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alumina catalyst on the selective hydrogenation of crotonaldehyde
Applied Catalysis A: General, 83 (1992) L7-L13 Elsevier Science Publishers B.V., Amsterdam
L7
APCAT 2256
Influence of sulphur poisoning of copper/alumina catalyst on the selective hydrogenation of Crotonaldehyde G.J. Hutchings Leverhulme Centre for Innovative Catalysis, Department of Chemistry, University of Liverpool, P.O. Box 147, Liverpool ,569 3BX (UK)
F. King ZCZKatalco, R&T Group, PO Box 1, Billingham, Cleveland TS23 11B (UK)
I.P. Okoye Leverhulme Centre for Innovative Catalysis, Department of Chemistry, University of Liverpool, P.O. Box 147, Liverpool L69 3BX (UK)
and C.H. Rochester Department of Chemistry, The University, Dundee DDl4HN
(UK)
(Received 24 January 1992, revised manuscript received 18 February 1992)
Abstract The effect of tbe presence of sulphur on the activity and selectivity of a Cu/Al,Os catalyst has been examined by selective hydrogenation of an a,~-unsaturated aldehyde, crotonaldehyde, at different reaction conditions. Cu/Al,O, in the absence of sulphur poisons produced preferentially I-butanol, whereas catalysts pre-dosed with a suitable amount of thiophene, shifted the product distribution towards formation of crotyl alcohol. The formation of crotyl alcohol under these conditions is favoured at low conversions and low temperature, and the maximum selectivity of 64% crotyl alcohol was achieved at a reaction temperature of 86°C. Keywords: copper/alumina, poisoning.
crotonaldehyde, hydrogenation, selectivity
(crotyl alcohol), sulphur
INTRODUCTION
The selective hydrogenation of the carbonyl functional group in the a$unsaturated aldehyde is considered by many researchers to be a challenging Correspondence to: Dr. G.J. Hutchings, Leverhuhne Centre for Innovative Catalysis, Department of Chemistry, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK.
0926-860X/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved.
LS
G.J. Hutchings et al.fAppl. Catal. A, 83 (1992) L7-L13
task [ 11. Previous studies on this problem have concentrated on the use of metal-support interaction. It has been shown that the carbonyl bond in crotonaldehyde can be preferentially hydrogenated by Ni/Cu/AIPOs [ 21, Pt/TiOz [ 31, Pt/Fe/SiOz [ 41, and Cu/Cr,O, [ 51, to allow the formation of crotyl alcohol. To date there have been no reported studies concerning the effect of partially poisoning the catalyst as a means of improving selectivity in the hydrogenation of a$-unsaturated compounds. Variation of catalyst selectivity by control of active sites using sulphur compounds as poisons have been widely studied and most reported work has, however, been on alkene hydrogenation. The effect of the presence of sulphur on the activity and selectivity of some transition metals, e.g. Ni, Co, MO, Ru, Pt and Pd for hydrogenation of alkenes have been reported by Moyes et al. [6-B], Comet et al. [ 91, Wolf [lo], and l’Argentiere and Figoli [ 111. Moyes et al. [ 6-81 examined the effect of the presence of sulphur on the activity and selectivity of metals during the hydrogenation of 1,3-butadiene at 100°C. It was concluded that adsorption of sulphur on the catalytically active metal by decomposition of H,S for example, modifies selectivity in that it converts the major process in buta-1,3diene hydrogenation from 1,2 addition to 1,4 addition. The selectivity changes were interpreted in terms of the electronic effect of adsorbed sulphur on the metal atoms remaining exposed at the surface. Furthermore, it has been shown that for the selective hydrogenation of styrene over Pd/Al,O,, in the presence of added thiophene [ 111, the X-ray photoelectron spectroscopy (XPS) data suggest that the electronic properties of palladium are modified during the poisoning reaction. The activity and selectivity for the hydrogenation of styrene to ethyl benzene is therefore reported to be modified by the addition of thiophene. It is the aim of this paper to present our results concerning the effect of sulphur of a 5% Cu/A1203 catalyst for the hydrogenation of coronaldehyde. EXPERIMENTAL
Catalyst preparation The support used in this work was y-A1203, surface area of 136 m2g-l from Condea SCF (Puralox SCFa-140). Supported copper catalyst precursors were prepared by adding the alumina to an aqueous solution containing an appropriate amount of copper nitrate (Aldrich, 99.999% ) so as to yield 5 wt.% Cu metal. The slurry was stirred at 80 oC and allowed to evaporate to a thick paste. The sample was then dried at 110°C for 16 h. The product was calcined in air at 450°C for 16 h to convert the nitrate to oxide. The catalyst sample (100 mg, 0.6-l mm particle size) was loaded into a reactor tube (9 mm O.D.) and held in place by a quartz frit. The sample was then reduced in situ in a flow of hydrogen (3.61/h) at 210°C for 2 h or 16 h,
L9
G.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-L13
and subsequently adjusted to the required hydrogenation 150°C).
