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Aromatization of hydrocarbons over Pt- and Pt-Re-containing zeolite-Al2O3 catalysts
Catalysis Today, 3 (1988) 437-443 Elsevier Science Publishers B.V., Amsterdam -Printed
437 in The Netherlands
OF HYDROCARBONS OVERPt- ANDPt-Re-CORTAIRIRG AROHATIZATIOB ZROLITE-Al203 CATALYSTS 3 1 1 S. RNGELS ’ , H. LAUSCH ’ , B. MATSCHRI ’ , O.V. BRAGIIO’, A.V. PREOBRAZRElWKI12 and T.V. VASIlJA2 ‘Chemletry Department, “Carl Schorlemrmer” Technical LeunaiHerzeburg, 4200 Yereeburg (G.D.R. ) 21netltute of Organlo Chemistry, U.S.S.R., GPS-1 Yozoow (U.S.S.R.)
Academy of Soienoe
University of the
ABSTRACT
The typloal reaotion of ethane in a hydrogen flow over Pt-Re/ ZSH-Al203 oatalgetz is hydrogenol~eie of the C2H moleoule. Rydrogenolyeiz activity le thereby enhanced by a h kgh dlzpereion of the formation the metal phaee. However, ia a helium atmosphere of aromatloe oan be obeerved rhloh reachee a IU Laum for ZSH oontents between 50 and 70 rt % and eurpaeeea the bfdrogenolysie aotivlty of the pure Pt-Re/ZSM oatalyet. The utilization of this ability to aromize during the converhydrooracking elan of hi er hydrocarbone iz hindered by the hi However, by adding ma1 !! amounts of aotlvitj o F the zeolitee. both a ZSH and a Y type zeolite to Al2O3, the aromatization aotivlty and seleotivitg in the conversion of n-hexane and n-heptane in the prezenoe of about 300 ppm water vapoPr oan be improved. IXTRODUC TIOB Sferba and Haenzel (ref. 1) have already pointed out that an aotive reforming oatalyet requires an optimum aoidio function that cau be produced by modifying zn alumina eupport with halides, eepeoially with chloride. Thermal treatment however, partlcrular4 where there are traoea of water In the reaotfon eyetea, reeulte in a signifiaant lose of ohlorlne, and henoe alao of acidity (ret. 2). However, keeping the ohloride level aonetznt oauaes too azny problems and therefore the zubetitutlon of ohloride by fluoride le much more promleing. Xevertheleza, the ability of pentaaile for aromatization (refe. 3-4) raieee the question of how far eeolitee are aleo euitable for controlling the eeleotivlty of reforming-type cztalyets. 0920-5861/88/$03.50
0 1988 Elsavier Science Publishers B.V.
438
RXPRR-TAL The catalyst8 were prepared by the following proaedure: The the H-Zm-5 or HY type zeolite was added to a boehmite slurry, was filtered, extruded, and calained at 550 Oc reeulting mixture (5 hre.); then impregnated with H2PtCl6 or mixtures of R2PtCl6 and HReO4 (24 hre., 0 ‘C) and after that the products were dried 110 ‘C), in situ caloined (1 hr., 500 ‘C) and reduoed (20 hrs., (2 hre., 500 ‘c). To ensure equivalent metal oontenta of 0.6 wt %, (the PttRe atomic ratio was 60:40), for all samples, the aolutiona were not deoanted after impregnation but were evaporated in vaouo for the pure ZSM sample and for that of 70 wt % ZSM, because of their low ion exohange capacity. Measurements of the CO chemieorption oapaoitg, the activity of n-hexane conversion, and the convereion of ethane in a hytiogen (hydrogenolgeie) and helium flow (aromatization)were carried out in a pulse syetem. The equipment6 and conditions have been described elsewhere (refe. 5-6). The oatalytio parameters of the n-heptane test were meaeured in a flow system at 480 ‘C and normal preaaure (ref. 7). RESULTSAl0 DISCUSSIOlV Ae ahown in Table 1, the dispersion of the metal inoreaeee with a ricing proportion of ZSM In the oarrier for eamplar.whioh were prepared in exaotlg the came way, i. 8. for the earrier compoeition of 50 ZSM/50 A1203. However, for ZSM-rich 8amplee (2 70 wt %), it 88888 that the addition of zeollte has the opposite effect, although it ie neoeeeary in this oonnection to point out that the CO chemieorption oapacitg only refleote an Integral value and doee not provide Information about the dietributlon of particle size. This is crepeclallg important in the oaee of euoh samples for whioh an inoreased aggregation and a rearrangement of the surface due to the preparation prooedure (op. EXPERIXRHTAL) oan be assumed (70 ZSy/30 Al 0 and 100 ZSY). Thus on the one 23 hand a higher temperature should stimulate hydrolysie prooeseea, while on the other, part of the dissolved A13+ ione (from the alumina) ie preoipitated on the eurfaoe of the mixed ZSH/A1203 sample during evaporation to dryness and partially block6 the metal oomponent (ref. 8). That is, the preparation conditiona firet cause the apparent differenoe of zeolite addition with regard to metal diepereion.
