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Implications of Analyses of used Resid Demetallation Catalyst
C.H. Bartholomew and J.B. Butt (Editors), Catalyst Deactiuation 1991 01991 Elsevier Science Publishers B.V.. Amsterdam
265
IMPLICATIONS OF ANALYSES O F USED RESID DEMETALLATION CATALYST
H. D. SIMPSON Unocal Corporation, Science & Technology Division, P. 0. Box 76, Brea, CA 92621 USA ABSTRACT Analyses on a used Unocal experimental demetallation catalyst after extended testing showed that the carbon level increased, and the metals and sulfur levels decreased, from top to bottom in the bed. The level of deposited metals (V+Ni+Fe) ranged from about 110% of the fresh catalyst at the top of the bed to about 15% at the bottom in fairly linear fashion. The average deposited metals level was 52 wt% of the fresh catalyst. The apparent stoichiometric molar ratio of metals to sulfur ranged from 1:l at the top of the bed to 1:2 at the bottom. At least some of the deposited metals occurred as (Fe,Ni)],,S, where x represents a small deviation from ideality resulting from structural defects.
v,
Electron microprobe line scans show that vanadium tends to deposit fairly uniformly throughout the particles, especially at high loadings. Nickel exhibits a "reverse rinding" effect, where the concentration is greater in the interior of the particles than on the outside. Iron exhibits a very high rinding effect, suggesting high affinity ol this element for the catalyst. ESCA results on particles from the top and bottom of the bed substantiate the lower metals/sulfur ratio at the bottom of the bed compared to the top. Also, some molybdenum was detected on the surface of ALL of these particles. This indicates that some molybdenum is always accessible to the reactants, even whcn high levcls of deposited metals are on the catalyst. INTRODUCTION For the readcr interested in background on the aspects of HDM catalysis in general, the recent comprehensive review by Quann, et al. (ref. 1 ) is recommended. The catalyst discussed in the present work was a Unocal experimental sample run for a prolonged period of time. When the run was terminated, the catalyst was unloaded in 11 sections for sampling and analysis. These sections arc depictcd schcmatically in Fig. 1.
Fig. 1. Reactor sample positions of HDM catalyst.
266
COMPOSITIONAL ANALYSES: VARIATION O F METALS, SULFUR AND CARBON WITH CATALYST BED POSITION The analyses themselves are presented in Table 1. The computed levels of the deposited elements on a fresh catalyst basis is shown in Table 2. The results show that the metals levels decrease down the bed from top to bottom, while the carbon level varies in the opposite direction. As expected, the sulfur level follows that of the metals. TABLE 1
Analyses on discharged HDM c a t a l y s t A n a l y t i c a l Value, wt% Emission Spectroscow co v Ni
Fe
Total Carbon
7.1 6.3 6.5 6.1 5.9 5.1 4.8 4.0 3.4 2.9 2.6
2.3 2.4 1.2 0.9 0.6 1.0 0.7 1.0 0.7 0.5 0.5
3.2 5.3 4.5 8.2 7.2 11.6 14.4 13.8 14.1 17.9 19.2
Mo
SamDle
K
15.0 18.0 19.0 19.0 22.0 23.0 23.0 26.0 28.0 29.0 30.0
J I
H G F E D C
B
A
2.3 2.7 2.8 2.9 2.9 3.2 3.4 3.5 3.9 4.3 4.2
28.0 23.4 23.6 21.3 20.0 16.5 15.1 12.1 9.9 7.9 6.9
1.0 1.1 1.2 1.1 1.0 1.3 1.2 1.2 1.5 1.5 1.4
Total Sulfur
27.5 24.3 24.2 23.3 20.5 17.5 16.4 14.7 13.0 9.8 9.2
TABLE 2 Deoosited element levels on fresh c a t a l y s t basis SamDl e
K J
I
H G
F
E
D C B A
v 84.9 59.2 56.8 51.1 42.2 33.0 30.1 21.6 16.3 12.5 10.6
Ni -
21.5 16.0 15.5 14.7 12.4 10.2 9.6 7.2 5.6 4.6 4.0
wt%
Fe -
7.0 6.0 2.8 2.2 1.4 2.1 1.5 1.8 1.2 0.7 0.8
C -
9.7 13.4 10.8 19.7 15.2 23.2 28.7 24.6 23.3 28.3 29.6
-S
83.3 61.5 58.3 55.9 43.2 35.0 32.8 26.3 21.6 15.5 14.2
