Palladium/Platinum Catalyst Preparation FAQ[ Back to the Chemistry Archive ] Palladium on Carbon (5% Pd/C) [1]Prepare a solution of 1.7 g of Palladium Chloride (or an equimolar amount of palladium chloride dihydrate, PdCl2*2H2O) in 1.7 ml of concentrated hydrochloric acid and 20 ml of water by heating on a water bath for 2 hours or until solution is complete, and add this to a solution of 30 g of sodium acetate trihydrate (Note 1) in 200 ml of water contained in a 500 ml hydrogenation flask. Add 20 g of acid washed activated charcoal (Note 2) and hydrogenate in an atmospheric hydrogenation apparatus until absorption ceases. Collect the catalyst on a buchner funnel and wash it with five 100 ml portions of water and suck dry as possible. Dry the catalyst at room temperature over potassium hydroxide pellets or anhydrous calcium chloride in a vacuum dessicator. Powder the catalyst (approx 20 g yield) and store in a tightly stoppered glass bottle. Alternate procedure [2] Heat 7.5g activated charcoal (Note 2) on a steam bath for 2-3 hours with conc. hydrochloric acid (5 ml) and water (150 ml). Wash the charcoal by decantation with hot water until free of acid, filter it off, and dry it in an oven below 100°C. Heat palladium chloride (0.5 g) in conc. hydrochloric acid (0.75 ml) and water (5 ml) on the steam bath for ~20 min. Add the solution to AnalaR sodium acetate (17.5 g) in water (50 ml) contained in a hydrogenation flask. Introduce the purified charcoal (5.8 g) and hydrogenate the mixture until no more hydrogen is absorbed (~2 h). Collect the catalyst on a 7 cm Buchner filter (3 thicknesses of Whatman No. 1 filter paper), wash it with water (5 x 100 ml) and drain it on the filter with suction. Dry the catalyst over fresh silica gel in a vacuum desiccator and store it in a tightly stoppered bottle. Palladium on Carbon (30% Pd/C)Prepare a solution of 8.25 g of palladium chloride (or an equimolar amount of palladium chloride dihydrate, PdCl2*2H2O) in 5 ml of concentrated hydrochloric acid and dilute with 50 ml distilled water. Cool the solution in an ice-salt bath and add 50 ml of 40% formaldehyde solution and 11 g of acid-washed activated charcoal*. Stir the mixture mechanically and add a solution of 50 g of potassium hydroxide in 50 ml water, keeping the temperature below 5°C. When the addition is complete, raise the the temperature to 60°C for 15 minutes. Wash the catalyst thoroughly by decantation with water as above and finally with dilute acetic acid, collect on a buchner filter and wash with water free from chlorine or alkali. Dry at 100°C and store in a desiccator. Palladium Black (Precipitated Pd metal)Dissolve 5 g palladium chloride in 30 ml concentrated hydrochloric acid and dilute with 80 ml water; cool in an ice-salt bath and add 35 ml 40% formaldehyde solution (or equimolar amount of 37% formaldehyde). Add a cold solution of 35 g potassium hydroxide in 35 ml water dropwise during 30 min to the vigorously stirred palladium solution. Warm to 60°C for 30 minutes and the wash the palladium precipitate six times by decantation with water. Filter on a sintered crucible, wash with 1 liter water and suck dry (approx 3.1 g yield) and transfer to a dessicator charged with silica gel for storage. Alternate procedure [3] Heat a mixture of palladium chloride (0.50 g) and water (100 ml) to 80°C and carefully neutralise the suspension, to wide-range indicator paper, with 20% sodium hydroxide solution (if the end point is overshot, palladium hydroxide precipitates). Add 2.6% formic acid (2.5 ml) and, after about 2 min make the solution strongly alkaline with 20% sodium hydroxide solution (5 ml). Add more of the formic acid (5 ml) and make sure that the solution is still alkaline. Heat the mixture on a steam bath for 2 hours. Filter off the precipitate with a small ('Hirsch') funnel (Whatman filter paper No. 541), wash it free from alkali and dry it over calcium chloride in a vacuum desiccator. Palladium black from PdCl2 and NaBH4, by Rocketdoc Magnetically stir PdCl2 in water (100-200ml per gram PdCl2). If it does not dissolve, add conc. HCl until complete dissolution. The solution should now look like tea. Now add a pinch of sodium borohydride to the solution. The water immediately turns black. Add a little more sodium borohydride and then stop the stirring. Once the Pd black has settled, the water should be clear, and not tan colored anymore. If the color is still present, this means all of the PdCl2 has not been reduced, so then add some more sodium borohydride with stirring. The final color of the water should be clear. Filter off the precipitate and wash it with dH20. Preparation