439
TABLE 1
CO chemieorption
capacity
Carrier composition at % ZSM/wt t,A1203 n(JO, pole*
l3
of Pt-Re/ZSH-A1203
0.5/99.5 16
2/98
5/95
17
21
lo/90 22
oatalgeta 50/50 70/30 29
23
100/O 21
Because the aluminium eolubilitg of pure ZSH zeolite should be lower than that of alumina (which ie aleo why a partial instion of the metale cannot occur in the same manner) it ie clear too that after a sharp decreaee in ethane hydrogenolyeie activity between the 50 ZSH/50 A1203 sample and 70 ZSH/30 Al203 a new increase for the pure pentasil eample can be obeeroed (Fig. 1). In thie connection it ehould also be mentioned that the values of activation energy of ethane conversion in the hydrogen flow lead to the conclusion that only the rhenium oomponent determines hydrogenolyeis activity. Eiven rhenium which 18 of little importanoe for aromatization activity ie preferred for Insertion in alumina (ref. 9). All in all, it therefore seems useful for discus&on purposes to dietinguiah between ZSH-rich (170 wt Se) and ZSM-poor samples, particularly up to 10 wt % ZSM. Comparing Pig. 1 and 2, it ie surprising that the eequence of methane formation as a function of the ZSY content up to 10 $ le approximately the same for the oonvereion of ethane In both the hydrogen and helium flow, and that it correlates directly with the aromatization aotivltg. These non-systematic changes may depend on an inhomogeneous distribution of the zeolite component in the alumina matriz and/or on pentaeil. de a first oonclualon, one can suppose that only the ability of the metal for C-C bond rupture continues to be a decisive faotor in the aromatization activity of such catalyete for omall addition6 of ZSH. For ZSH rich eamples (270 wt Se), there is no longer an analogy between the methane formation behaviour under hydrogenolyeis and aromatization conditiona. A strikingly higher aromatization activity than for W&poor catalyete ia now typical without a proporthonal inorease In methane formation. Thle improved eelectivity ie not due to the epeclal impregnation oonditione utsedfor both 70 ZSr/30 Al203 and 100 ZSH, beoauee the new quality ie already refleoted in the 50 ZSH/50 Al203 aample impremted in the
usual way.
60
R I
I \ \ /
I \
40
20
0
Pig. 1. Speoific activity of Pt-Re/ZSH-Al203 catalyafsin ethane hydroge 0413is.
Fig. 2. Ethane conversion to methane (0) and C6-Cg aromatice (01 at 600 oc over Pt-Re/ ZSM-Al203 catalyste In a helium atmcephzre.
in epite of the high hydrogenolyeie activity of the metal phaee (Fig. l), the inoreased pentaail content caueea an enhanced formation of aromatlc~, but this Is accompanied by a oomparatlvely mall-eoale improvement of methane production (Fig. 2). From this point of view, an increaee in eelectivltg for the conversion of higher hydrocarbona ehould be expected, eepeoially for ZSM contenta 250 rt $. However, as shown in Fig. 3, the yield of C2-C5 hydrocarbona In a helium atmoephere surpaseee the yield of aromatics, particularly for high ZSN contents. There is no doubt about the fact that the moat drastic change6 in the production of aromatic8 from hexane ocour in the range of low ZSH contents, where the particular ability of the carrier to promote the aromatization of ethane seema to be ineignifioant (eee above and aleo ref. 3). !Phle should mean in this caee that the enhanoed Br&ksted acidity of the carrier ie at flret lmportent In giving rise to the lncreaeed aromatization activity by a claeslc bifunctional medani~ of dehydrooyclizatlon; that is, other zeolites which are unable to promote aromatization themselves (zeclitee poaseeeiag larger pores, e.g. Y-type seolltee) should also enhance the formation of aromatice b7 their addition
to alumina in low concentration.
