Note: Descriptions are shown in the official language in which they were submitted.
WO90/08~92 PCT/GB90/00l30
2~ S6~
CATALYST
This invention relates to catalysts. In
particular it relates to a Group VIII metal catalyst.
According to the present invention there is
provided a catalyst comprising a supported reduced Group
VIII metal comprising a support and up to about 10 percent
by weight of a Group VIII metal which is characterised by a
Group VIII metal surface area of at least about 45 m2/g of
Group VIII metal present in the catalyst as measured by
adsorption of carbon monoxide thereon.
In measuring the Group VIII metal surface area we
have assumed that the are~ occupied by an adsorbed carbon
monoxide molecule is 16.8 x 10 20 m2 (16.8 A2).
In contrast to the catalysts of the present
invention, which are characterised by a Group VIII metal
surface area of at least about 45 m2/g of Group VIII metal
present in the catalyst, we have found that a supported
Group VIII metal catalyst Drepared from the same catalyst
precursor by a conventional pre-reduction technique has an
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exposed Group VIII metal surface area that is significantly
lower than about 45 m2/g of Group VIII metal present in the
catalyst.
The li~erature suggests that the catalytic
activity of Group VIII metal hydrogenation catalysts is due
to the reduced metal particles present following pre-
reduction. Hence it follows that the activity of the
catalyst will tend to bear a more or less direct
relationship to the exposed surface area of reduced metal.
Thus the larger is the surface area of exposed reduced
metal, the greater will be the activity of the catalyst. In
the limit the Group VIII metal is in the form of individual
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metal atoms on the support.
In preferred forms of catalyst in accordance with
the invention substantially all of the Group VIII metal
content thereof is present as particles of reduced metal.
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WO90/08592 PCT/GB90/00130
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The catalyst precursors contain a Group VIII metal
oxide or salt and a support. Suitable precursors can be
obtained by impregnation of a support with a solution of a
Group VIII metal salt, followed if desired by ignition.
Coprecipitation can be used in suitable cases. Methods of
making suitable catalyst precursors are well known to those
skilled in the art of catalyst manufacture. Such catalyst
precursors consist, it is believed, of crystallites of a
reducible form of the Group VIII metal more or less
uniformly distributed over the support. The size of these
crystallites will depend upon the conditions prevailing
during preparation of the catalyst precursor. The smaller
that such crystallites are, the larger the surface area of
metal in the reduced catalyst can be, it is postulated.
Thus the method of manufacture of the catalyst precursor
will have an influence on the final surface area of Group
VIII metal in the reduced catalyst, as will also the method
of catalyst reduction used.
The Group VII~ metal may be any of those
conventionally used in production of supported catalysts,
especially those used for production of Group VIII metal
hydrogenation catalysts. Examples include platinum,
palladium, rhodium and ruthenium.
Any suitable support can be used, for example
alumina, silica-alumina, thoria, silicon carbide, titania,
chromia, zirconia, or carbon. The Group VIII metal content
of the catalyst precursor will usually range from about
0.01% by weight up to about 10% by weight, typically up to
about 5% by weight of the catalyst precursor, e.g~ about
0.5% by weight.
The catalyst precursor is typically in the form
of a powder having a particle size of not more than about
100 ~m~ Such a powder may be forme~ by conventional
techniques into any conventional catalyst shape, such as
cylindrical pellets, rings, saddles or the like using the
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- W090/08592 PCT/GB90/~0130
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usual binders, and die lubricants, so that the material can
be used in fixed bed operations.
