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Olefin metathesis over UV-irradiated silica
applied surface science ELSEVIER
Applied Surface Science 121 / 122 (1997) 296-300
Olefin metathesis over UV-irradiated silica Tsunehiro Tanaka *, Shigehiro Matsuo, Takashi Maeda, Hisao Yoshida Takuzo Funabiki, Satohiro Yoshida Department of Molecular Engineering, Kyoto Unit,ersiO', Kyoto 606-01, Japan Received 5 November 1996; accepted 1 February 1997
Abstract
Photoirradiated silica evacuated at temperatures higher than 800 K was found to be active for olefin metathesis reactions. The analysis of products shows that the metalacyclobutane intermediate is likely. The instantaneous response of the reaction to the irradiation and the activity change with various UV filter showed that the reaction is induced by UV-excitation of silica. The correlation between the evacuation temperature and the activity showed that the surface free from water molecules plays a role in the reaction and the removal of isolated OH groups strongly relates to the generation of active sites. © 1997 Elsevier Science B.V.
1. Introduction Olefin metathesis is one of the important reactions in organic synthesis and has been recognized to take place in the presence of the catalyst involving transition metal elements such as Mo [1], W [2,3], Re [4], etc. The metal oxo bond has been believed to be necessary for the reaction because the bond may play a signifcant role in the formation of the carbene a n d / o r metalacyclobutane intermediates [5] although these intermediates have not been evidenced in the heterogeneous catalyst systems. Silica is a common material often used as a catalyst support, an adsorbent etc., and it is widely accepted as an inert material. However, silica can function as a catalyst for some reactions [6-12], in
* Corresponding author. Tel.: + 81-75-7535703; fax: + 81-757535925; e-mail [email protected]. i Present address: Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-01, Japan.
particular when it is activated by photoirradiation [13-15]. So far, there have been no reports on catalysis by silica for metathesis. However, we have found [16] that olefin metathesis proceeds on UVirradiated silica and here we report the reactions with ethene, propene, butenes and pentenes under photoirradiation.
2. Experimental The silica samples employed here were mainly Cab-osil M5 and home-made silica prepared by hydrolysis of tetraethyl orthosilicate (TEOS) [ 17], which were impregnated with water and dried, followed by calcination in the air stream at 773 K for 5 h. The silica samples were heated under an atmosphere of 0 2 (50 Torr) at the given temperature in Table 2 for 1 h and evacuated at the same temperature for 1 h. An ultrahigh pressure 250 W Hg lamp was used as a light source. The experiment of the temperature pro-
0169-4332/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0 1 6 9 - 4 3 3 2 ( 9 7 ) 0 0 3 0 9 - 7
T. Tanaka et al. /Applied Surface Science 121 / 122 (1997) 296-300
grammed desorption (TPD) of water was carried out as described previously [18] and infrared absorption spectra (IR) were recorded with a Perkin Elmer IR spectrometer Paragon 1000 attached with an in situ cell.
297
1E. .
(b)
~ 10 3. Results and discussion Propene was introduced to the system and the catalyst bed made of quartz was irradiated by ultra high pressure Hg lamp, Fig. 1 shows the time course of the products found in the system. The products were ethene, trans-2-butene, cis-2-butene and a very small amount of l-butene. Other products were not detected. This indicates that propene was converted to these products only within the experimental error. The ratio of ethene to 2-butenes was around 1.03 as depicted in Fig. 1, showing that propene is disproportioned to C'2 and C'4 compounds. The result that the main products are 2-butenes as C'4 compounds strongly suggests that metathesis reaction occurs. The production of trans isomer is favorable. The reaction of ethene was also examined. In the case of ethene, if the only reaction was metathesis, then no new products should be observed. After the reaction under irradiation for 1 h on silica, nothing other than ethene was observed in the system. When a mixture of C H 2 = C H 2 and C D 2 = C D 2 was intro-
1.o~
O 0
~ 40 irradiation
0.0 80 time
120 /
rain
Fig. l. Time courses of the reaction: yields based on propene of (a) ethene, (b) trans-2-butene, (c) cis-2-butene, (d) l-butene and (e) the ratio of C ' 2 / C ' 4 . The powder samples (400 rag) was spread on the flat bottom (12 cm 2) of the reactor. Pretreatment temperature was 1073 K.
