Applied Catalysis, 29 (1987) 55-66 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
PROMOTER
ACTION
OF KC1 ON CuC12/SiO2
CATALYSTS
USED FOR THE OXYHYDROCHLORINATION
OF METHANE
Cristina INTEMA
L. GARCIA (Institute
and Daniel
Mar de1 Plata - Conicet,
(Received
E. RESASCO
of Materials
29 April
Science
and Technology),
Universidad
National
de
6. Justo 4302 - (7600) Mar de1 Plata, Argentina.
Juan
1986, accepted
1986)
28 August
ABSTRACT The effect of KC1 addition on the catalytic activity and product distribution of SiO2-supported CuC12 catalysts has been investigated. The activity of these K-containing catalysts can be related to the release of chlorine atoms from the surface which initiate a gas phase chain reaction. The active phase of these catalysts is molten under reaction conditions (700 Tort-, 670 K). In this case, the presence of KC1 in the melt increases the catalytic activity and favors the regeneration of the catalyst. However, overdoses of KC1 have a negative effect on both, catalyst activity and stability. When KC1 is not added to the CuC12 catalyst, the reaction can still proceed by an alternative path over the solid surface, probably involving the dissociative chemisorption of methane. As opposed to the effect observed at 670 K, at lower temperatures, e.g., 500 K, the addition of KC1 reduces the catalytic activity by blocking copper chloride active sites.
INTRODUCTION The catalytic copper
chloride
molten
alkali,
and methane chloride
can be carried
630 K and in the presence
mixtures,
(methyl
out on supported
hydrogen
chloride
of
chloride,
CH3C1,
oxygen
methylene
chloroform ChCl and carbon tetrachloride CC1 ). An obvious 3 4 of the oxyhydrochlorination process over the direct chlorination is of using a major
industrial
by-product,
hydrogen
chloride,
of chlorine.
about
this process
the nature
of the available while
has been
about
only a few scientific
the K-containing suggested
copper
papers
about
chloride
that the Deacon
0166-9834/87/$03,50
hand, Bakshi
occurs
catalysts
on the subject.
some studies through
producing
01987 Elsevier Science Publishers B.V.
action
of
have
a Deacon
step [S-7].
Cl2 and H20
et al. [8,9] from kinetic
in the whole
Most
literature
of the catalytic
For instance,
reaction
conditions.
is in the patent
have been published
chloride
step proceeds
[I], there still exists
under reaction
the description
mixtures.
takes place on copper
from HCl and 02. On the other
catalysts
this reaction
that the oxyhydrochlorination
reaction
concluded
known for many years
of the active
information
Some of them seem controversial
This
above
chloride
react to give chloromethanes
Even though
[Z-4],
At temperatures
rare earth and copper
the possibility
doubts
catalysts.
of methane
CH2C12,
advantage
instead
oxyhydrochlorination
data
have
bulk of the salt melt,
but
56
the methane different
chlorination
active
step takes
centers.
CuCl-CuC12
ternary
a complex
dependence
melts,
found a zero
with
respect
that the reaction
takes
melt
of chlorine
by evolution
A surface proposed
by Pieters
supported
copper
lyst was active oxygen
place
mechanism
contrast,
in our case, shown
The presence recently
catalyst,
of copper
chloride
resistant
to deactivation
with
treatment.
are activated species
adds another
properties.
By
and as we
to the problem.
occurring
when copper
an active
was used almost
that
(Cu'+).
mixtures,
1121. We have found
can generate
suggest
state
by
Cu ‘+ ions .
complication
than the non-interacting support
in 02/HCl
This cata-
deactivated
The authors
involves
interactions
and titania
the support
when the silica
of CH4 on a silica-
unique
ions in the lower oxidation
the salt-support alumina
exhibited
by hydrogen copper
the catalysts
on silica,
However,
which
[12], the active
supported
from the surface
has been recently
as low as 470 K. It was rapidly
of the support
studied
of methane
et al. [II] for the oxyhydrochlorination
involves
on KCl-
reaction order with respect to methane and 2+ concentration in the melt. They suggested
the chemisorption
at temperatures
have previously
to Cu
this reaction
atoms.
involving
chloride
species
of the melt using
in the gas phase but it is initiated
and it was reactivated
the active
place on the surface
et al. [IO], investigating
Gorin
copper
We have
chloride
is
that the interaction
species chloride
no salt-support
which
is more
particles.
interaction
was
observed. In particular,
we analyze
of silica-supported be possible
copper
here the influence
chloride.
to study the promoter
Investigations are currently
about
the effect
in progress
of KC1 on the catalytic
Using an inert support
action
of K avoiding
of the support
as silica
strong
on the promoter
support action
properties
it will effects. of potassium
in our laboratory.
