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Interaction of acetone with ammonia and alcohols over a HZSM-5 zeolite Part 2. Ethanol
Joumal
of Molecular
Catalysis,
78 (1993)
181-187
Elsevier Science Publishers B.V., Amsterdam
181
M3036
Interaction of acetone with ammonia and alcohols over a HZSM-5 zeolite Part 2. Ethanol J. Novakova,
V. Bosacek, Z. DolejBek and L. Kubelkova
J. Heyrovskg Institute of Physical Chemistry and Electrochemistry, Czechosbvak Academy of Sciences, DolejZkova 3, 182 23 Prague 8 [Czechoslovakia) (Received
March 8, 1992; accepted
May 8, 1992)
Abstract The reactions of ethanol and ethanol + ammonia with surface species formed from acetone on a HZSM-5 zeolite were investigated and compared with those of methanol. The studies were carried out using temperature-programmed conversion of adsorbed reactants with mass spectrometric analysis of the products evolved and 13C MAS NMB detection of surface species. It was found that ethanol alkylates the acetone surface species, whose decomposition increases the yield of propylene and especially aromatics in the products. The yield of aromatics is only slightly affected by the presence of ammonia, as was also observed for methanol + ammonia. This is considerably different from the reaction of ammonia alone with the surface acetone species. As the main product of the interaction of ethanol alone with the zeolite is ethylene, the reaction of ethylene with the acetone species was also studied. It was found that these two reactants, ethanol and ethylene, behave quite differently; the effects observed can thus be ascribed to the reaction of ethanol with the acetone species.
Introduction The reactions of ethanol and/or acetaldehyde with ammonia over HZSM5 zeolites yield pyridines and pyridinium bases [ 1, 2 1, which are of practical importance. Pyridinium bases are also formed from methanol, acetone and ammonia [3]. The latter reaction was studied in an earlier paper [4]; as the method employed, i.e., temperature-programmed desorption and conversion (TPDC) of preadsorbed acetone with added methanol and ammonia to the acetone surface species, was performed using low reactant-to-acid-centre ratios, and on a HZSM-5 zeolite with a high number of bridging hydroxyls (Si/Al ratio = 13.6), pyridinium bases were found only in trace amounts, and nitrogen-containing aliphatic compounds were observed instead. The methylation of an imino-like acetone surface species was assumed to explain the experimental results. The thermal decomposition of this species differed in product composition from that formed from only ammonia with the acetone species. The experimental conditions applied were convenient for the observation of the early reaction steps of the interaction of individual reactants,
0304-5102/93/$06.00
0 1993 - Elsevier
Science Publishers B.V. All rights reserved
182
as well as of their mixtures, with the acid active centers of the zeolite. The TPDC was studied both in the gaseous phase (analysis of the products evolved using a mass spectrometer) and on the zeolite (by 13C MAS NMR spectroscopy). To continue these studies, ethanol was employed in place of methanol and was left to react with the acetone surface species either alone or in a mixture with ammonia. Ethylene, the main product of the conversion of ethanol on the zeolite in the absence of acetone surface species, was also included in the experiments.