duced as reactant, the production of C 2 H 2 D 2 w a s observed. Neither C 2 H 3 D n o r C2HD 3 was found in the system. This confirms that the only reaction occurring over the silica was metathesis. Table 1 summarizes the results of the reactions of
Table 1 Reaction of olefins over photoirradiated silica. Gaseous composition after irradiation Reactants
lrrad, time (h)
Gaseous composition after irradiation
t-2-C4 c-2-C4
1 I
1-C4
1
t-2-C5
0.5
c-2-C5
0.5
t-2-C4 (95.6) c-2-C4 (4.4) t-2-C4 (6.6) c-2-C4 (93.4) (22 (1.4) C3 (0.6) 1-C4 (95.5) t-2-C4 (0.7) c-2-C4 (0.3) 3-C6 (1.3) t-2-C4 (0.85) c-2-C4 (0.13) 1-C5 (0.10) t-2-C5 (93.3) c-2-C5 (4.62) 3-C6 (0.97) C2 (0.01) t-2-C4 (0.08) c-2-C4 (0.08) 1-C5 (0.08) t-2-C5 (3.31) c-2-C5 (96.3)
C2 (49.8) t-2-C4 (50.2)
1
C2 (50.5) c-2-C4 (49.5)
1
3-c6 (0.13)
C2 (43.7) C3 (16.6) t-2-C4 (34.9) c-2-C4 (4.7) C2 (43.6) C3 (18.1) t-2-C4 (13.8) c-2-C4 (24.4)
30 /xmol of reactant(s) was introduced to the closed reactor. The compounds in italics are the products of metathesis reactions. The values in parentheses are the gaseous composition in percent. C n stands for the linear alkene of n carbon atoms. The marks t- and c- stand for t r a n s and cis isomers respectively.
7". Tanaka et al. / Applied Surface Science 121 / 122 (1997) 296-300
298
various olefins. All the products were those e x p e c t e d in metathesis reaction. Therefore, in the case of 2-butenes, no other products than 2-butenes were obtained. H o w e v e r , cis-trans isomerization was observed clearly. In particular, the isomerization of the cis-isomer to the trans-isomer is remarkable. In the case o f 2-pentenes, trans-2-pentene was 10 times more reactive than cis-2-pentenes and trans-2-butene is selectively f o r m e d from trans-2-pentene. This is expected from the result that the formation of trans2-butene is m o r e favorable than that of cis-2-butene in the metathesis of propene. The metathesis of cis-2-pentene proceeds slowly and trans-cis isomerization proceeds faster than the metathesis. This may be the reason why trans-2-butene is preferentially f o r m e d in the case o f cis-2-pentene metathesis. As a conclusion, the trans-isomer is more reactive possibly because the trans-intermediate on the catalyst is more stable. This presumably leads to the retention of the trans structure during the metathesis. If so, the intermediate c y c l o m e t a l a b u t a n e is likely. The d e p e n d e n c e of the reaction upon the excitation w a v e l e n g t h was e x a m i n e d by using an U V filter, as shown in Table 2 (entries 1-3). U p o n irradiation with visible light only (entry 1), the reaction was limited to low conversion levels with a high ratio of C ' 2 : C ' 4 . On the other hand, irradiation with U V light (entries 2, 3) e n h a n c e d the metathesis, indicating that U V light is required for the metathesis reaction on the silica surface. Fig. 2 shows the
12
light o f f ~ , . .
