HIGHLY DISPERSED PALLADIUM CATALYSTS
The invention relates to catalysts comprising palladium on a support in which the palladium is distributed in the support as an eggshell. The palladium surface area is at least 150 m 2 /gPd. A method for manufacturing such catalysts involves impregnating a support with an impregnation solution comprising palladium ions and citrate ions, followed by drying the resulting product. Also described is an impregnation solution comprising palladium ions, citric and/or citrate ions, and acetic acid, which is suitable for manufacturing the catalysts described.
1 . A method for preparing a supported palladium catalyst, comprising the steps of:
(i) preparing an impregnation solution by:
dissolving palladium citrate in deionized water; or
dissolving a palladium salt and citric acid in deionized water and heating the mixture at a temperature of 65-85° C. for a duration of at least 1 hour then impregnating an alumina trilobe support with an impregnation solution comprising palladium ions and citrate ions; and
(ii) drying the product of step (i); wherein
the impregnation solution used in step (i) is free of Group VIB metals;
the supported palladium catalyst has a palladium surface area of at least 150 m 2 /g Pd as measured by carbon monoxide chemisorption;
the palladium is distributed in the support as an eggshell; and
the catalyst is free of Group VIB metals.
2 . A method according to claim 1 , wherein the supported palladium catalyst comprises the catalyst has a palladium surface area of at least 150 m 2 /g Pd as measured by carbon monoxide chemisorption; the palladium is distributed in the support as an eggshell; and the catalyst is free of Group VIB metals.
3 . A method according to claim 1 , comprising a step (iii) of reducing the product of step (ii).
4 . A method according to claim 3 , wherein step (iii) is carried out in an atmosphere comprising a mixture of H 2 and N 2 .
5 - 7 . (canceled)
8 . A method according to claim 1 , wherein the impregnation solution is prepared by dissolving palladium acetate and citric acid in deionized water and heating the mixture at a temperature of 65-85° C. for a duration of 4-8 hours.
9 . A method according to claim 1 , wherein 1 to 2 molar equivalents of citric acid are used per mole of palladium.
10 . A method according to claim 1 , wherein the volume of impregnation solution used in step (i) is less than the absorption volume of the support.
11 . A catalyst obtained by the method of claim 1 .
12 . A catalyst comprising palladium on an alumina trilobe support, wherein:
the catalyst has a palladium surface area of at least 150 m 2 /g Pd as measured by carbon monoxide chemisorption;
the palladium is distributed in the support as an eggshell; and
the catalyst is free of Group VIB metals.
13 . A catalyst according to claim 12 , wherein the catalyst has a palladium surface area of 150 to 250 m 2 /g Pd as measured by carbon monoxide chemisorption.
14 . A catalyst according to claim 12 , wherein the palladium content is 0.1 to 2 wt % based on the total weight of catalyst.
15 - 17 . (canceled)
18 . A catalyst according to claim 12 , wherein:
the catalyst has a palladium surface area of 160 to 220 m 2 /g Pd as measured by carbon monoxide chemisorption;
the catalyst comprises palladium in an amount of 0.5 to 1.5 wt %;
the support is an alumina trilobe; and
the palladium is distributed in the support in the form of an eggshell.
19 . An aqueous impregnation solution comprising palladium ions, citric acid and/or citrate ions, and acetic acid, in which at least a portion of the palladium is in the form of palladium citrate.
20 . An aqueous impregnation solution according to claim 19 , wherein 1 to 2 molar equivalents of citric acid and/or citrate are present per mole of palladium.
21 . An aqueous impregnation solution according to claim 19 , wherein 1 to 1.2 molar equivalents of citric acid and/or citrate are present per mole of palladium.