Cobalt catalyst compositions useful for conducting carbon...

Details Cobalt catalyst compositions useful for conducting carbon... Cobalt catalyst compositions useful for conducting carbon...

2000-08-01

2003-02-18

Bell, Mark L. (Department: 1755)

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

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S324000, C502S326000, C502S331000

Reexamination Certificate

active

06521565

ABSTRACT:

FIELD OF THE INVENTION
An oxidized catalyst precursor for forming highly active and selective catalysts useful for conducting hydrogenation reactions, particularly carbon monoxide hydrogenation reactions, especially Fischer-Tropsch reactions; and the catalyst produced from the oxidized catalyst precursor.
BACKGROUND
Processes for the hydrogenation of carbon monoxide to produce waxy and/or oxygenated products for upgrading to highly valued chemical raw materials and/or hydrocarbon fuels are well documented in the technical and patent literature. For example, in the Fischer-Tropsch (F-T) process, it is well known that the carbon monoxide component of synthesis gas can be catalytically converted by reaction with the hydrogen to reduction products constituting a range of waxy liquid hydrocarbons; hydrocarbons which can be readily upgraded to transportation fuels. In these processes, e.g., catalysts constituted of Group VIII metals (Periodic Table of the Elements, Sargent-Welch Scientific Company, Copyright 1968), notably the Iron Group metals, particularly iron, ruthenium and cobalt, are generally preferred for the synthesis of C
5
+ hydrocarbons; and copper has become the catalytic metal of choice for alcohol synthesis. These metals can exist in multiple valence states in the catalyst precursors and each state can display quite different behavior from the others during the reduction treatments, hence impacting the catalytic properties of the active catalyst. Each of the metals can be promoted or modified with an additional metal, or metals, or oxide thereof, to improve, e.g., the activity and/or selectivity of the catalyst in conducting these reactions.
It is known that Iron Group metal surfaces exhibit higher activities for catalytic reactions such as hydrogenation, methanation and F-T synthesis when catalysts on which these metals are dispersed are subjected to high temperature oxidation, and subsequent reduction. Recent art can be found in Applied Catalysis, A, General 175 (1998) pp 113-120 and references therein. U.S. Pat. Nos. 4,492,774; 4,399,234; 4,493,905; 4,585,789; 4,088,671; 4,605,679; 4,670,414 and EPO 253924 disclose activation of cobalt catalysts by means of a reduction/oxidation/reduction (R-O-R) cycle, resulting in an increase in activity for F-T synthesis. Thus, typically such catalyst, e.g., supported reduced Co, is contacted at high temperature ranging from about 300° C. to about 600° C. with a gaseous oxygen-containing stream to oxidize the metal, or metals, to its most stable oxide form, e.g., Co
3
O
4
. Precautions are taken during such treatments to control the exothermicity of the reaction to avoid sintering of the oxide metal particles, which can be detrimental to the activity of the catalyst. On reduction, i.e., on completion of the oxidation-reduction cycle, the dispersed oxide particles, (e.g., the Co
3
O
4
) are reduced to dispersed metal particles and the catalytic activity is increased.
Considerable progress has been made in the development of catalysts, and processes, these providing good activity, and selectivity in alcohol synthesis, and in the conversion of hydrogen and carbon monoxide to distillate fuels, predominantly C
5
+ linear paraffins and olefins, with low concentrations of oxygenates. Nonetheless, there remains a pressing need for improved catalysts, and processes; particularly more active catalysts, and processes, for producing transportation fuels and lubricants of high quality at good selectivity at high levels of productivity.
SUMMARY OF THE INVENTION
This and other needs are achieved in accordance with the present invention embodying a low temperature oxidation process which requires, beginning with a catalyst precursor constituted of a composite of a solids support, or powder, and a compound or salt of a metal, or metals, inclusive of cobalt, catalytically active for conducting hydrogenation reactions, notably hydrogenation reactions, contacting the catalyst precursor with liquid water or steam, or a mixture of liquid water and steam, at sufficiently low temperature to oxidize and convert at least a portion of the metal, or metals component of the catalyst precursor to a metal hydroxide, low oxygen-containing metal oxide, or mixture of metal hydroxide and low oxygen-containing metal oxide. By oxidation is meant the conversion of a metal species to a low valence state, e.g., Co, the Co species, to a Co
2
+ species. For example, in a low temperature oxidation treatment of a cobalt/TiO
2
catalyst precursor treated with liquid water or steam, or a mixture of liquid water and steam, all or a portion of the cobalt component of the catalyst precursor is oxidized and converted to Co
2
+, i.e., a hydroxide of cobalt, Co(OH)
2
, low oxide of cobalt, CoO, or mixture of these components; these components becoming intimately contacted with the surface of the support, or powder. On reduction, as may be produced by contact and treatment of the oxidized catalyst precursor with hydrogen, the dispersed metal oxide or hydroxylated catalytic metal, or metals component of the catalyst, e.g., CoO or Co(OH)
2
, or mixture thereof, is reduced to elemental or metallic metal, e.g., Co; and the catalyst thereby activated. Optionally, the oxidized catalyst precursor may be dried in a non-oxidizing atmosphere and the hydroxide converted to a low oxygen content oxide, i.e., CoO. Optionally also, the oxidized catalyst precursor may be dried and calcined at elevated temperature in an oxidizing atmosphere to obtain a metal oxide or metal oxides, e.g., Co
3
O
4
. In both options, the catalyst is activated by reduction of the oxidized catalyst precursor. The oxidized catalyst precursor, and catalyst made therefrom are useful compositions of matter, the activated catalyst being particularly useful for efficiently conducting hydrogenation reactions, notably carbon monoxide hydrogenation, especially F-T synthesis reactions, to provide a variety of useful products.
The composition, comprising the support and catalytic metal, or metals component, on contact with the water or steam, or mixed phase water and steam, at low temperature is transformed: the catalytic metal(s), component of the catalyst, e.g., Co, is oxidized and converted into metal hydroxides, low oxygen-containing metal oxides, or metal hydroxides admixed with oxides of the metal in low valence state, e.g., CoO, Co(OH)
2
. It is found that the transformed metal, or metals, e.g., CoO or Co(OH)
2
, is more readily, widely and intimately dispersed on the surface of the support than a higher valence more stable oxide form, e.g., Co
3
O
4
; providing on reduction smaller crystallites of the metal, or metals which are a more highly active species than is produced by reducing Co
3
O
4
to form the catalyst. The greater activity and stability of catalysts made by this process, and the fact that the oxidation step can be carried out at low temperature in an aqueous medium, or by simple contact with liquid water, or steam, or mixed phase of water and steam, are consequences of considerable import in the development of an F-T process.
The catalytic metal(s) of the catalyst precursor, on contact with the oxidizing liquid water or steam, or mixture thereof, converts at low temperature to its hydroxide or low valence oxide. Reactions taking place in this conversion for a cobalt based catalyst precursor thus include the following:
Co+H
2
O<=>CoO+H
2
  (1)
CoO+H
2
O<=>“Co(OH)
2
”,  (2)
or the sum of reaction 1 and reaction 2:
Co+2H
2
O<=>“Co(OH)
2
”+H
2
  (3)
The hydroxide of cobalt is shown as “Co(OH)
2
” in the above equations since its exact form can be more complicated than the pure metal hydroxide because with the low temperature treatment with liquid water or steam, the hydroxide of cobalt that is formed can interact with the support material (e.g., the TiO
2
). The oxidation of the metal, as depicted in reactions 1 and 3, with liquid water or steam is considerable less exothermic than the oxidation of

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