1o
light off 6
\
c
c 4
light on
2
o 0
I 20
40
I 60 time / min
I 80
I 100
120
Fig. 2. Response of the reaction to the irradiation.
response of the reaction to photoirradiation. It reveals that the reaction p r o c e e d e d only under irradiation. The instantaneous response indicates clearly that the metathesis reaction was induced by irradiation. In order to e x a m i n e whether or not the photometathesis is general for all the silica, we carried out the propene reaction on other kinds o f silica, the results of which are listed in Table 2 (entries 6 and 7). The metathesis reaction was o b s e r v e d for each of the silicas. The difference is found in the activity only. W e tested other typical metal oxides such as
Table 2 Effects of pretreatment temperature and irradiation wavelength a Entry
T (K)
Filter
Conv. (%)
C2 : C4
1 2 3 4 5 6 '~ 7~
1073 1073 1073 873 673 1073 1073
Y-43 ~ UV-29 c none none none none none
0.27 4.75 11.4 6.95 5.86 26.3 30.1
1.25 1.05 1.02 1.00 0.78 1.12 1.06
Yields (%) C2
trans-C4
cis-C4
I -C4
0.15 2.43 5.74 3.47 1.37 13.93 15.48
0.07 1.59 4.08 2.50 0.92 0.03 0.10
0.05 0.73 1.56 0.95 0.70 9.06 10.75
0.00 0.0l 0.05 0.01 0.13 3.31 3.78
a The measurement was carried out under irradiation for l h in a closed static system (39.5 ml; sample 100 rag; propene 30 /.zmol). The catalyst was Cab-osil M5 except for entries 6 and 7. t, Y-43 filter admits light with / > 430 nm. UV-29 filter admits light with l > 290 nm. d Home-made silica was used. e Used silica, JRC-SIO4, was supplied from Catalysis Society of Japan.
T. Tanaka et al./ Applied Surface Science 121 / 122 (1997) 296-300
MgO, A1203, SiO2-A1203. On these oxides, although other reactions occurred to a small extent, the distribution of products was quite different from that for the metathesis reaction. The metathesis reaction under irradiation seems to be characteristic for the silica surface. The effect of the pretreatment temperature is shown in Table 2 (entries 3-5). The silica is activated by pretreatment at a higher temperature, suggesting that the desorption of the hydroxyl groups on the silica surface might relate to active sites. In Fig. 3, the TPD profile of water from home-made silica is shown. There are two maxima at 560 and 995 K. From the aid of infra-red spectra of the silica evacuated at several temperatures depicted in Fig. 4, it is clearly exhibited that the first maximum at 560 K in TPD corresponds to the desorption of hydrogen bonded water molecules and the second maximum at 995 K is that of water resulting from the recombination of isolated OH groups. In Fig. 3, the activity of the home-made silica is also plotted and it indicates that metathesis reaction occurs on the surface free from hydrogen bonded OH groups and the activity increases with the desorption degree of isolated OH groups. In general, the surface area of silica is greatly reduced by evacuation at a temperature higher than 800 K. Nevertheless, the reaction activity increased with an evacuation temperature, suggesting
1.4
--16
1.2
-- 14
=1.0
12
=0.8
<
0 E0.6
1.6-
299
,~.,4¢e..~ -
'S 0.5
o0L
4000
3800
3600
,
3400
,
3200
3000
wavenumber / cm "1
Fig. 4. OH region of infrared absorption spectra of the home-made silica sample evacuated at (a) 373, (b) 473, (c) 573, (d) 673, (e) 773, (f) 873, (g) 973 and (h) 1073 K.
that structural reconfiguration of the silica surface by the removal of the isolated OH groups strongly correlates to the generation of active sites. The nature of active sites including the excitation mechanism is still under investigation.
Acknowledgements This work was partially supported by a grant-inaid from the Japan Ministry of Education, Science, Art, Sports and Culture. H.Y. acknowledges support by the Fellowship of JSPS. We thank Mr. H. Aritani and Mr. S. Takenaka at the Kyoto University for their collaboration and suggestions.
_~. o
"~
6
~0.4
4
._E 0 . 2
~e
2 0.0 400
600
800
1000
1200
I 1400
0
temperature / K
Fig. 3. TPD profile of water molecules desorbed from silica and the change of the activity of the home-made silica with the evacuation temperature.
