Molecular sieve abstract
Method for impregnating a Group VIII metal on a molecular sieve-binder
extrudate wherein the binder comprises a low acidity refractory
oxide binder material, which is essentially free of alumina, by
a) contacting the molecular sieve-binder extrudate with an aqueous
solution of a corresponding Group VIII metal nitrate salt having
a pH of below 8 wherein the molar ratio between the Group VIII
metal cations in the solution and the number of sorption sites present
in the extrudate is equal to or larger than 1 and b) drying the
molecular sieve-binder extrudate obtained from step a).
Molecular sieve claims
We claim:
1. A method comprising: a) contacting a molecular sieve-binder
extrudate having sorption sites, with an aqueous solution of a corresponding
Group VIII metal nitrate salt having a pH of below 8 and in the
essential absence of ammonium ions, wherein the molar ratio between
the Group VIII metal cations in the solution and the number of sorption
sites present in the extrudate is equal to or larger than 1 wherein
the binder comprises a silica binder material, wherein the number
of sorption sites in the molecular sieve-binder extrudate is reduced
prior to the impregnation of the Group VIII metal by means of a
dealumination treatment which treatment comprises contacting the
molecular sieve-binder extrudate with a solution of ammonium hexafluorosilicate;
and wherein the molecular sieve is in its H-form; and, b) drying
the molecular sieve-binder extrudate obtained from step a) in accordance
with an accelerated drying profile by which the temperature of the
molecular sieve-binder extrudate obtained from step a) is raised
to no more than 300.degree. C. and for a duration of less than 90
minutes prior to the use of the resulting dried, impregnated molecular
sieve-binder extrudate.
2. The method of claim 1 wherein the molar ratio between the Group
VIII metal cations and the number of sorption sites is between 1
and 20.
3. The method of claim 1 wherein the Group VIII metal is Ni, Pt,
and/or Pd.
4. The method of claim 1 wherein the Group VIII metal nitrate salt
is Ni(NO.sub.3).sub.2 Pt(NH.sub.3).sub.4 (NO.sub.3).sub.2 or Pd(NH.sub.3).sub.4
(NO.sub.3).sub.2.
5. The method of claim 1 wherein the molecular sieve is of the
MFI, TON, MTT or MTW type.
6. The method of claim 1 wherein step a) is performed with an aqueous
solution of the corresponding Group VIII metal nitrate salt having
a pH in the range from 3.5 to 7.
7. The method of claim 1 wherein step a) is performed by pore volume
impregnation.
8. The method of claim 1 wherein the molecular sieve is in its
H-form before impregnation.
9. A method of claim 1 wherein the accelerated drying profile
comprises the steps of: raising the temperature of the molecular
sieve-binder extrudate obtained from step a) at a rate in the range
of from 10.degree. C. to 20.degree. C. per minute to a first temperature
in the range of from 150.degree. C. to 200.degree. C.; maintaining
the first temperature for a time period in the range of from 5 to
15 minutes; thereafter raising the temperature at a rate in the
range of from 10.degree. C. to 40.degree. C. per minute to a second
temperature in the range of from 250.degree. C. to 300.degree. C.;
maintaining the second temperature for a time period in the range
of from 10 to 20 minutes; and thereafter reducing the temperature.
Molecular sieve description
FIELD OF THE INVENTION
The invention relates to a method for impregnating a Group VIII
metal on a molecular sieve binder extrudate.
BACKGROUND OF THE INVENTION
PCT patent publication No. WO-A-9641849 describes an impregnation
of platinum or palladium on a dealuminated silica-bound ZSM-5 with
an aqueous solution of tetramine platinum hydroxide or tetramine
palladium hydroxide. The impregnation of the silica-bound ZSM-5
was followed by drying for 2 hours at 120.degree. C. and calcined
for 2 hours at 300.degree. C. Thereafter the catalyst was activated
by reduction of the platinum or palladium.