EXPERIMENTAL Catalyst
preparation
The K-promoted
copper
chloride
a sequential
impregnation
200 m2 g-l).
In the first preparation
aqueous
solution
and further by atomic
dried
of CuC12.
aqueous
The support
in this study were prepared
used was silica
step the support
The sample was then dried
analysis
three aliquots solutions
after
K/Cu ratio as K-Cu-0,
K-Cu-0.5,
are summarized
extraction
of the CuC12/Si02
of increasing
of 0.5, 1.0 and 2.0. In this paper,
catalysts
used
overnight
we identify
1.
sample
380,
with an
at room temperature
Cu content,
were further
as determined
impregnated
to give K/Cu molar
the catalysts
and K-Cu-2.
by
HN03, was 0.096 g Cu/g cat.
KC1 concentration
K-Cu-1
in Table
with
(SiO2 Aerosil
was impregnated
in oven at 380 K for 2 h. The resulting
absorption
After drying, with
method.
catalysts
according
The characteristics
ratios
to their of the
TABLE
1
Characterization
of the CuC12/SiO2
catalysts DTA peaks
K/Cu ratio
Cu Content
Catalyst
Support
K-Cu-0
SiO2
9.6%
0.0
760, 780 K
K-CU-C.5
SiO2
9.6%
0.5
607, 623 K
K-Cu-1
SiO2
9.6%
1.0
565, 654 K
K-Cu-2
SiO
9.6%
2.0
542, 554 K
2
578, 596 K
Activity
measurements
Most activity
measurements
which was operated prepared
in a second
was measured catalyst Before
flask connected
in a gaseous
the reactant
mixture
the reaction
HCl/oxygen
(CH4:HC1:02
to take place
A set of similar in order
kept cooled.
temperature. were
were
runs were
followed.
(HCl O2 2:1, total pressure
introduced
and the reaction
hydrogen
purified
reactor
carbon
at a much
and operation
pure oxygen
activated
specially
the reactor
in the average,
conditions
chloride,
through
time,
A fresh sample was
by gas chromatography.
bed at 670 K while
Anhydrous
was
of 700 Torr. After a given
was,
the same reaction
=
670 K) for 30 min. Subsequently,
in a non-isothermal
mixture
controller.
ning 3.0 mg of fresh catalyst
to have only the catalyst the gaseous
in the reactor
placed near the
emperature
off the reactor.
were analyzed
conducted
were
up to 380 K. The sample was
pressure
cooling
t
Thus,
Otherwise,
gas (98% methane)
total
by suddenly
used for each run. The products
mixture
(usually
= 5:Z:l) was
at an initial
was stopped
The temperature
conta
was increased
temperature
mixtures
the 'rimocouple,
by an electronic the reactor
60 cm3 Pyrex flask,
The reactant
to the reactor.
the temperature
100 Torr) at the reaction
in a spherical
reactor.
iron-constantan
determination,
off while
then pre-treated
designed
batch
bed, and it was controlled
was pumped
were
conducted
with a glass-covered
each activity
allowed
were
as an isothermal
lower
procedures
(La Oxigena)
and molecular
walls
and natural
sieve traps
used as reactants.
Thermal
analysis
The catalysts 990 calorimeter. the K-Cu-0 silica
were
exothermic
Otherwise,
the main
in the DTA spectra in Table
390 K). it can be noted K/r11 ratio
increases.
thermal
was analyzed
For studying
was used as a reference.
were observed.
are indicated
sample
as a reference.
impure N2 was used, strong
peaks
by differential
Each K-containing
catalyst
support
characterized
observed
catalyst
the bare
with the presence
peaks were detected.
of O2
The position
for the four catalysts
1 (except those related to water evolution, that the DTA peaks appear
N2 using
rate was IO K min -'. When
peaks associated
only endothermic
in a DuPont
under flowing
the K-CU-0
The heating
analysis
of
investigated i.e., 360-
at lower temperatures
as the
58
K/Cd FIGURE
1
samples
Oxyhydrochlorination
as a function
P'CILERRFTIO Catalytic
of methane.
