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Acid-Base Properties of Sulfided Ni-Mo-Y Zeolite Catalysts for Water-Gas Shift Reaction
Ouczi, L u uf. (Editors), New Frontiers in Ccualysir Proceedings of the 10th International Congreas on Catalysis, 19-24 July, 1W, Budapest, Hungary 0 1993 Elsevier Science Publishers B.V.All rights reserved
ACID-BASE PROPERTIES OF SULFIDED NI-Mo-Y ZEOLITE CATALYSTS FOR WATER-GAS SHIFT REACTION
M.Laniecki and W. Zmierczak Faculty of Chemistry,A. Mickiewicz University,Grunwaldzka 6,60-780 Poznan,Poland
Abet ract The ability of Y zeolites containing nickel and molybdenum to catalyze the water-gas shift reaction with the sulfided feed was tested. Sulfided Ni-Mo-Y catalysts and zeolitic supports were characterized by the NO, NH,, BF, sorption capacity and by the capability to decompose diacetone and isopropyl alcohols. The influence of acid-base properties of studied catalysts on their activity in the WGS reaction was considered. It hae been found that high WGS activity is caused not only by the synergy between Ni and Mo sulfided species but is also influenced by the the acidic OH groups originating both from the support itself and dissociative adsorption of hydrogen sulfide. 1. INTRODUCTION
Alumina supported Co-Mo sulfides were found to be active catalysts in the water-gas shift (WGS) reaction operating under the sulfided feeds. Results presented by Lee et al. (ref. 1) and our recent studies (refs. 2 - 4 ) indicate that sulfided Mo-Y and Ni-Mo-Y zeolites can be also used as the effective catalysts for the WGS reaction in a presence of significant amount of hydrogen eulfide. In addition, our catalysts prepared with the use of Mo(CO), were always much more active then thoee a better obtained from ammonium heptamolybdate, due to dispersion of sulfided Mo species. Whereas previous papers focused on the relation between redox properties of the sulfided CoMo/Al,O, catalysts and their catalytic activity, this paper attempts to show the importance of the acid-base propertiee of studied Catalysts on catalytic behaviour in the WGS reaction. 2 . EXPERIMENTAL
NaY (Si/A1=2.56) from Katalistiks was used as the starting material for preparation of NH,, K , Cs exchanged samples and series of stabilized Y-zeolites. Nickel was always introduced into Y-zeolites before Mo, either by the solution-ion-exchange or by solid-state exchange of NiC1, with HY zeolites.
2570 Molybdenum was introduced v i a sublimation of Mo(CO), at room temperature i n a stream of highly purified hydrogen. Samples were characterized with XRD, ESR and FTIR spectroscopy a s well as the sorption capacity of NO, NH, and BF,. Reactions of the selected samples with isopropyl and diacetone alcohols (ref. 6 ) were performed at 395 K and 345 K, respectively. After presulfidation at 675 K , the WGS reaction was studied at 625 K with the feed containing 2 vol. % of hydrogen sulfide. More experimental details can be found elsewhere ( r e f s 2-6). 3. RESULTS AND DISCUSSION
The molybdenum-free, sulfided nickel containing catalysts in every case were inactive i n the WGS. Introduction of Ma v i a Mo(CO), sublimation onto the nickel-exchanged zeolites resulted in a n appearance of relatively h i g h catalytic activity.
-
Inn
4uu
I
‘5 I
300
T,,;.-475
KB,
U
c
1
TI
3 3 V
P 5 L
L
L
0 -
0.5 0
1
2
Ni CONTENT,
3
4
wt.%
n
I
Fig. 1. The W G S activity and ammonia uptake of sulfided Mo-containing Ni-exchanged ( i n solut i o n ) catalysts. Open circles represent the support pretreated in H, at 475 K ; filledsupport pretreated i n H, at 675 K. NH, uptake (triangles) meesured for samples presulfided at 6 7 4 K.