temperature
(60-
Catalyst evaluution The vapour-phase hydrogenation of crotonaldehyde ( > 99% purity, Aldrich) was performed using a continuous flow fixed-bed reactor at atmospheric pressure. The crotonaldehyde was introduced into the reactor system via a calibrated syringe pump and vaporised in the preheated reactor inlet zone. Hydrogen was utilised as a carrier gas and a hydrogen/coronaldehyde ratio of 14 was used in all studies. Sulphided catalysts were prepared by injection of thiophene or thiophene/pentane solution (0.1-l ~1) directly onto the reduced catalyst in a hydrogen carrier gas. Product separation and analysis was achieved using an on-line gas chromatography. The experimental errors associated with the conversion and selectivity data reported in this paper are ca. t 1%. RESULTS AND DISCUSSION
Temperature-programmed reduction of the calcined 5% Cu/A120, precursor in 5% hydrogen in helium diluent showed that reduction of the oxide to the metal occurred at 210-220’ C. Consequently catalyst precursor samples were reduced under a range of conditions and the copper metal surface area was measured using a standard nitrous oxide adsorption method (Table 1). On this basis, subsequent catalyst reductions were carried out at 210°C using 100% hydrogen as reductant. The duration of reduction was not found to be significant with respect to the activity and selectivity of the reduced catalyst for crotonaldehyde hydrogenation and the same catalytic performance could be obtained for samples reduced for 2-16 h. The effect of reaction temperature on the hydrogenation of crontonaldehyde over 5% Cu/A120, in the presence and absence of thiophene (1 pl/O.l g Cu/ A1203) is shown in Fig. 1. There are three possible products for the hydrogenation of crotonaldehyde which involve two parallel pathways to 1-butanol via crotyl alcohol and butanal as intermediates [ 21. In the absence of thiophene, crontonaldehyde conversion increases rapidly from 80 “C to 150” C and the TABLE 1 Copper surface area data Reduction condition
Cu (N,O) surface area/m’g- *
100% HP, 35O”C, 16 h 100% Hz, 21O”C, 16 h 5% H,/95% He, 21O”C, 16 h
15 22 20
G.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-L13
60
100 Reaction
120
140
temperature/
OC
160
8 - 10
-5
* I
70
1
90 Reaction
I
I
I
110
130
150
0
temperaturePC
Fig. 1. Effect of reaction temperature on the performance of 5% Cu/A1203 catalysts: reduction temperature = ZlO”C, WHSV= 1.2 h-l, H,/crotonaldehyde= 14 mole ratio, data collected at 30 min time-on-line: (a) unsulphided (b) sulphided with 1 fl thiophene/O.l g catalyst at 210°C. ( 0 ) Crotyl alcohol; ( + ) butanal; ( * ) butanol; ( 0 ) crotonaldehyde conversion.
G.J. Hutch&s
et al. jApp1. Catal. A, 83 (1992) L7-L13
Lll
selectivity to 1-butanol increases in a similar manner. At low conversions for the unsulphided catalyst the major product is butanal and very low selectivity to crotyl alcohol is observed ( < 10%). This indicates that the 5% Cu/A1203 preferentially hydrogenates the carbon-carbon double bond rather than the carbonyl group. Sulphiding with 1~1 thiophene at 210°C leads to a marked decrease in conversion when the sulphided catalyst is compared to the unsulphided catalyst at the same conditions. It is clear that the selectivity to both butanal and 1-butanol have been significantly decreased on thiophene addition and now at low conversion significant selectivity ( > 50%) to crotyl alcohol is observed. Comparison of data at the same conversion level indicates that the sulphided catalyst gives significantly higher selectivities to crotyl alcohol, indicating that the increased selectivity to crotyl alcohol is not merely a function of the decreased conversion level observed with the sulphided catalyst. The effect of the level of thiophene is shown in Fig. 2 for crotonaldehyde hydrogenation at 150°C. This temperature was selected for study as the unsulphided 5% Cu/A1203 catalyst demonstrated very low selectivity to crotyl alcohol. It is clear that on increasing the thiophene level the selectivity to crotyl alcohol increases steadily, while both the conversion and 1-butanol selectivity decline. Experiments using an on-line sulphur sensitive flame photometric detector demonstrated that ca. 80% of thiophene was adsorbed by the
Amount of thiophene/ul
Fig. 2. Effect of amount of thiophene on Cu/A1203 catalyst performance. Temperature of sulphiding= 15C”C, reduction temperature=21O”C, reaction temperature= 15O”C, WHSV= 1.2 h-l, H,/ crotonaldehyde = 14 mole ratio. ( 0 ) Crotyl alcohol; ( + ) butanal; ( * ) butanol; ( 0 ) crotonaldehyde conversion.
