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1.8 Direct Amination of Lower Alkenes with Ammonia over Zeolite Catalysts
1.8 Direct Amination of Lower Alkenes with Ammonia over Zeolite Catalysts Noritaka Mizuno, Masahiro Tabata, Takeshi Uematsu, and Masakazu Iwamoto Catalysis Research Center, Hokkaido University, Sapporo 060, Japan
Abstract The reaction between ethene or 2-methylpropene and ammonia in the presence or absence of water vapor was studied over various zeolite catalysts, solid acid catalysts, and solid base MgO. The proton-exchanged zeolites were effective for the amination. The addition of water vapor increased the activit of H-MFI-41 for the amination of ethene while the activity for the amination o 2-methylpropene was hardly changed. It was'clarified that amounts and strength of Brclnsted acid sites are factors controllin the direct amination of %-methylproene and that due to the proper possession o above two factors proton-exchanged SM-5 zeolite with silicdalumina ratio of 81 was the most active among the catalysts tested.
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1. INTRODUCTION
Zeolites can catalyze a wide variety of reactions and have practically been of importance in the catalytic cracking and residual hydrocracking because of their acidic properties and microporous structures 111. We also reported that the hydration (Eq.(1))[2-41 and ketonization [5-71of lower alkenes were efficiently catalyzed by proton-exchanged zeolites. R-CHzCH2 + H20 +R-CH(OH)-CH3 R-CH(OH)-CHs + NH3 +R-CH(NH21-CH3+ H20 R-CH=CH2 + NH3 +R-CH(NH2)-CH3
(1) (2) (3)
Aliphatic amines are commercially im ortant and have been industrially made by the reaction between the correspon&g alcohols and ammonia (Eq.(2)) [81. Recently, selective s nthesis of dimethylamine from methanol and ammonia on small pore zeolites xas also been reported [91. Since the alcohols are usually obtained through the direct or indirect hydration of the alkene with the same carbon number (Eq.(l)),it would be more desirable to avoid the alcohol and synthesize the amine by a direct reaction between alkene and ammonia (Eq.(3)) [lo]. Direct amination of ethene to ethylamine has been achieved using alkali metal catalysts in homogeneous system [ll]. However, these system provide low yields of higher alkylamines. As for the direct amination of alkenes with the carbon number more than two, Deeba et al. reported that the amination of 2-methylpropene was promoted by Y-type and mordenite zeolites in heterogeneous system [12,13]. Recently, we reported that the direct amination of 2-methylpropene was most efficiently catalyzed by proton-exchanged ZSM-5 zeolite with silicdalumina ratio of 50 among various oxide catalysts [141. In the present paper the amination of ethene and 2-methylpropene over zeolite catalysts, solid acid catalysts, and solid base MgO has been studied. 71
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N. MIZUNO, M. TABATA, T. UEMATSU and M. IWAMOTO
2. EXPERIMENTAL
2.1. Catalysts Parent zeolites, ZSM-5 (denoted as MFI) with silicdalumina ratio of 23, 40, and 50, ferrierite (FER), L-type (LTL), offretite/erionite (OFFERI), mordenite (MOR), and Y-type (FAU) zeolites were su plied by Tosoh Corporation. ZSM-5 zeolites with silicdalumina ratio of 93 a n 8 1340 were s u plied by Catalysis Society of Japan. The other ZSM-5 zeolites were prepared by ydrothermal crystallization of alkaline reaction mixtures in a similar method to that described in Mobil's patent [ E l . Ultrastable Y-type zeolites were prepared by steaming. C S ~ H ~ - ~ P W (x =~ ~ O ~ O 2.5 - 3.15) catalysts were prepared according to ref. 1161. The other catalysts were commercially obtained. Each proton-exchanged zeolite was prepared according to the literatures [2-41. The amounts of Al, Si, and Na or K in each zeolite were determined by atomic absorption spectrosco y after the zeolite samples were dissolved in hydrogen fluoride solution a n 8 silica/alumina ratios in the zeolite framework were determined by 2% MASNMR as described previously [6,71. The catalysts were abbreviated as H-MFI-81 (cation-zeolite structure-silidalumina ratio). The exchange level of proton in each zeolite was approximately 100% except for H-FAU6 (72%). The SiO~/A1203ratio obtained by atomic absorption s ectrosco well agreed with those obtained by 49Si MASNMR in the case of H - M h , H - M J J , and H-LTL zeolites, showing that there is no extraframework aluminum ion on these zeolites and that little dealumination was occurred during the preparation. Therefore, the later discussion would not be affected by the extraframework aluminum ion. The Si02/A1203 ratios of two kinds of ultrastable Y-type zeolites (H-FAU) were 5.9 and 14 by atomic absorption spectroscopy and 12 and 40 by 29Si MASNMR. Clearly, the difference is due to dealumination and therefore the latter values were used hereafter for the abbreviation. The Si02/A1203 ratios of zeolite numbers 1 - 19 correspond to 1340, 129, 113, 93, 81, 50, 40, 23, 23 (Na form), 19, 15, 15 (Na form), 40, 12, 5.6, 5.6 (Na form), 17, 8.0, and 6.0, respectively. Sample numbers 20 - 22 correspond to cS2.5HO.5pw 1 2 040 cS2.85HO.15pw 1 2 0 4 0 and cS3.15pw120 40 res ectivel , The totay amount of acidic sites on zeolites were obtained from the profiles of temperature programmed desorption of ammonia as has been described previously
K
El.