The normalized levels are shown in more dramatic form in the graphs of Figs. 2 and 3. The total metals level exceeds 110 wt% of the fresh catalyst at the top end of the bed. This represents a measure of the minimum metals absorption capacity of the catalyst. The average deposited metals level was calculated to be 52 wt% on a fresh catalyst basis. The sulfur level
267
follows the metals level, indicating that the metals deposit as sulfides, This would not necessarily prevent them from competing for the alumina oxygen, however, especially if the sulfides are relatively reduced. Stoichiometric calculations indicate that the deposited metals
are indeed in reduced sulfided form, and the extent of reduction varies directly with the
metals level. The average formula is MS at the top of the bed and MS2 at the bottom, where
M = 213 V + 116 Ni + 1/6Fe.
BOTTOM
FRACTIONAL BED LENGTH
Fig. 2. Carbon, sulfur and deposited metals on discharged HDM catalyst (fresh catalyst basis).
TOTAL METALS
'0
02
04
06
FRACTLONAL BED LENGTH
08
10
BOTTOM
Fig. 3. Component metals deposited on discharged HDM catalyst (fresh catalyst basis).
268
XRD RESULTS
A compound identified as iron vanadium sulfide (JCPDS No. 31-657)was found in every
sample of the material submitted for analysis. This compound has the stoichiometrc formula (V, Fe)>&, where x represents a small deviation from ideality resulting from structural defects. It is believed that the Fe in this structure could be replaced by Ni without changing the diffraction
pattern, providing a means for the incorporation of all three deposited metals together in one compound.
ELECTRON MICROPROBE LINE SCANS Profiles of nickel and vanadium across the lobes of particles from the top, middle and bottom of the catalyst bed are shown in Figs. 4,s and 6 respectively. Iron was detected in samples from
the top and middle sections of the bed, but not in samples from the bottom. A typical profile is shown in Fig. 7. The profiles show the Eollowing: 1.
Nickel has a tendency toward "inverse rinding," where the concentration is higher
2.
Vanadium tends to deposit uniformly throughout the particles, especially at high
in the interior of the pellet than it is at the exterior. concentrations.
3.
Iron exhibits a strong rinding tendency.
The relatively uniform profiles of nickel and vanadium are desirable, because this pattern
results in maximum metals storage capacity without pore mouth plugging. The strong rinding tendency of iron can be a problem in commercial use, because it can accelerate pore mouth plugging and lead to degradation of the catalyst support.
NICKEL
Fig. 4. Line scans on sample from top of discharged bed.
VANADIUM
269
NICKEL
VANADIUM
4
I
Fig. 5. Line scans o n sample from middle of discharged bed.
NICKEL
Fig. 6. Line scans on sample from bottom of discharged bed.
Fig. 7. Typical line scan for Fe (top and middle of bed only).
VANAOlU M
270
ESCA ANALYSIS
Six samples were analyzed three from the top of the bed (K-2,5-2, and I-2), and three from the bottom (C-2, B-2 and A-2). In each case, the outer surface of the pellets was examined first (pellets mounted on double-sided tape on a standard stub); the pellets were then pulverized in
a mortar and the resulting powder was analyzed (powder also mounted on double-sided tape). Typical spectra from top and bottom samples of the catalyst bed are shown in Figs. 8-11. The elements detected and approximate sufrace mole percentages are tabulated in Table 3. For comparison, previous results obtained on the fresh catalyst are included also. Uncorrected elemental sensitivity factors supplied by VG were used in calculations of surface concentrations
for most of the elements. Absolute concentrations may be off by a factor of two, but relative concentrations for a given element should be significantly better than this.
s I SZP
-
0
BINDING ENERGY (EV)
5
1000
800
600
400
BINDING ENERGY (EV)
Fig. 9. ESCA data for K-2, powdered.