C.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-Ll3
Ix (a)
100
116
I(
6
60
90
120
180
160
210
Time-on-stream/min
M
70
6
60
0
30
60
90
120
Time-on-rtream/mln Fig. 3. Effect of time-on-line on the performance of 5% Cu/A1203 catalyst. Reduction temperature 21O”C, reaction temperature=6O”C, WHSV= 1.26 h-l, H,/crot.onaldehyde= 14 mole ratio, (a) unsulphided (b) sulphided with 1 plthiophene at 210” C. (0 ) Crotyl alcohol; ( + ) butanal, ( * ) butanol; (Cl ) crotonaldehyde conversion.
G.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-L13
L13
5% Cu/A1203 catalyst and that no sulphur was eluted from the catalyst during the subsequent hydrogenation reaction. Furthermore, it was observed that subsequent injections of thiophene resulted in very little of the additional thiophene being adsorbed and did not significantly affect the experimental results. Hence on a bulk copper basis, the amount of sulphur added varies from 3 ppm (0.1 ,~l thiophene) to 32 ppm (1 ,~l thiophene). The effect of catalyst deactivation with time-on-line is shown in Fig. 3 for crotonaldehyde hydrogenation at 80°C for both sulphided and unsulphided catalysts. Conversion decreases quite rapidly during the initial period of operation (15-60 min) and declines relatively slowly after that time. The deactivation profiles for the two systems are similar and in particular the selectivity to 1-butanol decreases in line with conversion. At 80°C very high selectivity to crotyl alcohol can be observed and a maximum selectivity of 64% was observed. The results of this study demonstrate that sulphur added in the form of thiophene selectively poisons the hydrogenation of the carbon-carbon double bond in crotonaldehyde in preference to hydrogenation of the carbonyl bond. The levels of sulphur utilised are relatively high (32 ppm on the basis of total copper), however, these lead only to partial poisoning of the 5% Cu/A1,03 for the hydrogenation of crotonaldehyde. The observed maximum selectivities to crotyl alcohol are higher than those reported in previous studies for non sulphided catalyst (e.g. 54% for Ni/Cu/AlzOB [2], 37% for Pt/TiOz [3], 20% for Pt/Fe/SiO, [ 4 ] and 7.8% Cu/Cr,O, [ 51) . Hence this study demonstrates that partial catalyst poisoning represents a viable research approach to control selectivity in the hydrogenation of @-unsaturated compounds. ACKNOWLEDGEMENT
We thank SERC and ICI Katalco for financial support for this work.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11
J. Jenck and J.E. Germain, J. Catal., 65 (1980) 133. H. Noller and W.M. Lin, J. Catal., 85 (1984) 25. M.A. Vannice and B. Sen, J. Catal., 115 (1989) 65. J. Somonik and P. Berannek, Coll. Czech. Chem. Comm., 37 (1972) 353. T.R. Bonnelle, R. Hubaut and M. Daage, Appl. Catal., 22 (1986) 231. R.B. Moyes, P.B. Wells, M. George and D. Ramanarao, J. Catal., 51 (1978) 355. R.. Moyes, P.B. Wells, M. George and D. Ramanarao, J. Catal., 52 (1978) 486. R.B. Moyes, P.B. Wells, M. George and D. Ramanarao, J. Catal., 52 (1978) 472. D. Comet, J. Legliee, A. Janin and J.C. Lavailey, J. Catal., 114 (1988) 388. D. Wolf, J. Catal., 75 (1982) 396. P.C. I’Argentiere and N.S. Figoli, Appl. Catal., 61 (1990) 275.