A disadvantage of the impregnation method described in PCT patent
publication No. WO-A-9641849 is the long drying time. The use of
shorter drying times results in a less favourable distribution of
the platinum or palladium on the silica-bound ZSM-5. It is generally
known that a better distribution is possible when the molecular
sieve is transformed before impregnation from its H-form to a NH.sub.4
-form. By an "NH.sub.4 -form" is understood that (part
of) the H+ ions in the molecular sieve are exchanged for ammonium-ions.
An example of the transformation of a molecular sieve in a NH.sub.4
-form before impregnation is described in US patent publication
U.S. Pat. No. 5397454. This patent publication describes the impregnation
of SSZ-32 zeolite powder with palladium. Before impregnation the
zeolite was subjected to a sequence of 4 NH.sub.4 NO.sub.3 -ion
exchanges. Hereafter it was slurried into an aqueous solution of
NH.sub.4 OH. Then a tetramine palladium nitrate solution, of which
the pH was adjusted to 9.5 with NH.sub.4 OH, was added slowly.
A disadvantage of this method is the long processing time for impregnation.
It would be advantageous if the extrudate with the molecular sieve
in its H-form could be used directly in the process of impregnating
a molecular sieve-binder extrudate.
The object of the present invention is to provide a method for
impregnating a Group VIII metal on a molecular sieve-binder extrudate,
which allows a short drying time and results in a good distribution.
Short drying times are desirable when a catalyst is prepared on
a commercial scale.
SUMMARY OF THE INVENTION
This object has been achieved when the following steps are used
for impregnating a Group VIII metal on a molecular sieve-binder
extrudate wherein the binder comprises a low acidity refractory
oxide binder material, which is essentially free of alumina. In
particular it relates to a method for impregnating a Group VIII
metal on such a molecular sieve-binder extrudate by ion exchange
with an aqueous solution of a Group VIII metal salt. Such steps
comprise: a) contacting the molecular sieve-binder extrudate with
an aqueous solution of a corresponding Group VIII metal nitrate
salt having a pH of below 8 wherein the molar ratio between the
Group VIII metal cations in the solution and the number of sorption
sites present in the extrudate is equal to or larger than 1 and
b) drying the molecular sieve-binder extrudate obtained from step
a).
DETAILED DESCRIPTION OF THE INVENTION
It has been found that with the process according to the invention
a good group VIII metal distribution is obtained, while short drying
times are possible. A further advantage is that the molecular sieve
or molecular sieve-binder extrudate can be directly used in its
H-form without the need to first transform the molecular sieve in
a NH.sub.4 -form.
The choice of molecular sieve is not essential for obtaining the
advantages of the invention, namely good distribution and short
drying times. Examples of molecular sieves include metallosilicates,
metallophosphates and silica metallophosphates. Possible metallo
components in the framework of these molecular sieves include metals
such as Al, Fe, B, Ga or Ti or combinations of these metals. Preferred
molecular sieves are aluminosilicates, alumino phosphates and silica
aluminium phosphates, such as SAPO-11 SAPO-31 and SAPO-41. Especially
preferred molecular sieves are aluminosilicates, further referred
to as zeolites. Examples of suitable zeolites include ZSM-4 (Omega),
ZSM-5 ZSM-11 ZSM-12 ZSM-22 ZSM-23 ZSM-35 ZSM-48 ZSM-50 Beta,
X,Y and L as well as ferrierite and mordenite and isotypic framework
structures thereof. When the catalyst, resulting after impregnation
of the molecular sieve-binder extrudate, is to be used for catalytic
dewaxing purposes, the preferred zeolite crystallites suitably have
pores with a maximum diameter in the range of from 0.35 to 0.80
nm. Preferred zeolite crystallites include MFI-type zeolites having
pores with diameters of 0.55 and 0.56 nm, such as ZSM-5 and silicalite,
offretite having pores with diameters of approximately 0.68 nm and
zeolites of the ferrierite group having pores with diameter of 0.54
nm, such as ZSM-35 and ferrierite. Another preferred class of zeolite
crystallites include TON-type zeolites. Examples of TON-type zeolite
crystallites are ZSM-22 Theta-1 and Nu-10 as described in U.S.