Fig. 8. ESCA data for K-2, outer surface.
200-
100-
50 -
1000
BOO
so0
400
BINDING ENERGY (EV)
Fig. 10. ESCA data for A-2, outer surface.
200
BINDING ENERGY (EV)
Fig. 11. ESCA data for A-2, powdered.
200
271
Table 3 Surface mole percentages on used HDM catalyst
- - __
-
1 OlSTRlBUTlDY
Al -
0 Ho co 1 loll1 -- -
FRESH OUTER SURFACf
42
43
FRESH. POWOER
45
47
36 I1
15
-
K-2. OUTfR SURFACE
04
20
009
1
I .5
39%
K Z POWDER
57
30 0 1
7
1.0
wiO davo
5-2. OUTER SURFACE
05
28
006
7
1.5
-
5-2. POWDER
72
35
01
7
0.9
44%
1.2 OUTER SURFACE
03
26
003
7
1.4
1-2. POWOER
60
33
01
7
0.9
C-2. OUTER SURFACE
0 3 25
007
7
0.7
-
C 2. POWDER
48
22
008
7
05
30%
B 2. OUTER SURFACE
04
24
008
7
0.8
8 2. POWOER
43
20
007
7
03
-
1-2. OUTER SURFACE
04
23
01
7
1-2. POWOER
44
21
008
SAMPLE AH 4532
--
8
15135
I .o
-7
0.3
W511
-
-NI
-
61%
IGO%
0 09
n.2 0 09
Fa
C
-
I1
-
0.09
-
01
-JTION __ % S 162.5 S169 Si
5
-
-
72
52
90%
57
52
40%
ID%
65
3a
74%
26%
1.0
51
50
03 %
17%
0.4
10%
0.9
0.6
56%
03
-
-
100%
01
0.1
67
13%
27%
0.7
58%
02
-
44
42%
54
53
86%
14%
0.3
100%
0.1
01
44
73%
27%
06
0 05
-
68
60%
70
25
71%
23%
02
100%
01
0.09
44
66%
34%
0.7
IOO%
0 05
-
69 73
23
1I %
29%
03
0 08
0.07
71
39
64 Yo
36 %
0.7
100%
004
71
2.2
71%
29%
03
-
-
IOO%
-
-
-
-
The composition of the outer surfaces of all the samples were fairly similar. The concentration
gradients observed for the various elements by emission spectroscopy do show up in the analyses of the powdered samples (e.g., carbon increases while V, Ni and S decrease from the top to the bottom of the bed). The interferences of Ni and V Auger peaks with thc major Co peaks made it impossible to
determine whether Co still appears in the surface region. Mo, however, is clearly detected; its surface concentration is fairly uniform from the top to the bottom of the bed and appears to be about 10% of that observed on the fresh cataIyst. This finding seems rather astonishing, and indicates that some molybdenum will always be accessible to the reactants, even at high levels of deposited metals. Other workers (ref. 2 ) have also obtained evidence that molybdenum remains exposed to reactants in HDM catalysts, however, and it is wcll known that migration of metals and phases can occur in catalysts (ref. 3). The evidence cited above constitutes a strong argument for continued incorporation of molybdenum in HDM catalysts, because some of the active molybdenum centcrs will always be available.