2.2. Infrared Spectra All self-supporting disks of H-MFI-40 (7 - 20 mg, 2 cm in diameter) were prepared by pressing owder under a pressure of 300 kg-cm-2for 30 min and the IR s ectra were recordeaat 298 K with an IR-810 spectrometer (Japan Spectroscopic LM.). The ratio of the amount of Bransted acid sites to that of Lewis acid sites on H-MFI-40 was studied by the pyridine adsorption method. After a H-MFI-40 disk was evacuated in an in situ IR cell a t 423 - 973 K for 1h, it was exposed to pyridine vapor (ca. 10 mmHg) a t 423 K for 2 h and evacuated at the same temperature for 1 h. The IR spectra were recorded a t 298 K. In a similar way, the acidic pro erties of H-MFI-93, -81, and -23, H-MOR-15 and -19, Cs2.85H0 15PW12040 and Si 2-A1203 were measured. The IR bands a t 1545 and 1455 cm-I assigned to pyridinium ion and coordinatively bound pyridine, respectively, were used to determine the relative concentrations of Bransted and Lewis acid sites. Due to the difficulty in measuring the weak IR absorption bands of pyridine adsorbed on high-silica zeolites, this method could be applied to the zeolites with the Si02/A1203 ratios of 93 or less.
&.,
8
2.3. Reaction The reaction of ethene and 2-methylpropene with ammonia was carried out in a conventional flow reactor at 473 K a t an atmospheric pressure using 0.5 - 1.0 g
Amination of Alkenes with Ammonia over Zeolite
73
catalysts. Before the experimental run the catalysts were treated in a N2 stream (20 ~ m 3 . m i n - ~ at) 573 - 973 K for 1 h except for CsXH3-,PW1204o (x = 2.5 - 3.15) samples, which were used without the treatment due to the thermal instability. The standard treatment temperature in N2, flow rates of alkene and ammonia, and catalyst weight were 773 K, 4.0 cm3.min-1, 16.0 cm3.min-1, and 1.0 g, respectively, unless otherwise stated. The reactants and products were analyzed by gas chromatography. 3. RESULTS AND DISCUSSION
3.1. Reaction Figure 1 shows the time course of the conversion into t-butylamine from 2-methylpropene a n d ammonia on H-MFI-40 at 473 K. The conversion into t-butylamine increased with time and a n approximately steady formation of t-butylamine was attained after 2 h. The same product distribution and similar increases of the conversion with time to those on H-MFI-40 were observed for the other catalysts. Little oligomerization a n d isomerization products were observed and the selectivity was less Fig. 1. Time course of the conversion than 1%. The number of t-butylamine i n t o t-butylamine from formed per number of A1 content or 2-methylpropene and ammonia on Bransted acid site after a 30 h reaction H-MFI-40 at 473 K. Catalyst weight, on H-MFI-40 was greater than 2, 0.5 g. 2-Methylpropene, 4.0 cm3.min-1; showing t h a t the reaction is catalytic. ammonia, 16.0 cm3.min-1. The initial small value (0.14%) of the conversion into t-butylamine at 0:67 h is probably due to the adsorption of the basic t-butylamine on the acidic sites of the catalysts. A similar increase in the conversion into ethylamine was observed for the amination of ethene. The low conversion of 2-methylpropene to t-butylamine is probably due to t h e equilibrium limitation between starting materials (2-methylpropene and ammonia) and the product (t-butylamine). The activities of various catalysts at 473 K are summarized in Table 1. H-MFI-81 showed the highest activity among the zeolite catalysts, solid acid catalysts (CsXH3.,PW12040 (x = 2.5 - 3.15), Si02-Al203, SiO2-TiOz), and solid base MgO. It is noted that the selectivity to t-butylamine is more than 95% for each zeolite. When the water vapor was added to the reactant gases of 2-methylpropene and ammonia, the activity of each zeolite little changed and the selectivity to t-butylamine slightly decreased to 87 - 97% from 95 - 100% due to the formation of 2-methyl-2-propanol. Thus, the addition of water vapor did not improve the catalytic properties. On the other hand, the addition of water vapor increased the activity of H-MFI 40 for the reaction of ethene with ammonia by a factor of about two. Table 2 summarizes the catalytic properties of various oxide catalysts in the presence of water vapor. The activities decreased in the order of proton-exchanged zeolites > mixed metal oxides 2 metal ion-exchanged zeolites except for H-FAU-12 and -40. HMOR-15 was the most active among the catalysts tested. The selectivity to ethylamine was 33 - 77% upon proton-exchanged zeolites and the major by-product was ethyl alcohol.