Figure 1 shows the WGS activity for the series of Ni-Mo-Y catalysts and their NH, sorption capacity. These results, as well a s those presented in refs 2-4, indicate that at least two main factors influence catalytic activity i n the WGS reaction with a sulfided feed: synergetic effect between Ni and M o eulfided species and acidity of these catalysts. Similar effects as for the presented NaNiY supports ( F i g . 1 ) were also found for the series of KNiY and CsNiY based catalysts but with respectively lower values of activity (ref.4). Experiments in which the most active catalysts were impregnated after sulfidation with a diluted solution of K,CO, , next dried and activated again i n H,S/H, mixture, showed the decrease i n activity from 50 to 75 S T h e ammonia uptake for these impregnated samples was always lower of about 50 % than for non-impregnated. Data presented in Table 1 for the selected catalyete indicate that the WGS activity, irrespective from the synergy between Ni and Mo eulfided species, is rather related t o the catalyst acidity than basicity. It i s known that during presulfidation with H,S/H, mixture the formation of acidic groups occurs even
.
2571 Table 1 Catalytic activity (WGS) and NO, NH, and BF, sorption capacity of sulfided molybdenum-loaded Y-zeolites Sample
Nay-Mo HY-8 0-MO USY - 1 -Mo USY-l-Ni;Mo** NaNiY-Mot+ NaNiY -Mo COY-MO CeNi Y -Mo
*
-
++
-
** + -
Rate cone t ant * 3 -1 -1 (cm g min )
Amount of adsorbed NO NH, BF3 (nun01 9 - 7
32.0 73.6 14.9 63.4 232.8 34.7 21.2 152.8
0.184 0.166 0.053 0.136 0.134
-----
0.112 0.100
and and ~
Zeolite
NaY Nay-Mo
BY-MO USY-1 USY - 1 -Mo NaNiY* NaNiY-Mo* NaNiY * * NaNiY-Mo** CSY CBY-MO CsNiY CsNiY -Mo
* -
**
-
3.90 3.34 4.11 3.11 3.68 1.41 2.69 2.36
measured after 2 hours, H,O:CO = 1 Ni content - 1.2 wt.9, Mo content 5.0 wt.% solution-ion exchange solid-state exchange
Table 2 Activity of Mo-Y, Ni-Mo-Y decomposition of isopropyl
HY
0.840 2.249 0.548 1.446 1.390 0.520 0.137 0.605
~
Mo-free diacetone _
_
_
_
_
_
Y-zeolites alcohols ~
for
~
Isopropyl alcohol Diacetone alcohol Conversion (mol 9 ) to propene
propane
acetone
meeityl oxide
0.0 22.7 69.0 44.5 3.5 3.9 11.2 18.6 3.6 2.3
0.0 1.2 13.5 5.8 0.3 0.6 8.0 2.9 0.6 0.3 0.0 0.0 4.0 5.2
0.3 1.0 2.0 2.0 4.6 3.9 0.4 0.8
0.4 1.1 23.4 20.9 2.7 2.0 0.0 9.4
0.3 0.2 0.2 0.8
0.3 0.4 0.2 5.9
0.0
0.9 5.7 9.4
solution-ion exchange solid-state exchange
---
---
over Nay, KY or Cay. The low values of activity for NaY or CsY eupports (see Table 1) with highly "dispersed" Mo species (NO adsorption) are related both to the absence of nickel and to the low concentration of acid sites. The latter was confirmed by the very low activity of theee sulfided support8 during the decomposition isopropyl and diacetone alcohol8 to propene and mesityl oxide, respectively. Results presented in Table 2 for non-sulfided catalysts show that introduction of nickel and/or molybdenum to NaY or CsY supports usually resulte in the increase of catalyst acidity what was obeerved as higher yield of propene and mesityl oxide. After aulfidation the acidity wae always higher of about 10-20 % and this was reflected in catalytic reactions with alcohols. Whereae after introduction of nickel into Y zeolite8 both Lewie and Broneted acid site8 were generated (FTIR experiments), incorporation of molybdenum is responsible for the formation of Lewis acid sites and decreased basicity of sulfided samples. Formation of propane (Table 2) at relatively low temperature during decompoeition of isopropyl alcohol after the hydrogen-free condition can be explained by the disproportionation of oligomers formed from propene with simultaneous evolution of