Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2000-09-18
2004-03-09
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S344000, C502S345000, C502S414000, C502S415000, C502S439000
Reexamination Certificate
active
06703342
ABSTRACT:
This invention relates to copper-containing materials. Copper containing compositions, wherein some or all of the copper is in the form of elemental copper, or in the oxide form, i.e. as cupric and or cuprous oxides, or in the form of other copper species, e.g. sulphides, basic carbonates and the like, are widely used in industrial processes as catalysts or sorbents. For example compositions wherein some or all of the copper is in the elemental form are often used as catalysts for reactions involving hydrogen. As examples there may be mentioned the shift reaction wherein carbon monoxide is reacted with steam to form carbon dioxide and hydrogen; alcohol synthesis reactions wherein a mixture of hydrogen and carbon monoxide and/or carbon dioxide is reacted to form methanol or higher alcohols; hydrogenation reactions; and hydrogenolysis of esters. Compositions wherein some or all of the copper is in the form of elemental copper, copper oxides, copper hydroxide or basic copper carbonate, can be used as sorbents for purification of gases and liquids to remove contaminants such as sulphur compounds. Compositions wherein the copper is in the form of copper sulphides can be used as sorbents for the removal of contaminants such as arsenic compounds and mercury from gases and liquids.
For such applications it is generally desirable that the copper species is present in a highly dispersed form so that the active species is readily contacted with the reactants or material being treated. The degree of dispersion of the copper species can be assessed by determining the exposed surface area of the copper (after reduction of the copper species to elemental copper) per gram of copper. A high copper surface area per gram of copper implies a high degree of dispersion. The copper surface area is conveniently determined by the nitrous oxide decomposition method, for example as described by Evans et at in “Applied Catalysis”, 7, (1983), pages 75-83—a particularly suitable technique is described in EP 0 202 824.
It is known that compositions having, upon reduction, a high metal surface area per gram of metal may be made by impregnating a transition alumina support with a metal ammine carbonate solutions, followed by heating to decompose the ammine carbonate. Thus EP 0 092 878 describes the production of nickel on alumina compositions and WO 96 04 072 describes the production of the analogous cobalt compositions. However, the degree of dispersion of a metal obtained by impregnation of a support, such as alumina, with a solution of a salt or complex of the metal, depends on the ease of decomposition of the complex or on the solubility of the salt. If the salt is too soluble or the complex is too stable, agglomerates of the metal species are liable to be formed rather than a thin layer of the decomposition products upon the surfaces of the pores of the alumina support. Such agglomerates will give, upon reduction to the metal, materials having a relatively low metal surface area. The nickel and cobalt ammine carbonate complexes as employed in the aforesaid EP 0 092 878 or WO 96 04 072 have a relatively low stability. Thus they decompose very readily.
We have found that although copper ammine carbonate complexes are significantly different and are far more stable than the cobalt or nickel analogues, surprisingly high surface area copper materials can be obtained by this route. Whereas cobalt and nickel form hexa-ammine complexes, copper forms tetra-ammine complexes. The complex constants for the copper, cobalt and nickel ammonia complexes are as follows:
Co
Ni
Cu
K
1
M(NH
3
)
1
130
630
14000
K
2
M(NH
3
)
2
43
170
3200
K
3
M(NH
3
)
3
11
54
780
K
4
M(NH
3
)
4
6
16
135
K
5
M(NH
3
)
5
2
6
—
K
6
M(NH
3
)
6
0
1
—
As the composition is heated to decompose the ammine complex, the cobalt and nickel materials precipitate readily when only some of the ammonia has been driven off. On the other hand, on heating the copper complexes, since they are much more stable, it would be expected that the copper would remain longer in solution during evaporation of the water and ammonia and would be liable to be deposited unevenly at the locations where the last of the water is removed, and hence give rise to aggregates of the copper composition rather than as the desired thin coating on the pores of the alumina support. Indeed, in EP 0 259 911 it was proposed to make metal/alumina catalysts by combining an ammoniacal solution of a salt such as a carbonate of the metal with an aqueous solution of an aluminium compound and heating the mixture to boiling, or near boiling, to precipitate a mixed basic carbonate of the metal and aluminium. Whereas this method gave compositions which, when reduced, had a high metal surface area per gram of metal when the metal was nickel, the metal surface area was only 1-20 m
2
per gram of metal when the metal was copper.
Accordingly the present invention provides a process for the manufacture of a composition comprising a copper compound supported on a porous transition alumina comprising impregnating a porous transition alumina support with an aqueous solution of a copper ammine carbonate complex, draining off any excess of the impregnating solution, and then heating the impregnated support to a temperature above 80° C. to decompose the complex thereby depositing a basic copper carbonate compound on the surfaces of the pores of the transition alumina support.
The transition alumina may be of the gamma-alumina group, for example a eta-alumina or chi-alumina. These materials may be formed by calcination of aluminium hydroxides at 400-750° C. and generally have a BET surface area in the range 150-400 mu
2
/g. Alternatively, the transition alumina may be of the delta-alumina group which includes the high temperature forms such as delta- and theta-aluminas which may be formed by heating a gamma group alumina to a temperature above about 800° C. The delta-group aluminas generally have a BET surface area in the range 50-150 m
2
/g. The transition aluminas contain less than 0.5 mol of water per mole of Al
2
O
3
, the actual amount of water depending on the temperature to which they have been heated. The support should be porous, preferably having a pore volume of at least 0.2 ml/g, particularly in the range 0.3 to 1 ml/g.
The support may be in powder form, but is preferably in the form of shaped units, for example approximate spheres, pellets, cylindrical tablets, agglomerates. The shaped units preferably have a minimum dimension of at least 1 mm, and preferably have maximum and minimum dimensions in the range 1 to 15 mm, preferably 3 to 10 mm. The maximum dimension is preferably not more than 3 times the minimum dimension. Where a powdered alumina is employed, the alumina preferably has a surface-weighted mean diameter in the range 1 to 100 &mgr;m. [The term surface-weighted mean diameter D[3,2], otherwise termed the Sauter mean diameter, is defined by M. Alderliesten in the paper “A Nomenclature for Mean Particle Diameters”; Anal. Proc., vol 21, May 1984, pages 167-172, and is calculated from the particle size analysis which may conveniently be effected by laser diffraction for example using a Malvern Mastersizer]. Alternatively the support may be in the form of a monolith, e.g. a honeycomb. In the latter case, the honeycomb may be formed from a ceramic or metal support with a coating of the transition alumina.
The amount of the copper ammine carbonate complex employed is preferably such that the composition has a copper to aluminium atomic ratio in the range 0.025 to 0.5, corresponding to a copper content, in a binary copper species/alumina composition, (after reduction of the copper species to elemental copper) of about 3 to 40% by weight.
The shaped units of the invention may be made by impregnating the support with an aqueous solution of a copper ammine carbonate complex and, after draining off any excess of impregnation solution, then heating the impregnated support to decompose the copper ammine carbonate complex. Heating at temperatures above about 80° C. is sufficient to de
Johnson Matthey PLC
Silverman Stanley S.
Strickland Jonas N.
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