74
N. MIZUNO, M. TABATA, T. UEMATSU and M. IWAMOTO
Table 1. Catalytic activities of various catalysts for t h e amination of 2methylpropene into t-butylamine a t 473 Ka) Catalyst C0nv.b) Se1ect.c) 1% 1% H-MFI-8 1 1.73 99 H-MFI-93 1.18 99 H-MFI-113 0.90 98 H-MFI-50 0.85 99 H-MFI-129 0.80 99 H-MFI-40 0.68 99 H-MFI-23 0.62 99 H-MOR-19 0.53 99 H-MOR-15 0.42 99 H-FAU-40 0.22 95 H-LTL-6 0.11 99 H-FAU-12 0.06 99 H-OFFERI-8 0.05 98 H-MFI-1340 0.04 99 H-FAU-6 0.04 99 H-FER-17 0.02 99 Na-MFI-40 0.01 99 Na-FAU-6 0.01 99 Na-MOR-15 0 0.17 89 Cs2.5H0.5PW12040 0.15 84 Cs2.85H0.15PW12040 Si02-Al203 0.08 98 SiOa-Ti02 0.03 100 0.01 99 A1202 cS3.15p~;2040 0 MgO 0 a ) 2-Methylpropene, 4.0 cm3.min-1; ammonia, 16.0 cm3.min-1; catalyst weight, 1.0 g. b) Mol t-butylamine formed/mol 2-methylpropene introduced. c ) Mol t-butylamine formedltotal mol of products.
Table 2. Catalytic properties of v a r i o u s c a t a l y s t s for t h e a m i n a t i o n of e t h e n e into ethylamine a t 623 Ka) Catalyst C0nv.b) Se1ect.c) 1% 1% H-MOR-15 0.19 77 H-FER-17 0.17 72 H-MFI-50 0.14 87 H-MFI-40 0.14 60 H-MOR-11 0.14 48 H-MFI-23 0.11 48 H-FAU-40 0.04 38 H-FAU-12 0.01 33 Cu-MOR-11 0.07 57 Mg-MOR-15 0.03 73 Ni-MOR-15 0.03 6 CO-MOR-15 0.02 4 Zn-MOR-15 Trace 2 Na-MOR-15 Trace 16 Si02-Al203 0.11 79 TiOz-ZrOa 0.07 72 SiOz-TiOa 0.06 94 SiOa-ZrOz 0.05 80 a) E t h e n e , 7.5 c m 3 . m i n - l ; ammonia, 7.5 cm3.min-1; water vapor, 0.68cm3.min-1; catalyst weight, 1.0 g. b) Mol ethylamine formedlmol ethene introduced. c ) Mol ethylamine formedltotal mol of products.
3.2. Factors Controlling Catalytic Activity of Direct Amination of 2-Methylpropene The conversions into t-butylamine were much decreased from 0.68 to O.Ol%.by the Na+ substitution for H+ in H-MFI-40, the preadsorption of diisopropylamine reatly decreased the initial rate of t-butylamine formation on H-MFI-40, and b g 0 showed little activity, suggesting that the amination of 2-methylpropene is catalyzed by the acidic sites. Next, we investigated how the catalytic activities can be recognized by B r ~ n s t e d or Lewis acidity. Figure 2 shows the changes in the catalytic activity and the number of Bransted acid sites of H-MFI-40 with the pretreatment (evacuation) temperature. The conversion ( 0 )was constant in the range of 473 - 773 K and then a little decreased above 773 K. The number of B r ~ n s t e dacid sites ( 0 ) similarly changed with the evacuation temperature, but that of Lewis acid sites
75
Amination of Alkenes with Ammonia over Zeolite
changed in a different way. The parallel change of the catalytic activity of H-MFI40 with the amount of Bransted acid site at elevated temperatures supports that the direct amination of 2-methylpropene is catalyzed by the Brensted acidity. The (x = fact that C S ~ H ~ - ~ P W ~ ~2.5, O 2.85) ~ O heteropoly com ounds having only Bransted acid sites showed the activity for the amination whi e A1203 having only Lewis acid sites showed little activity also supports the above idea. Figure 3 shows the correlation between the activity of the various catalysts and the amounts of Brensted acid sites. The conversions increased with the amounts of Bransted acid sites, reached the maximum at H-MFI-81, and then decreased. The increase was consistent with the idea that Bransted acid sites are the active centers. The decrease shows that the amination is not a simple function of the amount of Bransted acid sites and is probably due to the lower acid strength as investigated in the later part. Figure 4 shows the correlation between the turnover frequencies per Bransted acid site and the Si02/A1203 ratios of zeolites. The turnover frequencies can be expressed by one line and increased with the increment of the SiOdA1203 ratios up to 93. Therefore, the decrease of the conversion above the amount of Bransted acid site of 0.09 mmo1.g-1 in Fig. 3 is probably due to the change of the turnover frequencies. On the basis of the report that the acid strength increases with increasing the Si02/A1203 ratios 1181, the increase of the turnover frequencies in Fig. 4 is probably due to the increment of the acid strength. Thus, not only the amounts of Bransted acid sites but also the acid stren h is an important factor for the present reaction as has been usually interprete in the cracking of alkanes [191. Due to the proper possession of the above two factors, H-MFI-81 is the most active for the reaction to form directly t-butylamine among the catalysts tested. Consequently, the above consideration made clearer the proposal by Deeba et al. that the formation of t-butylamine would involve a cationic intermediate on the zeolite surface 1131. By analogy with the observation of t-butyl and isopropyl cation on H-FAU zeolite [20] and the reaction mechanism for the hydration of ethene [211, the cationic intermediate is probably the t-butyl cation. t-Butyl cation may be formed through the protonation of 2-methylpropene by a surface
P
fit
. 8
0.81
- -4 .