L7
APCAT 2256
Influence of sulphur poisoning of copper/alumina catalyst on the selective hydrogenation of Crotonaldehyde G.J. Hutchings Leverhulme Centre for Innovative Catalysis, Department of Chemistry, University of Liverpool, P.O. Box 147, Liverpool ,569 3BX (UK)
F. King ZCZKatalco, R&T Group, PO Box 1, Billingham, Cleveland TS23 11B (UK)
I.P. Okoye Leverhulme Centre for Innovative Catalysis, Department of Chemistry, University of Liverpool, P.O. Box 147, Liverpool L69 3BX (UK)
and C.H. Rochester Department of Chemistry, The University, Dundee DDl4HN
(UK)
(Received 24 January 1992, revised manuscript received 18 February 1992)
Abstract The effect of tbe presence of sulphur on the activity and selectivity of a Cu/Al,Os catalyst has been examined by selective hydrogenation of an a,~-unsaturated aldehyde, crotonaldehyde, at different reaction conditions. Cu/Al,O, in the absence of sulphur poisons produced preferentially I-butanol, whereas catalysts pre-dosed with a suitable amount of thiophene, shifted the product distribution towards formation of crotyl alcohol. The formation of crotyl alcohol under these conditions is favoured at low conversions and low temperature, and the maximum selectivity of 64% crotyl alcohol was achieved at a reaction temperature of 86°C. Keywords: copper/alumina, poisoning.
crotonaldehyde, hydrogenation, selectivity
(crotyl alcohol), sulphur
INTRODUCTION
The selective hydrogenation of the carbonyl functional group in the a$unsaturated aldehyde is considered by many researchers to be a challenging Correspondence to: Dr. G.J. Hutchings, Leverhuhne Centre for Innovative Catalysis, Department of Chemistry, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, UK.
0926-860X/92/$05.00
0 1992 Elsevier Science Publishers B.V. All rights reserved.
LS
G.J. Hutchings et al.fAppl. Catal. A, 83 (1992) L7-L13
task [ 11. Previous studies on this problem have concentrated on the use of metal-support interaction. It has been shown that the carbonyl bond in crotonaldehyde can be preferentially hydrogenated by Ni/Cu/AIPOs [ 21, Pt/TiOz [ 31, Pt/Fe/SiOz [ 41, and Cu/Cr,O, [ 51, to allow the formation of crotyl alcohol. To date there have been no reported studies concerning the effect of partially poisoning the catalyst as a means of improving selectivity in the hydrogenation of a$-unsaturated compounds. Variation of catalyst selectivity by control of active sites using sulphur compounds as poisons have been widely studied and most reported work has, however, been on alkene hydrogenation. The effect of the presence of sulphur on the activity and selectivity of some transition metals, e.g. Ni, Co, MO, Ru, Pt and Pd for hydrogenation of alkenes have been reported by Moyes et al. [6-B], Comet et al. [ 91, Wolf [lo], and l’Argentiere and Figoli [ 111. Moyes et al. [ 6-81 examined the effect of the presence of sulphur on the activity and selectivity of metals during the hydrogenation of 1,3-butadiene at 100°C. It was concluded that adsorption of sulphur on the catalytically active metal by decomposition of H,S for example, modifies selectivity in that it converts the major process in buta-1,3diene hydrogenation from 1,2 addition to 1,4 addition. The selectivity changes were interpreted in terms of the electronic effect of adsorbed sulphur on the metal atoms remaining exposed at the surface. Furthermore, it has been shown that for the selective hydrogenation of styrene over Pd/Al,O,, in the presence of added thiophene [ 111, the X-ray photoelectron spectroscopy (XPS) data suggest that the electronic properties of palladium are modified during the poisoning reaction. The activity and selectivity for the hydrogenation of styrene to ethyl benzene is therefore reported to be modified by the addition of thiophene. It is the aim of this paper to present our results concerning the effect of sulphur of a 5% Cu/A1203 catalyst for the hydrogenation of coronaldehyde. EXPERIMENTAL
Catalyst preparation The support used in this work was y-A1203, surface area of 136 m2g-l from Condea SCF (Puralox SCFa-140). Supported copper catalyst precursors were prepared by adding the alumina to an aqueous solution containing an appropriate amount of copper nitrate (Aldrich, 99.999% ) so as to yield 5 wt.% Cu metal. The slurry was stirred at 80 oC and allowed to evaporate to a thick paste. The sample was then dried at 110°C for 16 h. The product was calcined in air at 450°C for 16 h to convert the nitrate to oxide. The catalyst sample (100 mg, 0.6-l mm particle size) was loaded into a reactor tube (9 mm O.D.) and held in place by a quartz frit. The sample was then reduced in situ in a flow of hydrogen (3.61/h) at 210°C for 2 h or 16 h,
L9
G.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-L13
and subsequently adjusted to the required hydrogenation 150°C).