The invention also provides a process for
producing a catalyst in which a supported Group VIII metal
catalyst precursor is subjected to a pre-reduction treatment
by heating in a hydrogen containing atmosphere at a pre-
reduction temperature at which appreciable pre-reduction of
the catalyst can be detected characterised in that, prior to
effecting said pre-reduction treatment, the catalyst
precursor is subjected to an ante-pre-reduction treatment by
soaking it under hydrogen starvation conditions in an
atmosphere comprising a major amount of an inert gas and a
minor amount only of hydrogen at a temperature below said
pre-reduction temperature. Conveniently heating to said
pre-reduction temperature rom ambient temperature is
effected in said atmosphere. Hydrogen starvation conditions
are maintained throughout the ante-pre-reduction step of the
process of the present invention, that is to say the
catalyst precursor is always starved of hydrogen so that the
rate of reduction of Group VIII metal oxide or salt is
limited by the availability of hydrogen at the catalyst
precursor surface. In this way the rate of reduction to
Group VIII metal is conducted at a controlled rate. This
procedure differs from procedures conventionally
recommended by manuacturers of such catalyst precursors in
that heating from ambient temperature up to about 140C is
effected throughout in the presence of a gas mixture
containing only a minor amount of a reducing gas rather than
in the conventional manner in a 100% hydrogen atmosphere.
It is not known exactly what mechanism may ~e involved in
production of an active Group VIII metal catalyst from the
catalyst precursor but it would appear that the mechanism
involves reduction of at least a portion of the Group VIII
metal oxide or salt present on the support to the
corresponding Group VIII metal.
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Wo90/085g2 ~ PCr/GB90/00130
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It would appear that, although no discernible
reaction can be detected between the catalyst precursor and
the hydrogen containing gas at temperatures below the pre-
reduction temperature (which is typ:ically about 14~C), yet
some miniscule amounts of Group VIII metal oxide or salt are
in fact reduced whereby sub-microscopic nucleation of Group
VIII metal atoms occurs in a manner analogous to the sub-
microscopic nucleation of silver atoms that occurs upon
exposure o~ a photographic film in a camera. Although the
latent image cannot be detected visually in an exposed
photographic film yet it can be rendered visible as a result
of the conventional development process by exposure to a
reducing agent. In an analogous fashion, it is postulated,
the ante-pre-reduction step of the present invention
produces a "latent image" consisting of numerous sub-
microscopic nucleations of Group VIII metal atoms which can
grow individually to form a large number of small particles
of Group VIII metal, thus ensuring that the resulting
reduced Group VIII metal catalyst has a correspondingly
large exposed surface area of Group VIII metal. On the
other hand, if conventional pre-reduction techniques are
used, so that rapid pre-heating to temperatures of about
180C and higher in the presence of a hydrogen-containing
gas is used, or if the catalyst precursor is pre-heated to a
temperature of at least about 180C in an inert gas
atmosphere prior to contact with a hydrogen-containing gas,
the first relatively few nucleations of Group VIII metal
atoms that form serve as a focus for subse~uent reduction of
Group VIII metal oxide or salt to metal, with the result
that relatively large crystallites of Group VIII metal may
~orm, thus resulting in a lower exposed surface area of
Group VIII metal and in a lower catalyst activity in
hydrogenation reactions.
By adopting a suitable temperature~time profile
and monitoring the inlet and exit gas compositions to and
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WO9Ot08592 PCT/GBsO/00l30
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from the pre-reduction zone, it can be ensured that any
reactions involved in the ante-pre-reduction step or soaking
step occur always at the lowest possible temperature and are
permitted to occur as completely as possible before the
temperature is again raised significantly. In addition any
heat produced as a result of exothermic ante-pre-reduction
reactions is removed by the hydrogen containing gas with
minimum risk of thermal damage to the catalyst.
The process of the invention involves use of a gas
soaking step. In this gas soaking step no liquid is present
but the gas is allowed to permeate fully the catalyst
precursor and to equilibriate therewith.
In the gas soaking step of a preferred process o~
the invention the Group VIII metal catalyst precursor is
maintained in a hydrogen containing atmosphere at
temperatures intermediate ambient temperature ~e.g. about
15C to about 25C, typically about 20C) and the pre-
reduction temperature ~which is typically about 180C). Gas
soaking can be commenced at temperatures below ambient
temperature, e.g. 0C or below. In this gas soaking step
the hydrogen containing atmosphere typically contains
hydrogen in a minor amount only, typically not more than
about 1% by volume and preferably 0.5~ by volume or less, in
addition to an inert gas, such as nitrogen" helium or argon.