of Palladous Oxide (PdO) [4]In a 350-cc. casserole, 2.2 g. (0.02 moles) of palladium metal is dissolved in a small amount of aqua regia, and the solution is treated with 55 g of sodium nitrate and enough distilled water to make a thick paste. The substances are thoroughly mixed and then heated gently to drive off the water. The heating is increased until the mixture melts (about 270-280°C) and continued cautiously. Just above the melting point the mixture must be stirred and heated carefully as oxides of nitrogen are evolved and foaming occurs. After the evolution of gases is nearly complete (about five minutes) the full flame of a Bunsen burner is applied for about ten minutes. The entire time of heating should be about 30 min. As the mass cools, the casserole is rotated to allow the melt to solidify on the sides of the dish. After digestion with about 200 ml of distilled water until the sodium salts are completely dissolved, the dark brown precipitate of palladous oxide is filtered and washed thoroughly with 1% sodium nitrate solution (Note 3). The oxide must not be washed with pure water since it shows a marked tendency to become colloidal. After drying in a vacuum desiccator the palladous oxide weighs 2.3-2.4 g (91-95% yield). A small amount of palladous oxide adheres to the casserole and cannot be removed by the ordinary means. The oxide is not dissolved readily by aqua regia but is easily removed by boiling with 48% hydrobromic acid. Lindlar's Catalyst (5% Pd on CaCO3, poisoned with Pb) [5]Stir calcium carbonate (precipitated, light; 1.1 g) in water (10 ml) in a flask which is fitted with a thermometer and mounted on a magnetic stirrer/hotplate. Whilst continuing the stirring, add palladium chloride (90 mg) to the suspension and after 5 min., raise the temperature to 80°C for a further 10 min. Cool the mixture and transfer it to a hydrogenation flask, using ~10 ml of water for rinsing. Hydrogenate the mixture until hydrogen absorption (10-20 ml) is complete (ca. 15 min). Collect the reduced catalyst on a small 'Hirsch' funnel (Whatman filter paper No. 1) and wash the catalyst with distilled water (20 ml). Add the damp catalyst to distilled water (10 ml) in a flask on the magnetic stirrer/hotplate. Switch on the stirrer, add a 5% (w/v) solution of AnalaR lead acetate in water (2 ml) and, after 10 min, raise the temperature to 90°C for 40 min. During this time, add distilled water as necessary, to compensate for evaporation losses. Cool the mixture, collect the catalyst on Whatman No. 1 paper in a small 'Hirsch' funnel and wash the catalyst with distilled water (total, ~50 ml). Transfer the catalyst to a clean, tared specimen tube and dry the catalyst in a drying pistol at 40°C to constant weight (~1-3 h). Crush the dry catalyst to a powder with a clean spatula or glass rod and stopper and label the tube (catalyst yield: 0.9-1 g). Platinum on Carbon (30% Pt/C)Cool a solution of the nitrate-free dichloride prepared from or equivalent to 5.0 g of platinum, in 50 ml of water and 5 ml of concentrated hydrochloric acid in a freezing mixture, and treat it with 50 ml of formalin (40% formaldehyde) and 11 g of charcoal (Note 2). Stir the mixture mechanically and add a solution of 50 g potassium hydroxide in 50 ml of water, keeping the temperature below 5°C. When the addition is complete, raise the temperature to 60°C for 15 minutes. Wash the catalyst thoroughly by decantation with water and finally with dilute acetic acid, collect on a suction filter and wash with hot water until free from chloride or alkali. Dry at 100°C and store in a desiccator. Platinum Dioxide (Adam's Catalyst)Platinum dioxide (PtO2) for use in hydrogenations is available commercially. It may alternatively be prepared by either of the following methods. Method 1 (from ammonium chloroplatinate) [2] Place 3.0 g of ammonium chloroplatinate and 30 g of sodium nitrate (AnalaR) (Note 4) in a Pyrex beaker or porcelain dish and heat gently at first until the evolution of gas slackens and then more strongly until a temperature of 300 °C is reached. This occupies about 15 minutes, and there is no spattering. Maintain the fluid mass at 500 - 530 °C for 30 minutes, and allow the mixture to cool. Treat the solid mass with 50 ml of water. The brown precipitate of platinum oxide (PtO2.H2O) settles to the bottom. Wash it once or twice by decantation, filter through a hardened filter paper and wash on the filter until practically free from nitrates. Stop the washing process immediately when the precipitate tends to become colloidal (Note 5): traces of sodium nitrate do not affect the efficiency of the catalist. Dry