Palladium asbestos catalyst

Phthalazine suffered 80%-complete deuteration in the presence of a special palladium-on-asbestos catalyst (D2O, Pd/asbestos, N2, 220°C, sealed, 72 h preparation of the catalyst and the individual percentage of deuteration at each position of phthalazine are reported). ... 

Preparation of 30 per cent, palladium or platinum catalysts (charcoal or asbestos carrier). 

Method A. Cool a solution of the nitrate-free dichloride, prepared from or equivalent to 5 0 g. of palladium or platinum, in 50 ml. of water and 5 ml. of concentrated hydrochloric acid in a freezing mixture, and treat it with 50 ml. of formahn (40 per cent, formaldehyde) and 11 g. of the carrier (charcoal or asbestos). Stir the mixture mechanically and add a solution of 50 g. of potassium hydroxide in 50 ml. of water, keeping the temperature below 5°. When the addition is complete, raise the temperature to 60° 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° and store in a desiccator. 

Broadly speaking, the differences in effectiveness of palladium and platinum catalysts are very small the choice will generally be made on the basis of availability and current price of the two metals. Charcoal is a somewhat more efficient carrier than asbestos. 

Palladium catalysts have been prepared by fusion of palladium chloride in sodium nitrate to give palladium oxide by reduction of palladium salts by alkaline formaldehyde or sodium formate, by hydrazine and by the reduction of palladium salts with hydrogen.The metal has been prepared in the form of palladium black, and in colloidal form in water containing a protective material, as well as upon supports. The supports commonly used are asbestos, barium carbonate, ... 

A typical catalyst for the final stage would be 10% palladium deposited on finely divided asbestos. 

The most active catalyst is platinum applied in finely divided form, for example platinised asbestos. Certain elements, especially arsenic and mercury, have a powerful effect in reducing the activity of the platinum, a quantity of arsenic equal to 0-2 per cent, of the weight of the platinum reducing the activity by 50 per cent.5 These poisons, as they are termed, also include less harmful substances such as antimony, lead, bismuth, etc. The presence of small quantities of rhodium, iridium or osmium in the platinum also causes diminished yields of trioxide, but the presence of palladium or ruthenium has the opposite effect.6... 

Carbon monoxide undergoes activated adsorption on the surface of palladium oxide. The maximum for this process, at about 350 mm. pressure, is at about 100°C. The gas taken up during activated adsorption can only be recovered as C02 for the most part (57). In a CO-air stream a slight initial reduction of PdO occurs at 23°C., but in the absence of oxygen, there is no reduction below 76°. This process of reduction decreases in rate with time and does not go to completion below 156°. Carbon dioxide, when present in the gas phase, inhibits the reduction of the palladium at 100°C. because it is adsorbed strongly by the PdO (56). Catalysts have been prepared by the deposition of palladium and platinum on asbestos, on silica gel, and on charcoal. 

Alkaline Fuel Cell The electrolyte for NASA s space shuttle orbiter fuel cell is 35 percent potassium hydroxide. The cell operates between 353 and 363 K (176 and 194°F) at 0.4 MPa (59 psia) on hydrogen and oxygen. The electrodes contain platinum-palladium and platinum-gold alloy powder catalysts bonded with polytetrafluoro-ethylene (PTFE) latex and supported on gold-plated nickel screens for current collection and gas distribution. A variety of materials, including asbestos and potassium titanate, are used to form a micro-porous separator that retains the electrolyte between the electrodes. The cell structural materials, bipolar plates, and external housing are usually nickel, plated to resist corrosion. The complete orbiter fuel cell power plant is shown in Fig. 27-62. 

Representative compounds having a pyrrolidine or piperidine nucleus have been dehydrogenated in benzene solution under pressure at 250-350° over a nickel catalyst, e.g., l-( -amyl)-pyrrolidine to l-( -aniyl)-pyrrole (88%), indoline to indole (75%), and 1,2,3,4-tetrahydrocarbazole to carbazole (95%). Indole is also prepared by the dehydrogenation of its 2,3-dihydro derivative over palladium in boiling xylene (62%)." Partially hydrogenated alkylpyridines are dehydrogenated over palladized asbestos." 2,4-Diphenylpyrrole is synthesized by the selenium dehydrogenation of its 2,3-dihydro compound (46%). ... 

Palladium, Pd, and platinum, Pt, usually on activated carbon or asbestos, are catalysts for the dehydrogenation of hydroaromatic and some heterocyclic compounds to aromatic compounds. The reaction takes place at high temperatures (300-350 °C), and consequently, side reactions such as rearrangements often take place [495, 496, 497, 945, 946, 947, 948], The catalytic dehydrogenations played a very important role in the elucidation of terpene and alkaloid structures. Because spectroscopic methods, especially NMR spectroscopy, can help to determine structures much more reliably, catalytic dehydrogenation over palladium and platinum are rare nowadays. 

Carbon monoxide reduced by hydrogen at low temperatures (100° C.) in the presence of active nickel or palladium catalysts mounted on asbestos, tends to form unsaturated hydrocarbons.102 The catalysts soon lose activity and relatively low yields are obtained.103... 

Hydrogenation of unsaturated compounds for identiflcation purposes was also employed successfully by Pankov et al. [58]. Hydrogenation was carried out outside the chromatographic system over palladium on asbestos as the catalyst. 

Other possible carriers for catalysts are asbestos, pumice, kieselgur, silica gel, silica, active charcoal, and oxides, carbonates, and sulfates of magnesium, calcium, barium, zinc, aluminum, iron, chromium, and zirconium. Details for the preparation of palladium catalysts on barium sulfate have been recorded by Mozingo.137... 

Zelinsky and Turowa-Pollak141 describe the specific properties of an osmium catalyst. Hydrogenation on osmium catalysts usually occurs at lower temperatures than on platinum, palladium, or nickel catalysts. Osmium asbestos is a very resistant catalyst that can be used for months on end without loss in activity disadvantages are that osmium catalysts that are not supported on carriers must be frequently regenerated and that when the temperature exceeds 150° osmium tends to decompose the material under hydrogenation. 

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