Although it is preferred to heat the catalyst precursor
during the gas soaking step from ambient temperature to the
pre-reduction temperature throughout in a hydrogen
containing atmosphere, it is alternatively possible to
commence heating in an inert gas atmosphere, and to
introduce the hydrogen containing atmosphere at ambient
temperature (if heating from below ambient temperature is
taking place) or at a moderately elevated temperature (e.g.
about 40C to about 50C). It is, however, an essential
feature of the process that, the nearer the temperature
during the gas soaking step reaches the pre-reduction
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W090/08592 PCT/G~90/00130
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temperature, the more important it is that the catalyst
precursor be always in contact with a hydrogen containing
gas atmosphere but with the catalyst precursor still under
hydrogen starvation conditions.
In the gas soaking step of a preferred process of
the invention the catalyst precursor is heated under
controlled conditions from ambient temperature (e.g. about
20C) in a stream of a hydrogen containing gas at a suitable
gaseous hourly space velocity, e.g. about 500 hr~1 to about
6000 hr 1. The hydrogen containing gas preferably comprises
a mixture of a minor amount of hydrogen (typically less than
about 1% by volume) and a major amount of one or more inert
gases, such as nitrogen, argon, neon, methane, ethane,
butane, or a mixture of two or ~ore thereo~. In a
particularly preferred process the reducing gas is a mixture
of a minor amount of hydrogen ~preferably less than about
0.5% by volume o~ hydrogen~ e.g. about 0.2~ by volume) and a
major amount of nitrogen, preferably substantially oxygen-
free nitrogen.
The gas soaking step of the process of the
invention may be operated at normal or reduced pressure but
is preferably operated at an elevated pressure in the range
of from about 1 bar to about 20 bar, preferably from about 2
bar to about 10 bar.
The partial pressure of the hydrogen need be no
more than about 0.01 bar, and can be in the range of from
about 0.0005 bar up to ab~ut 0.005 bar, during the gas
soaking step.
In a particularly preferred process of the
invention the catalyst precursor is heated from ambient
temperature to about 140C in a reducing atmosphere
containing a minor amount of hydrogen. Preliminary heating
of the catalyst precursor from ambient temperature to about
140C is preferably effected at a controlled rate; typically
this preliminary heating step takes from about 12 hours to
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WO90/08592 PCT/GB90/00l30
about 48 hours or more, e.g. about 24 hours. The
temperature can be increased at a substantially linear rate
during the soaking step or can be increased in an
approximately stepwise fashion, in steps of, for example
about 5C to about 10C, followed by periods during which
the temperature is maintained substantially constant before
the temperature is raised again. Over the range of from
about 140C to about 180C heating may follow any
` temperature-time curve, provided that the rate of heating is
such that at all times the catalyst precursor is maintained
under reducing conditions with the inlet and exit gas
compositions to the pre-reduction zone being substantially
identical one to another. Preferably the temperature is
; ~ increased in an approximately linear fashion from about
140C to about 180C. In one procedure heating is carried
out in a series o~ steps, conveniently steps of
approximately 10C, and a careful check of the inlet and
exit gas compositions to the pre-reduction zone is made
before, during and after each heating step~ Under typical
operating conditions the rate of increase of temperature
over the temperature range from about 140C to about 180C
is from about 1C/hour up to about 15C/hour, e.g. about
10C/hour.
In this heating step from about 140C to about
180C the gas flow rate generally corresponds to a gaseous
hourly space velocity ~measured at 0C and 1 bar) of from
about 400 hr~l to about 6000 hr~l or more, e.g. about
3000 hr~ .