the oxide in a dessicator, weigh out portions of the dried material a required. Method 2 (from chloroplatinic acid) [2] Dissolve 3.5 g of the purest commercial chloroplatinic acid in 10 ml of water contained in a 250-ml Pyrex beaker or porcelain basin, and add 35 g of sodium nitrate (AnalaR) (Note 4). Evaporate the mixture to dryness by heating gently over a Bunsen flame while stirring with a glas rod. Then raise the temperature to 350-370°C within about 10 minutes: fusion will occur accompanied by the evolution of brown oxides of nitrogen and the gradual separation of a precipitate of brown platinum oxide. If foaming occurs, stir the mixture more vigorously and direct an additional flame at the top of the reaction mixture, if necessary. If the burned beneath the beaker is removed when frothing commences, the top of the fused mass solidifies and material may be carried over the sides of the vessel. After 15 minutes, when the temperature has reached 400°C, the evolution of gas decreases considerably. Continue the heating until at the end of 20 minutes the temperature is 500-550°C; at this stage the evolution of oxides of nitrogen has practically ceased and there is gentle evolution of gas. Maintain the temperature at this point (best with the full force of a Bunsen burner) for about 30 minutes, by which time fusion is complete. Allow the mass to cool (the Pyrex beaker may crack), add 50 ml of water and proceed as in Method 1. Method 3 [6]In a fume cupboard, dissolve chloroplatinic acid (H2PtCl6.6H2O, 0.10 g) in water (ca. 0.5 ml) in a porcelain crucible (3-4 cm diameter). Add sodium nitrate (1 g) and evaporate the mixture to dryness, over a low flame, with continuous stirring. Turn the Bunsen burner full on and stir the contents of the crucible vigorously until the mass has melted completely and the initial decomposition has subsided. Keep the bottom of the crucible at a dull red heat for a further 30 min. (too strong a heat decomposes the oxide to the metal). Allow the crucible to cool and wash the contents into a 250 ml beaker with hot water from a wash bottle. Filter off the brown platinum oxide with a small ('Hirsch') funnel (Whatman paper No. 541) and wash the oxide with hot water (about 200 ml) until the washings are free from nitrate ion. Dry the catalyst over calcium chloride in a vacuum desiccator. Preparation of Platinum Oxide from Chloroplatinic Acid [9]Platinum Oxide for catalytic hydrogenations can be prepared more conveniently from ammonium chloroplatinate than from chloroplatinic acid by the well-known procedure of Adams (1). By adding an excess of ammonia to a solution of chloroplatinic acid, ammonium chloroplatinate is precipitated. This is the basis for a convenient method of recovering platinum in spent catatlysts (2). The amount of catalyst produced from a given weight of ammonium chloroplatinate is almost exactly ½ the weight of the ammonium salt and is therefore very easily calculated. Ammonium chloroplatinate is not hygroscopic and is therefore weighted more easily than chloroplatinic acid. In starting from the ammonium salt, no water is used, and hence no spattering occurs in heating the mixture to the fusion temperature. By the new procedure a given weight of ammonium chloroplatinate is well mixed with ten times its weight of powdered sodium nitrate, and the mixture is heated gradually to the fusion point. During this process much gas is evolved, due presumably to the decomposition of ammonium nitrate, but the evolution is gentle and no spattering occurs. The fused mixture is held at 500*C for 25-30 minutes and the platinum oxide is isolated according to Adam’s directions. From 3.0g of the salt was obtained 1.51g of platinum oxide, no different in general appearance or activity from that prepared in the usual way. This experiment has been duplicated in several other laboratories and shortens the procedure for converting spent catalyst to platinum oxide by 25% or more. Platinum Recovery [2]Platinum residues from hydrogenation reactions should be carefully preserved and subsequently recovered by conversion into ammonium chloroplatinate by the following method. Dissolve the platinum or platinum residues in aqua regia, evaporate just to dryness several times with concentrated hydrochloric acid, dissolve the final residue in a little water and filter. Precipitate ammonium chloroplatinate from the filtrate by addition of excess of a saturated solution of ammonium chloride. Filter and dry the precipitate at 100°C. Notes:
References [1] R. Mozingo, Organic Synthesis Collective Volume 3, 685 (1955)
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