272
The measured binding energies indicate that the coke on the catalyst occurs as amorphous
carbonaceous material with C-H and C-C bonding predominantly. Molybdenum occurs as MoS, or MOO,; MOO, was not detected. Nickel appears to occur as either NiAI,O,, NiMoO, or NiSO,
in most instances, but a lower binding energy for Ni on powdered K-2 suggests the presence of
Ni,S, or NiO in that sample. Since the latter species is detected as a shoulder on the major peak,
it might not be detected easily at low concentrations, and could have been overlooked in other samples. The predominant vanadium species on most samples appeared to be v+ sulfide or oxide (517 EV). A second major species (513.5 EV) which could be VS or MoVS, was also detected on some of the surfaces. Iron occurs predominantly as Fe3+.Sulfur occurs as both sulfide (162.5
EV) and sulfate (169 EV). The latter is probably indicative of some air exposure after unloading.
These findings suggest that nearly all of the non-support elements compete with aluminum for the available oxygen. This would reinforce the idea of metals incorporation in the support as a mechanism for support degradation. Additional interpretations of the observations are that the non-support metals were oxidized to some extent upon contact with air when the catalyst was unloaded, and/or that they carried their own oxygen into the system as partial oxides in the feed. ACKNOWLEDGEMENTS Dr. Carol S. Hemminger organized and managed the analytical program for this work, and she obtained and interpreted the ESCA data. Thanks are due Dr. E. L. Moorehead for several valuable discussions in connection with the catalyst handling and ESCA work.
I thank Ms. P. Borgens and Messrs. J. Kalinowski and k J. Doerr for their dedicated and
careful efforts in handling the material. Ms. Borgens also assisted in performing the computations and compiling the results. REFERENCES 1.
2.
3.
R. J. Quann, R. A. Ware, C. Hung and J. Wei, in James Wei (Ed. in chief), Advances in Chemical Engineering, Vol. 14, Academic Press (1988). T. H. Heisch, B. L. Meyers, J. B. Hall and G. L. Ott, J. Catal. 86, 147 (1984). B. Delmon and P. Grange in B. Delmon and G. F. Froment (Eds.), Catalyst Deactivation, Elsevier, Amsterdam (1980).
265
IMPLICATIONS OF ANALYSES O F USED RESID DEMETALLATION CATALYST
H. D. SIMPSON Unocal Corporation, Science & Technology Division, P. 0. Box 76, Brea, CA 92621 USA ABSTRACT Analyses on a used Unocal experimental demetallation catalyst after extended testing showed that the carbon level increased, and the metals and sulfur levels decreased, from top to bottom in the bed. The level of deposited metals (V+Ni+Fe) ranged from about 110% of the fresh catalyst at the top of the bed to about 15% at the bottom in fairly linear fashion. The average deposited metals level was 52 wt% of the fresh catalyst. The apparent stoichiometric molar ratio of metals to sulfur ranged from 1:l at the top of the bed to 1:2 at the bottom. At least some of the deposited metals occurred as (Fe,Ni)],,S, where x represents a small deviation from ideality resulting from structural defects.
v,
Electron microprobe line scans show that vanadium tends to deposit fairly uniformly throughout the particles, especially at high loadings. Nickel exhibits a "reverse rinding" effect, where the concentration is greater in the interior of the particles than on the outside. Iron exhibits a very high rinding effect, suggesting high affinity ol this element for the catalyst. ESCA results on particles from the top and bottom of the bed substantiate the lower metals/sulfur ratio at the bottom of the bed compared to the top. Also, some molybdenum was detected on the surface of ALL of these particles. This indicates that some molybdenum is always accessible to the reactants, even whcn high levcls of deposited metals are on the catalyst. INTRODUCTION For the readcr interested in background on the aspects of HDM catalysis in general, the recent comprehensive review by Quann, et al. (ref. 1 ) is recommended. The catalyst discussed in the present work was a Unocal experimental sample run for a prolonged period of time. When the run was terminated, the catalyst was unloaded in 11 sections for sampling and analysis. These sections arc depictcd schcmatically in Fig. 1.