References [1] R.L. Banks, G.C. Nailey, Ind. Eng. Chem. 3 (1964) 170. [2] N. Calderon, H.Y. Chen, K.W. Scott, Tetrahedron Lett. 34 (1967) 3327. [3] R.L. Banks, R.B. Regier, Ind. Eng. Chem. Prod. Res. Dev. 7 (1971) 29. [4] R. Nakamura, H. Iida, E. Echigoya, Chem. Len. (1972) 273. [5] J.L. Herrison, Y. Chauvin, Macromol. Chem. 141 (1971) 161. [6] J.N. Amor, J. Catal. 70 (1981) 72. [7] J.N. Amor, P.M. Zambi, J. Catal. 73 (1982) 57.
300
7~ Tanaka et al. /Applied SurJktce Science 121 / 122 (1997) 296-300
[8] M. Lacroix, G.M. Pajonk, S.J. Teichner, J. Catal. 101 (1986) 314. [9] Y, Matsumura, K. Hashimoto, S. Yoshida, J. Catal. i17 (1989) 135. [10] E.W. Bittner, B.C. Bockrath, J.M. Solar, J. Catal. 149 (1994) 206. [1 I] Y. Matsumura, K. Hashimoto, S. Yoshida, J. Chem. Soc. Chem. Commnn. (1987) 1599. [12] G.N. Kastanas. G.A. Tsigdinos, J. Schwank, J. Appl. Catal. 44 (1988) 33. [13] A. Morikawa, M. Hattori, K. Yagi, K. Otsuka, Z. Phys. Chem. (NF) 104 (1977) 309.
[14] M. Anpo, C. Yun, Y. Kubokawa, J. Catal. 61 (1980) 267. [15] A. Ogata, A. Kazusaka. M. Enyo, J. Phys. Chem. 90 (1986) 5201. [16] H. Yoshida, T. Tanaka, S. Matsuo, T. Funabiki, S. Yoshida, J. Chem. Soc. Chem. Commun. (1995) 761. [17] S. Yoshida, T. Matsuzaki, T. Kashiwazaki, K. Mori, K. Tarama, Bull. Chem. Soc. Jpn. 47 (1974) 1564. [18] Y. Tanaka, T. Yoshida, H. Yoshida, H. Aritani, T. Funabiki. S. Yoshida, J.-M. Jehng, I.E. Wachs, Catal. Today 28 (1996) 71.
Applied Surface Science 121 / 122 (1997) 296-300
Olefin metathesis over UV-irradiated silica Tsunehiro Tanaka *, Shigehiro Matsuo, Takashi Maeda, Hisao Yoshida Takuzo Funabiki, Satohiro Yoshida Department of Molecular Engineering, Kyoto Unit,ersiO', Kyoto 606-01, Japan Received 5 November 1996; accepted 1 February 1997
Abstract
Photoirradiated silica evacuated at temperatures higher than 800 K was found to be active for olefin metathesis reactions. The analysis of products shows that the metalacyclobutane intermediate is likely. The instantaneous response of the reaction to the irradiation and the activity change with various UV filter showed that the reaction is induced by UV-excitation of silica. The correlation between the evacuation temperature and the activity showed that the surface free from water molecules plays a role in the reaction and the removal of isolated OH groups strongly relates to the generation of active sites. © 1997 Elsevier Science B.V.
1. Introduction Olefin metathesis is one of the important reactions in organic synthesis and has been recognized to take place in the presence of the catalyst involving transition metal elements such as Mo [1], W [2,3], Re [4], etc. The metal oxo bond has been believed to be necessary for the reaction because the bond may play a signifcant role in the formation of the carbene a n d / o r metalacyclobutane intermediates [5] although these intermediates have not been evidenced in the heterogeneous catalyst systems. Silica is a common material often used as a catalyst support, an adsorbent etc., and it is widely accepted as an inert material. However, silica can function as a catalyst for some reactions [6-12], in
* Corresponding author. Tel.: + 81-75-7535703; fax: + 81-757535925; e-mail [email protected]. i Present address: Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-01, Japan.
particular when it is activated by photoirradiation [13-15]. So far, there have been no reports on catalysis by silica for metathesis. However, we have found [16] that olefin metathesis proceeds on UVirradiated silica and here we report the reactions with ethene, propene, butenes and pentenes under photoirradiation.