of K/Cu molar
activity
of the KCl-CuC12/Si02
batch
670 K.
Isothermal
ratio.
reactor,
RESULTS Catalyst
activity
The effect
of KC1 addition
samples
was evaluated
initial
reaction
The rates were
(not shown).
ratio
catalytic
Product
catalytic
batch
reactor
in terms of the amount
from the initial
slopes
of KCl. However,
addition
ratio
consumed.
of the catalysts reaches
1 shows
in the catalyst.
concentration
effect
of CuC12/SiO2
at 670 K. Figure
of methane
of methane
this beneficial
of about one. Further
activity
of the K/Cu molar
It can be noted that the activity
the addition molar
in the isothermal
rates as a function
are expressed
calculated
on the overall
These
values
vs. time curves increases
a maximum
of KC1 has then a negative
by
at a K/Cu effect
on
activity.
distribution
The evolution illustrated
of product
in Figures
as a function
of total
Clear differences that the catalysts
conversion
between differ
but also
in the product
indicate
that for catalyst
formed,
while
initial
product.
distributions
for catalysts These
2 and 3 respectively. obtained
the two catalysts not only
in the isothermal are immediately
in the level of activity
distribution
for catalyst
K-CU-1
figures
patterns.
K-Cu-1
only methyl
K-Cu-0,
methylene
reactor obvious. (as shown
The extrapolation chloride
chloride
and K-Cu-0
show product
(CH3C1) (CH2Cl2)
is
yields
at 670
K.
It appears in Figure
1)
to zero conversion was initially was the dominant
_
K-Cu-1 I
PER FIGURES
2 and 3
Isothermal
Evolution
reactor.
of product
CENT
CGN\iE2S
ICI’.;
distribution
on catalysts
K-&-l
and K-Cu-0.
distribution
on catalysts
K-Cu-1
and K-Cu-0.
670 K.
K-Cu-1
FIGURES
4 and 5
Non-isothermal
Evolution reactor.
The differences was carried
between
of the catalyst
the two catalysts
out in the non-isothermal
5 the variation
of product
be seen in Figure
concentration
the more
was methyl chlorinated
chloride. products
bed = 670 K.
were more
reactor.
evident
We have plotted
as a function
4, for catalyst K-Cu-1,
10 min of reaction disappear,
of product
Temperature
appeared.
in Figures
of reaction
the only product
Only after
when the reaction
observed
this chlorocarbon On the other
4 and
time. As can over the first started
to
hand, for catalyst
60
c
K-h- 1
FIGURES
catalysts
and K-Cu-0.
K-Cu-1
(Figure
5), it is clear
since the initial that for methyl The other
dropped
lysts K-Cu-1 catalyst increases a plateau apparent
K-Cu-1
is reached activation
K, which -1 same, 4 kcal mol . As described
Figure
appear whereas
energies
might
analysis
chloride
was initially
production
(0)
spectra.
formed
was even higher
and K-Cu-2)
than
yield
was observed
product
K-Cu-1.
For
but it rapidly
and later chloroform,
appeared.
analysis dependence
of the catalytic
initial
reactor
reaction
as a function
increases
of temperature.
section,
in a gaseous the observed
with
before
HCl/oxygen temperature
to the reaction
on Sudden
temperature. ranges
plateaus,
each
of cata-
each activity
over the temperature
to the two activity
activity
rates obtained
560 and 640 K. After
the rate slowly
not only be related
exhibited
to that of catalyst
chloride
calculated
in the experimental
were pre-treated
(K-Cu-0.5
chloride,
at about
correspond
ture for 30 min. Therefore, activity
chloride
similar
6 shows
in the isothermal
in activity
and 645-800
catalysts
and thermal
the temperature
and K-Cu-0.
very
100% methyl
zero as methylene
dependence
We have studied
catalysts
(not shown)
an initial
to almost
Temperature
thermal
for
temperature;
chloride.
patterns
both catalysts
differential
methylene
of temperature
at the reaction
that not only methyl
rate towards
two K-containing
distribution
rate as a function
(0) pre-treatment
at 715 K. Right axis:
pre-treatment
K-CU-0
reaction
Left axis:
6 and 7
jump, The
590-630
rate measurement,
mixture
at the reaction
dependence temperature
K
are both about
the
the tempera-
of the catalytic itself
but also
61 to the pre-treatment we performed
two separate
temperature.