Pig. 3. n-Hexane convert 8iOn to c2d5 ~drocarbone l) 8nd 0 8rOlD8tiW 0) 8t 406-08 00 over Pt-Re/ ZSM-Al20 oatalyate in 8 helium 82moaphere.
I
50 ZSM content, rt
’
loo %
Indeed, Pt-OOnt8iniIIgY zeolite-A1203 C8t8b8t8 re8oh 8 higher level of dehydrocyclization in n-hept8ne conversion thsn doee 8 pure Pt/A1203 sample with the s8me content of chloride, baaed on the etoichiotnetryof H2PtCl6 (Pig. 4a). It is remarkable that both the formation of cracking products and the dehydrocyclization activity increase only slightly, and still do not reach the values for the Pt/A1203 catalysts with 8n optimum chloridecontent Of 8bOUt 1.2 wt %. TABLE 2 Dehydrocyclization and crackingactivityrelated to the degree of n-heptans oonvereionin the preeenoeof <20 and 300 ppm I+0
Carrier modifier
toluene/conversion 20 Ppm 300 Ppm
C14g/oonvereion 20 Plrm 300 Ppnr
0.28
0.16
wt % 1)
0.31
0.31
:*22: 0:29
10 1.2By Cl
0.31 0.35
z-2 .
‘)onti
from H2PtCl6
7%
3Hy
c1
0.11
be can also be seen in 'Pable2, the oat84tio parameters releted to the degree of n-heptaneoonvereionof the reolite-rodifled 68RpleEI fall between those of a PUrO H/A1203 and 8 Oataljst containing1.2 wt P Cl for dry oonditione(I 20 ppm ?120).When a larger chloridelees appeara (i.e. partioularlyin the preeenoe
442
of about 300 ppm water vapour during reduction and catalytic reaction), the aromatization activity of the zeolite-containing catalyete not on4 exoeeds that of the pure Pt/A1203 catalyst but in the caee of zeolite content6 above 3 at Se aleo that of the Pt/A1203-1 .2 Cl sample (Fig. 4b and Table 2).
M30-
M 30
a
q
t:
‘; a p20h 0:
0
I
a 2 20 R
3
q q
0
y
10,
OF
,
b
I
5 HY content,
I
10 wt %
0
I 0
5 HY content,
I 10 rt %
Pig. 4. n-Heptane conversion over Pt/Al 0 -HY catalysts to C -C6 tidrocarbona (0) and toluene (I) in the2p$esencre of (20 PPIVI B_90 -(b>- or jO0 pg ii 0 (b). 60 Pt/Al 0 -0.65 cl (cl only from H2PtC16)0O Pt/Al 0 (WHSV: 1-g &g-1h’1, nR2:nC7H16 = 10, time on stream2r3;1&s!$ On this acoount, it should be concluded that the zeolite-containing catalysts inveetigated only represent an alternative to a chloride+odified alumina supported metal catalyst for euch conditiona in which complete abeenoe of traces of water cannot be effeoted. REFERENCES M. J. Sterbs and V. Baenael, Ind. En& Chem., Prod. Ree. DeVelODv. 15 (1976) 3-17. A. A. C&&o; 6.A; %lz& E.R. Benvenuto G. I. Baronet ti and J.Y. Parera, J. Catal., 69 (1981) 222-226. O.V. Bragin, T.V. Vasina, Ja. J.Ieakov, B.V. Poliehkina, A.V. Preobrazhenekii, B.K. Iefedov and Kh.Y. JUnachev, Izv. Akad. Kauk SSSR, Ser. Khim., (1983) 2002-2009. P.G. Riley and R.G. Anthony, J. Cataly., 100 (1986) 322-327. S.Engele, P. Mahlow,W. Pfeiffer, D. Sager and M. Wilde, Chem. Teahn., 36 (1984) 426-429. O.V. Bra in, A. V. Preobrazhenekii and A.L. Liberman, Izv. Akad. Bauk SSSf , Ser. Khim., (1974) 2751-2757.
443
7 S. Engele and R. Schwokoweki,Wies. Z. Se&n. Hoohechule "Carl Sohorlemmer"Leuna-Herseburg, 28 (1986) 667-679. 8 S. Engele,W. Hager, L-J. Kluge, M. HUnch, D. Sager, H. Seefluth R. Walter and 1, Wilde, Z. P&s. Chem. (Leipzig), 264 (1983) 1186-1194. 9 J. Haupt, Thesis, lechnicalUnivereitgof Merseburg, 1985.