temperature
(60-
Catalyst evaluution The vapour-phase hydrogenation of crotonaldehyde ( > 99% purity, Aldrich) was performed using a continuous flow fixed-bed reactor at atmospheric pressure. The crotonaldehyde was introduced into the reactor system via a calibrated syringe pump and vaporised in the preheated reactor inlet zone. Hydrogen was utilised as a carrier gas and a hydrogen/coronaldehyde ratio of 14 was used in all studies. Sulphided catalysts were prepared by injection of thiophene or thiophene/pentane solution (0.1-l ~1) directly onto the reduced catalyst in a hydrogen carrier gas. Product separation and analysis was achieved using an on-line gas chromatography. The experimental errors associated with the conversion and selectivity data reported in this paper are ca. t 1%. RESULTS AND DISCUSSION
Temperature-programmed reduction of the calcined 5% Cu/A120, precursor in 5% hydrogen in helium diluent showed that reduction of the oxide to the metal occurred at 210-220’ C. Consequently catalyst precursor samples were reduced under a range of conditions and the copper metal surface area was measured using a standard nitrous oxide adsorption method (Table 1). On this basis, subsequent catalyst reductions were carried out at 210°C using 100% hydrogen as reductant. The duration of reduction was not found to be significant with respect to the activity and selectivity of the reduced catalyst for crotonaldehyde hydrogenation and the same catalytic performance could be obtained for samples reduced for 2-16 h. The effect of reaction temperature on the hydrogenation of crontonaldehyde over 5% Cu/A120, in the presence and absence of thiophene (1 pl/O.l g Cu/ A1203) is shown in Fig. 1. There are three possible products for the hydrogenation of crotonaldehyde which involve two parallel pathways to 1-butanol via crotyl alcohol and butanal as intermediates [ 21. In the absence of thiophene, crontonaldehyde conversion increases rapidly from 80 “C to 150” C and the TABLE 1 Copper surface area data Reduction condition
Cu (N,O) surface area/m’g- *
100% HP, 35O”C, 16 h 100% Hz, 21O”C, 16 h 5% H,/95% He, 21O”C, 16 h
15 22 20
G.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-L13
60
100 Reaction
120
140
temperature/
OC
160
8 - 10
-5
* I
70
1
90 Reaction
I
I
I
110
130
150
0
temperaturePC
Fig. 1. Effect of reaction temperature on the performance of 5% Cu/A1203 catalysts: reduction temperature = ZlO”C, WHSV= 1.2 h-l, H,/crotonaldehyde= 14 mole ratio, data collected at 30 min time-on-line: (a) unsulphided (b) sulphided with 1 fl thiophene/O.l g catalyst at 210°C. ( 0 ) Crotyl alcohol; ( + ) butanal; ( * ) butanol; ( 0 ) crotonaldehyde conversion.
G.J. Hutch&s
et al. jApp1. Catal. A, 83 (1992) L7-L13
Lll
selectivity to 1-butanol increases in a similar manner. At low conversions for the unsulphided catalyst the major product is butanal and very low selectivity to crotyl alcohol is observed ( < 10%). This indicates that the 5% Cu/A1203 preferentially hydrogenates the carbon-carbon double bond rather than the carbonyl group. Sulphiding with 1~1 thiophene at 210°C leads to a marked decrease in conversion when the sulphided catalyst is compared to the unsulphided catalyst at the same conditions. It is clear that the selectivity to both butanal and 1-butanol have been significantly decreased on thiophene addition and now at low conversion significant selectivity ( > 50%) to crotyl alcohol is observed. Comparison of data at the same conversion level indicates that the sulphided catalyst gives significantly higher selectivities to crotyl alcohol, indicating that the increased selectivity to crotyl alcohol is not merely a function of the decreased conversion level observed with the sulphided catalyst. The effect of the level of thiophene is shown in Fig. 2 for crotonaldehyde hydrogenation at 150°C. This temperature was selected for study as the unsulphided 5% Cu/A1203 catalyst demonstrated very low selectivity to crotyl alcohol. It is clear that on increasing the thiophene level the selectivity to crotyl alcohol increases steadily, while both the conversion and 1-butanol selectivity decline. Experiments using an on-line sulphur sensitive flame photometric detector demonstrated that ca. 80% of thiophene was adsorbed by the
Amount of thiophene/ul
Fig. 2. Effect of amount of thiophene on Cu/A1203 catalyst performance. Temperature of sulphiding= 15C”C, reduction temperature=21O”C, reaction temperature= 15O”C, WHSV= 1.2 h-l, H,/ crotonaldehyde = 14 mole ratio. ( 0 ) Crotyl alcohol; ( + ) butanal; ( * ) butanol; ( 0 ) crotonaldehyde conversion.