Experimental All experimental conditions were the same as in the preceding paper [4], i.e., HZSM-5 zeolite (0.1 g, for NMR measurements 0.5 g) with Si/Al ratio = 13.5 (the number of bridging hydroxyls equal to 1 .O mm01 per g of the undried zeolite) was employed, on which 0.2 mm01 g-’ of acetone were adsorbed at room temperature and desorbed directly into the vacuum system of a Finnigan 400 quadrupole mass spectrometer. A 20 mm isothermal pause at 130 “C was used in the programmed heating (12 “C mm- ‘), during which the reaction vessel with the sample was cut off from the vacuum line and left either alone or with added: (i) ammonia, (ii) ethanol or (iii) ethanol +ammonia (0.4 mm01 g-’ of each of the added reactants were introduced into the reaction vessel, either to the zeolite with adsorbed acetone or to the zeolite alone). After the isothermal pause, when the added reactants were allowed to react with the surface species formed from preadsorbed acetone (or with zeolite without preadsorbed acetone), the TPDC was resumed. The samples for 13C MAS NMR measurements were prepared similarly (sealed off after the isothermal pause) and the spectra were scanned at room temperature using a Bruker 200 NMR spectrometer under the conditions given in [ 41. For these measurements, i3C,-enriched acetone and unlabelled ethanol were employed as well as the mixture of unlabelled ethanol + 13Cethanol-C, + ‘3C-ethanol-C, or 13C-ethanol-C, alone. 13C-labelled ethanol-C, (enrichment 99.8 at.%) was supplied by Merck (Canada) and 13C-ethanol-C, (enrichment 80 at.%) by Tekhsnabeksport (USSR). In [4] the experimental conditions and setup are described in more detail.
Results TPDC of acetone and of acetone with added ethanol or ethanol -I-ammonia; gas phase In Figs. l(a), (b) and (c) the TPDC curves of acetone, acetone with added ethanol and acetone with added ethanol + ammonia, respectively, are shown. Desorption of the products was negligible below 130 “C. It can be seen that the addition of ethanol (l(b)) decreases the yield of isobutene,
183
Fig. 1. TPDC curves of (a) acetone, (b) acetone + ethanol and (c) acetone + ethanol + ammonia on HZSM-5 zeolite. (-) isobutene; (. . . . .) acetone; (- -) propene; (- - -) COz; (UO)aromatics C&; (8) allene; (El) ethylene (decreased by a factor of 0.5); (I) acetonitrile. Fig. 2. Composition of aromatics in TPDC of (a) acetone, (b) acetone with methanol and (c) acetone with ethanol. (-) toluene, (- - -) xylenes, (. . .) trimethylbenzenes.
acetone and allene, suppresses that of COZ and substantially increases that of propylene and &_a aromatics, compared with the TPDC of acetone alone (l(a)). In addition, a large amount of ethylene appears in the products in the low-temperature region (maximum at about 200 “C). The simultaneous addition of ammonia and ethanol (l(c)) results in a decrease in the ethylene and propylene yields and in an increase in the allene yield, while the fraction of aromatics is almost the same. This is very different from the effect of addition of ammonia alone ([5], also shown in the preceding paper [4]), which almost completely suppresses the formation of aromatics, substantially increases the allene fraction and yields acetonitrile. A very small fraction of the latter compound also appears in the experiments with added ethanol + ammonia (1 (c)), being the only product that contains nitrogen incorporated from ammonia. The composition of the aromatics corresponding to the ethanol added to the acetone species is as follows: xylenes > trimethylbenzenes > toluene, and does not change with the addition of ammonia, while for acetone alone toluene predominates over xylenes and trimethylbenzenes. A comparison of
184