Pat. No. 5336478 EP-A-57049 and EP-A-65400. A further preferred
class of zeolite crystallites are of the MTW-type. Examples of molecular
sieve crystallites having the MTW-type topology are ZSM-12 Nu-13
TEA-silicate, TPZ-3 TPZ-12 VS-12 and Theta-3 as for example described
in U.S. Pat. No. 3832449 EP-A-513118 EP-A-59059 and EP-A-162719.
A next preferred class of zeolite crystallites are of the MTT-type.
Examples of zeolite crystallites having the MTT-type topology are
ZSM-23 SSZ-32 ISI-4 KZ-1 EU-1 EU-4 and EU-13 as for example
described U.S. Pat. Nos. 4076842 4619820 EP-A-522196 EP-A-108486
and EP-A-42226.
The primary crystallite size of the molecular sieve can vary within
a wide range of 0.001 mm to 5 mm. For catalytic dewaxing purposes
the crystallite size of the zeolite may suitably be as high as 100
micron. Preferably small crystallites are used in order to achieve
an optimum catalytic activity. Preferably crystallites smaller than
10 micron and more preferably smaller than 1 micron are used.
The binder of the molecular sieve-binder extrudate comprises a
low acidity refractory oxide binder material, which is essentially
free of alumina. Suitable binder materials, then, include low acidity
refractory oxides such as silica, zirconia, titanium dioxide, germanium
dioxide, boria and mixtures of two or more of these. The most preferred
binder, however, is silica. The binder may occur naturally or may
be in the form of gelatinous precipitates, sols or gels. The binder
may also be present as a mixture of those. Preferred extrudates
are those prepared by the method described in U.S. Pat. No. 5053374.
The weight ratio of the molecular sieve and the binder can be anywhere
between 5:95 and 95:5. Lower molecular sieve content may in some
cases be advantageous for achieving a higher selectivity and higher
molecular sieve content is to be preferred when a higher activity
is desired.
After extrusion the molecular sieve-binder extrudate is dried for
a time in the range of 15 minutes to 24 hours, more preferably from
1 to 3 hours, at a temperature in the range from 10 to 350.degree.
C., more preferably from 120 to 150.degree. C. Thereafter the catalyst
composition is subjected to calcining under normal conditions, suitably
at a temperature of between 400 to 900.degree. C. by heating in
air for 1 to 48 preferably 1 to 10 hours.
Step a) of the method of the invention comprises contacting the
molecular sieve-binder extrudate with an aqueous solution of a corresponding
Group VIII metal nitrate salt having a pH of below 8 wherein the
molar ratio between the Group VIII metal cations in the solution
and the number of sorption sites present in the extrudate is equal
to or larger than 1. Preferably the molar ratio between the Group
VIII metal cations and the number of sorption sites is between 1
and 20. A sorption site is a site where theoretically one Group
VIII cation can be adsorbed. Calculation of the number of sorption
sites per gram extrudate can be done as follows. An extrudate has
a fixed value of moles H+ per gram extrudate. The number of moles
H+ per gram extrudate is determined by means of NH.sub.3 -temperature
programmed desorption (TPD) as is described in Zeolites, 19:288-396
1997. The molar number of sorption sites according to the present
invention is the number of moles H+ per gram extrudate divided by
the valency of the cation to be impregnated. The molar ratio between
the Group VIII metal cations and the number of sorption sites is
thus defined as the number of moles of the Group VIII metal cation
divided by the molar number of sorption sites as defined above.
It is to be understood that after impregnation, the resulting catalyst
(containing the modified molecular sieve-binder extrudate) may,
and normally will, contain more Group VIII metals than the amount
of which would be expected when the number of sorption sites is
taken into account. Preferably the final catalyst has a molar ratio
of Group VIII metal cations present in the extrudate and the number
of sorption sites present in the extrudate equal to the ratio defined
above.