0.08 I
I
I
T
Y
1 8
I
2 s d
10
A 11A 0 600 800 1000 Pretreatment or evacuation temperature / K
400
Fig. 2. Change in the conversion into t-butylamine and the amount Of Bransted acid sites with the retreatment temperature. Sample, h-MFI-40. 0 , the conversion into t-butylamine; 0 , the relative inte rated intensities of the 1545-cm-1 ban of pyridine.
%
1
$
,
.
,
.
0.6 0.8 1.0 Amount of BrBnsted acid site / mmobg-'
Fig. 3. Correlation between the conversions into t-butylamine and the amounts of B r ~ n s t e dacid sites. 0 , MFI; A MOR; , FAU; , CsxH3-xP~12040~
76
N. MIZUNO, M. TABATA, T. UEMATSU and M. IWAMOTO
Brclnsted acid s i t e o r ammonia. Subsequently the Brclnsted a c i d s i t e i s regenerated by the desorption of t-butylamine.
1
10'
4. ACKNOWLEDGMENTS
We thank Prof. T. Yashima (Tokyo Institute of Technology) for helping to synthesize ZSM-5 zeolite catalysts. This work was supported by a Grant-in-Aid for Scientific Research from t h e Ministry of Education, Science a n d C u l t u r e of Japan.
10-3 I
5
1
8
I
' - * I
10' SiOZ/AI,O3 ratio
102
I
Fig. 4. Correlations between the Si02/A120 3 ratios the turnover fre uencies.a a T u r n o v e r frequencies, amounts o t-butylamine formed er 1 h / amounts of Br@nstedacid sites. 0 , H5. REFERENCES h F I ; A ,H-MOR; H,H-FAU. 1) Y. Ono, Cutul. Rev.-Sci. Eng., 1992, 34, 179; J . A. Rabo and G. J. Gajda, Catal. Rev.-Sci.Eng., 1989-90, 31, 385. 2) M. Iwamoto, M. Tajima, and S . Kagawa, J. Cutul., 1986, 101, 195. 3) M. Iwamoto, H. Yahiro, H. Mori, and I. Takasu, in "Catalytic Science and Technology", (S. Yoshida, N. Takezawa, and T. Ono, Eds.), Vol. 1, p. 415. Kodansha. Tokvo. 1991. 4) H. Mori, N. M i k n o , T. Shirouzu, S. Kagawa, and M. Iwamoto, Bull. Chem. SOC. Jm..1991.64. 2681. 5) H. Mori, H. Ueno, N. Mizuno, H. Yahiro, and M. Iwamoto, Chem. Lett., 1990, 2289. 6) H. Mori, N. Mizuno, M. Tajima, S. Kagawa, and M. Iwamoto, Catal. Lett., 1991, 10,35. 7) N. Mizuno, H. Mori, M. Tajima, S . Kagawa, H. Ueno, H. Yahiro, and M. Iwamoto, J. Mol. Cutal., 1993, 80, 229. 8) A. E. Schweizer, R. L. Fowlkes, J. H. McMakin, and T. E. Whyte, i n "Encyclopedia of Chemical and Technology", (H. F. Mark, D. F. Othmer, C. G. Overberger, and G. T. Seaborg, Eds.), Vol. 2, p. 272. John Wiley, New York, 1978. K. Segawa and H. Tachibana, J. Cutul., 1991, 131,482. J. F. Roth, Stud. Surf Sci. Cutul., 1990,54,3. M. R. Gagne, C. L. Stern, and T. J. Marks, J. Am. Chem. SOC.,1992, 114, 275. M. Deeba, M. E. Ford, and T. A. Johnson, in "Catalysis", (J. W. Ward, Ed.), p. 221. Elsevier Science Publishers B. V., Amsterdam 1987. M. Deeba and M. E. Ford, J. Org. Chem., 1988, 53,4594. M. Tabata, N. Mizuno, and M. Iwamoto, Chem. Lett., 1991, 1027; N. Mizuno, M. Tabata, T. Uematsu, and M. Iwamoto, J. Chem. SOC.,Furaday Trans., 1993, 89, 3513; idem., J. Cutul., in press. British Patent 1972, 1,402,981. S. Tatematsu, T. Hibi, T. Okuhara, and M. Misono, Chem. Lett., 1984, 865. S. Namba, N. Hosonuma, and T. Yashima, J. Cutul., 1981, 72, 16. P. A. Jacobs, W. J. Mortier, and J. B. Uyterhoeven, J. Inorg. Nucl. Chem., 1978, 40, 1919; W. J . Mortier and P. Geerlings, J. Phys. Chem., 1980, 84, 1982. I. Wang, T. J. Chen, K. J. Chao, and T. C. Tsai, J. Cutul., 1979,60, 140. N. D. Lazo, B. R. Richardson, P. D. Schettler, J. L. White, E. J. Munson, and J. F. Haw, J. Phys. Chem., 1991, 95,9420. K. Tanabe, M. Misono, Y. Ono, and H. Hattori, "New Solid Acids and Bases", p. 252. Kodansha-Elsevier, Tokyo-Amsterdam, 1989.
