Palladium chloride on carbon

The presence of hydrogen chloride during the hydrogenation of many organic compounds is desirable or without effect, so that the washing operations may be omitted in such cases. Thus, the palladium chloride on carbon may be used in the same manner as the prereduced catalysts, i.e., simply added before reduction to the solvent and the hydrogen acceptor. 

A. Palladium chloride on carbon. Prepare a solution of 4-2 g. of anhj drous palladium chloride (1) in 10 ml. of concentrated hydrochloric acid and 26 ml. of water by heating on a boiling water bath for 2 hours or imtil solution is complete. Add 70 ml. of water and pour all the resulting solution over 46 g. of nitric acid - washed activated carbon (2) contained in an evaporating dish or Pyrex crystallising dish. Mix the palladium chloride solution thoroughly with the carbon, and dry the mixture first on a water bath and then in an oven at 100° stir occasionally. Powder the mass (49 g.) and store in a tightly-stoppered bottle. 

An attractive property of Pd is its ability to catalyze the partial reduction of phenols to cyclohexanones. TWs is important industrially, and many adjustments have been made on the choice of carrier and promoter, to limit overhydrogenation. Palladium-on-BaCOj, palladium chloride-on-carbon, palladium-on-CaCOs, palladium-on-carbon, and pallad-ium-on-alumina ° have been used, but the last two generally are satisfactory. 

Precipitation or coprecipitation methods are also often used. Suh et al. [40] analyzed the effect of the oxygen surface functionalities of carbon supports on the properties of Pd/C catalysts prepared by the alkali-assisted precipitation of palladium chloride on carbon supports, followed by liquid-phase reduction of the hydrolyzed salt with a saturated solution of formaldehyde. They observed that the metal dispersion increased with increasing amount of oxygen surface groups. Nitta et al. [41] also used a deposition-precipitation method, with sodium carbonate and cobalt chloride or nitrate, to prepare carbon-supported Co catalysts for the selective hydrogenation of acrolein. 

C. Palladium chloride on carbon (5% Pd). A solution of 8.2 g. (0.046 mole) of palladium chloride in 20 ml. (0.24 mole) of concentrated hydrochloric acid and 50 ml. of water is prepared (Note 2). The solution is diluted with 140 ml. of water and poured over 92 g. of nitric acid-washed Darco G-60 (Note 10) in an 8-in. evaporating dish (Note 3). After the palladiiun chloride solution has been thoroughly mixed with the carbon, the whole mixture is dried, first on a steam bath and then in an oven at 100°, with occasional mixing imtil completely dry. The mass (98-100 g.) is powdered and stored in a closed bottle. 

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