For the first
second
reaction
which
temperature
in Figure
these
two peaks to melting
Figure pattern.
identify
conclude
under
K-Cu-0
are present almost
in Figure
K-Cu-1
monotonously activation
(high
Accordingly,
of
it would appear
in the catalyst.
is essentially
of molten
concentration
tha-:
In that case, phase
than phase
inactive
at high temperatures
II
I. Therefore,
until phase
I
has to be ascribed
increase
two catalysts
good agreement
with
the trend
that for catalyst
increases
with
temperature.
obtained
start melting
this sample
presented
phases.
An alternative
the melting
reaction
the deactivation
zones of phase
plateau
to phase
these measurements the two phases.
zones.
I while allowed
By varying
in Figure
is almost
active
1. However,
of time. These
above,
at 715 K it should us to study the amount
observed
chloride
for
to the presence
of
in the next section. at two different
two temperatures,
I and II respectively,
As mentioned
more active.
that the copper
the activity
K-Cu-1
tempera-
i.e., just
corresponding
to the
at 600 K the activity
should
be mostly
separately of catalyst,
6
at lower temperatures,
of magnitude
be ascribed
path is discussed
in Figures
than the K-free one, in
indicates
of catalyst
the activity
As indicated
one order
K-Cu-0
700 K cannot
600 and 715 K as a function
two activity
is more
700 K. Therefore,
below
Below
For that temperature
to compare
temperatures.
for catalyst
for
K-Cu-1.
17 kcal mol -'. Only above 700 K a
It is interesting
catalyst
at about
at temperatures
We have followed
is about
at various
500 K, the pure CuC12 catalyst
The DTA spectrum
of the activity
from
is evident.
and 7, at 670 K the K-containing
dependence
different
energy
of these
ascribed
II
and the activity
to the presence
of the relative
7, the temperature
activity
above
chloride
to a DTA peak. This clearly
ten times higher
observed
is significantly
levels
tures,
copper
peak) and phase
the DTA spectrum
is related
the DTA peaks.
activity
sudden
molten
K-containing
II.
range the apparent
particles
between
of the catalyst
that catalyst
700 K, the activity
e.g.,
is also
at 565 and 654 K. We ascribe
very closely
to do a rough estimation
of both phases
As illustrated catalyst
to the
temperature.
I (low temperature
relationship
but most of the activity
to phase
in
was indeed related
of two different
jump corresponds
that the activity
amounts
we might
down to the reaction
of the K-Cu-1 catalyst
peaks are observed
processes
a clear
have a catalytic
melts,
(DTA) spectrum
them as phase
each phase from the areas similar
the we-treatment
at 600 K. For the
peak). 6 evidences
It is possible
should
pattern
than to the pre-treatment
6. Two distinct
Each activity
indicates phases.
at 715 K and then cooled
analysis
shown
temperature
was pre-treated
that the activity
rather
thermal
We will
at 600 K varying
run, the sample
indicates
A differential
phases.
to rule out this possibility
600 K. As shown in Figure 6, the rates were identical
i.e.,
both cases,
in order
rate measurements
one, it was pre-treated
temperature,
Then,
temperature.
ascribed
to phase
the deactivation
II.
patterns
we were able to measure
be
Thus, of the
62
evolution
of activity
catalyst
deactivates
indicate
that phase
deactivation
conversions.
It was observed
at 600 K than at 715 K. This
I. On the other
As shown
in a previous
on alumina-supported
of a regenerable
initial
rapidly
is at the same time more active
II
than phase
very rapidly. pronounced
at constant more
species
work
resistant
catalyst
[12], this deactivation
CuC12 catalysts
K-free
interacting
and more
hand, the K-free
that the
result would to
deactivates is much
less
due to the stabilization
with the support.
DISCUSSION K-containing
catalysts
The KCl-CuC12-CuCl
system
in their
investigations
proposed
that the promoter
energy study
of chlorine presents
melt
Likewise, the addition
while
causes
K/Cu ratios.
observed
reaction
As shown in Figures
670 K, but the opposite,
observed
the alkali-copper
describe
The sequential most
probably
chloride
We relate
melts.
Then, with
impregnation
it would the actual
throughout increases ranges
be impossible
as indicated
series,
et al. [IO], studying
gas phase chain
reaction
evolution
of chlorine
initiated
gas phase reaction
from the melt.
for which
from
particle.