B
Abstract The reaction between ethene or 2-methylpropene and ammonia in the presence or absence of water vapor was studied over various zeolite catalysts, solid acid catalysts, and solid base MgO. The proton-exchanged zeolites were effective for the amination. The addition of water vapor increased the activit of H-MFI-41 for the amination of ethene while the activity for the amination o 2-methylpropene was hardly changed. It was'clarified that amounts and strength of Brclnsted acid sites are factors controllin the direct amination of %-methylproene and that due to the proper possession o above two factors proton-exchanged SM-5 zeolite with silicdalumina ratio of 81 was the most active among the catalysts tested.
P 31
f
1. INTRODUCTION
Zeolites can catalyze a wide variety of reactions and have practically been of importance in the catalytic cracking and residual hydrocracking because of their acidic properties and microporous structures 111. We also reported that the hydration (Eq.(1))[2-41 and ketonization [5-71of lower alkenes were efficiently catalyzed by proton-exchanged zeolites. R-CHzCH2 + H20 +R-CH(OH)-CH3 R-CH(OH)-CHs + NH3 +R-CH(NH21-CH3+ H20 R-CH=CH2 + NH3 +R-CH(NH2)-CH3
(1) (2) (3)
Aliphatic amines are commercially im ortant and have been industrially made by the reaction between the correspon&g alcohols and ammonia (Eq.(2)) [81. Recently, selective s nthesis of dimethylamine from methanol and ammonia on small pore zeolites xas also been reported [91. Since the alcohols are usually obtained through the direct or indirect hydration of the alkene with the same carbon number (Eq.(l)),it would be more desirable to avoid the alcohol and synthesize the amine by a direct reaction between alkene and ammonia (Eq.(3)) [lo]. Direct amination of ethene to ethylamine has been achieved using alkali metal catalysts in homogeneous system [ll]. However, these system provide low yields of higher alkylamines. As for the direct amination of alkenes with the carbon number more than two, Deeba et al. reported that the amination of 2-methylpropene was promoted by Y-type and mordenite zeolites in heterogeneous system [12,13]. Recently, we reported that the direct amination of 2-methylpropene was most efficiently catalyzed by proton-exchanged ZSM-5 zeolite with silicdalumina ratio of 50 among various oxide catalysts [141. In the present paper the amination of ethene and 2-methylpropene over zeolite catalysts, solid acid catalysts, and solid base MgO has been studied. 71
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N. MIZUNO, M. TABATA, T. UEMATSU and M. IWAMOTO
2. EXPERIMENTAL
2.1. Catalysts Parent zeolites, ZSM-5 (denoted as MFI) with silicdalumina ratio of 23, 40, and 50, ferrierite (FER), L-type (LTL), offretite/erionite (OFFERI), mordenite (MOR), and Y-type (FAU) zeolites were su plied by Tosoh Corporation. ZSM-5 zeolites with silicdalumina ratio of 93 a n 8 1340 were s u plied by Catalysis Society of Japan. The other ZSM-5 zeolites were prepared by ydrothermal crystallization of alkaline reaction mixtures in a similar method to that described in Mobil's patent [ E l . Ultrastable Y-type zeolites were prepared by steaming. C S ~ H ~ - ~ P W (x =~ ~ O ~ O 2.5 - 3.15) catalysts were prepared according to ref. 1161. The other catalysts were commercially obtained. Each proton-exchanged zeolite was prepared according to the literatures [2-41. The amounts of Al, Si, and Na or K in each zeolite were determined by atomic absorption spectrosco y after the zeolite samples were dissolved in hydrogen fluoride solution a n 8 silica/alumina ratios in the zeolite framework were determined by 2% MASNMR as described previously [6,71. The catalysts were abbreviated as H-MFI-81 (cation-zeolite structure-silidalumina ratio). The exchange level of proton in each zeolite was approximately 100% except for H-FAU6 (72%). The SiO~/A1203ratio obtained by atomic absorption s ectrosco well agreed with those obtained by 49Si MASNMR in the case of H - M h , H - M J J , and H-LTL zeolites, showing that there is no extraframework aluminum ion on these zeolites and that little dealumination was occurred during the preparation. Therefore, the later discussion would not be affected by the extraframework aluminum ion. The Si02/A1203 ratios of two kinds of ultrastable Y-type zeolites (H-FAU) were 5.9 and 14 by atomic absorption spectroscopy and 12 and 40 by 29Si MASNMR. Clearly, the difference is due to dealumination and therefore the latter values were used hereafter for the abbreviation. The Si02/A1203 ratios of zeolite numbers 1 - 19 correspond to 1340, 129, 113, 93, 81, 50, 40, 23, 23 (Na form), 19, 15, 15 (Na form), 40, 12, 5.6, 5.6 (Na form), 17, 8.0, and 6.0, respectively. Sample numbers 20 - 22 correspond to cS2.5HO.5pw 1 2 040 cS2.85HO.15pw 1 2 0 4 0 and cS3.15pw120 40 res ectivel , The totay amount of acidic sites on zeolites were obtained from the profiles of temperature programmed desorption of ammonia as has been described previously
K
El.
