and carbon
dioxide were calculated as previously.16 The carbon balances
before and after the catalytic oxidation of benzyl alcohol were
80È100%, usually [90%.
/NaZSM-5 zeolite] added to the NaZSM-5 zeolite
imp1
/NaZSM-5 cata-
imp1
Thermal gravimetry (TG)–di†erential thermal analysis (DTA)
measurement of the carbonaceous material produced
/NaZSM-5 and K(4)ÈCu(1)
/NaZSM-5 (K/
imp2
Carbonaceous material (coke) accumulated on the catalyst
during the benzyl alcohol oxidation was oxidized using
DTAÈTG apparatus (Shimazu Model DTG-40) into which a
controlled mixed gas of O and N can be introduced. The
imp2
/NaZSM-
imp1
2
2
rate of temperature increase was 20 K min~1.
Measurement of O uptake
2
The amount of O uptake of the pre-reduced catalysts was
2
measured using conventional semi-micro gas adsorption
sed by the Cu
imp1
supported Cu was appreciably lower than the yield of benz-
/NaZSM-5 zeolite relative to the amount of
equipment made of a capillary-glass tube to make the dead
volume as small as possible. Details of the procedure are given
elsewhere.16
aldehyde. The K(4)ÈCu
/NaZSM-5 zeolite showed con-
imp1
siderably higher oxidation activity than the Cu
imp1
zeolite with no potassium [Fig. 2(b)]. The yield of benz-
/NaZSM-5
Measurement of CO adsorption
aldehyde catalysed by the K(4)ÈCu
sharply increased with an increase in the amount of supported
Cu up to ca. wt.% Cu. Adding potassium to the
/NaZSM-5 zeolite
imp1
The amount of CO adsorption was measured using the semi-
micro gas adsorption equipment used for the measurement of
1
Cu /NaZSM-5 zeolite was thus conÐrmed to promote
O uptake. Details of the procedure are given elsewhere.16
imp1
2
selectively partial oxidation activity with benzaldehyde forma-
tion.
Measurement of X-ray di†raction (XRD) pattern of
K–Cu-supported NaZSM-5 catalysts
The yield of benzaldehyde catalysed by Cu
/NaZSM-5
imp2
zeolite increased with an increase in the amount of impreg-
nated Cu up to ca. 0.5 wt.%, but a further increase in Cu led
essentially to a plateau in the yield of benzaldehyde [Fig.
3(a)].
K(1)ÈCu
initial increase in the amount of supported Cu and increased
to a lesser degree with a further increase in the supported Cu
[Fig. 3(b)]. Yields of carbon dioxide catalysed by both cata-
lysts were very low and scarcely increased with Cu loading.
The yield of benzaldehyde increased with an increase in the
added alkali metal/Cu (alkali metal \ Na or K) atomic ratio
The powder XRD patterns of the catalyst samples were mea-
sured at room temperature using Rigaku XRD equipment
with Cu-Ka radiation as the X-ray source.
The
yield
of
benzaldehyde
catalysed
by
/NaZSM-5 zeolite also sharply increased with an
imp2
Results
Gas-phase catalytic oxidation of benzyl alcohol
The oxidation of benzyl alcohol was performed using alkali-
metalÈCu
(1.0
wt.%)
supported
NaZSM-5
[Cu(1)
/NaZSM-5] zeolites (Table 1). The Cu species pre-
imp1
pared by impregnation method 1, as well as by the ion-
exchange method reported previously,14h16 was found to
show catalytic activity for benzyl alcohol oxidation as evi-
denced from the comparison between NaZSM-5 and
Table 1 The e†ect of added alkali metal on the benzyl alcohol oxi-
dation catalysed by M-Cu
(M \ alkali metal)
/Na-ZSM-5 (Si/Al \ 40) zeolitesa
imp1
catalyst
benzaldehyde yield (%)
CO yield (%)
2
NaZSM-5
Na-NaZSM-5
Cu /NaZSM-5
0.4
0.4
1.8
2.9
3.8
7.2
5.7
4.7
trace
trace
0.2
0.2
0.2
0.5
0.4
0.4
imp1
LiÈCu
/NaZSM-5
/NaZSM-5
imp1
NaÈCu
KÈCu
imp1
/NaZSM-5
/NaZSM-5
imp1
RbÈCu
CsÈCu
imp1
/NaZSM-5
imp1
Fig. 1 E†ect of reaction temperature on the yields in the benzyl
alcohol oxidation. Catalyst, 0.5 g; catalyst mass/Ñow rate (W /
F) \ 21.7 g cat. min mol~1; PN2 \ 9.02 ] 104 Pa; PO2 \ 8.34 ] 103
a Catalyst, 0.5 g, Cu \ 1.0 wt.%, added M/Cu atomic ratio \ 1, Si/Al
atomic ratio \ 40; reaction temperature, 573 K; W /F \ 21.7 g cat.