hydrogen and subsequent hydrogenation. The hydrogenation of propene was always higher for eamples containing only nickel and slightly decreased after molybdenum incorporation. In this study adsorption of BF, (ref. 7) and conversion of diacetone alcohol into acetone (ref. 8) were applied to examine the basicity of the studied catalysts. Data presented in Table 1 and Table 2 indicate that catalysts with increased basicity expreseed here either as BF, sorption capacity or as the yield of acetone formed ueually indicate poor activity in the WGS react ion. The presented resulte a e well those not ehown in thie report (0.g. IR experiments) indicate the importance of Bronsted acid sites engaged in the water-gas shift reaction. The detailed investigations concerning acid-base propertiee of Ni-Mo-Y zeolite catalyst8 in the WGS reaction in planed to be a eubject of a subsequent contribution. REFERENCES 1 A.L. Lee, K.C. Wei, T.Y. Lee and J. Lee, Stud. Surface Sci. Catalyeie, vo1.5, Elsevier, 1980, pp. 327-333. 2 M. Laniecki and W. Zmierczak, Zeolites, 11 (1991) 18-26. 3 M. Laniecki and W. Zmierczak, Stud. Surface Sci. Catalyeis, vo1.65, Eleevier, 1991, pp. 377-386. 4 M. Laniecki and W. Zmierczak, Stud. Surface Sci. Catalysis, vo1.68, Elsevier, 1991, pp. 799-802. 5 M. Laniecki and W. Zmierczak, Stud. Surface Sci. Catalysis, vo1.69, Elsevier, 1991, pp. 331-338. 6 W. Przystajko, R. Fiedorow and I.G. Della Lana, Zeolites, 7 (1987) 477-481. 7 K . H . Rhee and M.R. Basila, J. Catal., 10 (19681 243-251. 8 Y. Fukuda, K. Tanabe and S . Okazaki, Nippon Kagaku Kaishi, 3 (1972) 513-517.
ACID-BASE PROPERTIES OF SULFIDED NI-Mo-Y ZEOLITE CATALYSTS FOR WATER-GAS SHIFT REACTION
M.Laniecki and W. Zmierczak Faculty of Chemistry,A. Mickiewicz University,Grunwaldzka 6,60-780 Poznan,Poland
Abet ract The ability of Y zeolites containing nickel and molybdenum to catalyze the water-gas shift reaction with the sulfided feed was tested. Sulfided Ni-Mo-Y catalysts and zeolitic supports were characterized by the NO, NH,, BF, sorption capacity and by the capability to decompose diacetone and isopropyl alcohols. The influence of acid-base properties of studied catalysts on their activity in the WGS reaction was considered. It hae been found that high WGS activity is caused not only by the synergy between Ni and Mo sulfided species but is also influenced by the the acidic OH groups originating both from the support itself and dissociative adsorption of hydrogen sulfide. 1. INTRODUCTION
Alumina supported Co-Mo sulfides were found to be active catalysts in the water-gas shift (WGS) reaction operating under the sulfided feeds. Results presented by Lee et al. (ref. 1) and our recent studies (refs. 2 - 4 ) indicate that sulfided Mo-Y and Ni-Mo-Y zeolites can be also used as the effective catalysts for the WGS reaction in a presence of significant amount of hydrogen eulfide. In addition, our catalysts prepared with the use of Mo(CO), were always much more active then thoee a better obtained from ammonium heptamolybdate, due to dispersion of sulfided Mo species. Whereas previous papers focused on the relation between redox properties of the sulfided CoMo/Al,O, catalysts and their catalytic activity, this paper attempts to show the importance of the acid-base propertiee of studied Catalysts on catalytic behaviour in the WGS reaction. 2 . EXPERIMENTAL
NaY (Si/A1=2.56) from Katalistiks was used as the starting material for preparation of NH,, K , Cs exchanged samples and series of stabilized Y-zeolites. Nickel was always introduced into Y-zeolites before Mo, either by the solution-ion-exchange or by solid-state exchange of NiC1, with HY zeolites.