2.2. Infrared Spectra All self-supporting disks of H-MFI-40 (7 - 20 mg, 2 cm in diameter) were prepared by pressing owder under a pressure of 300 kg-cm-2for 30 min and the IR s ectra were recordeaat 298 K with an IR-810 spectrometer (Japan Spectroscopic LM.). The ratio of the amount of Bransted acid sites to that of Lewis acid sites on H-MFI-40 was studied by the pyridine adsorption method. After a H-MFI-40 disk was evacuated in an in situ IR cell a t 423 - 973 K for 1h, it was exposed to pyridine vapor (ca. 10 mmHg) a t 423 K for 2 h and evacuated at the same temperature for 1 h. The IR spectra were recorded a t 298 K. In a similar way, the acidic pro erties of H-MFI-93, -81, and -23, H-MOR-15 and -19, Cs2.85H0 15PW12040 and Si 2-A1203 were measured. The IR bands a t 1545 and 1455 cm-I assigned to pyridinium ion and coordinatively bound pyridine, respectively, were used to determine the relative concentrations of Bransted and Lewis acid sites. Due to the difficulty in measuring the weak IR absorption bands of pyridine adsorbed on high-silica zeolites, this method could be applied to the zeolites with the Si02/A1203 ratios of 93 or less.
&.,
8
2.3. Reaction The reaction of ethene and 2-methylpropene with ammonia was carried out in a conventional flow reactor at 473 K a t an atmospheric pressure using 0.5 - 1.0 g
Amination of Alkenes with Ammonia over Zeolite
73
catalysts. Before the experimental run the catalysts were treated in a N2 stream (20 ~ m 3 . m i n - ~ at) 573 - 973 K for 1 h except for CsXH3-,PW1204o (x = 2.5 - 3.15) samples, which were used without the treatment due to the thermal instability. The standard treatment temperature in N2, flow rates of alkene and ammonia, and catalyst weight were 773 K, 4.0 cm3.min-1, 16.0 cm3.min-1, and 1.0 g, respectively, unless otherwise stated. The reactants and products were analyzed by gas chromatography. 3. RESULTS AND DISCUSSION
3.1. Reaction Figure 1 shows the time course of the conversion into t-butylamine from 2-methylpropene a n d ammonia on H-MFI-40 at 473 K. The conversion into t-butylamine increased with time and a n approximately steady formation of t-butylamine was attained after 2 h. The same product distribution and similar increases of the conversion with time to those on H-MFI-40 were observed for the other catalysts. Little oligomerization a n d isomerization products were observed and the selectivity was less Fig. 1. Time course of the conversion than 1%. The number of t-butylamine i n t o t-butylamine from formed per number of A1 content or 2-methylpropene and ammonia on Bransted acid site after a 30 h reaction H-MFI-40 at 473 K. Catalyst weight, on H-MFI-40 was greater than 2, 0.5 g. 2-Methylpropene, 4.0 cm3.min-1; showing t h a t the reaction is catalytic. ammonia, 16.0 cm3.min-1. The initial small value (0.14%) of the conversion into t-butylamine at 0:67 h is probably due to the adsorption of the basic t-butylamine on the acidic sites of the catalysts. A similar increase in the conversion into ethylamine was observed for the amination of ethene. The low conversion of 2-methylpropene to t-butylamine is probably due to t h e equilibrium limitation between starting materials (2-methylpropene and ammonia) and the product (t-butylamine). The activities of various catalysts at 473 K are summarized in Table 1. H-MFI-81 showed the highest activity among the zeolite catalysts, solid acid catalysts (CsXH3.,PW12040 (x = 2.5 - 3.15), Si02-Al203, SiO2-TiOz), and solid base MgO. It is noted that the selectivity to t-butylamine is more than 95% for each zeolite. When the water vapor was added to the reactant gases of 2-methylpropene and ammonia, the activity of each zeolite little changed and the selectivity to t-butylamine slightly decreased to 87 - 97% from 95 - 100% due to the formation of 2-methyl-2-propanol. Thus, the addition of water vapor did not improve the catalytic properties. On the other hand, the addition of water vapor increased the activity of H-MFI 40 for the reaction of ethene with ammonia by a factor of about two. Table 2 summarizes the catalytic properties of various oxide catalysts in the presence of water vapor. The activities decreased in the order of proton-exchanged zeolites > mixed metal oxides 2 metal ion-exchanged zeolites except for H-FAU-12 and -40. HMOR-15 was the most active among the catalysts tested. The selectivity to ethylamine was 33 - 77% upon proton-exchanged zeolites and the major by-product was ethyl alcohol.