The composition of the hydrogen containing gas is
dependent upon the operating pressure; the higher the total
pressure is, the lower is the maximum permitted hydrogen
concentration. Conversely, the lower the total pressure is
,~ the higher can be the concentration of hydrogen in the..
reducing gas. Typically the H2 concentration is from about
0.01% v/v up to about 1% v/v, e.g. about 0.2~ v/v, under
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WO90/08~92 ~ ~3~ PCT/GB90/~0130
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preferred operating conditions.
Once the catalyst precursor has reached the final
temperature of about 180C the hydrogen partial pressure is
gradually increased. However, during this phase of catalyst
activation the inlet and exit gas compositions to the pre-
reduction zone should still be closely monitored so that the
two compositions are substantially identical at all times.
Further heating up to about 210C or more can then be
carried out if desired.
It is important to ensure that, when the catalyst
precursor reaches the pre-reduction temperature, there
should not be a substantial excess of hydrogen present so as
to minimise any danger of damage to the catalyst resulting
from a thermal runaway due to the exothermic catalyst pre-
reduction step.
The pre-reduced catalyst produced in accordance
with the teachings of the invention is sensiti~e to
oxidation, probably due to some re-oxidation of Group VIII
metal particles. Hence the pre-reduced catalyst is
preferably maintained under an inert gas or hydrogen
containing atmosphere after it has been prepared.
The catalysts of the invention can be used in a
wide variety of reactions for hydrogenation of an
unsaturated organic compound to produce at least one
hydro~enation product thereof.
The invention is further illustrated in the
following Examples.
Examples 1 and 2
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Two samples of PG 88/10 0.5% Ru on alumina
catalyst precursor tobtainable from Davy McKee tLondon)
Limited of Davy House, 68 Hammersmith Road, London, W14 8YW)
in the form of 3.0 x 3.0 mm pellets were in each case loaded
into a reaction chamber. The amount of catalyst precursor
was between 2~5 g and 2.6 g in each case and was carefully
~ weighed. Oxygen-free nitrogen was passed through the
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WO90/08592 PCT/GB90/00130
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reaction chamber at an exit pressure of 4.45 bar and a flow
rate of 200 litres/hour (measured at 0C and 1 bar) at room
temperature ~20C) for 30 minutes. Then hydrogen was
admitted to the nitrogen flow to give a 0.2% hydrogen in
nitrogen flow at the same total flow rate. The temperature
of the reaction chamber was gradually raised at 5C per hour
to 140C, the 0.2% hydrogen in nitrogen flow being
maintained at the same flow rate. The inlet and outlet
gases were cont~nuously monitored by thermal conductivity.
The hydrogen level in the gas flow was then gradually
increased in small steps to 1% over approximately 24 hours.
When no further uptake of hydrogen could be detected, the
temperature was increased at 15C per hour to 160C and
maintained at this temperature until the inlet gas
composition was the same as the outlet gas composition, thus
indicating that hydrogen uptake had ceased. The catalyst
temperature was then increased over a period of 2 hours to
180C. Next the hydrogen level was gradually increased to
100% with the catalyst temperature still at 180C and the
system conditions maintained for a period of 18 hours. When
a 100% hydrogen gas flow had been established the
temperature is increased to 200C and maintained at this
level for 1 hour before the catalyst is used.
After this reduction procedure, ~he catalyst was
cooled in an oxygen free helium flow to 20C, and the
ruthenium surface area was determined by reaction of the
reduced ruthenium surface with carbon monoxide. Assuming
that one molecule of carbon monoxide occupies 16.8 x 10-2
m2 (16.8 A~) of surface, the extent of reaction, and hence
the number of carbon monoxide molecules adsorbed on the
ruthenium surface, was determined by successive injections
of carbon monoxide into the helium flow until no further
reaction was detected. In this way an area of exposed
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metallic ruthenium in the reduced catalyst was calculated.
j The following uptakes and the corresponding Ru
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WO90/08592 PCT/GB90/00130
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metal surface areas were recorded:-
TABLE 1
Example Amount CO reacted 1 Ru Surface Area 1
No. (molecules/q) tm2/q of catalvst ~ m2/g Ru)_¦
1 1.70 x 1ol8 0.287 57.4
2 1.43 x 1018 0.240 48.0
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ComDarative ExamDles A and B
Comparative runs using the same catalyst precursor
as was used in Examples 1 and 2 were carried out in the
following mannex.