The above mentioned ratio can be achieved in every way known in
the art. For example such a ratio can be achieved by using a high
amount or a high concentration of Group VIII metal nitrate salt
in an aqueous solution to such an extent that the above mentioned
ratio is obtained.
In a preferred embodiment the above mentioned ratio is obtained
by reducing the number of sorption sites in the molecular sieve
or molecular sieve-binder extrudate before contacting the molecular
sieve-binder extrudate with the solution in step a). The number
of sorption sites in the molecular sieve or molecular sieve-binder
extrudate can be reduced by reducing the number of acid sites of
the molecular sieve crystallites. A reduction of the number of acid
sites can be achieved by methods known in the art, for example by
subjecting the molecular sieve-binder extrudate to a hydrothermal
treatment, for example by steaming the particles at a temperature
of between 400 and 900.degree. C.
If the molecular sieve-binder extrudate contains aluminosilicates
as a molecular sieve, it has been found advantageous to subject
the molecular sieve or molecular sieve-binder extrudate to a dealumination
treatment prior to impregnation with the group VIII metal according
to the method of the invention. Dealumination results in a reduction
of the number of alumina moieties present in the aluminosilicate
and hence in a reduction of the mole percentage of acid sites and
hence in the number of sorption sites. Dealumination can be attained
by methods known in the art. Particularly useful methods are those,
wherein the dealumination selectively occurs, or anyhow is claimed
to occur selectively, at the surface of the crystallites of the
molecular sieve.
Examples of dealumination processes are described in WO-A-9641849.
Preferably dealumination is performed by a process in which the
molecular sieve or the molecular sieve-binder extrudate is contacted
with an aqueous solution of a fluorosilicate salt wherein the fluorosilicate
salt is represented by the formula:
wherein `A` is a metallic or non-metallic cation other than H+
having the valence `b`. Examples of cations `b` are alkylammonium,
NH.sub.4.sup.+, Mg.sup.++, Li.sup.+, Na.sup.+, K.sup.+, Ba.sup.++,
Cd.sup.++, Cu.sup.+, Ca.sup.++, Cs.sup.+, Fe.sup.++, Co.sup.++,
Pb.sup.++, Mn.sup.++, Rb.sup.+, Ag.sup.+, Sr.sup.++, Tl.sup.+, and
Zn.sup.++. Preferably `A` is the ammonium cation. The molecular
sieve or molecular sieve-binder extrudate material may be contacted
with the fluorosilicate salt in an amount of at least 0.0075 moles
per 100 grams of the molecular sieve or molecular sieve-binder extrudate
material. The pH is suitably between 3 and 7. An example of the
above described dealumination process is described in U.S. Pat.
No. 5157191.
The method according to the invention can suitably be used for
impregnation of any Group VIII metal, for example Pt, Pd, Ni, Ru
and Co. The corresponding Group VIII metal nitrate salt can be a
simple salt, such as for example Ni(NO.sub.3).sub.2 or a complex
salt, such as for example Pt(NH.sub.3).sub.4 (NO.sub.3).sub.2 Pd(NH.sub.3).sub.4
(NO.sub.3).sub.2 Pt(NH.sub.3).sub.6 (NO.sub.3).sub.4 or Pd(NH.sub.3).sub.6
(NO.sub.3).sub.4. For catalytic dewaxing purposes, salts of Pt,
Pd, Ni, and mixtures thereof are preferred, and Pt is especially
preferred. Preferred Group VIII metal nitrate salts for catalytic
dewaxing are Ni(NO.sub.3).sub.2 Pt(NH.sub.3).sub.4 (NO.sub.3).sub.2
and Pd(NH.sub.3).sub.4 (NO.sub.3).sub.2.
The total amount platinum, palladium or nickel, impregnated on
the molecular sieve-binder extrudate, is suitably lower than 10%
by weight calculated as element and based on total weight of molecular
sieve-binder extrudate, and preferably is in the range of from 0.01
to 5.0% by weight, more preferably from 0.1 to 1.0% by weight.