Fig. 1. Reactor sample positions of HDM catalyst.
266
COMPOSITIONAL ANALYSES: VARIATION O F METALS, SULFUR AND CARBON WITH CATALYST BED POSITION The analyses themselves are presented in Table 1. The computed levels of the deposited elements on a fresh catalyst basis is shown in Table 2. The results show that the metals levels decrease down the bed from top to bottom, while the carbon level varies in the opposite direction. As expected, the sulfur level follows that of the metals. TABLE 1
Analyses on discharged HDM c a t a l y s t A n a l y t i c a l Value, wt% Emission Spectroscow co v Ni
Fe
Total Carbon
7.1 6.3 6.5 6.1 5.9 5.1 4.8 4.0 3.4 2.9 2.6
2.3 2.4 1.2 0.9 0.6 1.0 0.7 1.0 0.7 0.5 0.5
3.2 5.3 4.5 8.2 7.2 11.6 14.4 13.8 14.1 17.9 19.2
Mo
SamDle
K
15.0 18.0 19.0 19.0 22.0 23.0 23.0 26.0 28.0 29.0 30.0
J I
H G F E D C
B
A
2.3 2.7 2.8 2.9 2.9 3.2 3.4 3.5 3.9 4.3 4.2
28.0 23.4 23.6 21.3 20.0 16.5 15.1 12.1 9.9 7.9 6.9
1.0 1.1 1.2 1.1 1.0 1.3 1.2 1.2 1.5 1.5 1.4
Total Sulfur
27.5 24.3 24.2 23.3 20.5 17.5 16.4 14.7 13.0 9.8 9.2
TABLE 2 Deoosited element levels on fresh c a t a l y s t basis SamDl e
K J
I
H G
F
E
D C B A
v 84.9 59.2 56.8 51.1 42.2 33.0 30.1 21.6 16.3 12.5 10.6
Ni -
21.5 16.0 15.5 14.7 12.4 10.2 9.6 7.2 5.6 4.6 4.0
wt%
Fe -
7.0 6.0 2.8 2.2 1.4 2.1 1.5 1.8 1.2 0.7 0.8
C -
9.7 13.4 10.8 19.7 15.2 23.2 28.7 24.6 23.3 28.3 29.6
-S
83.3 61.5 58.3 55.9 43.2 35.0 32.8 26.3 21.6 15.5 14.2
The normalized levels are shown in more dramatic form in the graphs of Figs. 2 and 3. The total metals level exceeds 110 wt% of the fresh catalyst at the top end of the bed. This represents a measure of the minimum metals absorption capacity of the catalyst. The average deposited metals level was calculated to be 52 wt% on a fresh catalyst basis. The sulfur level
267
follows the metals level, indicating that the metals deposit as sulfides, This would not necessarily prevent them from competing for the alumina oxygen, however, especially if the sulfides are relatively reduced. Stoichiometric calculations indicate that the deposited metals
are indeed in reduced sulfided form, and the extent of reduction varies directly with the
metals level. The average formula is MS at the top of the bed and MS2 at the bottom, where
M = 213 V + 116 Ni + 1/6Fe.
BOTTOM
FRACTIONAL BED LENGTH
Fig. 2. Carbon, sulfur and deposited metals on discharged HDM catalyst (fresh catalyst basis).
TOTAL METALS
'0
02
04
06
FRACTLONAL BED LENGTH
08
10
BOTTOM
Fig. 3. Component metals deposited on discharged HDM catalyst (fresh catalyst basis).
268
XRD RESULTS
A compound identified as iron vanadium sulfide (JCPDS No. 31-657)was found in every
sample of the material submitted for analysis. This compound has the stoichiometrc formula (V, Fe)>&, where x represents a small deviation from ideality resulting from structural defects. It is believed that the Fe in this structure could be replaced by Ni without changing the diffraction
pattern, providing a means for the incorporation of all three deposited metals together in one compound.