the compositions of aromatics is given in Pig. 2 for the TPDC of: (a) acetone alone, (b) acetone with added methanol and (c) acetone with added ethanol. TPDC of ethylene and ethylene +ammonia with and without acetone sutiace species; gas phase As ethanol alone is almost completely converted to ethylene (with no observable effect due to ammonia addition), it is possible that we were examining the reaction of ethylene with preadsorbed acetone and not the reaction of ethanol. Thus experiments identical to those shown in Pig. 1 were carried out with ethylene, either alone or together with ammonia, over HZSM-5 with or without preadsorbed acetone. It was found that ethylene without preadsorbed acetone yields aliphatics &, at lower temperatures and aromatics above 250 “C and that the yield of aromatics is strongly suppressed in the presence of ammonia, while that of aliphatics increases. No nitrogencontaining organic compounds were observed in the presence of ammonia. The addition of ethylene to the acetone surface species increases the yield of aliphatic compounds, especially propylene, and roughly doubles the yield of aromatics. The aromatic compounds, however, disappear in the presence of ammonia (unlike the addition of ethanol + ammonia to the acetone species), while aliphatics and allene appear instead. Acetonitrile is probably also formed under these conditions, but it was impossible to determine its yield. The behaviour of ethylene (and ethylene with ammonia) when added to preadsorbed acetone is thus completely different from the behaviour of ethanol (and ethanol with ammonia); the effects shown in Figs. l(b) and (c) can, therefore, be ascribed to the reaction of ethanol with the species formed from preadsorbed acetone. 13C MAS NMR spectra of surface compounds The NMR spectra scanned after the isothermal pause at 130 “C are depicted in Pigs. 3 and 4. In Fig. 3(a), the acetone species alone gives the signals of the protonized car-bony1 group (223.5 ppm) and of the methyl group (28 ppm). The latter signal is weak, as the acetone was enriched by 13C in the car-bony1 group only. After the addition of unlabelled ethanol (Pig. 3(b)), the signal at 223.5 ppm remains unchanged (no reaction with ethanol) and new signals in the O-40 ppm region appear. They can probably be assigned to the C2_3 aliphatic chains formed through the reaction of ethanol with the acetone surface species. The addition of ammonia together with the unlabelled ethanol (Pig. 3(c)) results especially in the shift of the protonized acetone group from 223.5 ppm to 200 ppm; this signal corresponds to the formation of a protonized imino group [ 51. The signals in the low-ppm region are weaker than in the preceding case; however, their presence points to a reaction similar to that in case 3(b). The weak signals around 60 ppm can be assigned to the unreacted ethanol (see Pig. 4). Pigs. 4(a) and (b) depict the spectra of adsorbed ethanol, enriched in both the CH, and CHZ groups, and ethanol enriched only in the CH2 group, respectively. They exhibit signals at 68-69 and 60-62 ppm characteristic
185
a *
300
200
-._ -~100
1 0
PPm
300
200
100
0
PPm
Fig. 3. r3C MAS NMR spectra of surface species after the isothermal pause at 130 “C; %Oacetone and unlabelled ethanol. (a) acetone, NS(number of scans) = 1600; (b) acetone + ethanol, NS = 480; (c) acetone + ethanol + ammonia, NS = 2048. Signals normalized to the highest peak; * = side bands. Fig. 4. ‘% MAS NMR spectra of surface species after the isothermal pause at 130 “C. (a) ‘3C-ethanol-C1,z, NS= 160; (b) %Hz-ethanol, NS= 1024; (c) r3CO-acetone with r3C-ethanolC r, z, NS = 2448; (d) r3CO-acetone with ‘3CH,-ethanol, NS = 1600.
of the 13CHz group and at 14.6 ppm characteristic of the 13CH3group (4(a)*). When these ‘3C-enriched ethanol molecules (4(a) and 4(b)) were left to react with the acetone surface species (13C in the carbonyl group), the signals shown in Fig. 4(c) and 4(d), respectively, were obtained. It can be seen that the intensity of the signals in the low ppm region is much lower for 13CHzethanol than for ethanol enriched in both C1 and C2 groups. The intensity of the signal of the protonized acetone carbonyl group seems low owing to the high intensity of signals in the low-ppm region; the signals are always normalized to the highest peak in the spectrum. The signal at about 184 ppm can be tentatively assigned to carboxylate groups. No signals that could be ascribed to polyethylene species (120-130 ppm) were observed. *The spectra of adsorbed ethanol on zeolites will be described and discussed in detail elsewhere.