2570 Molybdenum was introduced v i a sublimation of Mo(CO), at room temperature i n a stream of highly purified hydrogen. Samples were characterized with XRD, ESR and FTIR spectroscopy a s well as the sorption capacity of NO, NH, and BF,. Reactions of the selected samples with isopropyl and diacetone alcohols (ref. 6 ) were performed at 395 K and 345 K, respectively. After presulfidation at 675 K , the WGS reaction was studied at 625 K with the feed containing 2 vol. % of hydrogen sulfide. More experimental details can be found elsewhere ( r e f s 2-6). 3. RESULTS AND DISCUSSION
The molybdenum-free, sulfided nickel containing catalysts in every case were inactive i n the WGS. Introduction of Ma v i a Mo(CO), sublimation onto the nickel-exchanged zeolites resulted in a n appearance of relatively h i g h catalytic activity.
-
Inn
4uu
I
‘5 I
300
T,,;.-475
KB,
U
c
1
TI
3 3 V
P 5 L
L
L
0 -
0.5 0
1
2
Ni CONTENT,
3
4
wt.%
n
I
Fig. 1. The W G S activity and ammonia uptake of sulfided Mo-containing Ni-exchanged ( i n solut i o n ) catalysts. Open circles represent the support pretreated in H, at 475 K ; filledsupport pretreated i n H, at 675 K. NH, uptake (triangles) meesured for samples presulfided at 6 7 4 K.
Figure 1 shows the WGS activity for the series of Ni-Mo-Y catalysts and their NH, sorption capacity. These results, as well a s those presented in refs 2-4, indicate that at least two main factors influence catalytic activity i n the WGS reaction with a sulfided feed: synergetic effect between Ni and M o eulfided species and acidity of these catalysts. Similar effects as for the presented NaNiY supports ( F i g . 1 ) were also found for the series of KNiY and CsNiY based catalysts but with respectively lower values of activity (ref.4). Experiments in which the most active catalysts were impregnated after sulfidation with a diluted solution of K,CO, , next dried and activated again i n H,S/H, mixture, showed the decrease i n activity from 50 to 75 S T h e ammonia uptake for these impregnated samples was always lower of about 50 % than for non-impregnated. Data presented in Table 1 for the selected catalyete indicate that the WGS activity, irrespective from the synergy between Ni and Mo eulfided species, is rather related t o the catalyst acidity than basicity. It i s known that during presulfidation with H,S/H, mixture the formation of acidic groups occurs even
.
2571 Table 1 Catalytic activity (WGS) and NO, NH, and BF, sorption capacity of sulfided molybdenum-loaded Y-zeolites Sample
Nay-Mo HY-8 0-MO USY - 1 -Mo USY-l-Ni;Mo** NaNiY-Mot+ NaNiY -Mo COY-MO CeNi Y -Mo
*
-
++
-
** + -
Rate cone t ant * 3 -1 -1 (cm g min )
Amount of adsorbed NO NH, BF3 (nun01 9 - 7
32.0 73.6 14.9 63.4 232.8 34.7 21.2 152.8
0.184 0.166 0.053 0.136 0.134
-----
0.112 0.100
and and ~
Zeolite
NaY Nay-Mo
BY-MO USY-1 USY - 1 -Mo NaNiY* NaNiY-Mo* NaNiY * * NaNiY-Mo** CSY CBY-MO CsNiY CsNiY -Mo
* -
**
-
3.90 3.34 4.11 3.11 3.68 1.41 2.69 2.36
measured after 2 hours, H,O:CO = 1 Ni content - 1.2 wt.9, Mo content 5.0 wt.% solution-ion exchange solid-state exchange
Table 2 Activity of Mo-Y, Ni-Mo-Y decomposition of isopropyl
HY
0.840 2.249 0.548 1.446 1.390 0.520 0.137 0.605
~
Mo-free diacetone _
_
_
_
_
_