ELECTRON MICROPROBE LINE SCANS Profiles of nickel and vanadium across the lobes of particles from the top, middle and bottom of the catalyst bed are shown in Figs. 4,s and 6 respectively. Iron was detected in samples from
the top and middle sections of the bed, but not in samples from the bottom. A typical profile is shown in Fig. 7. The profiles show the Eollowing: 1.
Nickel has a tendency toward "inverse rinding," where the concentration is higher
2.
Vanadium tends to deposit uniformly throughout the particles, especially at high
in the interior of the pellet than it is at the exterior. concentrations.
3.
Iron exhibits a strong rinding tendency.
The relatively uniform profiles of nickel and vanadium are desirable, because this pattern
results in maximum metals storage capacity without pore mouth plugging. The strong rinding tendency of iron can be a problem in commercial use, because it can accelerate pore mouth plugging and lead to degradation of the catalyst support.
NICKEL
Fig. 4. Line scans on sample from top of discharged bed.
VANADIUM
269
NICKEL
VANADIUM
4
I
Fig. 5. Line scans o n sample from middle of discharged bed.
NICKEL
Fig. 6. Line scans on sample from bottom of discharged bed.
Fig. 7. Typical line scan for Fe (top and middle of bed only).
VANAOlU M
270
ESCA ANALYSIS
Six samples were analyzed three from the top of the bed (K-2,5-2, and I-2), and three from the bottom (C-2, B-2 and A-2). In each case, the outer surface of the pellets was examined first (pellets mounted on double-sided tape on a standard stub); the pellets were then pulverized in
a mortar and the resulting powder was analyzed (powder also mounted on double-sided tape). Typical spectra from top and bottom samples of the catalyst bed are shown in Figs. 8-11. The elements detected and approximate sufrace mole percentages are tabulated in Table 3. For comparison, previous results obtained on the fresh catalyst are included also. Uncorrected elemental sensitivity factors supplied by VG were used in calculations of surface concentrations
for most of the elements. Absolute concentrations may be off by a factor of two, but relative concentrations for a given element should be significantly better than this.
s I SZP
-
0
BINDING ENERGY (EV)
5
1000
800
600
400
BINDING ENERGY (EV)
Fig. 9. ESCA data for K-2, powdered.
Fig. 8. ESCA data for K-2, outer surface.
200-
100-
50 -
1000
BOO
so0
400
BINDING ENERGY (EV)
Fig. 10. ESCA data for A-2, outer surface.
200
BINDING ENERGY (EV)
Fig. 11. ESCA data for A-2, powdered.
200
271
Table 3 Surface mole percentages on used HDM catalyst
- - __
-
1 OlSTRlBUTlDY
Al -
0 Ho co 1 loll1 -- -
FRESH OUTER SURFACf
42
43
FRESH. POWOER
45
47
36 I1
15
-
K-2. OUTfR SURFACE
04
20
009
1
I .5
39%
K Z POWDER
57
30 0 1
7
1.0
wiO davo
5-2. OUTER SURFACE
05
28
006
7
1.5
-
5-2. POWDER
72
35
01
7
0.9
44%
1.2 OUTER SURFACE
03
26
003
7
1.4
1-2. POWOER
60
33
01
7
0.9
C-2. OUTER SURFACE
0 3 25
007
7
0.7
-
C 2. POWDER
48
22
008
7
05
30%
B 2. OUTER SURFACE
04
24
008
7
0.8
8 2. POWOER
43
20
007
7
03
-
1-2. OUTER SURFACE
04
23
01
7
1-2. POWOER
44
21
008
SAMPLE AH 4532
--
8
15135
I .o
-7
0.3
W511
-
-NI
-
61%
IGO%
0 09
n.2 0 09
Fa
C
-
I1
-
0.09
-
01
-JTION __ % S 162.5 S169 Si
5
-
-
72
52
90%
57
52
40%
ID%
65
3a
74%
26%
1.0
51
50
03 %
17%
0.4
10%
0.9
0.6
56%
03
-
-
100%
01
0.1
67
13%
27%
0.7
58%
02
-
44
42%
54
53
86%
14%
0.3
100%
0.1
01
44
73%
27%
06
0 05
-
68
60%
70
25
71%
23%
02
100%
01
0.09
44
66%
34%
0.7
IOO%
0 05
-
69 73
23
1I %
29%
03
0 08
0.07
71
39
64 Yo