C.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-Ll3
Ix (a)
100
116
I(
6
60
90
120
180
160
210
Time-on-stream/min
M
70
6
60
0
30
60
90
120
Time-on-rtream/mln Fig. 3. Effect of time-on-line on the performance of 5% Cu/A1203 catalyst. Reduction temperature 21O”C, reaction temperature=6O”C, WHSV= 1.26 h-l, H,/crot.onaldehyde= 14 mole ratio, (a) unsulphided (b) sulphided with 1 plthiophene at 210” C. (0 ) Crotyl alcohol; ( + ) butanal, ( * ) butanol; (Cl ) crotonaldehyde conversion.
G.J. Hutchings et al./Appl. Catal. A, 83 (1992) L7-L13
L13
5% Cu/A1203 catalyst and that no sulphur was eluted from the catalyst during the subsequent hydrogenation reaction. Furthermore, it was observed that subsequent injections of thiophene resulted in very little of the additional thiophene being adsorbed and did not significantly affect the experimental results. Hence on a bulk copper basis, the amount of sulphur added varies from 3 ppm (0.1 ,~l thiophene) to 32 ppm (1 ,~l thiophene). The effect of catalyst deactivation with time-on-line is shown in Fig. 3 for crotonaldehyde hydrogenation at 80°C for both sulphided and unsulphided catalysts. Conversion decreases quite rapidly during the initial period of operation (15-60 min) and declines relatively slowly after that time. The deactivation profiles for the two systems are similar and in particular the selectivity to 1-butanol decreases in line with conversion. At 80°C very high selectivity to crotyl alcohol can be observed and a maximum selectivity of 64% was observed. The results of this study demonstrate that sulphur added in the form of thiophene selectively poisons the hydrogenation of the carbon-carbon double bond in crotonaldehyde in preference to hydrogenation of the carbonyl bond. The levels of sulphur utilised are relatively high (32 ppm on the basis of total copper), however, these lead only to partial poisoning of the 5% Cu/A1,03 for the hydrogenation of crotonaldehyde. The observed maximum selectivities to crotyl alcohol are higher than those reported in previous studies for non sulphided catalyst (e.g. 54% for Ni/Cu/AlzOB [2], 37% for Pt/TiOz [3], 20% for Pt/Fe/SiO, [ 4 ] and 7.8% Cu/Cr,O, [ 51) . Hence this study demonstrates that partial catalyst poisoning represents a viable research approach to control selectivity in the hydrogenation of @-unsaturated compounds. ACKNOWLEDGEMENT
We thank SERC and ICI Katalco for financial support for this work.
REFERENCES 1 2 3 4 5 6 7 8 9 10 11
J. Jenck and J.E. Germain, J. Catal., 65 (1980) 133. H. Noller and W.M. Lin, J. Catal., 85 (1984) 25. M.A. Vannice and B. Sen, J. Catal., 115 (1989) 65. J. Somonik and P. Berannek, Coll. Czech. Chem. Comm., 37 (1972) 353. T.R. Bonnelle, R. Hubaut and M. Daage, Appl. Catal., 22 (1986) 231. R.B. Moyes, P.B. Wells, M. George and D. Ramanarao, J. Catal., 51 (1978) 355. R.. Moyes, P.B. Wells, M. George and D. Ramanarao, J. Catal., 52 (1978) 486. R.B. Moyes, P.B. Wells, M. George and D. Ramanarao, J. Catal., 52 (1978) 472. D. Comet, J. Legliee, A. Janin and J.C. Lavailey, J. Catal., 114 (1988) 388. D. Wolf, J. Catal., 75 (1982) 396. P.C. I’Argentiere and N.S. Figoli, Appl. Catal., 61 (1990) 275.