For the impregnation of the molecular sieve-binder extrudate according
to the method of the invention, use can be made of the various techniques
known in the art, such as for example circulating solution impregnation
and pore volume impregnation. Preferably pore volume impregnation
is used, which is a very time-efficient technique. In this technique
the volume of the solution containing the Group VIII metal salt,
which is contacted with the extrudate, is about equal to the pore
volume of the molecular sieve-binder extrudate to be impregnated
(see also Studies in Surface Science and Catalysis, vol. 58 Introduction
to zeolite science and practice, H. van Bekkum et.al. Elsevier,
1991 page 503).
The concentration of the aqueous solution of Group VIII metal salt
used to achieve the required amount of metal distributed on the
molecular sieve-binder extrudate can vary within wide ranges and
effects the duration of the impregnation. The preferred concentration
of Group VIII metal salt is less than 20%. When using pore volume
impregnation, the concentration is preferably within the range of
0.02 to 10.0% by weight, most preferably from 0.2 to 2.0%. The molecular
sieve-binder extrudate is contacted with the solution for a time
effective to impregnate the Group VIII metal salt. The duration
of the impregnation suitably varies from 5 minutes to 24 hours,
more preferably varies from 5 minutes to 3 hours.
The aqueous solution used in step (a) has a pH of less than 8
preferably between 3.5 and 7. The aqueous solution may contain ammonium
ions provided the pH is within the claimed range. Preferably ammonium-ions
are essentially absent from the solution.
The temperature applied in step (a) is not critical and can vary
within a range of below room temperature up to about 100.degree.
C., more preferably within a range of 15 to 65.degree. C. Preferably
the impregnation is performed at room temperature for reasons of
convenience.
The pressure may vary within wide ranges and is not critical. For
reasons of convenience the impregnation according to step (a) of
the method of the invention is preferably conducted under atmospheric
pressures.
Other metals may optionally be present in the molecular sieve or
molecular sieve-silica extrudate, before impregnation with the Group
VIII metal nitrate salt according to the method of the invention.
Step b) according to the method of the invention comprises drying
the molecular sieve-binder extrudate obtained from step a). The
in step a) modified molecular sieve-binder extrudate can suitably
be dried at temperatures ranging from room temperature to 350.degree.
C., according to any drying profile known in the art. In a preferred
embodiment the molecular sieve-binder extrudate is dried according
to an accelerated drying profile having a duration of less than
90 minutes, in which the temperature is increased from about room
temperature up to more than 200.degree. C., preferably up to more
than 250.degree. C. The drying profile can comprise a continuous,
linear or non-linear, increase of the temperature, or can comprise
stages in which the temperature is raised and stages in which the
temperature is maintained stable. For batch-wise processes a preferred
accelerated drying profile comprises the following steps: raising
the temperature at a rate in the range of 10.degree. C. to 20.degree.
C. per minute, to a temperature in the range of 150.degree. C. to
200.degree. C.; maintaining this temperature for an amount of time
in the range of 5 to 15 minutes; raising the temperature at a rate
in the range of 10.degree. C. to 40.degree. C. per minute, to a
temperature in the range of 250.degree. C. to 300.degree. C.; maintaining
this temperature for an amount of time in the range of 10 to 20
minutes; cooling down to room temperature. For continuous processes
a preferred accelerated drying profile comprises a continuous temperature
increase, wherein the increase can be gradually or wherein the rate
of temperature increase varies. The use of this accelerated drying
profile can decrease the drying time which is especially advantageous
when a catalyst is prepared on a commercial scale. As will become
clear from the examples, impregnation according to the method of
the invention allows one to use such an accelerated drying profile
while still obtaining a good distribution of the metal over the
molecular sieve-binder extrudate.
After drying, the molecular sieve-binder extrudate is optionally
calcined at a temperature between about 350.degree. C. and 500.degree.
C.
