INVESTIGADORES
QUERINI Carlos Alberto
artículos
Título:
Coking of SO4=2?ZrO2 Catalysts during Isomerization of n-Butane and Its Relation to the Reaction Mechanism
Autor/es:
VERA, C.; PIECK, C.L.; SHIMIZU, K.; QUERINI,C.A.; PARERA, J.M.
Revista:
JOURNAL OF CATALYSIS
Editorial:
ACADEMIC PRESS INC ELSEVIER SCIENCE
Referencias:
Año: 1999 vol. 187 p. 39 - 49
ISSN:
0021-9517
Resumen:
A study of the deactivation of SO2¡SO2¡
4 ?ZrO2 catalysts during isomerization
of n-butane showed that a small amount of a carbonaceous
deposit (1?1.2%) is formed. A high proportion of this deposit
is produced during the first minutes of the reaction and it seems to
be responsible for the initial short-term catalyst deactivation but it
is doubtful whether it is connected to the long-term loss of activity.
Activity in isomerization of n-C4 was very sensitive to activation
conditions while coking was more consistent; in all cases, SZ catalysts
had a limiting content of 1 to 1.2% coke when fully deactivated.
In an oxygen flow, the coke deposit could be burned at 500±C, but
it could also easily be removed by stripping with an oxygen-free
inert gas at higher temperatures. In the latter case, the coke was
oxidized by the catalyst surface groups, most likely sulfate. The
coke was soluble only in polar solvents (methanol, pyridine) and
was highly insoluble in benzene and hexane. An FD-mass spectrum
of the soluble fraction of the coke indicated the presence of compounds
with m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=zup to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
it could also easily be removed by stripping with an oxygen-free
inert gas at higher temperatures. In the latter case, the coke was
oxidized by the catalyst surface groups, most likely sulfate. The
coke was soluble only in polar solvents (methanol, pyridine) and
was highly insoluble in benzene and hexane. An FD-mass spectrum
of the soluble fraction of the coke indicated the presence of compounds
with m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=zup to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
conditions while coking was more consistent; in all cases, SZ catalysts
had a limiting content of 1 to 1.2% coke when fully deactivated.
In an oxygen flow, the coke deposit could be burned at 500±C, but
it could also easily be removed by stripping with an oxygen-free
inert gas at higher temperatures. In the latter case, the coke was
oxidized by the catalyst surface groups, most likely sulfate. The
coke was soluble only in polar solvents (methanol, pyridine) and
was highly insoluble in benzene and hexane. An FD-mass spectrum
of the soluble fraction of the coke indicated the presence of compounds
with m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=zup to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
it could also easily be removed by stripping with an oxygen-free
inert gas at higher temperatures. In the latter case, the coke was
oxidized by the catalyst surface groups, most likely sulfate. The
coke was soluble only in polar solvents (methanol, pyridine) and
was highly insoluble in benzene and hexane. An FD-mass spectrum
of the soluble fraction of the coke indicated the presence of compounds
with m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=zup to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
deposit (1?1.2%) is formed. A high proportion of this deposit
is produced during the first minutes of the reaction and it seems to
be responsible for the initial short-term catalyst deactivation but it
is doubtful whether it is connected to the long-term loss of activity.
Activity in isomerization of n-C4 was very sensitive to activation
conditions while coking was more consistent; in all cases, SZ catalysts
had a limiting content of 1 to 1.2% coke when fully deactivated.
In an oxygen flow, the coke deposit could be burned at 500±C, but
it could also easily be removed by stripping with an oxygen-free
inert gas at higher temperatures. In the latter case, the coke was
oxidized by the catalyst surface groups, most likely sulfate. The
coke was soluble only in polar solvents (methanol, pyridine) and
was highly insoluble in benzene and hexane. An FD-mass spectrum
of the soluble fraction of the coke indicated the presence of compounds
with m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=zup to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to be directly linked to the coking process
3
m=z
it could also easily be removed by stripping with an oxygen-free
inert gas at higher temperatures. In the latter case, the coke was
oxidized by the catalyst surface groups, most likely sulfate. The
coke was soluble only in polar solvents (methanol, pyridine) and
was highly insoluble in benzene and hexane. An FD-mass spectrum
of the soluble fraction of the coke indicated the presence of compounds
with m=z up to 2700, but the distribution was concentrated
aroundm=zD350 to 500. The latter value, when compared with the
small amount of total carbon, indicates that only a small fraction
of the surface sites was affected by the coke, or that deactivation
proceeded by a mechanism other than site blocking. A surface reduction
process by the reacting hydrocarbon may also be linked to
the activity loss. ESR results indicated that the catalyst was also
reduced during the reaction; the intensity of the Zr3C signal was
higher on the coked catalysts. The probable concurrence of reduction
could explain the long-term activity decline which seems not
to