Y-zeolites alcohols ~
for
~
Isopropyl alcohol Diacetone alcohol Conversion (mol 9 ) to propene
propane
acetone
meeityl oxide
0.0 22.7 69.0 44.5 3.5 3.9 11.2 18.6 3.6 2.3
0.0 1.2 13.5 5.8 0.3 0.6 8.0 2.9 0.6 0.3 0.0 0.0 4.0 5.2
0.3 1.0 2.0 2.0 4.6 3.9 0.4 0.8
0.4 1.1 23.4 20.9 2.7 2.0 0.0 9.4
0.3 0.2 0.2 0.8
0.3 0.4 0.2 5.9
0.0
0.9 5.7 9.4
solution-ion exchange solid-state exchange
---
---
over Nay, KY or Cay. The low values of activity for NaY or CsY eupports (see Table 1) with highly "dispersed" Mo species (NO adsorption) are related both to the absence of nickel and to the low concentration of acid sites. The latter was confirmed by the very low activity of theee sulfided support8 during the decomposition isopropyl and diacetone alcohol8 to propene and mesityl oxide, respectively. Results presented in Table 2 for non-sulfided catalysts show that introduction of nickel and/or molybdenum to NaY or CsY supports usually resulte in the increase of catalyst acidity what was obeerved as higher yield of propene and mesityl oxide. After aulfidation the acidity wae always higher of about 10-20 % and this was reflected in catalytic reactions with alcohols. Whereae after introduction of nickel into Y zeolite8 both Lewie and Broneted acid site8 were generated (FTIR experiments), incorporation of molybdenum is responsible for the formation of Lewis acid sites and decreased basicity of sulfided samples. Formation of propane (Table 2) at relatively low temperature during decompoeition of isopropyl alcohol after the hydrogen-free condition can be explained by the disproportionation of oligomers formed from propene with simultaneous evolution of hydrogen and subsequent hydrogenation. The hydrogenation of propene was always higher for eamples containing only nickel and slightly decreased after molybdenum incorporation. In this study adsorption of BF, (ref. 7) and conversion of diacetone alcohol into acetone (ref. 8) were applied to examine the basicity of the studied catalysts. Data presented in Table 1 and Table 2 indicate that catalysts with increased basicity expreseed here either as BF, sorption capacity or as the yield of acetone formed ueually indicate poor activity in the WGS react ion. The presented resulte a e well those not ehown in thie report (0.g. IR experiments) indicate the importance of Bronsted acid sites engaged in the water-gas shift reaction. The detailed investigations concerning acid-base propertiee of Ni-Mo-Y zeolite catalyst8 in the WGS reaction in planed to be a eubject of a subsequent contribution. REFERENCES 1 A.L. Lee, K.C. Wei, T.Y. Lee and J. Lee, Stud. Surface Sci. Catalyeie, vo1.5, Elsevier, 1980, pp. 327-333. 2 M. Laniecki and W. Zmierczak, Zeolites, 11 (1991) 18-26. 3 M. Laniecki and W. Zmierczak, Stud. Surface Sci. Catalyeis, vo1.65, Eleevier, 1991, pp. 377-386. 4 M. Laniecki and W. Zmierczak, Stud. Surface Sci. Catalysis, vo1.68, Elsevier, 1991, pp. 799-802. 5 M. Laniecki and W. Zmierczak, Stud. Surface Sci. Catalysis, vo1.69, Elsevier, 1991, pp. 331-338. 6 W. Przystajko, R. Fiedorow and I.G. Della Lana, Zeolites, 7 (1987) 477-481. 7 K . H . Rhee and M.R. Basila, J. Catal., 10 (19681 243-251. 8 Y. Fukuda, K. Tanabe and S . Okazaki, Nippon Kagaku Kaishi, 3 (1972) 513-517.