186
Discussion
It follows from comparison of the TPDC curves of acetone species when desorbed alone and with added ethanol that ethanol considerably alters the product composition. The ethylene was formed most probably through reaction of ethanol with the bridging zeolite hydroxyls (only l/5 of the hydroxyls corresponded to the amount of preadsorbed acetone); isobutene, COa, allene and part of the propylene and aromatics can be related to the conversion of acetone species that do not react with ethanol, while most of the propylene and aromatics clearly result from decomposition of the ethylated acetone surface species. -The assumed ethylation agrees with the alkylation of ketones with alcohols reported in [S-S]. Ganesan and Pillai [ 8 ] observed the methylation and ethylation of acetophenone by relevant alcohols instead of the formation of ketals, familiar in organic chemistry. This also follows from the NMR spectra: the protonated car-bony1 acetone group does not react with ethanol, similar to what was observed for methanol [4]. Nevertheless, the intensity of the signals created due to the interaction of ethanol with the acetone surface species (O-40 ppm) is high, even when nonlabelled ethanol was employed (Fig. 3(b)). This can be caused either by isotope mixing (of 13C from the acetone car-bony1 group) or by ethylation proceeding at the C =C bond of mesityl-oxide-like species formed from the carbonyl acetone group. Such ethylated acetone species could be cyclized and dehydrated to xylenes, whose yield actually predominates in aromatics. The enhanced yield of propylene can arise from the cracking of the surface species with the formation of acetate-like fragments (or acetaldehyde, whose formation and role is assumed in [2]), which can participate in aldolization and aromatization reactions: H ,Si CH,CH,OH
+ KCH,),COH]+O-,
-Hz0
,Si
P
b
[CH,CH,CH,CCH,]+O-
Al
‘Al 1
CH,CH:CHs
H P + [CH,CH]+O-
1 CH,CHO
,Si \ ‘Al
,Si + HO \ Al
187
Mesityl oxide from acetone aldolization + acetaldehyde: H ,Si 0 + CH,CHO a --) [(CH&C:CHCHCH3]+0-\ Al 9n zeolite
,Si + 2H,O + HO, Al
cavities.
As the yield of aromatics is very high, these reaction paths are probably favored and that corresponding to the TPDC of acetone alone (Fig. l(a) and [4]) is suppressed. The aromatization proceeds even in the presence of ammonia (similar to what was observed with methanol+ammonia), which again supports the assumption of ethylation of the acetone surface species. The ethylene formed is probably immediately released into the gas phase. As with methanol, almost no pyridine or pyridinium bases are observed under our experimental conditions. The ethylation of acetone species and enhanced aromatization are probably steps that also occur in reactions under normal conditions (atmospheric pressure, stream of reactants) and with a more suitable (less acidic) catalyst. The reaction of ethylene with the surface acetone species increases the yield of aromatics, which, however, disappear in the presence of ammonia. Thus ethylene, when added to the acetone surface species, exhibits behaviour quite different from that of ethanol. Therefore, it can be concluded that the changes in product composition after the addition of ethanol to the surface acetone species are due to the reaction of ethanol and not ethylene.
Conclusions The addition of vapours of ethanol to the surface species created from acetone on HZSM-5 zeolite results in the cyclization and aromatization of the ethylated species. The ethylation is assumed to proceed on both the protonized acetone-like species and the mesityl-oxide-like species. The protonized car-bony1 group was found not to react with ethanol. The presence of ammonia, which, on the contrary, does react with the carbonyl group, does not substantially change the yield of the aromatics. References C. D. Chang and W. H. Lang, U.S. Put. 4 220783 (1980). F. J. van der Gaag, F. Louter, J. C. Oudejans and H. van Bekkum, Appl. Catal., 26 (1986) 191. F. J. van der Gaag, R. J. 0. Adriaansens, H. van Bekkum and P. C. van Geem, in J. Khnowski and P. J. Barrie (eds.), Studies in Surface Science and Catal@s, Vol. 52, Elsevier, Amsterdam, 1989, p. 283. J. Novakova, V. BodEek, Z. DolejSek and L. Kubelkova, J. Mol. Catal., 78 (1992) 43. 2. Dolejsek, J. Novakova, V. BosaEek and L. Kubelkova, Zeolites, II (1991) 244. Mamoru Ai, J. Catal., 106 (1987) 273. T. Wang, W. Ueda, Y. Morikawa and T. Ikava, C&m. L&t., (1988) 1991. K. Ganesan and C. N. Pillai, J. Catal., 118 (1989) 371.