The reaction chamber was charged in each case with
a further 3ml sample of the catalyst precursor pellets. The
catalyst prec1rsor was heated to 210C over a period of 1.5
hours in a 100% hydrogen stream dt an exit pressure o~ 4.45
bar and a gaseous hourly space velocity of 3000 hr 1 and
maintained at this temperature for 30 minutes before
characterisation.
Using the carbon monoxide reaction technique of
Examples 1 and 2 the following results were obtained:-
TABLE 2
¦Compar. ¦ Amount CO reacted ¦ Ru Surface Area
tmolecules/q) _ tm2/q = catalyst~_¦ (m
A 7.9 x ~ol7 0.134 26.8
I_ - 1.03 x 1013 0.173 34.6
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Comparison of these results shows that the gas
, soaking step of Examples 1 and 2 leads to a greatly
' increased ruthenium surface area compared with that obtained
'. in the corresponding one of Comparative Examples A and B.
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W090tO8592 PCT/GB90/00l30
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Examples 3 to 6
In these Examples a sample of catalyst was in each
case loaded into the reactor of Example 1 and subjected to
the following steps:
1. O2-free nitrogen at 4.45 bar was passed through
the reactor at room temperature at a gaseous hourly space
velocity of 1800 hr~l; this gaseous hourly space velocity
was maintained throughout the experiment.
2. 0.2% H2 in N2 was flowed over the catalyst at 20C
for 24 hours.
3. The temperature was raised at 5C per minute to
140C whilst monitoring the inlet and outlet gas
compositions.
4. When the inlet and outlet gas compositions were
equal the H2 content was slowly raised to 1% over 24 hours.
5. The temperature was raised to 160C at 0.25C per
minute and held at 160C for 4 hours, after which the inlet
and outlet compositions were equal.
6. The H2 content was increased slowly to 5~ over 4
hours and the gas flow was maintained at this concentration
for a further 4 hours.
; 7. The temperature was raised to 180C at 0.25C per
minute and maintained at this value for a further 4 hours.
8. The temperature was further increased to 200C at
0.25C per minute and then the H2 content was gradually
increased to 100% over the next 6 to 8 hours.
9. The 100% H2 gas was maintained at 200C for a
minimum of a further 8 hours.
,i'~ 10. The system was flushed with 100% N2 at 200C and
then cooled to 25C under N2 for subsequent adsorption
' studies.
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~- their ability to chemisorb carbon monoxide irreversibly in a
.
pulsed flow dynamic mode, using the following experimental
technique:
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WO90/08592 PCT/GB90/00130
11. The system was flushed at 25C with pure helium at
a gaseous hourly space velocity of 1800 hr 1.
12. A 500 ~1 pulse of 5~ carbon monoxide in helium was
injected into the flowing gas stream and the amount of
carbon monoxide eluted from the reactor measured by a
thermal conductivity detector. The amount of CO in the
pulse adsorbed by the catalyst sample was then calculated as
the difference between the area of the peak obtained from a
standard 500~1 5% CO in the pulse and that of the eluted
peak following adsorption.
13. Step 12 was repeated until it was evident that no
further adsorption was occurring. From the results obtained -
the total amount of CO which was irreversily adsorbed was
, determined.