36 %
0.7
100%
004
71
2.2
71%
29%
03
-
-
IOO%
-
-
-
-
The composition of the outer surfaces of all the samples were fairly similar. The concentration
gradients observed for the various elements by emission spectroscopy do show up in the analyses of the powdered samples (e.g., carbon increases while V, Ni and S decrease from the top to the bottom of the bed). The interferences of Ni and V Auger peaks with thc major Co peaks made it impossible to
determine whether Co still appears in the surface region. Mo, however, is clearly detected; its surface concentration is fairly uniform from the top to the bottom of the bed and appears to be about 10% of that observed on the fresh cataIyst. This finding seems rather astonishing, and indicates that some molybdenum will always be accessible to the reactants, even at high levels of deposited metals. Other workers (ref. 2 ) have also obtained evidence that molybdenum remains exposed to reactants in HDM catalysts, however, and it is wcll known that migration of metals and phases can occur in catalysts (ref. 3). The evidence cited above constitutes a strong argument for continued incorporation of molybdenum in HDM catalysts, because some of the active molybdenum centcrs will always be available.
272
The measured binding energies indicate that the coke on the catalyst occurs as amorphous
carbonaceous material with C-H and C-C bonding predominantly. Molybdenum occurs as MoS, or MOO,; MOO, was not detected. Nickel appears to occur as either NiAI,O,, NiMoO, or NiSO,
in most instances, but a lower binding energy for Ni on powdered K-2 suggests the presence of
Ni,S, or NiO in that sample. Since the latter species is detected as a shoulder on the major peak,
it might not be detected easily at low concentrations, and could have been overlooked in other samples. The predominant vanadium species on most samples appeared to be v+ sulfide or oxide (517 EV). A second major species (513.5 EV) which could be VS or MoVS, was also detected on some of the surfaces. Iron occurs predominantly as Fe3+.Sulfur occurs as both sulfide (162.5
EV) and sulfate (169 EV). The latter is probably indicative of some air exposure after unloading.
These findings suggest that nearly all of the non-support elements compete with aluminum for the available oxygen. This would reinforce the idea of metals incorporation in the support as a mechanism for support degradation. Additional interpretations of the observations are that the non-support metals were oxidized to some extent upon contact with air when the catalyst was unloaded, and/or that they carried their own oxygen into the system as partial oxides in the feed. ACKNOWLEDGEMENTS Dr. Carol S. Hemminger organized and managed the analytical program for this work, and she obtained and interpreted the ESCA data. Thanks are due Dr. E. L. Moorehead for several valuable discussions in connection with the catalyst handling and ESCA work.
I thank Ms. P. Borgens and Messrs. J. Kalinowski and k J. Doerr for their dedicated and
careful efforts in handling the material. Ms. Borgens also assisted in performing the computations and compiling the results. REFERENCES 1.
2.
3.
R. J. Quann, R. A. Ware, C. Hung and J. Wei, in James Wei (Ed. in chief), Advances in Chemical Engineering, Vol. 14, Academic Press (1988). T. H. Heisch, B. L. Meyers, J. B. Hall and G. L. Ott, J. Catal. 86, 147 (1984). B. Delmon and P. Grange in B. Delmon and G. F. Froment (Eds.), Catalyst Deactivation, Elsevier, Amsterdam (1980).