of Molecular
Catalysis,
78 (1993)
181-187
Elsevier Science Publishers B.V., Amsterdam
181
M3036
Interaction of acetone with ammonia and alcohols over a HZSM-5 zeolite Part 2. Ethanol J. Novakova,
V. Bosacek, Z. DolejBek and L. Kubelkova
J. Heyrovskg Institute of Physical Chemistry and Electrochemistry, Czechosbvak Academy of Sciences, DolejZkova 3, 182 23 Prague 8 [Czechoslovakia) (Received
March 8, 1992; accepted
May 8, 1992)
Abstract The reactions of ethanol and ethanol + ammonia with surface species formed from acetone on a HZSM-5 zeolite were investigated and compared with those of methanol. The studies were carried out using temperature-programmed conversion of adsorbed reactants with mass spectrometric analysis of the products evolved and 13C MAS NMB detection of surface species. It was found that ethanol alkylates the acetone surface species, whose decomposition increases the yield of propylene and especially aromatics in the products. The yield of aromatics is only slightly affected by the presence of ammonia, as was also observed for methanol + ammonia. This is considerably different from the reaction of ammonia alone with the surface acetone species. As the main product of the interaction of ethanol alone with the zeolite is ethylene, the reaction of ethylene with the acetone species was also studied. It was found that these two reactants, ethanol and ethylene, behave quite differently; the effects observed can thus be ascribed to the reaction of ethanol with the acetone species.
Introduction The reactions of ethanol and/or acetaldehyde with ammonia over HZSM5 zeolites yield pyridines and pyridinium bases [ 1, 2 1, which are of practical importance. Pyridinium bases are also formed from methanol, acetone and ammonia [3]. The latter reaction was studied in an earlier paper [4]; as the method employed, i.e., temperature-programmed desorption and conversion (TPDC) of preadsorbed acetone with added methanol and ammonia to the acetone surface species, was performed using low reactant-to-acid-centre ratios, and on a HZSM-5 zeolite with a high number of bridging hydroxyls (Si/Al ratio = 13.6), pyridinium bases were found only in trace amounts, and nitrogen-containing aliphatic compounds were observed instead. The methylation of an imino-like acetone surface species was assumed to explain the experimental results. The thermal decomposition of this species differed in product composition from that formed from only ammonia with the acetone species. The experimental conditions applied were convenient for the observation of the early reaction steps of the interaction of individual reactants,
0304-5102/93/$06.00
0 1993 - Elsevier
Science Publishers B.V. All rights reserved
182
as well as of their mixtures, with the acid active centers of the zeolite. The TPDC was studied both in the gaseous phase (analysis of the products evolved using a mass spectrometer) and on the zeolite (by 13C MAS NMR spectroscopy). To continue these studies, ethanol was employed in place of methanol and was left to react with the acetone surface species either alone or in a mixture with ammonia. Ethylene, the main product of the conversion of ethanol on the zeolite in the absence of acetone surface species, was also included in the experiments.
Experimental All experimental conditions were the same as in the preceding paper [4], i.e., HZSM-5 zeolite (0.1 g, for NMR measurements 0.5 g) with Si/Al ratio = 13.5 (the number of bridging hydroxyls equal to 1 .O mm01 per g of the undried zeolite) was employed, on which 0.2 mm01 g-’ of acetone were adsorbed at room temperature and desorbed directly into the vacuum system of a Finnigan 400 quadrupole mass spectrometer. A 20 mm isothermal pause at 130 “C was used in the programmed heating (12 “C mm- ‘), during which the reaction vessel with the sample was cut off from the vacuum line and left either alone or with added: (i) ammonia, (ii) ethanol or (iii) ethanol +ammonia (0.4 mm01 g-’ of each of the added reactants were introduced into the reaction vessel, either to the zeolite with adsorbed acetone or to the zeolite alone). After the isothermal pause, when the added reactants were allowed to react with the surface species formed from preadsorbed acetone (or with zeolite without preadsorbed acetone), the TPDC was resumed. The samples for 13C MAS NMR measurements were prepared similarly (sealed off after the isothermal pause) and the spectra were scanned at room temperature using a Bruker 200 NMR spectrometer under the conditions given in [ 41. For these measurements, i3C,-enriched acetone and unlabelled ethanol were employed as well as the mixture of unlabelled ethanol + 13Cethanol-C, + ‘3C-ethanol-C, or 13C-ethanol-C, alone. 13C-labelled ethanol-C, (enrichment 99.8 at.%) was supplied by Merck (Canada) and 13C-ethanol-C, (enrichment 80 at.%) by Tekhsnabeksport (USSR). In [4] the experimental conditions and setup are described in more detail.