We would
particles.
of these catalysts
K/Cu ratio
as the K/Cu ratio
of K on the particles points
particles.
in the catalysts increases also
to lower temperature release
as a function
correct. on CuCl-CuC12-KC1 the rate-limiting
Our results
mechanism.
is
with the
release
K-containing
trend of chlorine
this reaction
at about
of KC1 over the CuC12
However,
the concentration
mechanism,
at high
of activity
in every
the overall
be qualitatively
of the catalysts
catalyst,
of chlorine
by different
distribution
the proposed
still
activity
is the opposite
we do not imply that the same K/Cu
by the shifts of the melting
by DTA. Thus,
that
the
that at low K/Cu ratios
used for the preparation
to relate
increase
it.
then the variation
K/Cu ratio in the particles.
of the K/Cu ratio would Gorin
method
a heterogeneous
the catalyst
observed
as composed
for
it can be expected will
+
have observed
is only observed
in the extent
Of course,
They
on the K-containing
has to be maintained
the catalysts
renders
the effect
6 and 7, this trend
at 670 K to changes
ratio used for the preparation rather
while
thermodynamic
(I) solid CuC12
concentration
catalysts
indicate
in the free
in their
alkali
in the initial
i.e., lower activity
at lower temperatures.
K/Cu ratio
with
will decrease
1, our results
an increase
for the oxyhydrochlorination
shown
(II) and (III). Then,
KC1 addition
as shown in Figure of alkali
they have
KC1 + melt.
increases
of KC1 to CuC12/SiO2
excessive
et al. [I31
K/Cu ratio:
and (III) solid
for zones
by Sachtler In that case,
to a decrease
diagram
zones at increasing
pressure
of small amounts
release
of KC1 is related
phase
chlorine
studied
catalysts.
At 670 K the phase
molten
(I) but it decreases
chlorine
action
release.
(II) completely
the addition
the Deacon-type
three different
that the equilibrium zone
has been extensively
about
are consistent
It. is believed
melts,
proposed
a
step is the with
such surface-
that in the homogeneous
63 gas phase
reaction
of methane
is the H abstraction process
the rate-determining
from the CH4 molecule.
The reported is remarkably
of the two activity
6. (4 kcal mol-I). in Figures catalyst.
At the melting
the sudden
point,
although
increases
with
temperature
the rate of chlorine
production
shown
from the
chlorine
strong
atoms
below
atoms at
reaction
and, therefore,
reaction
temperature gas phase
are available,
the melting
for this
in Figure
activity
with the proposed
for a chain
is lowered
K-Cu-1
released
release
the observed
free chlorine
as expected
phase. When the temperature
atoms
energy
step
to that obtained
in the oxyhydrochlorination
seem contradictory
it is not. When enough
similar
in catalytic
mixtures
an increase
activation
for catalyst
of chlorine
at first glance,
of the rate would
mechanism,
regions
the chloride
rate [13], causing
rate. Therefore, pendence
We explain
plateau
6 and 7 in terms of the extent
higher
varies
atoms,
is 3.8 kcal mol -I [14]. This value
from the slopes
a much
with free chlorine
proceeding
dereaction
the rate in the gas
zone of the mixture,
the overall
reaction
rate decrease
dramatically. Even though speculate oroceed
a detailed
mechanism
cannot
be proposed
(i.e., primary
that at low conversions
at this time, we might
products)
the reaction
could
as follows:
- release
of free chlorine
catalyst
(CuC12-KCl)
- initiation
atoms from the catalyst:
+
of the chain
Cl' + CH4
Cl'+ used catalyst
(CuCl-KCl)
reaction: +
CH;
+
CH3C1
+ HCl
- propagation CH;
+ HCl (or C12)
+
H' (or Cl')
- termination 2 CHj
+
Cl
i
+ CH' 3
- catalyst
+ n O2
[(CUC~)~O]~
+ 2n HCl
We have detected
with molecular
oxygen
a product
2C(CuCl
+
2n CuC12 + n H20
the extent reaction
distribution
be sequentially
short
times only methyl chloromethanes
chloride
would
products
oxidation
of this reaction mechanism
during would
be formed
(e.g., formic
that some of these radicals
a secondary
independent
chlorinated
other
of oxygenated
it is possible
initiating
chain
)$u,
+
Thus,
conditions
If the proposed
would
I
small amounts
at high conversions.
expect
products
regeneration
4 [CuClln
our working
non-radical
+
2 Cl'
reaction.
