METHOD FOR THE PRODUCTION OF ACTIVE PALLADIUM(0) POWDER

Abstract

The present invention relates to a method for the production of palladium(0) powder in which a palladium(0) starting powder is subjected to a thermal treatment in a furnace at a temperature of no more than 370° C. in a hydrogen gas atmosphere.

Claims

1. A method for the production of palladium(0) powder, comprising subjecting a palladium(0) starting powder to a thermal treatment in a furnace at a temperature of no more than 370° C. in a hydrogen gas atmosphere.

2. The method according to claim 1, wherein the palladium(0) starting powder is obtained by reducing a Pd(II) compound or a Pd(IV) compound.

3. The method according to claim 1, whereby the hydrogen content of the hydrogen gas atmosphere is at least 5% by volume, relative to the total amount of the gases present in the hydrogen gas atmosphere.

4. The method according to claim 1, whereby the hydrogen gas atmosphere is generated by continuously supplying hydrogen into the furnace.

5. The Method according to claim 1, wherein the heating of the furnace is interrupted by one or more temperature ramp(s).

6. The method according to claim 1, wherein the thermal treatment of the palladium(0) starting powder proceeds at a temperature in the range of 150° C. to 370° C.

7. A palladium(0) powder, wherein the powder is obtained by the method according to claim 1.

8. A palladium(0) powder, wherein the powder exhibits an increase in mass of at least 13.0% by weight when heated to a temperature of 990° C. while being exposed to air.

9. A method of producing a palladium salt comprising using the palladium(0) powder according to claim 7 as an educt for the production.

10. A method for the production of a palladium salt, comprising (i) producing a palladium(0) powder by the method according to claim 1; and (ii) converting the palladium(0) powder with a mineral acid.

11. The method according to claim 10, wherein the mineral acid is nitric acid, sulfuric acid, hydrochloric acid or a mixture of at least two of these mineral acids.

12. The method according to claim 10, wherein the conversion in step (ii) proceeds in the presence of a carboxylic acid, a carboxylic acid anhydride, or a mixture thereof.

Description

EXAMPLES

[0061] The same palladium(0) starting powder was used in all experiments below and was produced as follows in accordance with the example of DE 102 49 521 A1:

[0062] Pd(NH.sub.3)2Cl.sub.2 was transferred to a beaker and hot, deionized water was added until the suspension was easy to stir. Subsequently, 5-10 mL ammonia solution (25% solution) were added while stirring such that a slightly alkaline solution was generated. Then, 30-60 mL hydrazine solution (22% solution) were added slowly and in aliquots. The suspension foams during the addition of hydrazine. The addition of hydrazine must be adapted to the foaming. Another 3 mL of hydrazine solution were added as an excess. Subsequently, stirring was continued for one more hour and the Pd sponge thus generated was then filtered through a funnel filter. The Pd sponge was washed approx. 10 times with hot, deionized water. The Pd sponge, still slightly wet, was transferred to quartz glass boats and these were pushed into a lockable tube furnace. The furnace was equipped with an interior tube made of quartz glass. Subsequently, nitrogen gas was supplied through the interior tube. The exit of the tube was connected to a gas washing bottle filled with 2N sulfuric acid. After a period of 10 minutes, in which the oxygen was completely displaced from the interior tube, the oven was heated linearly to a temperature of 250° C. over the course of two hours. Said temperature was maintained for 4 hours and then the furnace was heatedly further linearly to a temperature of 600-650° C. After a holding time of 5 hours, the furnace was allowed to cool down to approx. 50° C. while rinsing with nitrogen. The Pd sponge was removed and mechanically disintegrated.

Reference Example 1

[0063] The palladium(0) starting powder produced according to the method described above was tested for its activity in the production of palladium acetate. The procedure was as follows:

[0064] 30 mL acetic acid anhydride and 300 mL acetic acid were added to 30 g of the palladium(0) starting powder. Then, nitric acid was added.

[0065] There was no formation of NO.sub.x at room temperature and the palladium(0) powder did not react with acetic acid and nitric acid to form palladium acetate. Even heating to 60° C. did not start the reaction.