2. Experimental The silica samples employed here were mainly Cab-osil M5 and home-made silica prepared by hydrolysis of tetraethyl orthosilicate (TEOS) [ 17], which were impregnated with water and dried, followed by calcination in the air stream at 773 K for 5 h. The silica samples were heated under an atmosphere of 0 2 (50 Torr) at the given temperature in Table 2 for 1 h and evacuated at the same temperature for 1 h. An ultrahigh pressure 250 W Hg lamp was used as a light source. The experiment of the temperature pro-
0169-4332/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0 1 6 9 - 4 3 3 2 ( 9 7 ) 0 0 3 0 9 - 7
T. Tanaka et al. /Applied Surface Science 121 / 122 (1997) 296-300
grammed desorption (TPD) of water was carried out as described previously [18] and infrared absorption spectra (IR) were recorded with a Perkin Elmer IR spectrometer Paragon 1000 attached with an in situ cell.
297
1E. .
(b)
~ 10 3. Results and discussion Propene was introduced to the system and the catalyst bed made of quartz was irradiated by ultra high pressure Hg lamp, Fig. 1 shows the time course of the products found in the system. The products were ethene, trans-2-butene, cis-2-butene and a very small amount of l-butene. Other products were not detected. This indicates that propene was converted to these products only within the experimental error. The ratio of ethene to 2-butenes was around 1.03 as depicted in Fig. 1, showing that propene is disproportioned to C'2 and C'4 compounds. The result that the main products are 2-butenes as C'4 compounds strongly suggests that metathesis reaction occurs. The production of trans isomer is favorable. The reaction of ethene was also examined. In the case of ethene, if the only reaction was metathesis, then no new products should be observed. After the reaction under irradiation for 1 h on silica, nothing other than ethene was observed in the system. When a mixture of C H 2 = C H 2 and C D 2 = C D 2 was intro-
1.o~
O 0
~ 40 irradiation
0.0 80 time
120 /
rain
Fig. l. Time courses of the reaction: yields based on propene of (a) ethene, (b) trans-2-butene, (c) cis-2-butene, (d) l-butene and (e) the ratio of C ' 2 / C ' 4 . The powder samples (400 rag) was spread on the flat bottom (12 cm 2) of the reactor. Pretreatment temperature was 1073 K.
duced as reactant, the production of C 2 H 2 D 2 w a s observed. Neither C 2 H 3 D n o r C2HD 3 was found in the system. This confirms that the only reaction occurring over the silica was metathesis. Table 1 summarizes the results of the reactions of
Table 1 Reaction of olefins over photoirradiated silica. Gaseous composition after irradiation Reactants
lrrad, time (h)
Gaseous composition after irradiation
t-2-C4 c-2-C4
1 I
1-C4
1
t-2-C5
0.5
c-2-C5
0.5
t-2-C4 (95.6) c-2-C4 (4.4) t-2-C4 (6.6) c-2-C4 (93.4) (22 (1.4) C3 (0.6) 1-C4 (95.5) t-2-C4 (0.7) c-2-C4 (0.3) 3-C6 (1.3) t-2-C4 (0.85) c-2-C4 (0.13) 1-C5 (0.10) t-2-C5 (93.3) c-2-C5 (4.62) 3-C6 (0.97) C2 (0.01) t-2-C4 (0.08) c-2-C4 (0.08) 1-C5 (0.08) t-2-C5 (3.31) c-2-C5 (96.3)
C2 (49.8) t-2-C4 (50.2)
1
C2 (50.5) c-2-C4 (49.5)
1
3-c6 (0.13)
C2 (43.7) C3 (16.6) t-2-C4 (34.9) c-2-C4 (4.7) C2 (43.6) C3 (18.1) t-2-C4 (13.8) c-2-C4 (24.4)
30 /xmol of reactant(s) was introduced to the closed reactor. The compounds in italics are the products of metathesis reactions. The values in parentheses are the gaseous composition in percent. C n stands for the linear alkene of n carbon atoms. The marks t- and c- stand for t r a n s and cis isomers respectively.