applied
However,
for our catalysts
the evolution
be observed
CO)
under
was not significant.
of the catalyst
as secondary
acid,
may react
we would
composition
[15]. Methane
of the reaction.
as a primary products.
product
A simple
Thus, while
analysis
at the of
64 the selectivity
patterns
in Figures
in fact, observed
when K-containing
catalysts,
chloride
methyl
and chloroform
2-5 evidences catalysts
was the only primary
just appeared
when
the methyl
that the proposed
were
investigated.
product
chloride
while
behavior
was,
For all these
methylene
concentration
chloride
started
to
diminish. The fast decreases be ascribed reaction
in methyl
to a diffusion
proceeds
chloride
the formation
of methyl
a thin gas layer near the catalyst of methyl
chloride
even at overall
concentration,
observed
for longer
for K-containing
the promoting
KC1 concentration on the activity a Cu(I1)
by the formation is added,
However,
of KC1 on the re-oxidation
is
is hindered.
was the only product
I and II indicate
also depends
II.
than phase
Thus,
on the activity
[I21 that when
as demonstrated
by Fontana
when
chloride
KC1 is added
of the copper
in
melt
is greatly
increased.
This promoting
has been explained
however,
of KCl, which
would
deactivation.
I of our K-Cu-1
and rapidly
et al. [16], if KC1
melt
a more rapid catalyst phase
an excess
deactivates
in the presence
of that complex,
on the KC1
level but also
in excess.
chloride
complex
that
no KC1 is present,
the catalyst
to be the case for the K-rich
be inhibited This
catalyst.
catalysts
Contrasting methylene
with
chloride
isothermal
the formation
as a primary
evident
appear
catalysts,
product
The difference
product
products
that the chain
reaction
and K-Cu-1
reactor,
K-Cu-0 mechanism
catalyst
the isothermal
K-Cu-0
is reduced.
for catalyst
the K-Cu-0
for both,
between
in the non-isothermal
of secondary
is a primary
it would
the K-containing
reactors.
particularly
CH2C12
chloride
stability
effect
of a cuprous
causing
from
higher
reaction
by the support,
The formation
at high KC1 concentrations,
removed
as the gas phase
by phases
of the copper
is suppressed
greatly
in a much
of the chain
exhibited
We have shown
Cl71 in terms of the formation
appears
chlorinated,
gradient
is more easily
In addition,
in potassium
is not stabilized
oxidized.
in
in this reactor.
patterns
the rate of re-oxidation
is more easily
are evolved
takes place
low rate of diffusion
temperature
of time, methyl
not only has a negative
This rate enhancement
K-free
chlorinated.
I is richer
of C&l.
the
and so methane,
the propagation
catalysts
maintenance.
species
atoms
probably
it to be further
chloride
reactor,
of KC1 on the catalyst
Phase
make
the pronounced
periods
deactivation
effect
concentration.
Therefore,
would
Thus, methyl
low temperature
The different
effect
reactor,
is preferentially
As a consequence,
most
can
that the chlorination
as the chlorine
surface.
than in the isothermal
at a relatively
for these catalysts above
as low as 1-Z.
the gas circulation.
the surface
observed
chloride
away from the catalyst
conversions
In the non-isothermal enhances
However,
in the gas phase.
from the surface,
yields
We have proposed
phenomenum.
for which,
Thus,
yielded
and the non-
catalysts
as mentioned
it can be clearly
but not for K-Cu-1. proposed
was above,
seen that
Therefore,
for K-containing
cata-
65 lysts would
not operate
on this K-free
this catalyst,
the copper
to K-containing
particles
evolution
from catalyst
the equilibrium magnitude
K-Cu-0.
may still
K-Cu-0 must
However,
the reaction
the alkali
active
We speculate
involve
chloride
the dissociative
be able to occur non-sequential Accordingly, followed
would
chemisorption
evolution
reaction
suggest
poison
A multiple
to the surface.
distribution
of two H atoms
catalyst at low
ascribed
due to the presence
to
of KCl.
by blocking
c?loride
surface
may
s;bstitution
would
This m;~culcexplain
observed
that the chemisorption
substitution
of
chloride observed
activity
on the copper
of methane.
journey
of the product
by a selective
for the activity
act as a catalyst
of
at this temperature,
over the solid copper
may not be evident
For instance,
two orders
low in the presence
the low temperature
that surface
our data would
be very
be responsible
in each molecular
The rate of chlorine
[13]. Therefore,
must
reaction
catalyst,
on the solid surface
In this case, sites.
molten.
that, for
at 670 K, as opposed
melt at 670 K is about
reaction
a surface
On the K-Cu-1
keep in mind solid
be much lower than for K-Cu-1.
of a CuCl-CuC12
gas phase
We must
are mostly
are essentially
take place, which would
temperatures.
catalyst.
particles
than that of a KCl-CuCl-CuC12
the surface-initiated catalyst
which
pressure
higher
chloride
for catalyst
of methane
the
K-Cu-0.
would
be
by two Cl atoms.