437 in The Netherlands
OF HYDROCARBONS OVERPt- ANDPt-Re-CORTAIRIRG AROHATIZATIOB ZROLITE-Al203 CATALYSTS 3 1 1 S. RNGELS ’ , H. LAUSCH ’ , B. MATSCHRI ’ , O.V. BRAGIIO’, A.V. PREOBRAZRElWKI12 and T.V. VASIlJA2 ‘Chemletry Department, “Carl Schorlemrmer” Technical LeunaiHerzeburg, 4200 Yereeburg (G.D.R. ) 21netltute of Organlo Chemistry, U.S.S.R., GPS-1 Yozoow (U.S.S.R.)
Academy of Soienoe
University of the
ABSTRACT
The typloal reaotion of ethane in a hydrogen flow over Pt-Re/ ZSH-Al203 oatalgetz is hydrogenol~eie of the C2H moleoule. Rydrogenolyeiz activity le thereby enhanced by a h kgh dlzpereion of the formation the metal phaee. However, ia a helium atmosphere of aromatloe oan be obeerved rhloh reachee a IU Laum for ZSH oontents between 50 and 70 rt % and eurpaeeea the bfdrogenolysie aotivlty of the pure Pt-Re/ZSM oatalyet. The utilization of this ability to aromize during the converhydrooracking elan of hi er hydrocarbone iz hindered by the hi However, by adding ma1 !! amounts of aotlvitj o F the zeolitee. both a ZSH and a Y type zeolite to Al2O3, the aromatization aotivlty and seleotivitg in the conversion of n-hexane and n-heptane in the prezenoe of about 300 ppm water vapoPr oan be improved. IXTRODUC TIOB Sferba and Haenzel (ref. 1) have already pointed out that an aotive reforming oatalyet requires an optimum aoidio function that cau be produced by modifying zn alumina eupport with halides, eepeoially with chloride. Thermal treatment however, partlcrular4 where there are traoea of water In the reaotfon eyetea, reeulte in a signifiaant lose of ohlorlne, and henoe alao of acidity (ret. 2). However, keeping the ohloride level aonetznt oauaes too azny problems and therefore the zubetitutlon of ohloride by fluoride le much more promleing. Xevertheleza, the ability of pentaaile for aromatization (refe. 3-4) raieee the question of how far eeolitee are aleo euitable for controlling the eeleotivlty of reforming-type cztalyets. 0920-5861/88/$03.50
0 1988 Elsavier Science Publishers B.V.
438
RXPRR-TAL The catalyst8 were prepared by the following proaedure: The the H-Zm-5 or HY type zeolite was added to a boehmite slurry, was filtered, extruded, and calained at 550 Oc reeulting mixture (5 hre.); then impregnated with H2PtCl6 or mixtures of R2PtCl6 and HReO4 (24 hre., 0 ‘C) and after that the products were dried 110 ‘C), in situ caloined (1 hr., 500 ‘C) and reduoed (20 hrs., (2 hre., 500 ‘c). To ensure equivalent metal oontenta of 0.6 wt %, (the PttRe atomic ratio was 60:40), for all samples, the aolutiona were not deoanted after impregnation but were evaporated in vaouo for the pure ZSM sample and for that of 70 wt % ZSM, because of their low ion exohange capacity. Measurements of the CO chemieorption oapaoitg, the activity of n-hexane conversion, and the convereion of ethane in a hytiogen (hydrogenolgeie) and helium flow (aromatization)were carried out in a pulse syetem. The equipment6 and conditions have been described elsewhere (refe. 5-6). The oatalytio parameters of the n-heptane test were meaeured in a flow system at 480 ‘C and normal preaaure (ref. 7). RESULTSAl0 DISCUSSIOlV Ae ahown in Table 1, the dispersion of the metal inoreaeee with a ricing proportion of ZSM In the oarrier for eamplar.whioh were prepared in exaotlg the came way, i. 8. for the earrier compoeition of 50 ZSM/50 A1203. However, for ZSM-rich 8amplee (2 70 wt %), it 88888 that the addition of zeollte has the opposite effect, although it ie neoeeeary in this oonnection to point out that the CO chemieorption oapacitg only refleote an Integral value and doee not provide Information about the dietributlon of particle size. This is crepeclallg important in the oaee of euoh samples for whioh an inoreased aggregation and a rearrangement of the surface due to the preparation prooedure (op. EXPERIXRHTAL) oan be assumed (70 ZSy/30 Al 0 and 100 ZSY). Thus on the one 23 hand a higher temperature should stimulate hydrolysie prooeseea, while on the other, part of the dissolved A13+ ione (from the alumina) ie preoipitated on the eurfaoe of the mixed ZSH/A1203 sample during evaporation to dryness and partially block6 the metal oomponent (ref. 8). That is, the preparation conditiona firet cause the apparent differenoe of zeolite addition with regard to metal diepereion.