74
N. MIZUNO, M. TABATA, T. UEMATSU and M. IWAMOTO
Table 1. Catalytic activities of various catalysts for t h e amination of 2methylpropene into t-butylamine a t 473 Ka) Catalyst C0nv.b) Se1ect.c) 1% 1% H-MFI-8 1 1.73 99 H-MFI-93 1.18 99 H-MFI-113 0.90 98 H-MFI-50 0.85 99 H-MFI-129 0.80 99 H-MFI-40 0.68 99 H-MFI-23 0.62 99 H-MOR-19 0.53 99 H-MOR-15 0.42 99 H-FAU-40 0.22 95 H-LTL-6 0.11 99 H-FAU-12 0.06 99 H-OFFERI-8 0.05 98 H-MFI-1340 0.04 99 H-FAU-6 0.04 99 H-FER-17 0.02 99 Na-MFI-40 0.01 99 Na-FAU-6 0.01 99 Na-MOR-15 0 0.17 89 Cs2.5H0.5PW12040 0.15 84 Cs2.85H0.15PW12040 Si02-Al203 0.08 98 SiOa-Ti02 0.03 100 0.01 99 A1202 cS3.15p~;2040 0 MgO 0 a ) 2-Methylpropene, 4.0 cm3.min-1; ammonia, 16.0 cm3.min-1; catalyst weight, 1.0 g. b) Mol t-butylamine formed/mol 2-methylpropene introduced. c ) Mol t-butylamine formedltotal mol of products.
Table 2. Catalytic properties of v a r i o u s c a t a l y s t s for t h e a m i n a t i o n of e t h e n e into ethylamine a t 623 Ka) Catalyst C0nv.b) Se1ect.c) 1% 1% H-MOR-15 0.19 77 H-FER-17 0.17 72 H-MFI-50 0.14 87 H-MFI-40 0.14 60 H-MOR-11 0.14 48 H-MFI-23 0.11 48 H-FAU-40 0.04 38 H-FAU-12 0.01 33 Cu-MOR-11 0.07 57 Mg-MOR-15 0.03 73 Ni-MOR-15 0.03 6 CO-MOR-15 0.02 4 Zn-MOR-15 Trace 2 Na-MOR-15 Trace 16 Si02-Al203 0.11 79 TiOz-ZrOa 0.07 72 SiOz-TiOa 0.06 94 SiOa-ZrOz 0.05 80 a) E t h e n e , 7.5 c m 3 . m i n - l ; ammonia, 7.5 cm3.min-1; water vapor, 0.68cm3.min-1; catalyst weight, 1.0 g. b) Mol ethylamine formedlmol ethene introduced. c ) Mol ethylamine formedltotal mol of products.
3.2. Factors Controlling Catalytic Activity of Direct Amination of 2-Methylpropene The conversions into t-butylamine were much decreased from 0.68 to O.Ol%.by the Na+ substitution for H+ in H-MFI-40, the preadsorption of diisopropylamine reatly decreased the initial rate of t-butylamine formation on H-MFI-40, and b g 0 showed little activity, suggesting that the amination of 2-methylpropene is catalyzed by the acidic sites. Next, we investigated how the catalytic activities can be recognized by B r ~ n s t e d or Lewis acidity. Figure 2 shows the changes in the catalytic activity and the number of Bransted acid sites of H-MFI-40 with the pretreatment (evacuation) temperature. The conversion ( 0 )was constant in the range of 473 - 773 K and then a little decreased above 773 K. The number of B r ~ n s t e dacid sites ( 0 ) similarly changed with the evacuation temperature, but that of Lewis acid sites
75
Amination of Alkenes with Ammonia over Zeolite
changed in a different way. The parallel change of the catalytic activity of H-MFI40 with the amount of Bransted acid site at elevated temperatures supports that the direct amination of 2-methylpropene is catalyzed by the Brensted acidity. The (x = fact that C S ~ H ~ - ~ P W ~ ~2.5, O 2.85) ~ O heteropoly com ounds having only Bransted acid sites showed the activity for the amination whi e A1203 having only Lewis acid sites showed little activity also supports the above idea. Figure 3 shows the correlation between the activity of the various catalysts and the amounts of Brensted acid sites. The conversions increased with the amounts of Bransted acid sites, reached the maximum at H-MFI-81, and then decreased. The increase was consistent with the idea that Bransted acid sites are the active centers. The decrease shows that the amination is not a simple function of the amount of Bransted acid sites and is probably due to the lower acid strength as investigated in the later part. Figure 4 shows the correlation between the turnover frequencies per Bransted acid site and the Si02/A1203 ratios of zeolites. The turnover frequencies can be expressed by one line and increased with the increment of the SiOdA1203 ratios up to 93. Therefore, the decrease of the conversion above the amount of Bransted acid site of 0.09 mmo1.g-1 in Fig. 3 is probably due to the change of the turnover frequencies. On the basis of the report that the acid strength increases with increasing the Si02/A1203 ratios 1181, the increase of the turnover frequencies in Fig. 4 is probably due to the increment of the acid strength. Thus, not only the amounts of Bransted acid sites but also the acid stren h is an important factor for the present reaction as has been usually interprete in the cracking of alkanes [191. Due to the proper possession of the above two factors, H-MFI-81 is the most active for the reaction to form directly t-butylamine among the catalysts tested. Consequently, the above consideration made clearer the proposal by Deeba et al. that the formation of t-butylamine would involve a cationic intermediate on the zeolite surface 1131. By analogy with the observation of t-butyl and isopropyl cation on H-FAU zeolite [20] and the reaction mechanism for the hydration of ethene [211, the cationic intermediate is probably the t-butyl cation. t-Butyl cation may be formed through the protonation of 2-methylpropene by a surface
P
fit
. 8
0.81
- -4 .