7". Tanaka et al. / Applied Surface Science 121 / 122 (1997) 296-300
298
various olefins. All the products were those e x p e c t e d in metathesis reaction. Therefore, in the case of 2-butenes, no other products than 2-butenes were obtained. H o w e v e r , cis-trans isomerization was observed clearly. In particular, the isomerization of the cis-isomer to the trans-isomer is remarkable. In the case o f 2-pentenes, trans-2-pentene was 10 times more reactive than cis-2-pentenes and trans-2-butene is selectively f o r m e d from trans-2-pentene. This is expected from the result that the formation of trans2-butene is m o r e favorable than that of cis-2-butene in the metathesis of propene. The metathesis of cis-2-pentene proceeds slowly and trans-cis isomerization proceeds faster than the metathesis. This may be the reason why trans-2-butene is preferentially f o r m e d in the case o f cis-2-pentene metathesis. As a conclusion, the trans-isomer is more reactive possibly because the trans-intermediate on the catalyst is more stable. This presumably leads to the retention of the trans structure during the metathesis. If so, the intermediate c y c l o m e t a l a b u t a n e is likely. The d e p e n d e n c e of the reaction upon the excitation w a v e l e n g t h was e x a m i n e d by using an U V filter, as shown in Table 2 (entries 1-3). U p o n irradiation with visible light only (entry 1), the reaction was limited to low conversion levels with a high ratio of C ' 2 : C ' 4 . On the other hand, irradiation with U V light (entries 2, 3) e n h a n c e d the metathesis, indicating that U V light is required for the metathesis reaction on the silica surface. Fig. 2 shows the
12
light o f f ~ , . .
1o
light off 6
\
c
c 4
light on
2
o 0
I 20
40
I 60 time / min
I 80
I 100
120
Fig. 2. Response of the reaction to the irradiation.
response of the reaction to photoirradiation. It reveals that the reaction p r o c e e d e d only under irradiation. The instantaneous response indicates clearly that the metathesis reaction was induced by irradiation. In order to e x a m i n e whether or not the photometathesis is general for all the silica, we carried out the propene reaction on other kinds o f silica, the results of which are listed in Table 2 (entries 6 and 7). The metathesis reaction was o b s e r v e d for each of the silicas. The difference is found in the activity only. W e tested other typical metal oxides such as
Table 2 Effects of pretreatment temperature and irradiation wavelength a Entry
T (K)
Filter
Conv. (%)
C2 : C4
1 2 3 4 5 6 '~ 7~
1073 1073 1073 873 673 1073 1073
Y-43 ~ UV-29 c none none none none none
0.27 4.75 11.4 6.95 5.86 26.3 30.1
1.25 1.05 1.02 1.00 0.78 1.12 1.06
Yields (%) C2
trans-C4
cis-C4
I -C4
0.15 2.43 5.74 3.47 1.37 13.93 15.48
0.07 1.59 4.08 2.50 0.92 0.03 0.10
0.05 0.73 1.56 0.95 0.70 9.06 10.75
0.00 0.0l 0.05 0.01 0.13 3.31 3.78
a The measurement was carried out under irradiation for l h in a closed static system (39.5 ml; sample 100 rag; propene 30 /.zmol). The catalyst was Cab-osil M5 except for entries 6 and 7. t, Y-43 filter admits light with / > 430 nm. UV-29 filter admits light with l > 290 nm. d Home-made silica was used. e Used silica, JRC-SIO4, was supplied from Catalysis Society of Japan.