439
TABLE 1
CO chemieorption
capacity
Carrier composition at % ZSM/wt t,A1203 n(JO, pole*
l3
of Pt-Re/ZSH-A1203
0.5/99.5 16
2/98
5/95
17
21
lo/90 22
oatalgeta 50/50 70/30 29
23
100/O 21
Because the aluminium eolubilitg of pure ZSH zeolite should be lower than that of alumina (which ie aleo why a partial instion of the metale cannot occur in the same manner) it ie clear too that after a sharp decreaee in ethane hydrogenolyeie activity between the 50 ZSH/50 A1203 sample and 70 ZSH/30 Al203 a new increase for the pure pentasil eample can be obeeroed (Fig. 1). In thie connection it ehould also be mentioned that the values of activation energy of ethane conversion in the hydrogen flow lead to the conclusion that only the rhenium oomponent determines hydrogenolyeis activity. Eiven rhenium which 18 of little importanoe for aromatization activity ie preferred for Insertion in alumina (ref. 9). All in all, it therefore seems useful for discus&on purposes to dietinguiah between ZSH-rich (170 wt Se) and ZSM-poor samples, particularly up to 10 wt % ZSM. Comparing Pig. 1 and 2, it ie surprising that the eequence of methane formation as a function of the ZSY content up to 10 $ le approximately the same for the oonvereion of ethane In both the hydrogen and helium flow, and that it correlates directly with the aromatization aotivltg. These non-systematic changes may depend on an inhomogeneous distribution of the zeolite component in the alumina matriz and/or on pentaeil. de a first oonclualon, one can suppose that only the ability of the metal for C-C bond rupture continues to be a decisive faotor in the aromatization activity of such catalyete for omall addition6 of ZSH. For ZSH rich eamples (270 wt Se), there is no longer an analogy between the methane formation behaviour under hydrogenolyeis and aromatization conditiona. A strikingly higher aromatization activity than for W&poor catalyete ia now typical without a proporthonal inorease In methane formation. Thle improved eelectivity ie not due to the epeclal impregnation oonditione utsedfor both 70 ZSr/30 Al203 and 100 ZSH, beoauee the new quality ie already refleoted in the 50 ZSH/50 Al203 aample impremted in the
usual way.
60
R I
I \ \ /
I \
40
20
0
Pig. 1. Speoific activity of Pt-Re/ZSH-Al203 catalyafsin ethane hydroge 0413is.
Fig. 2. Ethane conversion to methane (0) and C6-Cg aromatice (01 at 600 oc over Pt-Re/ ZSM-Al203 catalyste In a helium atmcephzre.
in epite of the high hydrogenolyeie activity of the metal phaee (Fig. l), the inoreased pentaail content caueea an enhanced formation of aromatlc~, but this Is accompanied by a oomparatlvely mall-eoale improvement of methane production (Fig. 2). From this point of view, an increaee in eelectivltg for the conversion of higher hydrocarbona ehould be expected, eepeoially for ZSM contenta 250 rt $. However, as shown in Fig. 3, the yield of C2-C5 hydrocarbona In a helium atmoephere surpaseee the yield of aromatics, particularly for high ZSN contents. There is no doubt about the fact that the moat drastic change6 in the production of aromatic8 from hexane ocour in the range of low ZSH contents, where the particular ability of the carrier to promote the aromatization of ethane seema to be ineignifioant (eee above and aleo ref. 3). !Phle should mean in this caee that the enhanoed Br&ksted acidity of the carrier ie at flret lmportent In giving rise to the lncreaeed aromatization activity by a claeslc bifunctional medani~ of dehydrooyclizatlon; that is, other zeolites which are unable to promote aromatization themselves (zeclitee poaseeeiag larger pores, e.g. Y-type seolltee) should also enhance the formation of aromatice b7 their addition
to alumina in low concentration.