The catalyst containing the molecular sieve-binder extrudate may
be activated before use, in any way known in the art, for example
by reducing of the Group VIII cation with hydrogen.
The catalyst resulting after the treatment of a molecular sieve-binder
extrudate according to the method of the invention can be used in
any hydrocarbon conversion reaction. Examples of such hydrocarbon
conversion reactions are hydrocracking, isomerization, alkylation,
hydrogenation, dehydrogenation, polymerization, reforming, catalytic
cracking and catalytic hydrocracking. The catalyst may be suitably
used in catalytic dewaxing. By catalytic dewaxing is meant a process
for decreasing the pour point of lubricating base oil products by
selectively converting the components of the oil feed which impart
a high pour point to products which do not impart a high pour point.
Products which impart a high pour point are compounds having a high
melting point. These compounds are referred to as waxes. Wax compounds
include for example high temperature melting normal paraffins, iso-paraffins
and mono-ringed compounds. The pour point is preferably reduced
by at least 10.degree. C. and more preferably by at least 20.degree.
C. Examples of such catalytic dewaxing processes are described in
the before mentioned PCT patent publication No. 9641849.
The catalyst can be used in the catalytic dewaxing of any kind
of hydrocarbon feed. Suitably the catalyst can be used in the catalytic
dewaxing of lubricants, base oil products, gas oils and feeds having
relatively high amounts of waxy compounds. Examples of feeds with
a high amount of waxy compounds are synthetic waxy raffinates (Fischer-Tropsch
waxy raffinates), hydrocracker bottom fractions (hydrowax) and slack
waxes obtained from the dewaxing of hydroprocessed or solvent refined
waxy distillates.
The method of the invention will now be illustrated by the following
non-limiting examples.
Comparative example A
ZSM-5/silica extrudate (30%/70% w/w, calcined at 800.degree. C.)
was treated with a 0.01 M aqueous ammonium hexafluorosilicate (AHS)
solution, washed, dried and calcined. The extrudate contained 0.048
H+ mmoles/gram extrudate. Hereafter 22.65 gram of the extrudate
was impregnated with about 0.7% w/w platinum by pore volume impregnation
in 5 minutes with 16.23 ml of a 5.0 M aqueous solution containing
2.79 gram of a tetramine platinum hydroxide (Pt(NH.sub.3).sub.4
(OH).sub.2)-solution (5.9% w/w Pt). The pH of the solution was >8.
The impregnated extrudate was not washed, but dried according to
a slow drying profile by; drying during 2 hours at 120.degree. C.;
whereafter the temperature was raised with 25.degree. C./minute
to 190.degree. C. and held stable during 1 hours; whereafter the
temperature was raised again with 50.degree. C./minute to a temperature
of 300.degree. C. and held stable during 1 hour. Hereafter the extrudate
was cooled down to room temperature. The 0.048 H+ mmoles/gram extrudate
correspond with 0.024 mmoles sorption sites for Pt 2+ cations. 22.65
gram extrudate contains 0.54 mmoles sorption sites. From the above
it can be calculated that the solution contained 0.84 mmoles Pt2+
cations. Thus the molar ratio between the Pt 2+ cations and the
number of sorption sites was 1.55. The obtained platinum distribution
was examined visually and was satisfactory.
Comparative example B
ZSM-5/silica extrudate (30%/70% w/w, calcined at 800.degree. C.)
was treated with 0.01 M AHS, washed, dried and calcined. The extrudate
contained 0.048 H+ mmoles/gram extrudate. Hereafter 29.15 gram of
the extrudate was impregnated with about 0.7% platinum by pore volume
impregnation in 5 minutes with 20.96 ml of an aqueous solution containing
3.59 gram of a tetramine platinum hydroxide (Pt(NH.sub.3).sub.4
(OH).sub.2)-solution (5.9% w/w Pt). The pH of the solution was >8.