- Since the dynamic pulsed flow mode of adsorption
only gives the amount of irreversibly adsorbed carbon
monoxide, it is important to determine the total amount of
carbon monoxide adsorbed in order to determine the metal
area of the catalyst. This was achieved using a radiotracer
method to determine the 14C carbon monoxide adsorption
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isotherm under static conditions at 25C, i.e. at the same
temperature as was used in the dynamic pulsed flow
experiments. The fraction of CO irreversibly adsorbed was
determined by flushing the catalyst sample with a flow of
helium and determining the decrease in surface count rate
due to removal of the reversibly adsorbed species. With all
samples examined the amount of irreversibly adsorbed C0
represented 50 +2% of the total adsorption capacity of the
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catalyst.
; The areas of exposed metal in the reduced catalyst
; were then determined from the absolute amounts of carbon
- monoxide irreversibly adsorbed using the dynamic pulsed flow
- procedure described above. In each case the amount of
irreversibly adsorbed carbon monoxide was assumed to be 50%
of the total adsorbed carbon monoxide capacity of the
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WO90/08592 PCT/GB90/00130
~ - 13 ~ 2~
catalyst. Assuming that the carbon monoxide is adsorbed in
a linear form, which is confirmed by infra red spectra, and
that the area of the adsorbed carbon monoxide molecule is
16.8 x 10 20 m2 (16.8 A2), the total area of the metal was
calculated.
Four portions of PG 88/10 0.5% Ru on alumina
catalyst precursor taken from two different batches were
used in Examples 3 to 6; these batches are identified as
samples A and B. Two portions, those of Examples 3 and 5,
were from samples A and B respectively in unreduced form;
those of the other two Examples 4 and 6 were portions from
samples A and B respectively which had been subjected to a
conventional pre-reduction technique followed by exposure to
air. The results obtained are set out in Table 3 below.
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WO90/08592 PCT/GB90/00130
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It will be seen by comparison of the results for
Examples 3 and 4, which are identical apart from the fact
that sample A had been already pre-reduced, that the method
by which the initial reduction step is performed has a
critical influence on the exposed surface area of metal in
the reduced catalyst. Thus conventional pre-reduction
apparently leads to some aggregation of reducible
- ruthenium-containing crystallites in the catalyst precursor,
whilst the method of the invention does not produce such
aggregation. Similar results are observed from Examples 5
and 6, which are identical apart from the fact that the
catalyst of Example 6 had been subjected to a conventional
,~ pre-reduction step. ~Examples 3 and 5 demonstrate catalysts
falling within the ambit of the invention but Examples 4 and
6 do not).
~ ~i Com~arative Examples C to G
,, In this Comparative Example further portions of
catalyst samples A and B were subjected to pre-reduction by
~;, a conventional technique in the reactor of Example l. This
,; pre-reduction regime consisted of the following steps:-
ydrogen at 4.45 bar was passed through the
reactor at 25C at a gaseous hourly space velocity of 1800
~, ~ hr~l.
; , 2. The temperature was increased, w~ile maintaining
the hydrogen flow rate, at 10C per minute to 200C.
3. The catalyst was maintained for a minimum of ll
; hours under these conditions.
4. The reactor was flushed with 100% N2 at 200C and
cooled to 25C whilst maintaining the N2 flow.
5. The CO adsorption method described in Examples 3
~ ; to 6 was then used to determine the metal surface area.
!', "`'' The results obtained are set out in Table 4 below.
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It will be noted that, in contrast to the results
of Examples 3 to 6, the metal surface area measured
following the conventional pre-reduction technique of these
Conmparative Examples did not change significantly between
the unreduced and pre-reduced samples, whereas using the
method of the invention set out in Examples 3 to 6, the
metal surface area from the unreduced catalyst precursor was
approximately double that from the pre-reduced samples.
Example 7
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.` Following the general procedure of Examples 3 to 6
;; there are treated samples of the following catalysts with
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. similarly good results:
'i 0.1% Pt on alumina
,,. 0.1% Rh on alumina
~ 0.1% Pd on alumina
i . 0.1% Ru on carbon
0.1% Pt on carbon
0.1% Rh on carbon
0.1% Pd on carbon.
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