0.08 I
I
I
T
Y
1 8
I
2 s d
10
A 11A 0 600 800 1000 Pretreatment or evacuation temperature / K
400
Fig. 2. Change in the conversion into t-butylamine and the amount Of Bransted acid sites with the retreatment temperature. Sample, h-MFI-40. 0 , the conversion into t-butylamine; 0 , the relative inte rated intensities of the 1545-cm-1 ban of pyridine.
%
1
$
,
.
,
.
0.6 0.8 1.0 Amount of BrBnsted acid site / mmobg-'
Fig. 3. Correlation between the conversions into t-butylamine and the amounts of B r ~ n s t e dacid sites. 0 , MFI; A MOR; , FAU; , CsxH3-xP~12040~
76
N. MIZUNO, M. TABATA, T. UEMATSU and M. IWAMOTO
Brclnsted acid s i t e o r ammonia. Subsequently the Brclnsted a c i d s i t e i s regenerated by the desorption of t-butylamine.
1
10'
4. ACKNOWLEDGMENTS
We thank Prof. T. Yashima (Tokyo Institute of Technology) for helping to synthesize ZSM-5 zeolite catalysts. This work was supported by a Grant-in-Aid for Scientific Research from t h e Ministry of Education, Science a n d C u l t u r e of Japan.
10-3 I
5
1
8
I
' - * I
10' SiOZ/AI,O3 ratio
102
I
Fig. 4. Correlations between the Si02/A120 3 ratios the turnover fre uencies.a a T u r n o v e r frequencies, amounts o t-butylamine formed er 1 h / amounts of Br@nstedacid sites. 0 , H5. REFERENCES h F I ; A ,H-MOR; H,H-FAU. 1) Y. Ono, Cutul. Rev.-Sci. Eng., 1992, 34, 179; J . A. Rabo and G. J. Gajda, Catal. Rev.-Sci.Eng., 1989-90, 31, 385. 2) M. Iwamoto, M. Tajima, and S . Kagawa, J. Cutul., 1986, 101, 195. 3) M. Iwamoto, H. Yahiro, H. Mori, and I. Takasu, in "Catalytic Science and Technology", (S. Yoshida, N. Takezawa, and T. Ono, Eds.), Vol. 1, p. 415. Kodansha. Tokvo. 1991. 4) H. Mori, N. M i k n o , T. Shirouzu, S. Kagawa, and M. Iwamoto, Bull. Chem. SOC. Jm..1991.64. 2681. 5) H. Mori, H. Ueno, N. Mizuno, H. Yahiro, and M. Iwamoto, Chem. Lett., 1990, 2289. 6) H. Mori, N. Mizuno, M. Tajima, S. Kagawa, and M. Iwamoto, Catal. Lett., 1991, 10,35. 7) N. Mizuno, H. Mori, M. Tajima, S . Kagawa, H. Ueno, H. Yahiro, and M. Iwamoto, J. Mol. Cutal., 1993, 80, 229. 8) A. E. Schweizer, R. L. Fowlkes, J. H. McMakin, and T. E. Whyte, i n "Encyclopedia of Chemical and Technology", (H. F. Mark, D. F. Othmer, C. G. Overberger, and G. T. Seaborg, Eds.), Vol. 2, p. 272. John Wiley, New York, 1978. K. Segawa and H. Tachibana, J. Cutul., 1991, 131,482. J. F. Roth, Stud. Surf Sci. Cutul., 1990,54,3. M. R. Gagne, C. L. Stern, and T. J. Marks, J. Am. Chem. SOC.,1992, 114, 275. M. Deeba, M. E. Ford, and T. A. Johnson, in "Catalysis", (J. W. Ward, Ed.), p. 221. Elsevier Science Publishers B. V., Amsterdam 1987. M. Deeba and M. E. Ford, J. Org. Chem., 1988, 53,4594. M. Tabata, N. Mizuno, and M. Iwamoto, Chem. Lett., 1991, 1027; N. Mizuno, M. Tabata, T. Uematsu, and M. Iwamoto, J. Chem. SOC.,Furaday Trans., 1993, 89, 3513; idem., J. Cutul., in press. British Patent 1972, 1,402,981. S. Tatematsu, T. Hibi, T. Okuhara, and M. Misono, Chem. Lett., 1984, 865. S. Namba, N. Hosonuma, and T. Yashima, J. Cutul., 1981, 72, 16. P. A. Jacobs, W. J. Mortier, and J. B. Uyterhoeven, J. Inorg. Nucl. Chem., 1978, 40, 1919; W. J . Mortier and P. Geerlings, J. Phys. Chem., 1980, 84, 1982. I. Wang, T. J. Chen, K. J. Chao, and T. C. Tsai, J. Cutul., 1979,60, 140. N. D. Lazo, B. R. Richardson, P. D. Schettler, J. L. White, E. J. Munson, and J. F. Haw, J. Phys. Chem., 1991, 95,9420. K. Tanabe, M. Misono, Y. Ono, and H. Hattori, "New Solid Acids and Bases", p. 252. Kodansha-Elsevier, Tokyo-Amsterdam, 1989.
B