The extrudate was not washed but dried by an accelerated drying
profile; by raising the temperature with 15.degree. C./minute to
180.degree. C.; maintaining this temperature for 10 minutes; raising
the temperature again with 30.degree. C./minute to 290.degree. C.;
maintaining this temperature for 15 minutes. Hereafter the extrudate
was cooled down to room temperature. The molar ratio between the
Pt 2+ cations and the number of sorption sites was 1.55. No distribution
of the platinum was obtained since the tetramine platinum hydroxide
complex did not decompose.
EXAMPLE 1
ZSM-5/silica extrudate (30%/70% w/w, calcined at 800.degree. C.)
was treated with 0.01 M AHS, washed, dried and calcined. The extrudate
contained 0.048 H+ mmoles/gram extrudate. Hereafter 29.15 gram of
the extrudate was impregnated with about 0.7% w/w platinum by pore
volume impregnation in 5 minutes with 20.96 ml of an aqueous solution
containing 6.82 gram of a tetramine platinum nitrate (Pt(NH.sub.3).sub.4
(NO.sub.3).sub.2 -solution (2.99% w/w Pt) The pH of the solution
was about 6. The extrudate was not washed but dried and calcined
by an accelerated drying profile; by raising the temperature with
15.degree. C./minute to 180.degree. C.; maintaining this temperature
for 10 minutes; raising the temperature again with 30.degree. C./minute
to 290.degree. C.; maintaining this temperature for 15 minutes.
Hereafter the extrudate was cooled down to room temperature. The
molar ratio between the Pt 2+ cations and the number of sorption
sites was 1.49. A good platinum distribution was obtained.
EXAMPLE 2
ZSM-5/silica extrudate (30%/70% w/w, calcined at 800.degree. C.)
was treated with an AHS solution, washed, dried and calcined. The
extrudate contained 0.048 H+ mmoles/gram extrudate. Hereafter 47.96
gram of the extrudate was impregnated with about 0.7% w/w Nickel
by pore volume impregnation in about 15 minutes with 30.74 ml of
a aqueous solution containing 1.68 gram of a nickel nitrate salt
(Ni(NO.sub.3).sub.2.6H.sub.2 O). The pH of the solution was about
4. The extrudate was washed and dried and calcined by an accelerated
drying profile; by raising the temperature with 15.degree. C./minute
to 180.degree. C.; maintaining this temperature for 10 minutes;
raising the temperature again with 30.degree. C./minute to 300.degree.
C.; maintaining this temperature for 15 minutes. Hereafter the extrudate
was cooled down to room temperature. The molar ratio between the
Ni 2+ cations and the number of sorption sites present in the extrudate
was 5.0. A good nickel distribution was obtained.
A summary of the results obtained in the examples is given in Table
1. In Comparative example A, a satisfactory distribution result
was obtained by using tetramine platinum hydroxide and a slow drying
profile. When an accelerated drying profile was used instead of
the slow drying profile, as illustrated in Comparative example B,
the tetramine platinum hydroxide complex was found not to decompose.
When this catalyst was subsequently activated in a reductive atmosphere,
a migration of Pt to the exterior of the catalyst was observed,
resulting in an unacceptable loss of performance. Examples 1 and
2 show that an accelerated drying profile can be used, while obtaining
at the same time full decomposition of the complex as well as a
good distribution, when a Group VIII metal nitrate complex is used
according to the invention.
TABLE 1 pH of ratio of Group Ex- Group VIII the Form of the VIII
metal peri- metal salt solu- molecular drying cations over Distribution
ment used tion sieve profile sorption Sites result A Pt(NH.sub.3).sub.4
(OH).sub.2 >8 H-form slow 1.55 satisfactory B Pt(NH.sub.3).sub.4
(OH).sub.2 >8 H-form accelerated 1.55 the complex did not decompose
1 Pt(NH.sub.3).sub.4 (NO.sub.3).sub.2 .+-.6 H-form accelerated 1.49
good 2 Ni(NO.sub.3).sub.2.6H.sub.2 O .+-.4 H-form accelerated 5.0
good |