Metallic sponges Catalysts, forms

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

Thermosetting Reactive Polymers. Materials used as thermosetting polymers include reactive monomers such as urea—formaldehyde, phenoHcs, polyesters, epoxides, and vinyls, which form a polymerized material when mixed with a catalyst. The treated waste forms a sponge-like material which traps the soHd particles, but not the Hquid fraction the waste must usually be dried and placed in containers for disposal. Because the urea—formaldehyde catalysts are strongly acidic, urea-based materials are generally not suitable for metals that can leach in the untrapped Hquid fractions. Thermosetting processes have greater utiHty for radioactive materials and acid wastes. 

The behavior of carbon monoxide-hydrogen mixtures in the presence of metals of the platinum group lias been made the subject of special study by a number of investigators. Orloff82 was the first to observe that under certain conditions in the presence of a nickel-palladium catalyst, a reaction took place which resulted in the formation of ethylene. This is in contradiction to the observations of Breteau,88 who stated that in the presence of palladium sponge, carbon monoxide and hydrogen react in the cold to form methane and that at 400° C. this transformation becomes fairly rapid. Recently it has seemed desirable that the experiments of Orloff... 

PALLADIUM BLACK or PALLADIUM SPONGE (7440-05-3, platinum metal) Powdered form is highly reactive catalyst, and may cause fire and explosions on contact with many substances including oxidizers, acetone, strong acids, finely divided aluminum, dioxygen difluoride, ethyl... 

The noble metals usually come from refiners in the form of sponge or ingot with 99.9% minimum purity. Sponge is a convenient form for catalyst and chemical preparation, whereas ingots are preferred for sheet, tube, and wire production. The metals are sold by the troy ounce with the price determined by purity, the general economy, and sudden changes in supply and demand. 

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