min mol~1; partial pressure of N \ 9.02 ] 104 Pa; partial pressure
Pa;
P
\ 2.78 ] 103 Pa; (…, =), KÈCu(1)
/NaZSM-5 (Si/
2
BOH
imp2
/NaZSM-5 (Si/Al \ 40) catalyst;
of
O \ 8.34 ] 103
Pa;
partial
pressure
of
benzyl
Al \ 40) catalyst; (L, K), Cu(1)
2
imp2
alcohol \ 2.78 ] 103 Pa.
(…, L), benzaldehyde yield; (=, K), CO yield.
2
660
J. Chem. Soc., Faraday T rans., 1997, V ol. 93

View Article Online
Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Fig. 2 (a) InÑuence of Cu loading on the yields using
Fig. 3 (a) InÑuence of Cu loading on the yields using
Cu
/NaZSM-5 (Si/Al \ 40) catalyst. Reaction temperature, 573 K;
Cu
/NaZSM-5 (Si/Al \ 40) catalyst. Conditions as in Fig. 2; (…),
imp1
imp2
other conditions as in Fig. 1; (…), benzaldehyde; (L), CO . (b) InÑu-
benzaldehyde; (L), CO . (b) InÑuence of Cu loading on the yields
2
2
ence of Cu loading on the yields using K(1)ÈCu(1)
/NaZSM-5 (Si/
using K(1)ÈCu(1)
/NaZSM-5 (Si/Al \ 40) catalyst. Conditions as in
imp1
imp2
Al \ 40) catalyst. Conditions as in (a); (…), benzaldehyde; (L), CO .
(a); (…), benzaldehyde; (L), CO .
2
2
for the alkali-metalÈCu
/NaZSM-5 catalysts, passed
imp1
results. Thus the addition of alkali metal to the
through a maximum value at the atomic ratio of ca. 1, and
decreased upon further increase of added alkali metal/Cu
atomic ratio, regardless of the alkali metal [Fig. 4(a), (b)].
Cu
/NaZSM-5 zeolite caused the formation of carbon-
imp1
aceous material on the zeolite to decrease appreciably, in
agreement with the reactivity in which the deactivation was
Yields of CO were very low and hardly varied with an
2
largely inhibited over the KÈCu
A sharp peak at 573 K and a broad peak having a maximum
/NaZSM-5 zeolite catalyst.
increase in the atomic ratio.
imp1
The e†ect of the amount of
K
added to the
at ca. 673 K, and a sharp peak at 673 K were observed in the
Cu(1) /NaZSM-5 zeolite on the oxidation activity is illus-
imp2
DTA spectra of the used Cu(1)
imp1
/NaZSM-5 zeolites (Fig. 7). These exothermic
/NaZSM-5 and used
trated in Fig. 5. An increase in the K/Cu atomic ratio caused
an increase in the yield of benzaldehyde and produced a
maximum value for the benzaldehyde yield at a K/Cu atomic
ratio of ca. 4.
K(1)ÈCu(1)
imp1
DTA peaks are considered to be due to the oxidation of car-
bonaceous materials accumulated on the samples.
Fig. 6 shows the e†ect of the added Na/Cu atomic ratio on
the oxidation activity for benzyl alcohol using
O uptake of pre-reduced Cu /NaZSM-5 and the alkali-
2
imp
NaÈCu(1) ÈNaZSM-5 zeolite as the catalyst. The yield of
metal–Cu /NaZSM-5 zeolites
ex
imp
benzaldehyde showed a maximum value at an added Na/Cu
atomic ratio of ca. 4, as observed using KÈCu(1)
5 catalyst (Fig. 5).
/NaZSM-
The amounts of O uptake of the Cu /NaZSM-5 and the
imp2
2
imp
alkali-metalÈCu /NaZSM-5 zeolites were measured after
imp
reducing both the Cu supported NaZSM-5 zeolites by evac-
uation at 773 K and treatment with CO at 773 K (Table 2).