Results TPDC of acetone and of acetone with added ethanol or ethanol -I-ammonia; gas phase In Figs. l(a), (b) and (c) the TPDC curves of acetone, acetone with added ethanol and acetone with added ethanol + ammonia, respectively, are shown. Desorption of the products was negligible below 130 “C. It can be seen that the addition of ethanol (l(b)) decreases the yield of isobutene,
183
Fig. 1. TPDC curves of (a) acetone, (b) acetone + ethanol and (c) acetone + ethanol + ammonia on HZSM-5 zeolite. (-) isobutene; (. . . . .) acetone; (- -) propene; (- - -) COz; (UO)aromatics C&; (8) allene; (El) ethylene (decreased by a factor of 0.5); (I) acetonitrile. Fig. 2. Composition of aromatics in TPDC of (a) acetone, (b) acetone with methanol and (c) acetone with ethanol. (-) toluene, (- - -) xylenes, (. . .) trimethylbenzenes.
acetone and allene, suppresses that of COZ and substantially increases that of propylene and &_a aromatics, compared with the TPDC of acetone alone (l(a)). In addition, a large amount of ethylene appears in the products in the low-temperature region (maximum at about 200 “C). The simultaneous addition of ammonia and ethanol (l(c)) results in a decrease in the ethylene and propylene yields and in an increase in the allene yield, while the fraction of aromatics is almost the same. This is very different from the effect of addition of ammonia alone ([5], also shown in the preceding paper [4]), which almost completely suppresses the formation of aromatics, substantially increases the allene fraction and yields acetonitrile. A very small fraction of the latter compound also appears in the experiments with added ethanol + ammonia (1 (c)), being the only product that contains nitrogen incorporated from ammonia. The composition of the aromatics corresponding to the ethanol added to the acetone species is as follows: xylenes > trimethylbenzenes > toluene, and does not change with the addition of ammonia, while for acetone alone toluene predominates over xylenes and trimethylbenzenes. A comparison of
184
the compositions of aromatics is given in Pig. 2 for the TPDC of: (a) acetone alone, (b) acetone with added methanol and (c) acetone with added ethanol. TPDC of ethylene and ethylene +ammonia with and without acetone sutiace species; gas phase As ethanol alone is almost completely converted to ethylene (with no observable effect due to ammonia addition), it is possible that we were examining the reaction of ethylene with preadsorbed acetone and not the reaction of ethanol. Thus experiments identical to those shown in Pig. 1 were carried out with ethylene, either alone or together with ammonia, over HZSM-5 with or without preadsorbed acetone. It was found that ethylene without preadsorbed acetone yields aliphatics &, at lower temperatures and aromatics above 250 “C and that the yield of aromatics is strongly suppressed in the presence of ammonia, while that of aliphatics increases. No nitrogencontaining organic compounds were observed in the presence of ammonia. The addition of ethylene to the acetone surface species increases the yield of aliphatic compounds, especially propylene, and roughly doubles the yield of aromatics. The aromatic compounds, however, disappear in the presence of ammonia (unlike the addition of ethanol + ammonia to the acetone species), while aliphatics and allene appear instead. Acetonitrile is probably also formed under these conditions, but it was impossible to determine its yield. The behaviour of ethylene (and ethylene with ammonia) when added to preadsorbed acetone is thus completely different from the behaviour of ethanol (and ethanol with ammonia); the effects shown in Figs. l(b) and (c) can, therefore, be ascribed to the reaction of ethanol with the species formed from preadsorbed acetone. 13C MAS NMR spectra of surface compounds The NMR spectra scanned after the isothermal pause at 130 “C are depicted in Pigs. 3 and 4. In Fig. 3(a), the acetone species alone gives the signals of the protonized car-bony1 group (223.5 ppm) and of the methyl group (28 ppm). The latter signal is weak, as the acetone was enriched by 13C in the car-bony1 group only. After the addition of unlabelled ethanol (Pig. 3(b)), the signal at 223.5 ppm remains unchanged (no reaction with ethanol) and new signals in the O-40 ppm region appear. They can probably be assigned to the C2_3 aliphatic chains formed through the reaction of ethanol with the acetone surface species. The addition of ammonia together with the unlabelled ethanol (Pig. 3(c)) results especially in the shift of the protonized acetone group from 223.5 ppm to 200 ppm; this signal corresponds to the formation of a protonized imino group [ 51. The signals in the low-ppm region are weaker than in the preceding case; however, their presence points to a reaction similar to that in case 3(b). The weak signals around 60 ppm can be assigned to the unreacted ethanol (see Pig. 4). Pigs. 4(a) and (b) depict the spectra of adsorbed ethanol, enriched in both the CH, and CHZ groups, and ethanol enriched only in the CH2 group, respectively. They exhibit signals at 68-69 and 60-62 ppm characteristic
185
a *
300
200
-._ -~100
1 0
PPm
300
200
100
0
PPm
Fig. 3. r3C MAS NMR spectra of surface species after the isothermal pause at 130 “C; %Oacetone and unlabelled ethanol. (a) acetone, NS(number of scans) = 1600; (b) acetone + ethanol, NS = 480; (c) acetone + ethanol + ammonia, NS = 2048. Signals normalized to the highest peak; * = side bands. Fig. 4. ‘% MAS NMR spectra of surface species after the isothermal pause at 130 “C. (a) ‘3C-ethanol-C1,z, NS= 160; (b) %Hz-ethanol, NS= 1024; (c) r3CO-acetone with r3C-ethanolC r, z, NS = 2448; (d) r3CO-acetone with ‘3CH,-ethanol, NS = 1600.
of the 13CHz group and at 14.6 ppm characteristic of the 13CH3group (4(a)*). When these ‘3C-enriched ethanol molecules (4(a) and 4(b)) were left to react with the acetone surface species (13C in the carbonyl group), the signals shown in Fig. 4(c) and 4(d), respectively, were obtained. It can be seen that the intensity of the signals in the low ppm region is much lower for 13CHzethanol than for ethanol enriched in both C1 and C2 groups. The intensity of the signal of the protonized acetone carbonyl group seems low owing to the high intensity of signals in the low-ppm region; the signals are always normalized to the highest peak in the spectrum. The signal at about 184 ppm can be tentatively assigned to carboxylate groups. No signals that could be ascribed to polyethylene species (120-130 ppm) were observed. *The spectra of adsorbed ethanol on zeolites will be described and discussed in detail elsewhere.
