ABSTRACT
This is an interesting and rather unique catalyst in that it comprises a combination of both an electron-deficient element-palladium, iron, or the like – and electron donor(s) such as silver or copper. The method of preparation is as follows.
Place in a pill-coating device (Fig. 37) a quantity of silica in the form of high-surface-area pills – 0.25-in. spheres, for example, or cylinders. To this silica, add sufficient 10% sodium hydroxide solution to wet the silica in the spheres uniformly but not excessively. Remove the wet spheres from the pill-coating device and put them into a corrosion-resistant open-top tank (Fig. 9) with a diameter such that the entire product from the pill-coating device can be accommodated in the bottom of the vessel at no more than a 2-in. depth. Now add to the support a solution that just covers the alkali-treated silica support. This solution should contain an amount of silver nitrate equal to 4% of the weight of the silica as metallic silver and palladium nitrate equivalent to 1% elemental palladium. Let the solution stand for 24 hr, during which time the Pd and Ag will be deposited on the outer skin of the support material. It is possible that a shorter time can be used if the observation is made that the palladium and silver are completely precipitated from the solution.
Either in the same vessel or in another vessel, wash the coated catalyst with distilled water until the sodium and nitrate have been essentially completely removed.
Remove the catalyst to drying trays (Fig. 22, 25, or 26) and dry it at 150°C in air. This drying completes the preparation of the catalyst. It is now ready for use.