The added alkali metal/Cu atomic ratios of the Cu supported
NaZSM-5 zeolites prepared by impregnation methods (A) and
Carbonaceous materials accumulated on the used
Cu
/NaZSM-5 and K–Cu /NaZSM-5 catalysts
imp1
imp1
Carbonaceous materials (coke) accumulated on both the used
Cu(1) /NaZSM-5 and K(1)ÈCu(1) /NaZSM-5 catalysts,
which were used over a process time of 4 h (reaction condi-
tions as in Table 1), were observed by di†erential thermal
analysis (DTA)Èthermogravimetry (TG). The temperature
programmed oxidation (TPO) spectra obtained by DTAÈTG
are illustrated in Fig. 7. The amount of coke accumulated on
(B) were
1
and 4, respectively, since the alkali
metalÈCu
/NaZSM-5 and alkali metalÈCu /NaZSM-5
imp1
imp1
imp1
imp2
zeolites showed maximum activities at these ratios, as illus-
trated in Fig. 4(b) and 5. The amounts of O uptake of the
alkali-metalÈCu supported NaZSM-5 zeolites which were pre-
reduced were found to be greater than those of the corre-
sponding Cu-supported zeolites without added alkali metal.
2
the Cu(1)
imp1
lysts was 1.70 and 1.25 mg, respectively, based on the TG
/NaZSM-5 and K(1)ÈCu(1)
/NaZSM-5 cata-
The amounts of O uptake of the pre-reduced alkali-
imp1
2
metalÈCu
/NaZSM-5 zeolites were found to be greater
imp1
J. Chem. Soc., Faraday T rans., 1997, V ol. 93
661

View Article Online
Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Fig. 6 InÑuence of added Na/Cu atomic ratio on the yield using
NaÈCu(1) -NaZSM-5 (Si/Al \ 40) catalyst. Conditions as in Fig. 2;
ex
(…), benzaldehyde; (L), CO .
2
at 773 K for 2 h, were measured at room temperature. The
amount of CO adsorption of the Cu(1)
/NaZSM-5 zeolite
imp2
was 8.1 ] 10~6 mol (g cat.)~1 In contrast, all the alkali-metalÈ
Cu(1) /NaZSM-5 zeolites (alkali metal \ Na, K, Rb or Cs;
imp2
Fig. 4 (a) InÑuence of added Na/Cu atomic ratio on the yields using
NaÈCu(1)
/NaZSM-5 (Si/Al \ 40) catalyst. Conditions as in Fig. 2;
imp1
(…), benzaldehyde; (L), CO . (b) InÑuence of added K/Cu atomic
2
ratio on the yields using KÈCu(1)
Conditions as in (a); (…), benzaldehyde; (L), CO .
/NaZSM-5 (Si/Al \ 40) catalyst.
imp1
2
than those of the pre-reduced alkali metalÈCu
zeolites, irrespective of the particular added alkali metal.
/NaZSM-5
imp2
CO adsorption of Cu
/NaZSM-5 and alkali-
imp2
/NaZSM-5 zeolites
metal–Cu
imp2
The amounts of CO adsorbed on the Cu
imp2
/NaZSM-5 zeolites, which were evacuated
imp2
/NaZSM-5 and
alkali-metalÈCu
Fig. 7 DTAÈTG spectra of used Cu(1)
/NaZSM-5 (Si/Al \ 40)
imp1
/NaZSM-5 (Si/Al \ 40). Rate of temperature
and used K(1)ÈCu(1)
imp1
increase, 20 K min~1; O ÈN (1/4) (30 cm3 min~1); a, TGA spectrum
2
2
of used Cu(1)
used Cu(1)
/NaZSM-5 (Si/Al \ 40) catalyst; b, DTA spectrum of
imp1
/NaZSM-5 (Si/Al \ 40) catalyst; c, TGA spectrum of
imp1
used K(1)ÈCu(1)
/NaZSM-5 (Si/Al \ 40) catalyst; d, DTA spec-
imp1
trum of used K(1)ÈCu(1)
/NaZSM-5 (Si/Al \ 40) catalyst.
imp1
Table 2
O uptake of Cu supported NaZSM-5 (Si/Al \ 40) zeolites
2
with and without alkali metala
Amount of O uptake 106 mol (g-cat)~1
2
catalyst
impregnation method 1
2
Cu(1) /NaZSM-5
23.4
26.8
27.5
33.8
27.3
27.5
23.6
24.2
24.2
30.3
27.1
26.3
imp
LiÈCu(1) /NaZSM-5
imp
NaÈCu(1) /NaZSM-5
imp
KÈCu(1) /NaZSM-5
imp
CsÈCu(1) /NaZSM-5
imp
RbÈCu(1) /NaZSM-5
imp
Fig. 5 InÑuence of added K/Cu atomic ratio on the yield using
KÈCu(1)
/NaZSM-5 (Si/Al \ 40) catalyst. Conditions as in Fig. 2;
a Impregnation method 1, added alkali metal/Cu (atomic ratio) \ 1;
impregnation method 2, added alkali-metal/Cu (atomic ratio) \ 4.
imp2
(…), benzaldehyde; (L), CO .
2
662
J. Chem. Soc., Faraday T rans., 1997, V ol. 93