CONCLUSIONS The main
conclusions
1. The activity
of our study can be summarized
of the silica-supported
of methane
at 670 K increases
a decrease
in activity.
2. The addition
of KC1 also
centrations
appear
But, higher
concentrations
of molten
phases.
influences
to improve
3. At 670 K, the activity
CuC12
by addition
catalysts
the catalyst
of KC1 cause
The reaction
overdoses
regeneration.
can cause
LOW KC1 con-
of the copper chloride
catalysts.
fast deactivation. catalysts
appears
for oxyhydrochlorination
of KCl. However,
the stability
of K-containing
as follows:
to proceed
can be related
to the presence
by a surface-initiated
gas
phase mechanism. 4. K-free catalysts reaction
appears
dissociative reaction
can still be active to follow
methane
a different
chemisorption.
may only be important
5. At low temperatures, K-containing
e.g.,
catalysts
at lower temperatures.
above
path, e.g., a surface
On these catalysts,
reaction
the gas phase
the
involving chain
700 K.
500 K, the solid surface reaction
because
In this case,
KC1 blocks
active
is very
low on
sites.
ACKNOWLEDGEMENTS The reaction
system was built by Mr. Hector
supported
by the Consejo
(CONICET)
and the Subsecretaria
National
T. Asencio.
de Investigaciones
de Ciencia
y Tecnica
This
research
has been
Cient'ificas y Tecnicas de Argentina.
66 REFERENCES 1
10 11 12 13
14 15 16 17
S. Rideal and H. Taylor, Catalysis in Theory and Practice, McMillan Publ., London, 1926. K. Roka and E. Kraus, U.S. Patent 1,654,821 (1925). E. Gorin. U.S. Patent 2.408.828 (1946). E. Gorin'and C.M. Fontana, 6.S. Patent 2,575,167 (1951). G. Germain and R. Mari, Bull. Sot. Chim. France, 5 (1972) 1713. H. Meissner and E. Thode, Ind. Eng. Chem., 43 (1951) 129. G. Caorara. G. Montorsi and G. LoVetere. Chim. Ind. Ital.. 50 (1968) 220. A.G. Aglulin, M. Bakshi and A.I. Gel'bshtein, Kinetika i Kataliz, 17 (1976) 670. M. Bakshi, A.G. Aglulin, M.D. Dmitrieva and A.I. Gel'bshtein, Kinetika i Kataliz, 18 (1977) 1472. E. Gorin, C.M. Fontana and G.A. Kidder, Ind. Eng. Chem., 4C (1948) 2128; Ind. Eng. Chem., 40 (1948) 2135. W.J.M. Pieters, W.C. Conner and E.J. Carlson, Appl. Catalysis, 11 (1984) 35; Appl. Catalysis, 11 (1984) 49; Appl. Catalysis, 11 (1984) 59. E.M. Fortini, C.L. Garcia and D.E. Resasco, J. Catal., 99 (1986) 12. W.M.H. Sachtler and J.N. Helle, Chemisorption and Catalysis, Inst. of Petrol., London, 1970, p.31; F. Wattimena and W.M.H. Sachtler, Stud. Surf. Sci. Catal., Elsevier Sci. Publ., 7 (1982) 816. M.L. Poutsma, Free Radicals, J.K. Kochy ed., J. Wiley, N. York, 1973. J.A. Allen and A.J. Clark, Rev. Pure and Appl. Chem., 21 (1971) 145. C.M. Fontana, E. Gorin and C.S. Meredith, Ind. Eng. Chem., 44 (1952) 373. J. Villadsen and H. Livbjerg, Catal. Rev. -Sci. Eng., 17 (1978) 203.
Report "Promoter action of KCl on CuCl2/SiO2 catalysts used for the oxyhydrochlorination of methane"