T. Tanaka et al./ Applied Surface Science 121 / 122 (1997) 296-300
MgO, A1203, SiO2-A1203. On these oxides, although other reactions occurred to a small extent, the distribution of products was quite different from that for the metathesis reaction. The metathesis reaction under irradiation seems to be characteristic for the silica surface. The effect of the pretreatment temperature is shown in Table 2 (entries 3-5). The silica is activated by pretreatment at a higher temperature, suggesting that the desorption of the hydroxyl groups on the silica surface might relate to active sites. In Fig. 3, the TPD profile of water from home-made silica is shown. There are two maxima at 560 and 995 K. From the aid of infra-red spectra of the silica evacuated at several temperatures depicted in Fig. 4, it is clearly exhibited that the first maximum at 560 K in TPD corresponds to the desorption of hydrogen bonded water molecules and the second maximum at 995 K is that of water resulting from the recombination of isolated OH groups. In Fig. 3, the activity of the home-made silica is also plotted and it indicates that metathesis reaction occurs on the surface free from hydrogen bonded OH groups and the activity increases with the desorption degree of isolated OH groups. In general, the surface area of silica is greatly reduced by evacuation at a temperature higher than 800 K. Nevertheless, the reaction activity increased with an evacuation temperature, suggesting
1.4
--16
1.2
-- 14
=1.0
12
=0.8
<
0 E0.6
1.6-
299
,~.,4¢e..~ -
'S 0.5
o0L
4000
3800
3600
,
3400
,
3200
3000
wavenumber / cm "1
Fig. 4. OH region of infrared absorption spectra of the home-made silica sample evacuated at (a) 373, (b) 473, (c) 573, (d) 673, (e) 773, (f) 873, (g) 973 and (h) 1073 K.
that structural reconfiguration of the silica surface by the removal of the isolated OH groups strongly correlates to the generation of active sites. The nature of active sites including the excitation mechanism is still under investigation.
Acknowledgements This work was partially supported by a grant-inaid from the Japan Ministry of Education, Science, Art, Sports and Culture. H.Y. acknowledges support by the Fellowship of JSPS. We thank Mr. H. Aritani and Mr. S. Takenaka at the Kyoto University for their collaboration and suggestions.
_~. o
"~
6
~0.4
4
._E 0 . 2
~e
2 0.0 400
600
800
1000
1200
I 1400
0
temperature / K
Fig. 3. TPD profile of water molecules desorbed from silica and the change of the activity of the home-made silica with the evacuation temperature.
References [1] R.L. Banks, G.C. Nailey, Ind. Eng. Chem. 3 (1964) 170. [2] N. Calderon, H.Y. Chen, K.W. Scott, Tetrahedron Lett. 34 (1967) 3327. [3] R.L. Banks, R.B. Regier, Ind. Eng. Chem. Prod. Res. Dev. 7 (1971) 29. [4] R. Nakamura, H. Iida, E. Echigoya, Chem. Len. (1972) 273. [5] J.L. Herrison, Y. Chauvin, Macromol. Chem. 141 (1971) 161. [6] J.N. Amor, J. Catal. 70 (1981) 72. [7] J.N. Amor, P.M. Zambi, J. Catal. 73 (1982) 57.
300
7~ Tanaka et al. /Applied SurJktce Science 121 / 122 (1997) 296-300
[8] M. Lacroix, G.M. Pajonk, S.J. Teichner, J. Catal. 101 (1986) 314. [9] Y, Matsumura, K. Hashimoto, S. Yoshida, J. Catal. i17 (1989) 135. [10] E.W. Bittner, B.C. Bockrath, J.M. Solar, J. Catal. 149 (1994) 206. [1 I] Y. Matsumura, K. Hashimoto, S. Yoshida, J. Chem. Soc. Chem. Commnn. (1987) 1599. [12] G.N. Kastanas. G.A. Tsigdinos, J. Schwank, J. Appl. Catal. 44 (1988) 33. [13] A. Morikawa, M. Hattori, K. Yagi, K. Otsuka, Z. Phys. Chem. (NF) 104 (1977) 309.
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