Precious metal compounds

Abstract

The invention relates to tetraalkylammonium-tetra- or hexahydroxometallates such as tetraethylammonium hexahydroxoplatinate, (N(alkyl)4)y[M(OH)x], a method for the production thereof, and the use thereof for producing catalysts.

Claims

1. A tetraalkylammonium tetra- or hexa-hydroxy metallate of the formula (N(alkyl).sub.4).sub.y[M(OH).sub.x], wherein M is a metal selected from the group consisting of rhodium or platinum; alkyl is an alkyl group selected from the group consisting of propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, sec-pentyl, 3-pentyl, 2-methylbutyl, isopentyl, 3-methylbut-2-yl, 2-methylbut-2-yl, neopentyl, n-hexyl, 3-methylpentyl, isohexyl, neohexyl, 2,3-dimethylbutyl, and combinations thereof; Y is 2, or 3; and X is 6.

2. A tetraalkylammonium tetra- or hexa-hydroxy metallate according to claim 1, wherein M is rhodium and Y=3, or M is platinum and Y=2.

3. A tetraalkylammonium tetra- or hexa-hydroxy metallate of the formula (N(alkyl).sub.4).sub.y[M(OH).sub.x], wherein M is rhodium; alkyl is an alkyl group selected from the group consisting of ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, sec-pentyl, 3-pentyl, 2-methylbutyl, isopentyl, 3-methylbut-2-yl, 2-methylbut-2-yl, neopentyl, n-hexyl, 3-methylpentyl, isohexyl, neohexyl, 2,3-dimethylbutyl, and combinations thereof; Y is 2, or 3; and X is 6.

4. A tetraalkylammonium tetra- or hexa-hydroxy metallate according to claim 3, wherein Y=3.

Description

EXAMPLES

Example 1: Production of Pt-TEAH (Tetraethylammonium Hexahydroxy Platinate)

(1) 758 g of demineralized water in a reactor having a capacity of five liters was provided, and 1.47 kg of aqueous tetraethylammonium hydroxide solution at a concentration of 35 wt % was added, corresponding to approximately 2 moles per mole of platinum.

(2) While stirring, 894.74 g of hexahydroxy platinic acid having a content of 38 g of platinum was then added. It was then stirred for one hour at a temperature of approximately 20° C. to 30° C., wherein a yellow-orange solution developed, which was filtered over a G4 glass frit and analyzed.

(3) The solution had a precious metal content of 10.9 wt % platinum and a pH value of 13.9.

(4) The product was also investigated using capillary electrophoresis, the result of which is shown in FIG. 1. The composition is characteristic of the compound, Pt-TEAH. The main peak corresponds to that of the [Pt(OH).sub.6].sup.2− complex. The smaller, second peak corresponds to an additional anionic Pt complex of unknown composition, [Pt(OH).sub.6-x(NEt).sub.x].sup.2−x (with x=1-2). The percentage distribution of the two main components can vary depending upon the production method and the quality of the reactants.

Example 2: Production of Rh-TEAH

(5) 13.5 g of rhodium hydroxide (RhOH.sub.3) were suspended in 10 g of water, and 61.594 g of aqueous tetraethylammonium hydroxide solution at a concentration of 35 wt % was added in one shot and stirred for one hour at a temperature of 22° C., wherein a brown solution developed after approximately 30 minutes, which was filtered through a G4 glass frit and analyzed.

(6) The solution had a precious metal content of 10 wt % and a pH value of approximately 10 (determined using universal indicator paper).

Example 3: Production of Pd-TEAH

(7) Production of the Hydroxide

(8) 866 g of aqueous tetraethylammonium hydroxide solution at a concentration of 35 wt % were provided, and, over 30 minutes, approximately 540 g of a palladium nitrate solution with a palladium content of 130 g was dripped in until the pH value was 3.6 to 3.7; the exact amount of the solution depends upon the palladium content and can vary depending on that. During the addition, a heat of reaction occurred which resulted in a heating to 40° C.

(9) It was stirred overnight for approximately 18 hours and filtered over a G4 glass frit. The solid obtained—the precipitated hydroxide—was washed with demineralized water until the filtrate took on a dark brown color, and was dried overnight in a vacuum.

(10) Production of Pd-TEAH

(11) Next, a 1.0 molar equivalent tetraethylammonium hydroxide solution with a concentration of 35 wt % was provided, and the dried filtrate was added and stirred for one hour at a temperature of 23° C. It was subsequently filtered over a G4 glass frit and dried.

(12) The yield of (N(alkyl).sub.4).sub.y[M(OH).sub.x] was 90%, relative to the palladium used.

(13) The solution had a precious metal content of 10.2 wt % and a pH value of approximately 11 (determined with universal indicator paper).

Example 4: Production of Pt-TPAH (Tetrapropylammonium Hexahydroxy Platinate; alkyl=n-propyl)

(14) The procedure was as in Example 1, although an aqueous solution of tetrapropylammonium hydroxide (40 wt %) was used, and an aqueous solution containing 31.92 wt % hexahydroxy platinic acid was provided and stirred for 180 minutes at 20° C. to 25° C., after which it was warmed to 50° C.; an additional 5 mL of the tetrapropylammonium hydroxide solution was added, left to stand overnight (approximately 18 hours), filtered over a G4 glass frit, and centrifuged for 15 minutes. The clear tetrapropylammonium hexahydroxy platinate solution thus obtained had a platinum content of 9.08%.

Example 5: Production of Pt-TBAH (Tetrabutylammonium Hexahydroxy Platinate; alkyl=n-butyl)

(15) The procedure was as in Example 4, although a frozen tetrabutylammonium hydroxide*30 H.sub.2O was used; an aqueous solution containing 39.3 wt % hexahydroxy platinic acid was provided and stirred overnight (approximately 18 hours) at 20° C. to 25° C., and centrifuged for 15 minutes. The clear tetrabutylammonium hexahydroxy platinate solution thus obtained displayed a dark yellow color.

(16) The solution had a precious metal content of 9.8 wt % and a pH value of approximately 10 (determined with universal indicator paper).

Example 6: Production of a Coating Suspension for Production of a Heterogeneous Catalyst

(17) 45 g of aluminum oxide and 16 g of a zeolite (Zeolite-HSZ-0940NHA from Tosoh) were suspended in water and stirred for 15 minutes. Next, the pH value was adjusted to 10 through the addition of tetraethylammonium hydroxide, then 0.81 g of dissolved platinum in the form of a soluble platinum compound were added and stirred for 15 minutes. Next, 0.54 g of palladium in the form of palladium nitrate in water were added and again stirred for 15 minutes. Next, the pH value was adjusted to a value of 5 with acetic acid, followed by 5 minutes of stirring. Next, the precious metal content remaining in water was determined.

Comparative Example 6a

(18) The platinum was added in the form of an ethanolamine-hexahydroxy platinate solution in water. It was determined that, after conclusion of the experiment, 10% of the original palladium concentration and 20% of the original palladium concentration were present in the solute. The rest of the precious metal had precipitated on the supports (aluminum oxide and zeolite) that were present.

Example 6b

(19) The platinum was added in the form of an aqueous solution of tetraethylammonium hexahydroxy platinate (Pt-TEAH). Following conclusion of the experiment, it was determined that there was no longer any platinum in the solution, and only 0.8% of the original palladium concentration remained in solution. The rest of the precious metal had precipitated on the supports (aluminum oxide and zeolite) that were present.