Example 1

[0066] The palladium(0) starting powder was placed in a tube furnace. Hydrogen was allowed to flow into the furnace. The flow of H.sub.2 was 2 m.sup.3/h. After formation of the hydrogen gas atmosphere, the furnace was heated to a maximal temperature of 340° C. according to the following temperature program: [0067] heating to 100° C.; [0068] holding the temperature of 100° C. for 60 minutes (first temperature ramp); [0069] further heating to 150° C.; [0070] holding the temperature of 150° C. for 30 minutes (second temperature ramp); [0071] further heating to 200° C.; [0072] holding the temperature of 200° C. for 30 minutes (third temperature ramp); [0073] further heating to 280° C.; [0074] holding the temperature of 280° C. for 30 minutes (fourth temperature ramp); [0075] further heating to 300° C.; [0076] holding the temperature of 300° C. for 30 minutes (fifth temperature ramp); [0077] further heating to 340° C. and continuation of the thermal treatment for another 150 minutes; [0078] allowing the furnace to cool down to room temperature.

[0079] During the cooling phase, the flow of H.sub.2 was stopped and nitrogen was supplied into the furnace instead.

[0080] A part of the palladium(0) powder thus obtained was subjected to a thermo-gravimetric analysis (TG unit: Netzsch TG 209). The heating rate was 10° C/min and the sample was heated in an air atmosphere up to a temperature of 990° C. The sample showed an increase in mass of 14.2% by weight.

[0081] A second sample of the palladium(0) powder was taken and again subjected to a thermo-gravimetric analysis under identical conditions. The sample showed an increase in mass of 14.1% by weight.

[0082] The remaining palladium(0) starting powder was tested for its activity in the production of palladium acetate. The procedure of Reference example 1 was adopted for this purpose, i.e., 30 mL acetic acid anhydride and 300 mL acetic acid were added to 30 g of the palladium(0) starting powder. Then, nitric acid was added.

[0083] There was some formation of NO.sub.x even without external heating and the palladium(0) powder reacted with acetic acid and nitric acid to form palladium acetate. This demonstrates that the palladium(0) powder according to the invention has very high activity.

Reference Example 2

[0084] The palladium(0) starting powder was placed in a tube furnace. Hydrogen was allowed to flow into the furnace. The flow of H.sub.2 was 2 m.sup.3/h. After formation of the hydrogen gas atmosphere, the furnace was heated to a maximal temperature of 380° C. according to the following temperature program: [0085] heating to 100° C.; [0086] holding the temperature of 100° C. for 60 minutes (first temperature ramp); [0087] further heating to 150° C.; [0088] holding the temperature of 150° C. for 30 minutes (second temperature ramp); [0089] further heating to 200° C.; [0090] holding the temperature of 200° C. for 30 minutes (third temperature ramp); [0091] further heating to 280° C.; [0092] holding the temperature of 280° C. for 30 minutes (fourth temperature ramp); [0093] further heating to 300° C.; [0094] holding the temperature of 300° C. for 30 minutes (fifth temperature ramp); [0095] further heating to 380° C. and continuation of the thermal treatment for another 150 minutes; [0096] allowing the furnace to cool down to room temperature.

[0097] During the cooling phase, the flow of H.sub.2 was stopped and nitrogen was supplied into the furnace instead.

[0098] A part of the palladium(0) powder thus obtained was subjected to a thermo-gravimetric analysis (TG unit: Netzsch TG 209). The heating rate was 10° C/min and the sample was heated in an air atmosphere up to a temperature of 990° C. The sample showed an increase in mass of 11.9% by weight.

[0099] The remaining palladium(0) starting powder was tested for its activity in the production of palladium acetate. The procedure of Reference example 1 and example 1 was adopted for this purpose, i.e., 30 mL acetic acid anhydride and 300 mL acetic acid were added to 30 g of the palladium(0) starting powder. Then, nitric acid was added.

[0100] There was formation of NOx only with additional external heating to the approx. 80° C. and the palladium(0) powder reacted with acetic acid and nitric acid to form palladium acetate.

[0101] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims