Cobalt catalysts

Details Cobalt catalysts Cobalt catalysts

2002-05-31

2004-10-19

Nguyen, Cam N. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S327000, C502S260000, C502S074000, C502S066000

Reexamination Certificate

active

06806226

ABSTRACT:

THIS INVENTION relates to cobalt catalysts. It relates in particular to a cobalt catalyst precursor, to a process for preparing a cobalt catalyst precursor, and to a process for preparing a cobalt catalyst.
Processes for preparing cobalt catalysts are, in general, well defined in the literature. For example, U.S. Pat. No. 5,733,839 describes a process for preparing an impregnated Fischer-Tropsch catalyst comprising an alumina carrier and an active component selected from the group consisting of cobalt, iron and mixtures thereof. However, it is an object of the present invention to provide a supported cobalt catalyst having higher productivities than known cobalt catalysts.
Thus, according to a first aspect of the invention, there is provided a cobalt catalyst precursor which includes a catalyst support impregnated with cobalt, with all reducible cobalt being present in the support as supported cobalt oxide of formula-unit CoO
a
H
b
, where a≧1,7 and b≧0.
In other words, according to the first aspect of the invention, there is provided a cobalt catalyst precursor which includes a catalyst support that has been impregnated with cobalt and calcined in such a manner that all reducible cobalt present therein, ie cobalt that is associated with the elements hydrogen and oxygen in the absence of cobalt-support interaction, such as the formation of cobalt aluminates or cobalt silicates, that would decrease its reducibility, is present as the supported cobalt oxide of formula-unit CoO
a
H
b
, where a≧1,7 and b≧0.
Thus, for example, all the reducible cobalt could be present as Co
2
O
3
.H
2
O or CoO(OH), ie where a=2 and b=1. However, instead, the reducible cobalt may be present, for example, as a mixture of Ci
3
O
4
and CoO(OH) or Co
2
O
3
.H
2
O with 45% of the reducible cobalt in the catalyst precursor being present as Co
3
O
4
and 55% of the reducible cobalt being present as CoO(OH) or Co
2
O
3
.H
2
O. This would result in a catalyst precursor in which all the reducible cobalt is present as supported cobalt oxide of formula-unit CoO
a
H
b
where a=1,7 and b=0,55. Another example would be a mixture of Co
2
O
3
and CoO(OH) or Co
2
O
3
.H
2
O with 60% of the reducible cobalt being present as Co
2
O
3
and 40% of the reducible cobalt being present as CoO(OH) or Co
2
O
3
.H
2
O. This would result in a catalyst precursor in which all of the reducible cobalt is present as supported cobalt oxide of formula-unit CoO
a
H
b
where a=1,7 and b=0,4.
The catalyst precursor may contain between 5 gCo/100 g support and 70 gCo/100 g support, preferably between 20 gCo/100 g support and 50 gCo/100 g support, more preferably between 25 gCo/100 g support and 40 gCo/100 g support.
According to a second aspect of the invention, there is provided a process for preparing a cobalt catalyst precursor, which process includes
in a support impregnation stage, impregnating a particulate porous catalyst support with a cobalt salt, and partially drying the impregnated support; and
in a calcination stage, calcining the partially dried impregnated support to obtain the cobalt catalyst precursor, with the calcination being effected at calcination conditions selected so that all reducible cobalt is present in the support as a supported cobalt oxide of formula-unit CoO
a
H
b
, where a≧1,7 and b≧0.
The resultant cobalt catalyst precursor will, in practice, be reduced to obtain a cobalt catalyst, which will thus have enhanced productivities as compared to catalysts of which Co
3
O
4
is the preferred product of calcination.
According to a third aspect of the invention, there is provided a process for preparing a cobalt catalyst, which process includes
in a support impregnation stage, impregnating a particulate porous catalyst support with a cobalt salt, and partially drying the impregnated support;
in a calcination stage, calcining the partially dried impregnated support to obtain a cobalt catalyst precursor, with the calcination being effected at calcination conditions selected so that all reducible cobalt is present in the support as a supported cobalt oxide of formula-unit CoO
a
H
b
, where a≧1,7 and b≧0; and
in a reduction stage, reducing the cobalt catalyst precursor, to obtain the cobalt catalyst.
The cobalt salt may, in particular, be cobalt nitrate, Co(NO
3
)
2
.6H
2
O.
Any commercially available porous oxide catalyst support, such as alumina (Al
2
O
3
), silica (SiO
2
), titania (TiO
2
), magnesia (MgO), and silica-alumina, may be used. The support preferably has an average pore diameter between 8 and 50 nanometers, more preferably between 10 and 15 nanometers. The support pore volume may be between 0,1 and 1,0 ml/g, preferably between 0,3 and 0,9 ml/g. The average particle size is preferably between 1 and 500 micrometers, more preferably between 10 and 250 micrometers, still more preferably between 45 and 200 micrometers.
The support may be a protected modified catalyst support, containing, for example, silicon as a modifying component, as described in WO 99/42214, which is hence incorporated herein by reference.
The impregnation of the catalyst support may, in principle, be effected by any known impregnation method or procedure such as incipient wetness impregnation or slurry phase impregnation. However, the impregnation stage may, in particular, comprise a process as described in WO 00/20116, and which is thus incorporated herein by reference. The support impregnation stage may thus involve a 2-step slurry phase impregnation process, -which is dependent on a desired cobalt loading requirement and the pore volume of the catalyst support.
During either of the two slurry phase impregnation steps, a water soluble precursor salt of palladium (Pd), platinum (Pt), ruthenium (Ru), or mixtures thereof, may be added, as a dopant capable of enhancing the reducibility of the cobalt. The mass proportion of the palladium, platinum or ruthenium metal, or the combined mixture of such metals when such a mixture is used, to the cobalt metal may be between 0,01:100 to 0,3:100.
The support impregnation and drying may typically be effected in a conical vacuum drier with a rotating screw or in a tumbling vacuum drier.
In the calcination stage, the calcination may include passing hot air over and around the partially dried impregnated support, thereby drying the impregnated support further by removal of residual moisture present therein; and calcining the resultant dried impregnated support by decomposition of the cobalt salt into decomposition products comprising oxide(s) and any water of hydration, with the decomposition products being released in vapour form, to enhance formation of a supported catalyst precursor containing the supported cobalt oxide of formula-unit CoO
a
H
b
, where a≧1,7 and b≧0.
In particular, since the cobalt salt is cobalt nitrate, the oxide (s) can be nitrogen dioxide, an equilibrium between NO
2
and N
2
O
4
, as well as nitric oxide (NO).
The process may include diluting the decomposition products that are obtained during the calcination. In other words, formation of the supported cobalt oxide, with the formula-unit CoO
a
H
b
, where a≧1,7 and b≧0, is enhanced by ensuring dilution of the decomposition products during calcination.
The presence of the supported cobalt oxide phase with the formula-unit CoO
a
H
b
, where a≧, 7 and b≧0, may be determined by using Temperature Programmed Reduction (TPR) as fingerprint technique.
The minimum temperature at which the calcination is performed is the temperature at which decomposition of the cobalt precursor, ie the cobalt salt, starts, while the maximum calcination temperature is the temperature at which the preferred supported cobalt oxide phase with the formula-unit CoO
a
H
b
, where a≧1,7 and b≧0, is converted to the undesired Co
3
O
4
spinel phase.
The calcination may be performed in any known calcination equipment such as a fluidized bed calciner, a rotary kiln, torbed calciner or a furnace.
In particular, the calcination may be performed in a fluidized bed calciner. P

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