186
Discussion
It follows from comparison of the TPDC curves of acetone species when desorbed alone and with added ethanol that ethanol considerably alters the product composition. The ethylene was formed most probably through reaction of ethanol with the bridging zeolite hydroxyls (only l/5 of the hydroxyls corresponded to the amount of preadsorbed acetone); isobutene, COa, allene and part of the propylene and aromatics can be related to the conversion of acetone species that do not react with ethanol, while most of the propylene and aromatics clearly result from decomposition of the ethylated acetone surface species. -The assumed ethylation agrees with the alkylation of ketones with alcohols reported in [S-S]. Ganesan and Pillai [ 8 ] observed the methylation and ethylation of acetophenone by relevant alcohols instead of the formation of ketals, familiar in organic chemistry. This also follows from the NMR spectra: the protonated car-bony1 acetone group does not react with ethanol, similar to what was observed for methanol [4]. Nevertheless, the intensity of the signals created due to the interaction of ethanol with the acetone surface species (O-40 ppm) is high, even when nonlabelled ethanol was employed (Fig. 3(b)). This can be caused either by isotope mixing (of 13C from the acetone car-bony1 group) or by ethylation proceeding at the C =C bond of mesityl-oxide-like species formed from the carbonyl acetone group. Such ethylated acetone species could be cyclized and dehydrated to xylenes, whose yield actually predominates in aromatics. The enhanced yield of propylene can arise from the cracking of the surface species with the formation of acetate-like fragments (or acetaldehyde, whose formation and role is assumed in [2]), which can participate in aldolization and aromatization reactions: H ,Si CH,CH,OH
+ KCH,),COH]+O-,
-Hz0
,Si
P
b
[CH,CH,CH,CCH,]+O-
Al
‘Al 1
CH,CH:CHs
H P + [CH,CH]+O-
1 CH,CHO
,Si \ ‘Al
,Si + HO \ Al
187
Mesityl oxide from acetone aldolization + acetaldehyde: H ,Si 0 + CH,CHO a --) [(CH&C:CHCHCH3]+0-\ Al 9n zeolite
,Si + 2H,O + HO, Al
cavities.
As the yield of aromatics is very high, these reaction paths are probably favored and that corresponding to the TPDC of acetone alone (Fig. l(a) and [4]) is suppressed. The aromatization proceeds even in the presence of ammonia (similar to what was observed with methanol+ammonia), which again supports the assumption of ethylation of the acetone surface species. The ethylene formed is probably immediately released into the gas phase. As with methanol, almost no pyridine or pyridinium bases are observed under our experimental conditions. The ethylation of acetone species and enhanced aromatization are probably steps that also occur in reactions under normal conditions (atmospheric pressure, stream of reactants) and with a more suitable (less acidic) catalyst. The reaction of ethylene with the surface acetone species increases the yield of aromatics, which, however, disappear in the presence of ammonia. Thus ethylene, when added to the acetone surface species, exhibits behaviour quite different from that of ethanol. Therefore, it can be concluded that the changes in product composition after the addition of ethanol to the surface acetone species are due to the reaction of ethanol and not ethylene.
Conclusions The addition of vapours of ethanol to the surface species created from acetone on HZSM-5 zeolite results in the cyclization and aromatization of the ethylated species. The ethylation is assumed to proceed on both the protonized acetone-like species and the mesityl-oxide-like species. The protonized car-bony1 group was found not to react with ethanol. The presence of ammonia, which, on the contrary, does react with the carbonyl group, does not substantially change the yield of the aromatics. References C. D. Chang and W. H. Lang, U.S. Put. 4 220783 (1980). F. J. van der Gaag, F. Louter, J. C. Oudejans and H. van Bekkum, Appl. Catal., 26 (1986) 191. F. J. van der Gaag, R. J. 0. Adriaansens, H. van Bekkum and P. C. van Geem, in J. Khnowski and P. J. Barrie (eds.), Studies in Surface Science and Catal@s, Vol. 52, Elsevier, Amsterdam, 1989, p. 283. J. Novakova, V. BodEek, Z. DolejSek and L. Kubelkova, J. Mol. Catal., 78 (1992) 43. 2. Dolejsek, J. Novakova, V. BosaEek and L. Kubelkova, Zeolites, II (1991) 244. Mamoru Ai, J. Catal., 106 (1987) 273. T. Wang, W. Ueda, Y. Morikawa and T. Ikava, C&m. L&t., (1988) 1991. K. Ganesan and C. N. Pillai, J. Catal., 118 (1989) 371.