Pig. 3. n-Hexane convert 8iOn to c2d5 ~drocarbone l) 8nd 0 8rOlD8tiW 0) 8t 406-08 00 over Pt-Re/ ZSM-Al20 oatalyate in 8 helium 82moaphere.
I
50 ZSM content, rt
’
loo %
Indeed, Pt-OOnt8iniIIgY zeolite-A1203 C8t8b8t8 re8oh 8 higher level of dehydrocyclization in n-hept8ne conversion thsn doee 8 pure Pt/A1203 sample with the s8me content of chloride, baaed on the etoichiotnetryof H2PtCl6 (Pig. 4a). It is remarkable that both the formation of cracking products and the dehydrocyclization activity increase only slightly, and still do not reach the values for the Pt/A1203 catalysts with 8n optimum chloridecontent Of 8bOUt 1.2 wt %. TABLE 2 Dehydrocyclization and crackingactivityrelated to the degree of n-heptans oonvereionin the preeenoeof <20 and 300 ppm I+0
Carrier modifier
toluene/conversion 20 Ppm 300 Ppm
C14g/oonvereion 20 Plrm 300 Ppnr
0.28
0.16
wt % 1)
0.31
0.31
:*22: 0:29
10 1.2By Cl
0.31 0.35
z-2 .
‘)onti
from H2PtCl6
7%
3Hy
c1
0.11
be can also be seen in 'Pable2, the oat84tio parameters releted to the degree of n-heptaneoonvereionof the reolite-rodifled 68RpleEI fall between those of a PUrO H/A1203 and 8 Oataljst containing1.2 wt P Cl for dry oonditione(I 20 ppm ?120).When a larger chloridelees appeara (i.e. partioularlyin the preeenoe
442
of about 300 ppm water vapour during reduction and catalytic reaction), the aromatization activity of the zeolite-containing catalyete not on4 exoeeds that of the pure Pt/A1203 catalyst but in the caee of zeolite content6 above 3 at Se aleo that of the Pt/A1203-1 .2 Cl sample (Fig. 4b and Table 2).
M30-
M 30
a
q
t:
‘; a p20h 0:
0
I
a 2 20 R
3
q q
0
y
10,
OF
,
b
I
5 HY content,
I
10 wt %
0
I 0
5 HY content,
I 10 rt %
Pig. 4. n-Heptane conversion over Pt/Al 0 -HY catalysts to C -C6 tidrocarbona (0) and toluene (I) in the2p$esencre of (20 PPIVI B_90 -(b>- or jO0 pg ii 0 (b). 60 Pt/Al 0 -0.65 cl (cl only from H2PtC16)0O Pt/Al 0 (WHSV: 1-g &g-1h’1, nR2:nC7H16 = 10, time on stream2r3;1&s!$ On this acoount, it should be concluded that the zeolite-containing catalysts inveetigated only represent an alternative to a chloride+odified alumina supported metal catalyst for euch conditiona in which complete abeenoe of traces of water cannot be effeoted. REFERENCES M. J. Sterbs and V. Baenael, Ind. En& Chem., Prod. Ree. DeVelODv. 15 (1976) 3-17. A. A. C&&o; 6.A; %lz& E.R. Benvenuto G. I. Baronet ti and J.Y. Parera, J. Catal., 69 (1981) 222-226. O.V. Bragin, T.V. Vasina, Ja. J.Ieakov, B.V. Poliehkina, A.V. Preobrazhenekii, B.K. Iefedov and Kh.Y. JUnachev, Izv. Akad. Kauk SSSR, Ser. Khim., (1983) 2002-2009. P.G. Riley and R.G. Anthony, J. Cataly., 100 (1986) 322-327. S.Engele, P. Mahlow,W. Pfeiffer, D. Sager and M. Wilde, Chem. Teahn., 36 (1984) 426-429. O.V. Bra in, A. V. Preobrazhenekii and A.L. Liberman, Izv. Akad. Bauk SSSf , Ser. Khim., (1974) 2751-2757.
443
7 S. Engele and R. Schwokoweki,Wies. Z. Se&n. Hoohechule "Carl Sohorlemmer"Leuna-Herseburg, 28 (1986) 667-679. 8 S. Engele,W. Hager, L-J. Kluge, M. HUnch, D. Sager, H. Seefluth R. Walter and 1, Wilde, Z. P&s. Chem. (Leipzig), 264 (1983) 1186-1194. 9 J. Haupt, Thesis, lechnicalUnivereitgof Merseburg, 1985.